To appear in Roessler., ed. Perception, Causation and Objectivity: Issues in Philosophy and Psychology (Oxford University Press) 
	
Causal Perception and Causal Cognition* 
Draft 8/13/08

Jim Woodward 
 		    Caltech 

 
1. Introduction 
 What is the role of causal perception in learning about causal relationships and in achieving causal understanding of why things behave as they do? Of course, perception plays a role in the acquisition of much and perhaps all causal knowledge. (Think of using sight to read a text in which one is told about a causal relationship by a reliable authority or of using some statistical or causal modeling procedure to reach a causal conclusion on the basis of data produced by an “observational” study.) My interest in this essay, however, is in a much narrower class of cases which are often described as involving the “perception of causation” . Very roughly, it is characteristic of these cases that it appears one can “read off” certain causal relationships from perceptual cues (often but not always visual cues involving spatio- temporal relationships.) Moreover, one does this in a way that, phenomenologically at least, seems to have the directness, immediacy and non-inferential character of other cases in which one detects properties and relations through sensory experience. The perception of causation in a simple collision, in which one appears to see the impact of one billiard ball cause another to move, is a paradigmatic example, but there are many more – it appears one can see one object push or pull another along or see the impact of a moving object (a thrown stone) cause another (a bottle) to break (cf. Scholl and Tremoulet, 2000). Similarly one can apparently see that one object is supported by another that a moving ball has been blocked by a solid barrier and will not pass through it, that a key will or will not fit into a lock of a certain shape, and so on. 
By no means all causal relationships seem to be detected in this way. Suppose that I am interested in whether a drug will cure a certain illness. I conduct a randomized controlled trial in which the drug is supplied to a treatment group with the illness and withheld from a control group also with the illness. If I observe a higher incidence of recovery in the treatment group, I may be entitled to infer that the drug does indeed cause recovery but in reaching this conclusion I do not seem to rely on causal perception in the sense illustrated above— whether the drug is efficacious is not something that I can read off from geometrical or spatio- temporal cues in the way in which I can apparently read off the role of the impact of the first billiard ball in causing the second to move. 
My interest in this essay is in the relationship between the kinds of causal learning illustrated by these two examples and more generally in the way in which the experience of causal perception influences causal cognition and the way we conceptualize causation. I will suggest that the differences between the abilities that, on the one hand, are exhibited in tasks involving causal perception, and, on the other hand, causal judgment tasks like the inference to drug efficacy closely tracks two very different ways of thinking about causation (and about causal learning and causal representation) that one finds in the philosophical and psychological literatures. 
In speaking of these “two different ways of thinking” about causation, I emphasize that what I have in mind is, in the first instance, how various researchers (particularly in philosophy and psychology) conceptualize (or theorize about) casual relationships themselves as they exist in the world or about the causal concepts/ representations that people employ. At this stage, I want to leave it open, as a further, independent question, whether these conceptualizations are accurate or defensible. Whether plausible or not as general accounts of causation and causal representation, I believe it is nonetheless true that an important part of the motivation for each of these ways of thinking can be found in the psychological phenomena and capacities for causal learning that I will be describing. 
 The first approach, which I take to be grounded in part in experiences having to do with causal perception, involves what I will call a geometrical/mechanical conception of causation. This way of thinking about causation focuses on cases in which there is a physical process connecting cause and effect and, more broadly, on phenomena that are mediated by contact -mechanical forces and in which spatio –temporal or geometrical relationships play an important role. Causal interactions themselves are conceptualized in terms of contact forces and energy/momentum exchange. This contrasts with a second way of thinking about causation involving a difference –making conception. This second conception focuses on causal judgments that are sensitive to contingency or difference-making information (roughly, information that compares what happens to the effect in presence versus the absence of its putative cause). Such judgments may not be guided, at least in any direct way, by spatio- temporal or contact-mechanical information. The randomized trial involving the drug provides an illustration—the trial shows that the drug makes a difference to recovery but does not exhibit a connecting process or contact forces mediating the relationship between drug and recovery. 
 As we shall see, at least as presented in the philosophical literature, there are deep conceptual differences between geometrical/mechanical and difference-making approaches to causation and these lead, in certain cases, to strikingly different causal judgments. Notoriously, these conceptual differences have made it difficult for philosophers to combine the two approaches into a single, integrated account of causation. Parallel to this, there is also empirical evidence for various sorts of dissociations between judgments guided by causal perception (and based on geometrical/ mechanical cues) and judgments based on difference-making or contingency information: that is, the psychological structures that underlie causal perception seem to be at least in part distinct from those that underlie causal judgments based on difference-making considerations and these different structures can lead to judgments or outputs that conflict with each other. My conjecture is that this parallelism is not accidental—I think that various features of causal perception help to motivate or make plausible the intuitions that seem to support geometrical/ mechanical accounts of causation, while the kinds of judgments that are based on information about difference-making play a similar role in motivating difference-making theories. The difficulty of putting these two philosophical approaches together into a single integrated account of causation is connected to (and in part a reflection of) the fact that the psychological processes and judgments with which they are associated also differ in important ways. Nonetheless and despite these facts, adult human causal thinking is characterized by an ability to (often) move back and forth relatively smoothly between these two conceptions – they are relatively well-integrated in adult causal thinking. (There is nothing inevitable about this—as we shall see, in non-human primates and perhaps in human infants, these two conceptions may not be well integrated). 
These considerations lead to a number of questions, of both philosophical and psychological interest, that will be explored in this essay. Is one of these two ways of thinking about causation more fundamental than or prior to the other, either developmentally or conceptually? For example, is it true, as some psychologists claim, that a broadly geometrical/mechanical way of thinking about causation, derived from experiences with causal perception, and leading us to conceptualize causation in terms of “forces”, serves as a basis for all human causal cognition, including cognition based on difference-making considerations ? Or is the difference-making conception and the kind of contingency-based learning associated with it instead more fundamental? Or, as a third alternative, is it more accurate to think of the two conceptions and the abilities associated with them, as instead developing in tandem, mutually influencing or bootstrapping one another? More generally, my hope is that a better understanding of the relationship, both conceptually and developmentally, between the way of thinking about causation naturally suggested by causal perception and the way suggested by difference -making causal judgments will help to clarify both approaches. 
The remainder of this essay is organized as follows. Sections 2 - 5 set out some of the differences between difference-making and geometrical/ mechanical accounts within philosophy, the (apparently) very different intuitions on which they draw, and the different core phenomena they attempt to describe. Parallels with theories within psychology that focus on causal perception (broadly understood) and theories that instead emphasize contingency based causal judgment are noted. Sections 6-8 then describe some relevant psychological results concerning dissociations between casual perception and contingency-based causal judgment and between causal perception and action and attempts to connect these with the ideas introduced in Sections 2-5. Section 9 then takes up some more general issues about the significance of causal perception for our understanding of causation and our capacities for causal cognition. 
2. Difference-Making Theories 
 As I shall understand Difference-making (DM) theories of causation, they rely on the guiding idea that, at least in many paradigmatic cases, and perhaps always, causes must make a difference to their effects. Typically such theories conceive of causal claims as at least implicitly contrastive or comparative in the sense that they imply that there is some possible state which is an alternative to the presence of the cause (a state in which the cause is absent or “different”) such that in that state the effect is or would be absent or different (or perhaps its probability would be different). In other words, the presence of the cause makes a difference to the effect in the sense that in a situation in which the cause is appropriately different, the effect will or would be different. In philosophy, this difference-making relationship is explicated in variety of different ways—for example, in terms of relations of necessity, sufficiency and non-redundancy among factors figuring in regularities, as in Mackie’s INUS condition account (Mackie, 1974), in terms of a relationship between the probability of the effect conditional on the cause (and other factors) and the probability of the effect conditional on the absence of the cause (and other factors) (Eells, 1991, Eells and Sober, 1983), and in terms of counterfactuals concerning what would happen to the effect if the cause were to occur and how this compares to what would happen to the effect if the cause were not to occur (Lewis, 1973). These differences will largely not matter to what follows. 
 Some difference-making accounts are “Humean” in the sense that they take causal claims to be fully reducible to claims about regularities or patterns of covariation, but not all difference- making accounts have this feature. (For example, the Eells/Sober 1983 account and the interventionist theory of Woodward, 2003 described below are non -Humean difference- making theories) Moreover, since the difference-making theories described above are theories of what causation is, rather than theories about how one learns about causal relationships, they are also not committed to the claim that the only way that we can learn about causal relationships is through the observation of regularities or patterns of covariation. However, in what follows, I will assume that difference-making accounts are committed to the claim that information about patterns of covariation (including covariation generated by interventions) is one important source of information about causal relationships; that is, I take such accounts to assume that causal judgments will at least be sensitive to contingency information, even if such information may not by itself be enough to fully fix which causal judgments are accepted or correct.
 As an empirical matter, the claim that causal judgment is (at least sometimes) sensitive to contingency information does not seem controversial. As Schlottman and Shanks (1992) remark, there is a huge body of experimental evidence supporting this claim. It is one of the virtues of difference-making accounts that they seem to provide a natural explanation of why contingency information is relevant to causal judgment. By contrast, as we will see, accounts that instead focus on the role of connecting processes (and geometrical/mechanical information) have a more difficult time making sense of the role of contingency information. 
As remarked above, I regard interventionist accounts of causation as one particular kind of difference-making theory. According to interventionist accounts, causes make a difference to their effects in the sense that if an intervention (roughly, an idealized experimental manipulation) were to occur which changes the value of a cause variable (e.g., by introducing the cause into an appropriate situation in which it was previously absent or removing it from a situation in which it was previously present) this would make a difference to the value of the effect variable. Interventionist theories don’t claim that the only way to learn abut causal relationships is to actually perform interventions -- they agree that one can sometimes learn about causal relationships from passive observation (typically these will be observations that provide covariational information). However, they hold that the causal claim one learns in such a case has an interventionist interpretation – roughly, it is information about what would happen if one were to perform an intervention. Interventionist accounts thus make the potential role of causal claims in guiding action and manipulation central to understanding the content of those claims As we shall see (Sec 8), this feature of interventionism puts it in some tension with at least some accounts that take causal perception to be central to the acquisition of casual knowledge. 
As remarked above, the philosophical treatments of causation just described are intended, in the first instance, as accounts of what causation is or of what causal claims correspond to “in the world”. By contrast, psychologists interested in causation tend to focus, unsurprisingly, on causal cognition: on such issues as how causal relationships are represented, learned, reasoned about and so on, both by humans and other animals. Nonetheless, many, perhaps most philosophers working on causation have also held views about human causal cognition and, depending on the details of their views, have often moved back and forth between worldly claims about what causation is and psychological claims about the nature of causal cognition. This is unsurprising: To the extent that one thinks that human causal thinking, at least sometimes, accurately tracks or reflects causal features of the world, as described by one’s philosophical theory of causation, one also will likely think there is some relation between these worldly features and what goes on in people’s heads when they engage in causal thinking and learning. For example, if one thinks that causal relationships are best represented in terms of relationships among conditional probabilities, then it is likely to seem plausible that successful causal cognition in some way involves the mental representation of facts about conditional probabilities. 
Similarly, suppose as some theorists in the causal process tradition claim (Salmon, 1984), that whether c causes e has to do only with the presence or absence of a “casual process” connecting c to e and not with the truth or falsity of comparative claims concerning whether e would or does occur in situations in which c is absent. Then, prima-facie at least, to the extent that human causal judgment is accurate or represents the causal facts as they are actually are, one would not expect it to be sensitive to such comparative information. To the extent that causal judgment is sensitive to such information, it would seem natural to conclude that either (i) people are making a mistake of some kind (their causal judgments are influenced by information that is irrelevant to the truth of those judgments) or else (ii) the causal process account is not the whole story about causal relationships, as they are in the world. 
	For these reasons, although it is of course true that causation is one thing and our representations or judgments about it another, I believe it is illuminating to group together philosophical accounts of what causal is with psychological accounts of causal cognition and representation insofar as these focus on the same sorts of information about or features of causal relationships. 
Proceeding in this way, one may identify a number of influential theories of causal learning and judgment within empirical psychology that also seem to embody a broadly difference- making conception of causation or of causal representation. These will include accounts that take causal learning and judgment to involve the representation of contingency information (understood as having to do with a comparison between the frequency of the effect in the presence of the cause with the frequency of the effect in the absence of the cause). Examples include accounts of judgments of causal strength according to which this depends on p = P(O/A)- P(O/-A) (where A is some action the subject chooses and O an outcome) and Patricia Cheng’s causal power theory. Accounts according to which causal representation has the structure of a Bayes net (and/or according to which causal learning involves learning the structure of a Bayes net) are also naturally understood as difference-making accounts, since they make predictions about claims about how the probabilities of the values of effect variables will change depending upon changes of various sorts in the value of cause variables. 
	3. Geometrical/mechanical theories. 
Standing in contrast to difference-making theories are geometrical/mechanical theories. These focus on the role of connecting processes or more broadly on the role of what Scholl and Leslie, 1999, call “contact mechanical” relationships between cause and effect. “Mechanical” in this context is not easy to define, but roughly it at least includes, at the level of folk physics, those causal relationships which physical objects enter into in virtue of their possession of properties like solidity rigidity, and impenetrability. Usually the idea is that the presence of such a contact mechanical relationship is signaled by the holding of a rather specific spatio-temporal relationship between cause and effect. On some versions of this idea, there is a single characteristic spatio –temporal signature (e.g spatio-temporal contiguity) that is common to all casual relationships; on other versions, it is held, more plausibly, that different causal relationships will have different spatio-temporal signatures—collisions will differ in this respect from, say, support. 
In the philosophical literature, the most familiar recent examples of geometrical/ mechanical theories are the causal process or conserved quantity theories of Salmon (e.g, 1984) and Dowe (2000). Here the guiding thought is that some particular event c causes some other event e if and only if there is a connecting casual process from c to e, where this means roughly that there is a spatio-temporally continuous process linking cause and effect that transmits a conserved quantity such as energy and/or momentum. A paradigmatic example of such an interaction is one rigid object striking another and causing it to move, as when two billiard balls collide.
Within empirical psychology, there are a number of theories and research programs that draw on ideas that are broadly similar to those on which causal process theories focus. It thus seems natural to group these within the general category of geometrical mechanical accounts. These approaches downplay the significance of covariational or contingency information (including covarational information generated by interventions) in causal learning and judgment and instead focus on the role of spatio- temporal cues that are readily perceptually accessible and/or on “mechanical” information which seems to be associated with such cues. 
 One of the most straightforward examples of psychological research focusing on geometrical/mechanical causation is so-called “causal perception” in connection with collisions or “launching events” – phenomena which has been extensively studied by Michotte (1963), Leslie ( e.g., 1995) and others. Here the details of the spatio-temporal relationship between colliding objects guide the perception (or not) of a causal interaction and, as we shall see, at least under some conditions, this perception apparently does not depend on contingency or difference-making information about how these or similar objects would have moved in the absence of spatio-temporal contact. But within the general category of the geometrical/ mechanical, one might also include interactions having to do with solidity, occlusion, support, containment, entrainment, and impenetrability. Our understanding of such phenomena again seems to involve, at least in adults, causal knowledge of some form which is strongly guided by spatio-temporal or geometrical cues that are readily perceptually accessible 
Consider support. Adult humans easily recognize (e.g., on the basis of visual inspection) that an apparently solid physical object at rest on a solid surface in such a way that the boundaries of the surface extend beyond the object (e.g., a plate on a table) is typically supported by that surface and will move with the surface if the latter is not moved too abruptly. This seems to involve recognition of a causal relationship between the surface and the object. Adults (but not sufficiently young children- see below) also recognize that not just any kind of spatial contact between surface and object is sufficient for support and can sometimes determine, again from visual inspection, whether the contact is of such a character as to provide support. In all of these cases, causal relationships between the object and its support seem to be read off from their geometrical relationship (via visual perception) in a straightforward way. 
Within psychology, subjects’ understanding or representation of phenomena like those just described (collisions, support etc.) is often taken to involve notions like “force transmission” (Leslie, 1995) or “force dynamics” (Wolff, 2007) or to involve the deployment of a “theory of body” (Leslie again) or various core physical principles (Spelke et al, 1995) which specify, for example, that moving solid objects follow spatio-temporally continuous paths and cannot pass through each other. Often this is accompanied by the claim that the concepts and principles deployed in the recognition/ understanding of mechanical interactions like those described above serve as the basis for more general notions of causation and causal mechanism, which are then taken to be central to causal cognition in other circumstances as well—in other words, the experience of causal perception and the processes and representations associated with this somehow give us the concepts and capacities that underlie adult causal cognition . For example, Schlottman and Shanks, 1992, suggest that the “mechanism of causal perception… would provide a robust intuitive understanding of the concept of cause that is not fraught with the ambiguities encountered when trying to define cause” (p. 341). Similar suggestions can be found in Pinker, 2007, Spelke et al, 1995, Wolff, 2007. 
Although this is not made explicit in the psychological literature, presumably part of the motivation for invoking notions like “force transmission” (rather than the narrower notion of “causal process” described by Salmon, and Dowe) is that many paradigmatically mechanical phenomena do not seem to be very adequately captured accounts of the latter type. Seeing that a table supports a (stationary) plate does not (at least prima-facie) involve tracing causal processes and their intersections since there is no energy momentum exchange involved in the support. The table and apple do, however, exert forces on one another and it is presumably this that prompts psychologists like Leslie to attempt to subsume such phenomena under the broader category of “force transmission”. Of course, according to current physical theory, forces are not literally “transmitted” but the basic idea that phenomena like support (and for that matter, collisions) are to be understood in terms of contact forces is certainly correct. 
I emphasized above that to the extent that causal perception involves vision, it seems to be based largely on spatio-temporal or geometrical cues. However, as already intimated, the way in which adult humans conceptualize or understand (at a common-sense or folk level) mechanical phenomena like collisions, support, and so on seems to involve ideas about the solidity, rigidity, and impenetrability of bodies, as well as an appreciation of facts about their spatio-temporal relationships and relative motions. Such facts about rigidity, solidity, and so on don’t seem to be reducible to facts about spatio-temporal relationships. Conceptually, it seems to be one thing for an object to be at rest on a larger surface and another thing for the object to be supported by the surface—the latter requires not just that the object be in spatio-temporal contact with the surface but also that the surface be strong or rigid enough to support the object and that the object be maintained in that position by forces exerted by the surface, rather than by some other set of forces. (This is part of the folk or common sense conception of support, but it is also true from the point of view of physics.) Parallel remarks apply to collisions, blocking of the path of one object by another and so on. 
 This distinction between mechanical and spatio-temporal properties also has an empirical psychological component. It is widely thought to be possible for the visual system to process (see) phenomena that appear to violate naïve physics expectations involving mechanical properties —for example, one can see one solid object apparently pass through another, even while recognizing that this is “physically impossible”. (Leslie, 1995) . This has suggested to a number of writers that that the neural systems that process information about trajectories and spatio-temporal relationships are in some respects distinct in their operation from the systems that process mechanical features like impenetrability . For example, Leslie suggests on this basis that we possess a “theory of body” that characterizes various simple mechanical features of objects that is distinct from our understanding of the purely spatio-temporal aspects of object behavior. 
How then are mechanical and spatio-temporal properties related in causal perception? Very roughly, what often seems to happen is this: we operate in an environment in which many of the objects we view have mechanical properties like rigidity etc. (This is not to say of course that we necessarily “assume” that this is the case, at least in any sense that implies conscious or explicit entertainment of this assumption. Adult humans may make such assumptions but perhaps infants do not). Because objects have these features, it is possible to read off (or perceive) causal relationships from information about their spatio-temporal relationships in a fairly reliable fashion. If the objects with which we were dealing did not have features like rigidity and solidity, spatio-temporal information would often be a much less reliable source of causal information—thus spatio- temporal contact between two objects that are not solid may tell us little about whether the motion of one causally influences the motion of another, we can’t read off from the shape of a non-rigid key whether it will open a lock, and so on. Of course it is also true that sometimes the absence of rigidity will show up in spatio-temporal clues: the object will deform etc. 
 Although writers like Leslie might claim other wise, I think that one implication of the distinction between the spatio-temporal and the mechanical is that we should be wary of moving too readily from the observation that a subject is capable of causal perception in the sense of reliably discriminating between causal and non-causal relationships on the basis of spatio-temporal cues to the conclusion that the subject must be explicitly conceptualizing those causal relationships in terms of mechanical categories like rigidity and force. Reliable discrimination may require nothing more than that the objects with which we are dealing have certain mechanical properties and that certain spatio-temporal relationships are recognized, not that the subject possesses explicit concepts of such mechanical properties or their causal role. 
4. The Relationship Between DM and GM Theories
How are difference-making and geometrical mechanical ways of thinking about causation related to each other? Let is begin by noticing some differences. 
4.1. Type versus token. There are a number of difference-making accounts of so-called token (or singular) causation, both in the philosophical literature and elsewhere, with David Lewis’ (1973) version of a counterfactual theory of event causation being perhaps the most prominent. Nonetheless, the most natural domain of such theories seems to be so- called type causal claims – claims that some type of factor C causes or is causally relevant to another factor E, where C and E are kinds that may be repeatedly realized. This in turn is presumably connected to the fact that contingency or difference-making information is most naturally described in terms of relationships among types of repeatable events. 
By way of contrast, geometrical/mechanical theories seem to apply in the first instance to particular causal interactions involving individual events or occurrences – to token causation- - although attempts have been made to extend them to contexts involving type causal claims. This is presumably because it is particular pairs of events that are connected by causal processes and particular objects which stand in geometrical/ mechanical relationships involving contact forces. As a matter of phenomeonology, it also appears that one first detects such particular causal interactions on the basis of perceptual cues (causal perception) and only later, if at all, generalizes to type relations involving other cases—any generalization follows the awareness of the particular case, rather than preceding it. (See below for experimental evidence supporting this picture.) It is thus not surprising to find such experiences are one of the primary sources of so-called “singularist” views about causation (cf. Armstrong, 2004).
4.2. Domain-general versus domain specific. 
 Difference- making theories are domain-general in the sense that virtually any kind of event, or factor which is capable of variation may (in principle) stand in a difference-making relationship to another such event or factor. (Of course, it is an empirical matter which such relationships in fact hold in any particular case). This is a reflection of the fact that difference-making relationships (whether understood in terms of regularities, conditional probabilities, or counterfactuals) do not restrict the content of causal claims in the sense of excluding certain kinds of items as candidates for causal relata on apriori grounds. Thus difference-making causal relationships can hold between physical items like billiard balls, but also between mental items like beliefs, between mental and physical items (beliefs and behavior) between social and economic variables and so on. 
In contrast, geometrical/mechanical theories are domain-specific. The natural domain of application of such theories concerns the interactions of solid objects bearing specific spatio-temporal relations to one another, and which we are able to describe in terms of processes like energy/momentum transfer or physical forces involving contact between objects or surfaces. It is not obvious how to apply geometrical/ mechanical theories to causal relationships between factors that lack these features such as relationships involving mental events or economic variables. (e.g., increases in the money supply cause increases in inflation) 
			4.3. Comparative versus non-comparative. 
			Conceptually one of the most obvious differences between difference-making accounts and causal process accounts is that the latter (at least in standard philosophical formulations, such as those due to Salmon and Dowe) do not conceive of causal claims as comparative in the way that the former do. According to causal process accounts, whether c causes e on some particular occasion depends just on whether the appropriate connecting process or contact relationship linking c to e is present on that occasion. In particular, whether c causes e on that occasion does not depend on what happens or would happen with respect to e or e-like events on other occasions—either on other occasions in which c or c-like events occur or in cases in which they are absent. Indeed, it is a common claim of causal process theorists (and many others who are sympathetic to geometrical/mechanical approaches to causation) that allowing such dependence would violate the (apparently natural) intuition that whether c causes e should depend just on the “local” or “intrinsic” character of the connecting relationship between c and e: facts about what would happen to e if c had not occurred or if c-like events had or had not occurred on other occasions seem “extrinsic” to whether or not there is a causal relationship between c and e on this particular occasion. 
I believe that this feature of causal process theories is paralleled by our common sense picture of what is involved in particular examples of causal perception. Suppose that we see a moving billiard ball strike a second stationary ball and then see the latter begin to move, the spatio-temporal parameters governing the collision being such that we perceive that the collision caused the second ball to move. Our common sense picture is that all that we need for this perception (and the judgment that we base on it) is contained in “local” non-comparative information about the trajectories of the balls, their spatial contact, and the almost immediate subsequent motion of the second ball. In particular, this perception does not seem to require that we compare the actual motion of the balls that we perceive with some alternative – e.g., that we consider what would happen to the trajectory of the second ball if there was no collision. Indeed, it appears that we can perceive/judge/know that the collision with the first ball caused the second to move, even if we don’t know how or whether the second ball would have moved in the absence of the collision (for all we may know, collision with a third ball would have caused the second ball to move even in the absence of a collision with the first). In other words, the perceptual judgment that the collision caused the second ball to move does not seem to be based on considerations having to do with difference-making. Of course, in many ecologically natural circumstances (e.g., if no other cause of motion of the second ball is present and if it does not move spontaneously), adults will readily (and correctly) connect this perceptual causal judgment based on geometrical/mechanical cues to a difference-making judgment: they will judge that the second ball would not have moved if the collision with the first ball had not occurred and so on. So in such cases, at least, we are willing to move relatively seamlessly from perceptual causal judgments to judgments about difference-making. Nonetheless, the latter judgment seems (that is, from the point of view of our folk psychology of causal judgment which may of course mislead us) independent of the former; it seems like an additional thought that follows from the perception of causation, rather than serving as a basis for it. 
4.4 Additional Differences Between the Two Accounts. 
 A number of other observations from the philosophical literature seem to support this picture according to which ordinary causal judgment is guided by at two (at least) partially distinct ways of thinking about causation. 
 First, as a conceptual matter, geometrical/mechanical causal connectedness (or the operation of contact forces) is apparently not necessary for difference-making. This is shown by the observation that it seems prima-facie possible that one factor should act as a difference-maker for another even if there is no connecting process or spatio-temporal contact between the two. Theories that postulate action at a distance, such as Newtonian gravitational theory, provide an illustration of difference-making without contact action. 
 	 Second, geometrical/mechanical causal connectedness is also not sufficient for difference-making. Basically, this is because the presence or absence of such connectedness is too coarse-grained to capture the judgments of causal relevance that difference-making accounts embody. If I rub the tip of a cue stick in blue chalk, use the stick to strike the cue ball, which in turn strikes the eight ball, sending it into the corner pocket, the blue chalk may be transferred to the eight ball, via a spatio-temporally continuous process in which energy and momentum is conserved but the presence of the blue chalk is not what made the difference for whether or not the eight ball drops and still less is it responsible for the detailed behavior of the eight ball – its velocity when it falls into the pocket and so on (Hitchcock, 1995). Similarly when I bounce a tennis ball against a brick wall, there is a connecting causal process from the motion of my hand to the wall, but this motion and the impact of the ball do not make a difference for whether the wall stands up. 
 	As these examples illustrate, the true claim that there is a causal process linking X and Y does not tell us which features of X make a causal difference for various features of Y. Indeed, the presence of the connecting process does not even ensure that there is some feature of the process that makes a difference to the particular feature of Y that is of interest. This seems connected to the point that even veridical causal perception often does not disclose fine-grained difference-making information. For example, the experience of seeing that a collision with one billiard ball has caused another to move does not disclose what properties of the first ball are causally relevant to the details of the subsequent motion of the second ball --it does not tell us that the energy and momentum of the first ball are the crucial difference-making variables. Similarly, seeing that one object supports another does not tell us in any detailed way which features of their relationship make a difference for successful support—for example, it does not tell us about the relevance of the position of the center of gravity of the supported object. One implication of this that is relevant to psychology is that the fact that a subject is sensitive to, e.g., the difference between collisions involving causal interactions and sequences that do not involve causation does not automatically ensure that the subject has a detailed understanding of the difference making features of the collision. 
 	Despite this, it worth noting that when there is a causal process or a geometrical/ mechanical connection between X and Y, it is often heuristically useful to examine X or this connecting process in order to locate difference-making features for Y (even if the mere existence of the connection does not tell us what those features are). In other words, when there is such a “physical” connection, some feature of X may be one locus of the difference making; in the absence of such a connection it will often be plausible to conclude that the difference-making features for Y are not contained in X. Thus if one perceives that a collision with X causes Y to move, it will be a good bet that there are properties of X that are difference-makers for Y’s subsequent movement, even though this perception does not by itself tell us what these features are and they instead must be identified in some other way. For example, to understand the breaking of the bottle in detail one should focus on features of the rock that hit it and the interaction of this rock with the bottle rather than on the rock that missed. I will suggest below that this has implications for one possible role of causal perception in development: causal perception can tell us where to look for more fine-grained difference-making features, without requiring that we have already identified those features. 
In addition to the conceptual differences between GM and DM described above, they seem to lead to different causal judgments about particular cases, such as those involving causation by omission and double prevention. This is a familiar theme in the philosophical literature (cf. Hall, 2004), but I will use results from a recent series of psychological experiments to illustrate the point. Walsh and Sloman, forthcoming presented subjects with two scenarios. In the first, a coin standing unstably on its edge is about to fall tails. Billy and Suzy roll marbles in such a way that each will strike the coin and after impact the coin will land heads but Billy’s marble strikes first. In this scenario, 74% of subjects judged that Billy’s marble caused the coin to land heads.
In the second scenario, we have an unstable coin about to land heads. A third party rolls a marble in such a way that if it strikes the coin, it will land tails. Both Frank and Jane reach out to stop the marble. Frank reaches it first, stops it, and the coin lands heads; Jane does not reach the coin but she would have if Frank had not. In this case, only 18% judged that Frank caused the coin to land heads. 
Note that both scenarios have a very similar counterfactual or difference-making structure: (a) it is not the case that if Billy’s marble had not struck the coin, the coin would not have landed heads (since Suzy’s would have struck it). (b) It is the case that holding fixed the fact that Suzy’s marble does not strike the coin, the coin’s landing heads is counterfactually dependent on the impact of Billy’s marble. The judgment that Billy’s marble caused the coin to land heads is made despite (a) and (some would claim) on the basis of (b). In the second scenario, (a’) it is not the case that if Frank had not reached the coin, it would have landed heads (because Jane would have stopped it) but (b’) given that Jane does not stop the coin, the coins landing heads is counterfactually dependent on whether Frank reaches it. Nonetheless, far fewer (although a non-negligible proportion of ) subjects judge that Frank’s action caused the coin to land heads than the proportion who make the corresponding judgment in the Billy scenario. 
It is a natural thought that the difference in judgments about the two cases reflects the different role that geometrical/mechanical information plays in them. In the first scenario, there is spatio-temporal contact and the transmission of energy from Billy’s marble to the coin ( a collision) that we readily interpret as causal. In the second scenario, there is no spatio-temporal contact or connecting process between Frank’s interception of the marble and the coin’s landing heads. Although a more sophisticated version of a DM theory might judge otherwise, a simple version diverges in its judgments from those recommended by GM theories, with the latter seeing a difference between the two scenarios that the former does not recognize. Moreover, the latter seems closer (in this particular case) to the judgments that the majority of subjects make. The example illustrates how in some cases GM based considerations seem to operate independently of DM based considerations in influencing causal judgment. 
	5. Two Concepts of Causation?
One possible reaction to the differences between geometrical mechanical and difference-making accounts of causation is that this shows that we operate with two distinct “concepts” or “senses” of causation. Something like this position is adopted by Ned Hall (2004), whose candidates for the two concepts, which he calls dependence and production, coincide in significant measure, although not entirely, with the distinctions that I have drawn. However, there are at least two reasons why this reaction does not seem entirely satisfactory. First, as Hall recognizes (p.255), it isn’t clear why we should describe the situation in terms of there being two concepts rather than in some other way—e.g., in terms of their being two different ways that one event can be a cause of another, or (for yet another alternative) in terms of their being different accounts of a single concept of causation that focus on different strands or elements in that concept. 
A more fundamental reason why it seems unilluminating simply to rest content with a “two concepts” diagnosis is this: both conceptually and as matter of empirical psychology, the two concepts (or whatever) seem interconnected or interrelated in all sorts of ways. As we have noted, adults bring together both information about difference –making and information deriving from geometrical mechanical cues in arriving at causal judgments, and often move relatively seamlessly from geometrical mechanical information to conclusions about difference-making and conversely. Seeing that one object supports another, we often readily make the difference-making judgment that second will fall if we remove the former and use this information to guide planning and action. It thus seems that in addition to appreciating the differences between the geometrical mechanical and difference making approaches, we also need to better understand how adult causal judgment combines elements of both. 
6. Causal Perception in Launching Experiments 
I turn now to a more detailed look at some psychological research concerning causal perception, with a particular focus on dissociations of various kinds between perception and contingency-based causal judgment. This will illustrate some of the ideas and contrasts described in previous sections. 
 The general contours of the collision or “launching” phenomena studied by Michotte (1963) and subsequently by many (e.g. Leslie, Scholl) others are probably known to the reader. In a typical experiment subjects view an object A which moves in such a way that it appears to collide with or closely approach a second object B. After the collision A stops and very shortly afterwards B begins to move in the same direction as A’s previous movement. Depending in various delicate ways on the spatio-temporal parameters characterizing the collision, most (or at least many) subjects will report either a strong perceptual impression of causality or no such impression. The impression of causation persists even though subjects are aware that they are viewing two dimensional shapes on a computer screen (or in Michotte’s case film images projected on a screen) – that is, even though subjects know that they are looking at illusory causal interactions rather than the real thing. 
Although the launching effect has been extensively studied, it is certainly not the only case involving interactions among moving objects in which there is perception of causation. For example, when shapes are lined up in a column on a screen and exhibit staggered motion, the first shape to move is perceived as pulling the others, even if no spatial contact is present. Simultaneous motion of the shapes does not give rise to this impression. Other stimuli giving rise to perceptual impressions of causation involve “disintegration” and “bursting” (cf. Scholl and Tremoulet, 2000). Although spatio-temporal contiguity is not required for causal perception in such cases, it is still true it is the appearance of a characteristic spatio-temporal pattern that seems to guide causal perception. 
 7. Causal Perception and Contingency-Based Causal Judgment. In a fascinating series of experiments, Schlottman and Shanks (1992) investigated the relationship between what they called “judged” (this being casual judgment influenced by contingency information) causality and “perceived” causality, finding evidence for a dissociation. In their first experiment, subjects viewed launching-like events in which the temporal delay between A and B was varied in such a way that impact of A did not predict (was not correlated with) when B would move However, in half of the viewings, a color change in A reliably predicted when B would move. The motivation for this experiment was that verbal judgments of the strength of causal relatedness are known to track the contingency or covariation between potential causes and the effect. In particular, even when there is spatio-temporal contiguity between events A and B, if A is not a reliable predictor of B, but some third event C is, judgments of causal strength between C and B should increase over the course of the trials and judgments for the relation between A and B should drop – A is said in this case to be “discounted” (or overshadowed by C) as a cause of B. The color change = C was chosen because it was known on the basis of other evidence that subjects do not report a perception of causation when a color change in A precedes movement in B, although the color change is sufficiently perceptually salient that subjects will notice its association with B’s motion. 
Subjects were asked to “rate” the relationship between A and B along a scale, one end of which was labelled "A caused B to move", and the other end, "A did not cause B to move". The rating task was introduced with the following words: 
 	Your task in this experiment will be to judge how confident you are that A caused B to move or that A did not cause B to move. In other words, you
will judge just how "good" or "bad" a collision looks to you. 
Subjects were also prompted in this task by such questions as, “Did it look to you as though A hit B and caused it to move?” (p. 328). Schlottman and Shanks take these rating to be measures of perceived causality and find, strikingly, that the color changes had no effect on these ratings at the various temporal delays between A and B, although the temporal delay itself did of course influence these ratings. Schlottman and Shanks interpret this as evidence for a “dissociation” between perceived and judged causality – the alternative candidate C for the cause of B has no effect on the perceived causality between A and B (that is, as far as perceived causation goes, there is no discounting of A as a cause of B) even though (at least in other circumstances) the presence of such an alternative is known to affect causal judgment. 
In a second, more direct experiment subjects viewed launching events in which the color change not only predicted when B would move but whether it would move at all. In contingent trials, subjects saw launch events with a color change at the point of impact, on half of the trials. For the other half, object A remained in its starting position and B changed color and did not move. Thus the probability of movement in B given launching by A was 1.0 and the probability of movement of B in the absence of launching was 0. In the non-contingent trials, the subjects saw the same number of launch events with color changes as in the contingent trials . On the other half of trials, subjects saw A remaining in its starting position and a color change in B preceding its movement. Thus while B would move whenever there was a collision, it would also move whenever there was a color change, even without a collision. There was thus no contingency between collision with A and B’s movement. 
As before, subjects were asked to rate perceived causality in single launch events. They were also asked to judge how “necessary” collisions with A were for making B move. Ratings of perceived causality “show[ed] a substantial contiguity effect but no contingency effect whatsoever” (1992, p. 337) – that is ratings fell with increased temporal delay but were uninfluenced by the contingency between collision with A and subsequent movement of B. On the other hand, judgments of causal necessity showed a “large contingency effect and a much smaller contiguity effect”. (p. 337). Subjects’ spontaneous comments reflected this dissociation; several commented that on contingent problems with delay, they were aware that collision was necessary for A to move but that “it just did not look as if it should be.” On non-contingent problems with no temporal delay, they commented that “they knew the collision was not necessary for B to move but it looked as if it should be”. (328). 
 As Schlottman and Shanks interpret these experiments, they involve situations in which subjects reported perceiving that collision with A caused B’s movement (because the appropriate spatio-temporal relationship between A and B’s motion was present), but also claimed that collision with A was not necessary for B to move, which sounds like the claim that A was not a difference-making cause of B. The authors take this to show that distinct “mechanisms” underlie perceived and judged causality. If this interpretation is accepted, it does not seem farfetched to also take to take the experiments to illustrate a dissociation between two kinds of causal judgment, resulting from different psychological mechanisms, one based on perceived causality and reflecting elements of a geometrical/ mechanical conception of causation and the other reflecting a difference-making conception. 
More recent neuro-imaging data shows that causal perception and contingency-based causal judgment involves distinct neural regions or mechanisms and hence supports the conclusion that the brain processes underlying these are in principle dissociable. In particular causal perception of collisions involves V5/ MT, STS (superior temporal sulcus), and left IPS (intra-parietal sulcus). (Blakemore et al., 2001) V5/ MT is a higher visual area known to be involved in motion processing, and STS is known to be involved in the processing and recognition of complex visual stimuli including including those having to do with facial movements, hand actions, and movements suggesting animacy. Finding activation in MT/V5 is not in itself surprising (the region is sensitive to relative motion) but the greater activation in this area when causal events (as opposed to non-causal events) are perceived may suggest that causal events are perceived as more complex or that they trigger more processing than non-causal events. The other two regions (STS and IPS) are also often involved in the higher-level interpretation of visual events, although not part of occipital cortex. 
By contrast, contingency influenced causal judgment, including such judgments concerning mechanical interactions like collisions, is believed to involve more frontal areas, in particular dorso-lateral prefrontal cortex and , especially when motor action and planning are involved (as in tool use), also portions of parietal cortex. To my knowledge, it is not known what neural areas are involved in causal perception associated with other contact/mechanical phenomena such as support. 
At this point, it is worth pausing and relating these observations explicitly to some of the claims made in section 4 . I noted there that it seemed to be part of our common sense picture of collisions that we can tell whether one object has caused another to move just by noting that a collision with the right spatio-temporal parameters occurred; it appears that the contingency information on which difference-making accounts focus (how the second ball would have moved in the absence of a collision with the first) is not required for this assessment. The experimental results from Schlottman and Shanks seem consistent with this common sense picture, since they seem to imply that perception- based causal judgments or assessments based on individual collisions are independent of and can even be inconsistent with what contingency information suggests about causal relationships. Of course ordinary subjects will not be aware of the Schlottman and Shanks experiment, but it is a natural conjecture that the partial independence or dissociability of causal assessments based on geometrical mechanical cues and those based on contingency information underlies and motivates (at least in part) some of causal intuitions that both ordinary people and philosophers have about cases involving both geometrical mechanical and contingency information. In other words, the thought that one can tell, just on the basis of information about the local spatio-temporal parameters governing the relationship between two objects, and in the absence of supporting contingency information, that a collision with the first has caused the second to move is one source of the intuitions that underlie causal process accounts of causation. (I should perhaps add that I do not mean that mere possession of causal perception abilities also means one will possess a worked-out GM account of causation; my suggestion is rather that reflection on certain judgments associated with causal perception helps to make GM accounts seem plausible and that the dissociation in the Schlottman/Shanks experiments mirrors the way in which GM-based and contingency based judgments can come apart in particular cases.)
Now consider a thought experiment. Imagine a creature who possesses just one but not both of the capacities for causal learning and judgment exhibited in the Schlottman/ Shanks experiment or alternatively, possesses both capacities but is unable to integrate them—that is, a creature who either (i) is able to make the kinds of perceptual discriminations that we associate with causal perception (discriminates causal-looking launching events from events that do not look causal), but does not make causal judgments based on contingency information or (ii) has the opposite profile or (iii) has both capacities but does not connect or integrate them. The possibility envisioned under (iii) is that in the Schlottmann/Shanks experiment the subject would make both the same perceptual causal judgments that normal subjects do and the same contingency-based judgments but would not be puzzled or surprised by any inconsistency between the two classes of judgments, as the subjects in the Schlottman/Shanks experiment are. That is, the subject would not be surprised to see an interaction between A and B that “looks causal” in individual cases, but is not accompanied by any contingency between A and B. We might think of such a subject as possessing two entirely distinct and unconnected concepts of causation, corresponding respectively to aspects of the geometrical/mechanical conception and the difference-making conception. 
Are the subjects described under (i) - (iii) a “conceptual” possibility? The quoted terms are of course vague, but given the apparent conceptual distinctness of the geometrical/mechanical and the difference-making views of causation and the empirical results about dissociability described above, there is an obvious case for answering “yes” for each of (i) - (iii). Now let us ask whether such a subject possesses the full range of capacities for causal cognition that adult humans possess. I take it that there are obvious reasons to answer “no” to these questions. Normal adult capacities for causal cognition involve capacities for both sorts of causal judgment or assessment exhibited in the Schlottman/Shanks experiment as well as the ability to appreciate the interconnections between the two. 
I draw several conclusions from this thought experiment. First, it reinforces the claim that a simple “two distinct concepts” diagnosis of the relationship between the geometrical/mechanical and difference-making conceptions is incomplete and unsatisfying— if what we are interested in understanding is adult human causal concepts and casual thinking, we need to understand how these two ways of thinking about causation (or of assessing casual relationships) are interconnected, both psychologically and conceptually. Second, it appears that there is nothing inevitable or logically required about the eventual integration of these two sets of abilities and two ways of thinking with which they are apparently associated. This means that the issue of how they eventually come to be integrated in normal adult human causal thinking and whether there might be a stage in human development (or among some non-human animals) in which they are not fully integrated should be regarded as live questions. Third, although we will return to this issue below, even at this point it is hard to see how one might develop a difference-making conception of causation just out of a geometrical/mechanical conception that does not in any way incorporate difference-making considerations. Both conceptually and (it would appear from the Schottman/Shanks experiment) empirically, it appears there is nothing about the capacity to discriminate whether individual token events are joined by a connecting process that automatically carries with it the idea of those events standing in a difference-making relationship. So to the extent that human adult concepts of causation incorporate difference-making commitments, it is hard to see how these can emerge just from a generalization or extension of experiences involving causal perception, unless these are already sensitive to or in some way incorporate difference-making considerations. Thus, contrary to what is sometimes suggested, it looks as though causal perception (at least insofar as this is insensitive to difference-making) or the representations that underlie causal perception cannot be the foundation for all other forms of causal thinking. 
This last observation suggests another possibility that may have already occurred to the reader—instead of taking causal perception or geometrical mechanical connectedness to be the foundation for causal thinking generally, why not turn things around and take difference-making to the fundamental notion? In other words, when subjects perceive episodes involving collisions, support etc as causal, we should think of them as engaging in perceptual judgments or perceptual recognition (or at least judgment/recognition that is based on perception) that certain features of those episodes are difference makers: the subject who perceives that the collision with the first ball caused the second to move judges or recognizes that the collision was a difference-maker for the motion of the second ball, the subject who sees that the table supports the plate recognizes that the presence of the table is a difference-maker for the position of the plate and so on. If this idea could be made to work, it would seem to suggest that the opposition we initially set up between difference-making and the geometrical mechanical (as well as the way philosophers formulate the geometrical mechanical) is misconceived—the geometrical/ mechanical approach is just a particular version of the difference-making approach, in which mechanical properties are taken to be the difference -makers. 
 Some apparent empirical support for this idea can be found in the observation that in some cases (e.g development of an appreciation of support) causal perception seems to involve learning which features are difference-makers (Cf. Baillargeon et al., 1995) . On the other hand, this idea doesn’t seem to do full justice to all of the features of causal perception. In particular, if causal perception just involves perceptual recognition of contingency relations among mechanical properties, it is not easy to see how to account for dissociation results like those reported by Schlottman and Shanks, in which subjects report causal perception that is not just unsupported by but actually inconsistent with contingency information.
I will return to these questions below, but I want first to take a brief look at some related issues involving causal perception and understanding in infancy. 
	 8. Causal Perception in Infancy. 
An important question that has long intrigued developmental psychologists concerns the origins of the capacity for causal perception in launching events. Is this capacity “innate”, as Michotte himself thought, (whatever “innate” might mean) or is it acquired or learned and if so, when? In a frequently cited experiment, Leslie and Keeble (1987) presented evidence, based on a looking time or dishabituation paradigm that this capacity is present at an early age – that, as the tile of their paper claims, six month old infants “perceive causality”. Since the dishabitutation paradigm will figure importantly in some aspects of what follows, a brief summary is in order. 
In a simple version of this paradigm, the infant is exposed repeatedly to a stimulus until her duration of looking at the stimulus falls back to some baseline. A novel stimulus is then presented and if this results in a significant increase in looking time (dishabitutation), this is taken to show (at least) that the infant can discriminate between the novel stimulus and the stimulus to which she has been previously habituated. This conclusion seems relatively uncontroversial; controversy arises, however, when infant differences in looking time are given richer, interpretations, involving more sophisticated forms of representation and cogniton/information processing, as they frequently are in the developmental literature. 
Here, it will be useful to distinguish two possibilities, which I will call the “violation of expectations interpretation” and the “causal knowledge and reasoning interpretation”. As a matter of empirical fact, infants will often look longer at events that adults consider physically or causally impossible, such as the apparent passage of one solid object through another, discontinuous object trajectories and so on. This is often taken to show that the infant is “surprised” by such events or that the events “violate the infant’s expectations”—that is, the infant has expectations regarding the usual or expected behavior of physical objects and responds to behavior that is inconsistent with these. Under some suitable construal, this interpretation also strikes me as often warranted. Note, though, that by itself this interpretation commits us to nothing very specific about the nature or content of the violated expectations—for all that has been said, the expectations in question might be merely implicit or procedural, perhaps reflecting in part features of visual or attentional processing that influence looking behavior, but that are not “explicitly” represented and not available for abstract reasoning or inference or naturally described as knowledge that certain principles hold. Nor should we necessarily assume that the expectations are casual in character (on any reasonable understanding of “causal”) After all, even adults have many expectations that various patterns will persist that don’t take the form of causal beliefs about those patterns – think of expectations about the seasons (violations of which are readily noticed) but which often do not take the form of any causal understanding of why summer follows spring. Association is not causation and expectations based on experience with associations need not involve causal beliefs, still less correct causal beliefs. 
 By contrast, the “causal knowledge and reasoning interpretation” does make much more specific claims about the nature of the infant’s expectations that are revealed in looking-time studies – it is claimed that these encode distinctively causal knowledge of principles governing the behavior and interaction of bodies, that in virtue of possessing these the infant is able reason about or make inferences regarding elementary features of physical causation, as exhibited in launching events etc. and that this in turn that explains features of infant looking-time behavior. Both the violations of expectations and the causal knowledge interpretations thus go beyond the mere observation that infants will distinguish in looking behavior among certain events, and offer explanations about why this behavior occurs (or of the processing that lies behind it) but the causal knowledge interpretation offers a much more specific and cognitively richer explanation. To support the causal knowledge interpretation, one would need to provide evidence that discriminates in favor of that interpretation and against the violation of expectations interpretation. For the moment, I want to postpone considering what evidence might play this role and whether (and when) this richer interpretation is justified; I will return to this issue below.
Earlier experiments by Leslie, using looking time methods, had shown that young infants are sensitive to the difference between launching type events in which there is a spatio-temporal gap (and which of course are not perceived as causal by adults) and those in which there is no such gap. However, this does not rule out the possibility that the infants respond differently simply because they perceive the difference in the spatio –temporal parameters that characterize the two sets of events, and not because they perceive the first interaction as causal and the second as not. Leslie and Keeble (1987) attempted to address this possibility by means of an experimental design that compared the responses of infants to two sequences of events and their ‘time reverses”. In the “causal” sequence, infants first saw moving A strike stationary B and B begin to move with a temporal delay that leads adults to perceive the interaction as casual; they also saw a reverse of this sequence in which B moved and struck A, which was stationary. The second “non-causal” sequence and its reverse were just like the first except that there was a noticeable temporal gap between the impact and subsequent movement, so that adults did not perceive the interaction as causal. Infants looked longer at the reversed sequence in the causal case than in the non- causal case. Leslie and Keeble interpreted this as showing that the infants were responding to the distinctively causal features of the interaction in the first sequence; their reasoning was that in the case of the casual sequence, the reverse sequence involved a causal change in the roles of A and B— the motion of A went from being the cause to being the effect. The second sequence and its reverse involved no such change in causal role but merely a change in spatio-temporal properties. According to Leslie and Keeble, infants looked longer at the first change because they saw it as a causal change rather than just a change in spatio-temporal properties. The authors conclude from this and other experimental results that infants can perceive causation in collisions in essentially the same way as adults do and that this capacity is innate, since it appears early in development.
Subsequent studies have challenged the claim of innateness, presenting instead a picture in which the capacity for causal perception develops over time, as the result of learning (Cohen et al, 1998). Nonetheless, there seems to be general agreement that the capacity to discriminate collision type events that look causal to adults from those that do not emerges relatively early. 
 Looking-time experiments have been used to probe many other phenomena in which infants seem visually sensitive to causal features of objects and their interactions and to “violations” of normal causal and physical behavior. These include experiments showing sensitivity to violations of object permanence (e.g. an object moving behind a screen fails to appear at gaps in the screen (Baillergon et al, 1995)) , object cohesion (objects whose parts fail to move together as cohesive wholes), Spelke et al (1995), impenetrability (a solid object moving behind a screen appears to pass through another solid object) and support (showing, e.g., that infants look longer at an event in which an object appears to be suspended in mid-air without support than at n otherwise similar event in which the object is supported by a platform in a normal fashion). Like the Leslie and Keeble experiment, these results are often interpreted as showing not just that infants make certain perceptual discriminations but that they have knowledge of or are capable of reasoning with basic physical ideas concerning mechanical or contact causation, impenetrability, support, and so on and that they possess adult-like concepts of physical causation.
One reason for skepticism about these last claims has already been alluded to—it isn’t obvious that the expectations the infants possess are distinctively causal. Another relevant consideration has to do with the distinction between, on the one hand, the ability to make perceptual discriminations based on membership (or not) in some category X, and, on the other hand, possession of the (or “a”) concept of X or the capacity to reason about X. Of course the notion of “possessing a concept” is notoriously murky. I assume, however, that if this notion has any utility at all, we cannot automatically conclude just from the fact that a subject has the capacity to perceptually distinguish between instances and non –instances of category X that the subject possesses adult human understanding of the concept of X or adult like appreciation of the principles governing X. A cat may be able to perceptually distinguish dogs from non-dogs, but this does not necessarily mean the cat possesses a human-like concept of “dog” (loyal, man’s best friend, related to wolves etc.) Similarly, it does not follow just from the fact that a subject is able to distinguish interactions that “look” causal from those that are not that the subject possesses a full fledged adult-like concept of causation that is available for other forms of reasoning or that the subject has abilities to generalize, conceptualize, theorize, and reason about causation that are similar to those of adult humans—it is always a further, empirical question whether subjects with the former, perceptual abilities also possess the latter abilities. This is so both for the concept of causation associated with causal process or geometrical/mechanical accounts, and even more obviously so (in view of the dissociation results above) for the concept of a cause as difference-maker 
 What evidence might be relevant to establishing that pre-verbal infants and non-verbal animals possess something like a concept of causation rather than just capacities for causal perception? Let me suggest two relevant considerations, which draw on my discussion in earlier sections. (I do not claim that either consideration or their conjunction is sufficient and am not sure whether either is strictly necessary.) 
Both considerations have to do with the extent to which the discriminations based on causal perception are connected to or integrated with an appreciation of the causal significance of difference-making considerations. In section 7, we considered a thought experiment involving a subject who failed to integrate the results of causal perception with information involving observed contingencies (“observed” as opposed to generated by the subjects own actions or manipulations) . To the extent that pre-verbal infants or nonverbal animals with a capacity for causal perception fail to exhibit such integration, it seems to me that this would be some evidence that their causal perception abilities did not provide them anything like a full adult-like concept of causation. 
Since I am a philosopher, I hesitate to suggest a specific experimental design, but one possibility might be a sort of an analogue to the Schlottman/Shanks experiment in which infants or non –human animals are shown displays involving both opportunities for causal perception (e.g. launching events involving X and Y) and contingency information involving the same events X and Y. In the first condition the contingency information is consistent with the launching relationships—that is, the interactions between X and Y look causal and there is contingency between X and Y. In the second condition, there is inconsistency between launching and contingency; there is again launching, but now no contingency between X and Y. The question would be whether the subjects look longer at the displays in the second condition, showing that they have the expectations about the relationship between geometrical mechanical contact and contingency that human adults have. 
9. Dissociations Between Seeing and Acting 
A second relevant set of considerations bearing on the possession of an adult-like concept of causation and capacity for causal cognition has to do with the extent to which there is integration between causal perception abilities and the appropriate use of difference making information in action. Consider a normal adult given a choice between (i) rolling a ball down a ramp in such a way that it will move via an unobstructed path to collide with a second ball and cause it move and (ii) rolling a ball down a ramp along which there is a visible barrier that will prevent the first ball from striking the second. The adult will be able to see at a glance that the impact of the first ball will cause the second to move in case (i) but not in case (ii). Moreover, if for some reason the adult wants to make the second ball move, she will choose to roll the ball down the first ramp rather than the second. In other words, the adult will be able to use causal information obtained perceptually on the basis of geometrical mechanical clues to guide her choice of action and manipulative activities. Ordinarily, we would think that an adult who had normal capacities for manipulation, but who behaved as though she failed to recognize that the choice of (i) rather than (ii) was superior from the point of view of manipulating the second ball had less than full causal understanding of the structures corresponding to (i) and (ii), even if other measures indicated perceptual sensitivity to the difference between (i) and (ii). 
Although there is empirical disagreement about how extensive such dissociations are, there is certainly evidence that in some situations, both infants and non –human animals fail to exploit in their behavior the geometrical-mechanical causal knowledge that they are claimed to possess on the basis of looking time results—that is, they do not behave like the “normal adult” described above. 
 As one illustration, consider an experiment by Spelke et al. (1992) in which four month old infants are exposed of one of two test events. In the first, the infants are shown an apparently sold table which is then placed being an occluded. A ball is then dropped toward the surface of the table. In the first test condition, the screen is removed to show the ball resting on the table—the outcome that respects ordinary physical or contact mechanical constraints. In the second condition, the dropped ball is shown under the table, a violation of these constraints. The infants look longer at the second outcome, suggesting (to a number of psychologists, including Spelke) that the infants “understand” that the ball could not pass through a solid object. However when similar display is used and much older children (two years old) are given the opportunity to search for the ball, they tend to search under the table rather than on top of it, suggesting that that they are unable to make use of the physical knowledge attributed to them on the basis of the looking time experiments in conducting their search. Interestingly, a similar dissociation is found in several species of adult monkeys (rhesus and cotton-top tamarins ) -- they also will look longer at a display in which removal of an occluder seems to suggest that a dropped object has fallen through a solid surface but will search for the object under the surface (Hauser, 2001) . A number of other experiments reveal similar patterns of dissociation (Santos and Hauser, 2002). 
In the experiment just described, the dissociation is between the causal or physical understanding (allegedly) revealed in looking-time experiments and the causal understanding revealed in actions involving searching. From the point of view of an interventionist framework for thinking about causation, it would be even more revealing to look for dissociations between apparent perceptual sensitivity to causal relationships (as assessed by looking time measures) and sensitivity to causal relationships as revealed in action tasks involving opportunities for manipulation. From an interventionist viewpoint an appreciation of the implications of casual information for manipulation and intervention plays a particularly central role in causal thinking and in the possession of full fledged causal concepts – it is particularly diagnostic of whether the subject has causal beliefs rather than just expectations based on associations. The hypothetical experiment described at the beginning of this section is one such “intervention” experiment. 
 		10. Consequences and Conclusion 
Suppose, for the sake of argument, that the causal perception/ action dissociation just described is (at least to some extent) “real”. What would follow from this about the role of causal perception in causal understanding and in the achievement of adult like capacities for casual cognition? 
 We may distinguish several different possibilities: 
10.1. Causal perception as expressed in sensitivity to geometrical/mechanical clues reveals possession of adult like causal concepts and capacities for causal cognition even if it is not integrated into action. This position is advocated by Spelke (e.g., 1992) among others. It is claimed that infant failure to act successfully on the causal knowledge that (it is supposed ) they can be shown to posses on the basis of looking time studies can be attributed to performance failures rather than limitations in competence in causal understanding. In other words, according to this position, looking-time experiments show that infants have adult- like competence in terms of their grasp of basic causal concepts and principles. However, because of various performance limitations, they are not always able to reflect this understanding in their actions – this is what accounts for seeing/ acting dissociations. A number of possible candidates for these performance limitations have been proposed: limitations on manual dexterity and motor control, failures to inhibit or control pre-potent responses that lead to normatively incorrect behavior in searching and reaching tasks, and more general limitations in planning, short term memory and/ or executive control. I take it to be is crucial to this position that these limitations are conceived of as “external” to the infant’s casual knowledge –- that is, they may affect the expression of that knowledge in action, but do not indicate that the knowledge in question is limited or underdeveloped in comparison with adults. 
A natural further extension of this line of thought is that to the extent that infants have causal knowledge in the absence of the ability to exploit it in successful manipulation, this shows that the infants capacities to intervene and manipulate are not fundamental to the acquisition/development of causal knowledge (perhaps Spelke et al, 1992). Indeed, it follows that there is no fundamental link between causal knowledge and knowledge relevant to manipulation at all. Instead, at a fundamental level causal understanding is about the appreciation of the significance of geometrical mechanical relationships of the sort associated with action by contact. Infants’ perceptual behavior (with respect to looking time etc.) is more reflective of their causal knowledge than their capacities for (non –perceptual) action involving searching grasping manipulating etc. 
Thus, at least when construed as a psychological/developmental theory about the origins and character of causal knowledge, interventionist accounts are mistaken—they assign too central a role to the connection between causation and action. To the extent there also exist dissociations between the causal information revealed by perception and appreciation of the significance of difference-making information more generally (whether this results from action of passive observation), one might argue for a similar negative assessment of difference-making treatments of causation generally, at least when construed as psychological theories. 
 10.2. Infant causal perception does not require adult like causal concepts and understanding although it may play a role in the development of these. According to this second position, adult causal concepts and reasoning involve abilities that genuinely develop over time and that are not fully present in infants with capacities for various forms of causal perception. Causal perception involving geometrical/mechanical cues may (in fact, probably does—see below) play an important bootstrapping role in facilitating the learning and development of full- fledged adult causal concepts and capacities for causal cognition, but the latter go well beyond the abilities that are deployed in causal perception tasks-- the content of what is learned is not just a generalization of whatever is at work in the perception of launching, or a concept/representation corresponding to the output of a “Michottean” module that is activated in causal perception. In particular, adult causal cognition requires some appreciation of the role of contingency information and some appreciation of the implications of causal knowledge for action and planning. 
There are a number of reasons why this second position (10.2) seems more plausible than the first position (10.1). In what follows I briefly review some new considerations and then return to some that have already been introduced. 
 As I have already argued, the results from looking time experiments do not seem to require an interpretation in terms of infant possession of rich causal knowledge – weaker, “violations of expectations” interpretations often seem at least as plausible. Moreover, prima-facie, the case for such weaker interpretations seems strengthened to the extent that infant causal perception abilities do not seem too carry with them the kind of appreciation of the significance of causal information for action and planning that are characteristic of adult causal cognition – this is exactly what we would expect if infant causal perception did not really show the possession of adult like causal concepts and understanding. In other words, the apparent failure of the looking time results, taken in themselves, to discriminate between a rich causal interpretation and a weaker violation of expectations interpretation, coupled with apparent perception/action dissociations seems to provide a prima facie case against the rich causal interpretation. Thus, in order to defend 9.1), the evidence that perception/action dissociations merely reflect performance limitations needs to be strong. 
However, many of the empirical arguments for these limitations seem problematic. Some perception/action dissociations persist for human two year olds even though they do not have the manual dexterity limitations of infants. Moreover, as noted, such dissociations are also present in adult rhesus and cotton-top tamerin monkeys who appear to have no problems with manual dexterity at all. In addition, two year old human children and adult monkeys succeed on many standard tests of inhibition, suggesting that something more specific than a general failure of inhibitory mechanisms underlies the dissociation. More fundamentally, many of the proposed performance limitations do not successfully explain a striking feature of dissociations, which is that they seem to occur much more frequently in connection with failures to exploit causal or mechanical information in action than in connection with spatio-temporal or numerical information. For example, Santos 2004 shows that adult rhesus monkeys perform successfully in searches for hidden objects when these can be located just by using spatiotemporal information but fail on otherwise similar search tasks requiring use of causal mechanical information. This pattern of failure suggests that there is some specific problem about the integration of geometrical /mechanical based causal information (as opposed to numerical or spatio- temporal information) into action, despite the fact subjects seem to exhibit sensitivity to this causal information in looking time studies.
We noted earlier that perception of causation in collisions seems to activate structures in the occipital (MT/V5) and temporal areas (STS), although it does also activate the IPS. By contrast, planning, and the organization/ carrying out of complex actions (as well as inhibition of prepotent responses) involves parietal and prefrontal areas, including dorsolateral PFC. As we have seen, DLPFC is also differentially activated in contingency sensitive causal judgments of various sorts (as opposed to causal perception). Various aspects of tool use and recognition also activate parietal areas. A natural although admittedly speculative conjecture is that some of the causal perception/action dissociations described above involve a failure in infants and non-human primates to integrate processing in visual and temporal areas involved in causal perception with processing in parietal and frontal areas —either because the former develop somewhat before the latter or because their full integration and coordinated use only occurs several years or more after birth in humans and may not occur at all in non-human primates. (cf. Johnson, 2005).
 Whether or not these neurobiological speculations are correct, it seems plausible that (as I have argued) mature human causal understanding involves the successful integration of systems involved in causal perception and systems involved in planning, action, and successful manipulation and that the action/causal perception dissociations described above suggest failures to achieve this kind of integration. To the extent this is so, it seems question-begging to describe subjects exhibiting the dissociations as possessing human adult like causal knowledge and abilities and merely facing performance limitations on its expression in action, especially if the source of those performance limitations is immaturity in or lack of integration with neural areas involved in planning of action. The monkeys and human infants described above do not suffer from “performance limitations” merely in the sense that, say, they know that (1) C causes E, recognize that (2) if C causes E, then if it is possible to manipulate C, this is a way of manipulating E, but (3) face obstacles to their ability to manipulate C, such as limitations in manual dexterity. Rather they act as though their alleged causal understanding does not incorporate the link between represented by (2). Or at least their causal understanding is such that recognition of (2) doesn’t get integrated into their action and planning in the way that it would in a normal human adult—again not because of an inability to perform the relevant action but because the relevance of the causal information they possess for action and planning doesn’t seem to be recognized. This seems more like a limitation on the subject’s causal understanding than an extrinsic obstacle to its expression in action. To put the point in terms of the neurobiological speculations described above, my suggestion is that immature development of prefrontal and parietal structures or their lack of integration with temporal and occipital structures involved in causal perception is not a mere performance limitation on the expression of causal competence—instead the involvement of the former structures is essential to human adult causal understanding. 
 A number of considerations discussed in earlier sections seem to reinforce the judgment that possession of causal perception abilities by themselves does not automatically yield adult like capacities for causal learning and judgment. The Schlottman/Shanks dissociation results show that the deliverances of causal perception are relatively insensitive to contingency or difference-making information, at least under appropriate conditions. This suggests that it is not just logically but also psychologically possible for subjects to have the experiences and to make the discriminations associated with causal perception, while failing to integrate this perceptual ability ( and whatever representations underlie it) with an appreciation of the role of contingency information in causal judgment. The fact within the philosophical literature the development of the ideas associated with causal perception (continuity of trajectories, the role of spatial contact etc) seem to yield a way of thinking about causation that is conceptually distinct from the difference-making conception (with respect to domain –specificity, the role of comparative information and so on) reinforces this point. 
I suggested above that although causal perception abilities do not necessarily require the presence of adult like capacities for causal cognition, the former may well play an important role in the development of the latter. I conclude by sketching one possible way in which this might occur, which draws on observations from Sec. 4.4. Suppose that we have a primitive (either innate or very early emerging) mechanism (the GM mechanism) that notes or keeps track of spatio-temporal coincidences and Michottean-type interactions, and perhaps certain other types of mechanical interactions that have distinctive spatio-temporal signatures as well. As a matter of empirical fact, in ecologically normal situations, these interactions will also exhibit contingency relations—the second ball tends to move when and only when the first ball strikes it and so on. Although young infants are sensitive to and learn from contingency information (e.g., they learn from classical and operant conditioning) they do not necessarily or automatically integrate such information with the information to which the GM mechanism is sensitive—instead this integration has to be achieved or learned. That is, it is only gradually that the infant comes to learn that there is a correlation or connection between whether the first ball exhibits a Michottean interaction with the second and whether the motion of the second is contingent on the movement of the first. The infant comes to learn which specific features of the first ball and its motion are difference-makers for the motion of the second even later. (Recall from 4.4 that perceptual awareness of a causal connection between the balls does not require or necessarily present us with fine-grained information about difference-makng). More generally, the infant comes to learn which spatio –temporal relations (to which it may be previously sensitive) are clues to the existence of a difference- making relation and which are not. For example, as we have seen, the infant gradually learns that not just any spatial contact is sufficient for support (the wrong sort of spatial contact makes no difference for whether there will be support), that more substantial spatial overlap will often make a difference for whether there is support and so on. Initial focus on these spatio temporal relationships in mechanical interactions thus allows the infant to begin to extract or appreciate a more general category of difference-making, of which difference-making relationships mediated by mechanical interactions are just one type. Thus the broader category of difference-making is taken to involve something that can be present even in the absence of obvious spatio-temporal connectedness. We may then conjecture that at least sometimes when difference making is present and there is no obvious mediating mechanism, that a hidden mechanism or connecting process is present – a conjecture that often turns out to be empirically correct and heuristically fruitful. 

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