Concepts in Perception Author(s): Tim Crane Source: Analysis, Vol. 48, No. 3 (Jun., 1988), pp. 150-153 Published by: Oxford University Press on behalf of The Analysis Committee Stable URL: https://www.jstor.org/stable/3328220 Accessed: 17-08-2018 13:31 UTC JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms The Analysis Committee, Oxford University Press are collaborating with JSTOR to digitize, preserve and extend access to Analysis This content downloaded from 94.192.49.60 on Fri, 17 Aug 2018 13:31:04 UTC All use subject to https://about.jstor.org/terms 150 ANALYSIS The real question is: what produces these conflicting inclinations, to believe thatamoves, and that it doesn't, at the same time? I think the answer is that motion includes two distinct concepts, each with its own perceptual mechanism: moving (motion at an instant), and having moved (being in different places at different times). We know we can see that a has moved without ever seeing it moving; and the converse is also true. We know we can see something moving without seeing that it's moved, since, as we know, a moving object can catch our eye when a stationary one wouldn't. In other words, we have an independent perceptual mechanism for seeing things moving. It may, of course, take time: aybe we can't see absolutely instantaneous motion. But the mechanism can still show us perceptibly instantaneous motion: that is, motion over an imperceptibly small time span, which we conceive to be instantaneous. And when this mechanism (rightly or wrongly) shows us a moving, it will naturally incline us also to believe that a has moved: since moving for any finite time entails having moved. So it also inclines us to believe simply that a moves: it gives us a perceptual experience whose content is Fa. And normally, of course, when that experience is veridical, it will be confirmed by the mechanism which shows us that, over a perceptible time span, a has moved. But it needn't be so confirmed; and in the Waterfall Illusion, it isn't: the two mechanisms simultaneously give us conflicting perceptual experiences. In short, not only must we credit the Waterfall Illusion experience with containing the concept F, in order to explain its contradictory content, we can. So we should. It is an illusion to suppose, as Crane does, that this illusion shows perceptual experience not to be composed of concepts.' Darwin College, ? D. H. MELLOR 1988 Cambridge CB3 9EU 'Notwithstanding our disagreement, the above owes much to Mr Crane's replies to my earlier criticisms of his paper. CONCEPTS IN PERCEPTION By TIM CRANE I CAN agree with much of what D. H. Mellor says in his response to my paper ('Crane's Waterfall Illusion' ANALYSIS, above pp. 147-152). I can agree that perception in some sense 'aims' at truth, that its function 'is to tell us how the world truly is' (p. 149). I can This content downloaded from 94.192.49.60 on Fri, 17 Aug 2018 13:31:04 UTC All use subject to https://about.jstor.org/terms CONCEPTS IN PERCEPTION 151 agree that perception normally inclines us to believe that what is perceived is the case we normally believe what we see. And I can agree with Mellor's proposal that the ability to perceive motion might be the product of two distinct but related mechanisms. The disagreement between us is over the tentative conclusion I drew from my reflections on the Waterfall Illusion: that the content of perception is not composed of concepts. Mellor seems to be sceptical about the thesis that there could be a state with a content which is not composed of concepts. On the face of it, there is something odd about this thesis, since concepts are often defined as the constituents of contents. If I am to defend my reading of the Waterfall Illusion, I must try and make this thesis more palatable. The substance of Mellor's criticism is that the content of the illusion should not be constructed (as I construe it) as Fa & -Fa, but as the conjunction of two distinct contents, Fa and Fa, each of which the perceiver is inclined to believe. One of these inclinations, as it were, 'wins out', presumably because of its support from other beliefs and perceptions. In my paper I argued that the problem for those who believe that the content of perception is conceptual arises because the Waterfall Illusion is an experience with a single contradictory content. On Mellor's interpretation of the illusion, this problem simply does not arise. His concern is to preserve the equation of perception with an inclination to believe, in order to capture the sense in which perception 'aims' at truth, for this sense (while distinct) cannot be unrelated to the sense in which belief aims at truth. But I doubt whether this is the whole story. How can the notion of an inclination to believe capture what is distinctive about the content of perception? In particular, how can it explain the general fact (of which the Waterfall Illusion is an illustration) that, unlike beliefs, the contents of one's perceptual states cannot be revised in response to further evidence? If perceptions were simply inclinations to believe, one would expect that the inclination which 'loses' (in our case, that a is moving) would no longer be present to the mind. This is surely so with non-perceptual inclinations to believe: once conclusive evidence is presented against one's (non-perceptual) inclination to believe that p, it would be irrational to continue to be inclined to believe that p. But in the case of the Waterfall Illusion, the (alleged) inclination to believe that a is moving remains even after conclusive evidence has been assembled against it. So the question remains: what distinguishes the perceptual inclination from the non-perceptual one? I can concede that perceptions normally involve an inclination to believe. But to say this is just to say that perceptions are generally reliable in the production of beliefs; and this is not news. The real question, as Mellor says, is how phenomena like the Waterfall Illusion come about, and what they tell us about the distinction This content downloaded from 94.192.49.60 on Fri, 17 Aug 2018 13:31:04 UTC All use subject to https://about.jstor.org/terms 152 ANALYSIS between perception and belief. Mellor has a proposal about this, which (in part) I find plausible: the perception of motion is the result of two mechanisms, corresponding to the ideas of moving and having moved. Mellor thinks that these two mechanisms deliver perceptual experiences whose contents are composed of concepts; I do not. But if I am to be right about the content of perception, then I have to explain why not; that is, I have to explain how a perception that p can have the content p without being composed of the concepts that the belief that p is. This explanation can only be complete when an adequate account of the possession of concepts is given; here I can only gesture at such an account. It is well known that the picture of perception suggested by much recent work in the philosophy and psychology of perception (and to my mind, supported by the existence of the Waterfall Illusion) is that of the perceptual system as an information processor. The system is in states with informational content, and they normally produce beliefs which have those very same contents. This idea is quite innocuous: the perception that p normally produces the belief that p. When we have beliefs, their contents are composed of concepts; we possess (whatever this might mean) the concepts which are the constituents of the contents. It may appear that the perception that p is composed of the concepts that the belief that p is. But this is a mistake, resulting from assimilating the nature of belief to the nature of perception. On the picture I favour, the possession of concepts is part of what marks the distinction between someone who has genuine beliefs (and other propositional attitudes) and a mere information processor. The contents of the states of the perceptual system are, of course, describable (by a theorist) in terms of certain concepts, but the system does not possess those concepts. It is not a thinker or an agent, and has no propositional attitudes. It is in states with content in the way that a thermometer is: a thermometer can indicate that the temperature is 70 degrees without possessing the concept of a degree, or of temperature. There is no general problem about things being in such states the perceptual system is just another instance. As I see it, one of the attractions for the philosophy of mind of the idea of an information processing theory of a perceptual system (e.g. the auditory or visual systems) is the possibility of an explanation of how perceivers can come to be in states of a certain kind in virtue of their perceptual systems being states of other kinds. (A simple analogy might help: our lungs expand and contract, and because they do so, we breathe. But the lungs do not breathe.) However, it may be responded that although perceptual systems are not possessors of concepts, perceivers do need to possess (perhaps tacitly) the concepts which can be used to characterize the informational output of the perceptual systems, in order to have beliefs based on perception. I do not agree. For one thing, this This content downloaded from 94.192.49.60 on Fri, 17 Aug 2018 13:31:04 UTC All use subject to https://about.jstor.org/terms CONCEPTS IN PERCEPTION 153 response rests on a dubious notion of concept possession, which entirely obscures the well-established distinction between personal and sub-personal psychological states. For another, it is prima facie implausible to suppose that perceivers need to possess the concepts which can be used to characterize the content of perceptual states, in order to be in those states. Of course, someone who knows a lot about (say) the visual system will possess these concepts, but he will not need to possess them in order to see. Information-processing theories of vision (such as David Marr's (1982)) attribute contents to states of the visual system which are extremely complex; it is implausible to suppose that a perceiver must be a master of the concepts involved in these contents in order for his visual system to be in those states (for a discussion of this sort of point, see Davies 1986, p. 144). In my view, it is more plausible to suppose that belief formation conceptualizes the content of perceptual states. In the Waterfall case, the output of the visual system is a contradiction, perhaps because (a) of a failure of the mechanism (perhaps in the way Mellor describes); and (b) because the states of the visual system are 'informationally encapsulated' in Fodor's sense. (This answers Mellor's query (p. 147) about what entitles me to talk about contradictions at all; the contradiction one which a believer would naturally describe as Fa & Fa, though the information-processing theory would give a more complex description is actually in the informational output of the visual system.) It seems to me that this picture of the structure of perception suggests the possibility of a clearer explanation than belief-theories give of why the contents of perceptual states cannot be revised in response to further evidence. But much more must be said about concept possession before it can be universally accepted that the Waterfall Illusion is evidence for the accuracy of this picture. Peterhouse ? TIM CRANE 1988 Cambridge CB2 1RD REFERENCES M. Davies 1986, 'Tacit Knowledge and the Structure of Thought and Language' in C. Travis (ed.) Meaning and Interpretation, Oxford: Blackwell D. Marr 1982, Vision, San Francisco: Freeman and Co This content downloaded from 94.192.49.60 on Fri, 17 Aug 2018 13:31:04 UTC All use subject to https://about.jstor.org/terms