Marking the Perception–Cognition Boundary: The Criterion of Stimulus-Dependence

ABSTRACT

Philosophy, scientific psychology, and common sense all distinguish perception from cognition. While there is little agreement about how the perception–cognition boundary ought to be drawn, one prominent idea is that perceptual states are dependent on a stimulus, or are stimulus-dependent, in a way that cognitive states are not. This paper seeks to develop this idea in a way that can accommodate two apparent counterexamples: hallucinations, which are prima facie perceptual yet stimulus-independent; and demonstrative thoughts, which are prima facie cognitive yet stimulus-dependent. The payoff is not only a specific proposal for marking the perception–cognition boundary, but also a deeper understanding of the natures of hallucination and demonstrative thought.

KEYWORDS:

• perception
• cognition
• stimulus-dependence
• stimulus-independence
• hallucination
• demonstrative thought

Notes

¹ In one form, the idea that perception is stimulus-dependent traces at least to Locke's [1689] account of the formation of simple ideas, which are the ‘effects of certain powers in things’ [II.xxxi.2] that ‘enter by the senses’ [II.ii.1]. In psychology, it has echoes in the pioneering work of nineteenth-century psychophysicists such as Weber and Fechner who sought to characterize law-like relations between stimuli and percepts. More recently, Prinz [2006], Camp [2009], Burge [2010a: 378], Beck [2012], and Nanay [2015: 1729] all invoke the concept of stimulus-(in)dependence while discussing perception and/or cognition.

² One might also seek to distinguish analogue magnitude representations from perceptions because they are amodal rather than modality specific [Beck 2012: 587; Burge 2014: 574]. It is controversial, however, whether perception is always modality-specific [O'Callaghan 2015; Briscoe 2016, forthcoming]. And, as we observed in the previous paragraph, imagistic memories and imaginations are modality specific but not perceptions.

³ Pluralism about the perception–cognition boundary is defended by Phillips [ms], although he congenially argues that stimulus-dependence is a common thread that runs through the boundary in all of its forms.

⁴ The qualification is necessary if there exist modules that are cognitive rather than perceptual—say, cheater detection modules [Cosmides 1989] or reorientation modules [Hermer and Spelke 1994]. In fact, since we're seeking an analysis of the perception–cognition border, the qualification is necessary if cognitive modules are so much as possible. One could address this concern by holding that the perceptual modules are the ones with stimulus-dependent outputs. But one would then want to know whether the appeal to stimulus-dependence isn't doing all of the work.

⁵ In fact, there is at least one respect in which direct realists might have an easier time using stimulus-dependence to draw the perception–cognition boundary. In so far as they embrace disjunctivism, they could welcome the result that hallucinations aren't perceptions because they aren't stimulus-dependent.

⁶ One challenge to this claim that I will be setting aside concerns so-called veridical hallucinations, in which one hallucinates a particular at such-and-such a location with such-and-such properties when, by some fortuitous accident, there just so happens to be a particular at such-and-such a location with such-and-such properties—perhaps even a particular that caused the hallucination through some deviant path [Lewis 1980]. Following Burge [2010a: 381–3], I will assume that such hallucinations are not, in fact, veridical since the perceiver is not related to the particular in the appropriate way for genuine reference to occur. But those who disagree could replace my use of the term ‘veridical’ (here and throughout) with ‘successful’, since all parties should agree that so-called veridical hallucinations are failures of a certain sort (they're hallucinations, after all).

⁷ Or at least if you take enough Philosophers’ LSD, which, I'm told, has somewhat different properties than the real stuff.

⁸ A position along these lines is defended by Allen [2015] for all hallucinations (endogenous or exogenous—he doesn't distinguish). He motivates it as a way of defending disjunctivism.

⁹ Perky asked subjects to visually imagine an object (e.g. a banana) while staring at a white screen. Unbeknownst to the subjects, an image of the object was then faintly projected onto the screen. The subjects reported images that were clearly influenced by the projection (e.g. in orientation), although the subjects remained unaware of the projection.

¹⁰ There are other elements of Millikan's account that I reject. In particular, Millikan [2004: 67–8] maintains that all functions must be effects. I agree that functions are often effects. Blood circulation is an effect of the heart. Stimulus-dependent mental states are effects of perceptual mechanisms. But I deny that all functions are effects. Beliefs have the function of representing truly, but truth is not an effect of belief (except in unusual cases). Nor is being stimulus-dependent an effect of perceptual states.

¹¹ Note that perceptual states and the brain mechanisms that produce them have related, but not identical, functions. (Only the mechanism has the function of producing mental states.) An analogous point holds in the chameleon and magnet examples.

¹² The difference in structure is meant to mark perception as being non-propositional. Because perceptual attributives cannot be divorced from a contextually specified particular, there is no ‘pure’ predication in perception, which Burge [2010a: 537–47, 2010b] takes to be necessary for propositional structure. But, for our purposes, it's the commonalities that matter. Both states contain demonstrative and attributive elements.

¹³ Thanks to Brad Thompson for the example.

¹⁴ Thanks to audiences at the Top-Down Influences Workshop at the University of Glasgow, the York University Centre for Vision Research, the Southern Society for Philosophy and Psychology meeting in New Orleans (where Zoe Jenkin commented), the American Philosophical Association Central Division meeting in Saint Louis (where Brad Thompson commented), the Society for Philosophy and Psychology meeting in Vancouver, the Perception and Concepts Symposium at the University of Latvia, and the Department of Philosophy at Carleton University. For helpful comments and/or conversations, I'm also grateful to Derek Brown, Tyler Burge, Brian Huss, Marta Jorba, Muhammad Ali Khalidi, Peter Langland-Hassan, Fiona Macpherson, Susanna Siegel, Kritika Yegnashankaran, and two anonymous referees.

Additional information

Funding

While writing this paper, I was supported by a fellowship from the American Council of Learned Societies.