Abstract
The thesis that the visual system represents objects has garnered empirical support from a variety of sources in recent decades. But what kinds of things qualify as “objects” in the relevant sense? Are they ordinary three-dimensional bodies? Are they the facing surfaces of three-dimensional bodies? I argue that there is no fact of the matter: what we have are equally acceptable ways of assigning extensions to the relevant visual states. The view I defend bears obvious similarities to Quine’s thesis that linguistic reference is inscrutable. Importantly, though, I argue that even if Quine was wrong about inscrutability as a thesis about language and thought, the case for the inscrutability of visual reference remains strong.
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Notes
I will use the term ‘facing surface’ to refer to the part of an object from which light is reflected onto the subject’s retinas. According to this usage, there is no such thing as a partially occluded facing surface. I will use the term ‘front surface’ to refer to the part of an object that would reflect light onto the subject’s retinas were there no occluding objects. Finally, I will use the term ‘facing portion’ more broadly to include both the facing surfaces of objects and the 3D object-parts of which these facing surfaces are parts. For instance, if my hand is protruding from behind the curtain then it counts as my facing portion, as does its facing surface (e.g. my palm).
The term “pre-attentive” must be used with caution. Single cell recordings in animals (Desimone and Duncan 1995) and functional imaging in humans (Kastner and Ungerleider 2000) have shown that many levels of processing (including processing within primary visual cortex) can be modulated by top-down selective attention.
See Nanay (2010) for an extended version of this argument.
See James et al. (2003).
See Tse (1999, p. 65) for a similar argument.
See Howe et al. (2010) for a study that directly tests, and supports, the claim that MOT occurs via parallel processing.
It is worth emphasizing that both 3D bodies and their front surfaces have facing portions in their own right. Thus, even if surface completion occurs prior to volume completion in order of visual processing, representations at both levels of processing exhibit the kind of indeterminacy that I’m positing.
In construing volume completion as a visual phenomenon, I’m not conceding that the states involved determinately refer to both 3D objects and their facing surfaces. For instance, consider a case of spherical volume completion. According to my view, the extension of the resulting state is indeterminate between being a sphere and being the facing surface of a sphere: two properties that are clearly not co-extensive. In the same way, claiming that one cannot refer to an undetached-rabbit-part without also determinately referring to a rabbit would not go any way towards undermining Quine’s inscrutability thesis: it would simply beg the question against Quine. See Gates (1996, p. 331) for further discussion of this issue.
Thank you to an anonymous referee for raising this concern.
See Burge (2011, p. 125) for a similar point.
In any case, even if one were convinced that tracking through occlusion requires explicit representations of facts concerning numerical identity, the inscrutability thesis I’m defending could accommodate this. For instead of construing the subject’s visual state as representing the object in question as being numerically identical to a previously indexed one, we could construe her as representing its current facing portion as belonging to the very same object whose facing portion was visible a moment ago. Quine (1969, p. 33) himself suggests this sort of re-interpretation of the identity predicate when accommodating speakers’ answers to the question, “Is this gavagai the same as that?”
Spelke (1990) develops a conception of objecthood that fits with what I’m calling the “thin” conception. One might think that the visual system also represents objects as solid—see Burge (2010, pp. 465–471) for a discussion of this question—but this is entirely compatible with the inscrutability of visual reference: on the deviant interpretation, the visual system picks out the facing surfaces of solid, cohesive, bounded, and spatiotemporally continuous bodies and represents them as such.
As an anonymous reviewer has pointed out, we often perceive particulars that don’t have facing surfaces: e.g. holograms, shadows, rainbows, and rays of light. Nonetheless, these entities do have facing portions. For instance, an appropriately positioned tree can occlude the bottom half of your shadow; a mountain can occlude a portion of a rainbow; and so on. The parts that are visible in these cases qualify as facing portions, even if they don’t qualify as facing surfaces. Perhaps it is possible to perceive an object with no occluded parts—the object and its facing portion are thus one and the same. However, the existence of degenerate cases like this would do nothing to undermine my thesis that in ordinary cases, the state in question is indeterminate between a three-dimensional body and its facing surface. In order to bring this point out, notice that Quine’s thesis that ‘rabbit’ is indeterminate between rabbits and undetached-rabbit-parts would not be undermined, in the slightest, if it turned out that there are simples with no undetached parts (e.g. fundamental entities, such as strings).
See Gates (1996) for a persuasive argument that Fodor’s argument is unsound.
Fodor (1994, p. 123) construes his own objection as a development of the insights found in Evans’ article.
For example, see Martin (2002).
Once again, it is important not to lose sight of the fact that being a body of such-and-such a 3D-shape and being the facing surface of a body of such-and-such a 3D-shape are not co-extensive properties.
For instance, see Schenk and McIntosh (2010).
See Carey (2009, p. 99) for a brief version of this argument.
I take it that the same point applies to teleological theories of content (e.g. the theories defended by Dretske 1986, 1988; Millikan 1984, 2004). If the different reference schemes described above each put us in an equally good position to explain successful acts of object-manipulation, then I fail to see how appeals to natural selection and biological function will adjudicate between them.
For a detailed and persuasive reply to Burge’s central argument, see DeChant & Quilty-Dunn (ms).
Some theorists have argued that whether S sees O (over and above its facing portion) is a context-sensitive affair: e.g. see Clarke (1965), Neta (2007), and Phillips (2015). If contextualism is right then that gives us another way to explain how the inscrutability of visual reference is compatible with folk intuitions about object-seeing. In brief, which reference-scheme (among the list of equally acceptable ones) the folk go with will simply vary according to their interests as ascribers.
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Acknowledgments
I would like to thank the following people for helpful input on various versions of this paper: Ryan DeChant, Uriah Kriegel, Jesse Prinz, Jake Quilty-Dunn, David Rosenthal, and three anonymous referees. I would also like to thank Laura Larocca for her help with the figures.
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Phillips, B. Inscrutability and visual objects. Synthese 194, 2949–2971 (2017). https://doi.org/10.1007/s11229-016-1083-3
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DOI: https://doi.org/10.1007/s11229-016-1083-3