Do the physical facts of the viewed environment account for the ordinary experiences we have of that environment? According to standard philosophical views, distal facts do account for our experiences, a phenomenon explained by appeal to perceptual constancy, the phenomenal stability of objects and environmental properties notwithstanding physical changes in proximal stimulation. This essay reviews a significant but neglected research tradition in experimental psychology according to which percepts systematically do not correspond to mind-independent distal facts. Instead, stability of percept values comes in degrees, and physical facts about the viewed environment alone do not account for our ordinary experiences of the world. I conclude that more attention to descriptive research in psychophysics is warranted if what is sought is a philosophical theory of the nature of our perceptual relation with the world.
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It is now widely accepted that stability in percepts occurs in non-conscious beings, that is, in perceivers that lack phenomenal awareness. For ease of expression, I limit the discussion that follows to phenomenal stability (experienced stability), and to visual phenomenal stability in particular.
Typically, information from accommodation—that is, information about the automatic adjustments of the lenses as the eyes focus on a distal stimulus—will be available to the visual system. Still, though it is correct that each lens must be accommodated differently for pencils of light arising at different distances, such information is far from metrically precise and is non-existent beyond distances that exceed 10 feet or so. Information is also available for binocularly sighted animals in which both eyes converge on a single point. But this information is for the point of fixation alone and it too is non-existent beyond the near range. Consequently, in the absence of additional cues or motion, the retinal information available to perceptual mechanisms remains highly ambiguous, an ambiguity that runs in the opposite direction as well: for any physical object of a fixed physical form, there is an infinite number of retinal projections for which it could be considered a cause, depending on the relative position of the perceiver.
We can trace the suggestion that our visual experiences are the result of cognitive processes supplementing unstable sensations to the 1600s. Following Kepler’s discovery that the lens focuses light on the retina, rendering the retinal image an inverted and reversed projection of the visual scene, it was natural to assume that retinal images are directly seen in perception, and form the experiential basis upon which judgment can operate (see Ross and Plug 1998). Early modern empiricist approaches such as those of Berkeley and Locke famously espouse the idea that perceptions are the result of a process of associative learning operating on two-dimensional sensations.
The suggestion that perception, independently of cognitive factors, presents object properties as more stable than are their corresponding retinal stimulations, predates Hering. According to Edwin Boring, even Euclid, who had no stake in which types of physiological mechanisms make possible the perception of objects, acknowledged that two identical objects at different distances look closer in size than their projected retinal images are in size (an observation Boring refers to as an ancient instance of “phenomenological insight” (Boring 1942, 290); but see (Lindberg 1976, 13) for an explanation of why this is likely to be a later interpolation). Recognition of a psychological distinction between the visual perception of object size and the discrimination of visual angle appears in Ptolomy’s work (see Hatfield and Epstein 1979, esp. 366).
Hering agreed that some cognitive elements aid in the attainment of phenomenal stability. For example, Hering believed that we come to have cognitive memories of particular colors belonging to particular objects or types of objects. These cognitive memories, or “reproductions of earlier experiences,” supplement retinal stimulation, and “help to determine what is seen at a given moment” (Hering 1920; see also Katz 1911). Snow looks white, even if we are viewing it in shadow, because we have come to associate whiteness with the idea of snow. For Hering, this “memory color” of an object can have a significant impact on our ability to see object properties as stable. Still, it is worth contrasting my reading of Hering with one in (Cohen 2015): according to Cohen, David Katz’s discovery that color constancy effects hold irrespective of cognitive contributions is evidence against the viability of Hering’s conception of memory color, and Hering and Helmholtz are grouped together in holding that perceptual constancy is the result of cognition. It should be evident from the above discussion why I take Katz’s finding to be compatible with Hering’s proposal about memory color. Hering did not take memory (or cognitive knowledge about objects) to be “necessary” (11) for color constancy, even if he emphasized that cognition could amplify the amount of stability experienced. And on my reading, Hurvich’s (1981) point that memory color could not plausibly be specific enough to account for phenomenal stability in color experience is not in tension with the core claims of Hering’s proposal, as Cohen claims.
The vista problem was studied long before the twentieth century. Leonardo da Vinci, for instance, noted that the courses of horses running away from a perceiver on parallel tracks will appear to converge the further the horses get from the perceiver (da Vinci 1956, Vol. 1, 113). Edwin Boring speculates that if the eighteenth century “had had railroads, the fact that apparent size follows neither a law of constancy [full stability] nor of visual angle would have been even more apparent to its scientists” (1942, 290).
There is of course convergence between the lines projected onto the retina, and this latter convergence can be explained using simple geometry: the further objects are from a perceiver, the smaller the area of the retina onto which they project. However, appeals to retinal projections cannot adequately account for how the tracks look. The apparent convergence will be much less severe than the convergence occurring in the corresponding retinal projection. This is because the apparent convergence occurs in depth, whereas the corresponding retinal projection occurs in a two-dimensional plane.
(Thouless 1931a, 1931b, 1932). In tribute to the fact that Thouless was an early advocate of the descriptive claim that percept values tend to fall between distal and retinal values, Christopher Hill and David Bennett (2008) label phenomenal properties “Thouless properties” on their appearance theory.
A related aspect of the Gestaltist program stressed that we need not appeal to cognitive factors to explain phenomenal experience (Koffka 1935). As I noted in Sect. 2, a tradition going back to Hering advocated for the importance of perceptual factors in understanding the vast difference between proximal values and the phenomenal appearances of a corresponding object’s properties. By the time the Gestalt program took hold in the early twentieth century, a significant body of developmental and comparative evidence affirmed that constancy is at least largely a distinctively perceptual phenomenon, and the Gestaltists became early twentieth-century champions of the importance of this thesis.
The idea of a one-to-one correspondence between percept and proximal stimulation was referred to by the Gestaltists and others after them as the “constancy hypothesis” to underscore the commitment they wanted to reject: that constant stimulation should produce constant perceptual experience. The Gestaltists rejected this commitment on the basis of evidence from figure-ground reversals (in which proximal stimulation stays the same and yet overall appearance changes dramatically), gestalt switches, and phenomenal stability (perceptual constancy). To avoid the natural confusion that can result from this distinct use of the word “constancy”, I refer to this idea simply in terms of one-to-one correspondence.
(Gibson 1950, 171–2). Gibson is thinking of how Koffka points to simple invariant relations between aspects of the percept and proximal stimulus here, such as a size-distance invariance relation. As an object gets further away, its corresponding retinal projection gets smaller such that the two variables, distance and size, are invariantly related. Furthermore, as Gibson notes, Koffka identified invariant relations between coupled aspects of the percept, such as orientation and shape, or distance and size. Shape and orientation, for instance, are “coupled together, so that if one changes, the other changes also.” In the case of perceived size and distance, for example, “a relation of proportionality exists between [them], so that if two equal retinal lines give rise to the perception of two behavioural lines of different length, these two lines appear at correspondingly different distances” (Koffka 1935, 229). It is plausible to think that both of these notions of invariance (simple and more complex invariance relations) profoundly influenced Gibson’s early thinking about perception.
Gibson is thus denying that the reduced-cue conditions tested by Thouless and Brunswik can teach us about ordinary cases of perception. For Gibson, if movement and gradient are aspects of the perceptual encounter, as they normally are, then perceptual mechanisms will achieve full constancy. (But see (Morales et al. 2020), according to which different distal shapes are representationally similar to one another when their perspectival shapes match.).
This is the position adopted by the majority of contemporary analytic philosophers of perception. For a representative example, see (Burge 2010).
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Daoust, L. Stability by degrees: conceptions of constancy from the history of perceptual psychology. HPLS 43, 17 (2021). https://doi.org/10.1007/s40656-021-00370-1
- Perceptual constancy
- Phenomenal stability
- Size perception