Perceptual Variation and Relativism

There is variation in how people perceive colors and other secondary qualities. The challenge of perceptual variation is to say whose perceptions are accurate. According to Sextus, Protagoras’ response is that all of our perceptions might be accurate. As this response is traditionally developed, it is difficult to explain color illusion and color constancy. This difficulty is due to a widespread assumption called perceptual atomism. This chapter argues that, if we want to develop Protagoras’ response, we need to give up perceptual atomism. It ends with a brief sketch of an alternative called perceptual structuralism.

‘Let us imagine that God has made a miniature earth and sky’: Malebranche on the Body-Relativity of Visual Size

Malebranche holds that visual experience represents the size of objects relative to the perceiver's body and does not represent objects as having intrinsic or nonrelational spatial magnitudes. I argue that Malebranche's case for this body-relative thesis is more sophisticated than other commentators—most notably, Atherton (1990) and Simmons (2003)—have presented it. Malebranche's central argument relies on the possibility of perceptual variation with respect to size. He uses two thought experiments to show that perceivers of different sizes—namely, miniature people, giants, and typical human beings—can experience the very same objects as having radically different sizes. Malebranche argues that there is no principled reason to privilege one of these ways of experiencing size over the others and, more specifically, that all three kinds of perceivers experience size veridically. From the possibility of this kind of veridical perceptual variation, Malebranche infers that visual experience represents only body-relative size.

Words for Sensible Qualities and the Problem of Perceptual Variation

This chapter proposes a picture of reference fixing for color adjectives and adjectives for other sensible qualities, according to which the relevant reference-fixing conventions allow those adjectives to be used with different intended standards in different contexts. It is argued that this explains the fact (used by secondary-quality theorists and eliminativists in “perceptual variation arguments”) that different equally normal people classify the same object by means of prima facie incompatible color adjectives, and that the explanation is perfectly compatible with the properties referred to by uses of these adjectives being primary qualities or objective properties. It is also argued that the picture satisfies a number of desiderata not satisfied by other objectivist theories in the literature.

Cross-Cultural Studies of Illusions

Cross-cultural studies are of interest primarily because they demonstrate the extent of perceptual variation that would not be observable if the samples were derived from a single population. They are also of interest because they show how variation of factors such as age, gender, environment, cultural background, and genetics affects perception. Topics addressed include horizontal-vertical illusions, the Muller-Lyer illusion, and the Sander parallelogram. Perceptual processes are explored including perception of depth.