Furry hippos and scaly sharks: Knowledge of animal appearance among sighted and blind adults

How does first-person sensory experience contribute to knowledge? Contrary to the suppositions of empiricist philosophers, people who are blind know about phenomena that cannot be perceived directly, such as color and light. Do blind individuals learn about appearance primarily by remembering sighted people’s descriptions of what they see (e.g. “elephants are grey”)? How is “verbally-acquired” knowledge about perception represented? We compared knowledge of animal appearance across congenitally blind (n=20) and sighted individuals (two groups, n=20 and n=35). Participants performed a battery of tasks, including ordering animals by size and height and sorting by shape, skin texture, and color (animal names presented in Braille or print). If people who are blind learn primarily from verbal description, blind and sighted groups should share less knowledge about perceptual dimensions that are more difficult to verbalize. We quantified verbalizability by applying the Simpson’s Diversity Index to participant labels of shape, texture and color sorting piles. Disagreement across groups was apparent for all dimensions tested, suggesting that visual perception and language convey partially non-redundant information. Contrary to the idea that blind individuals learn primarily from verbal descriptions, blind and sighted groups disagreed most on the dimension that was easiest to verbalize: animal color. Analysis of disagreement patterns suggests that blind individuals infer physical features from other animal properties, such as folk taxonomy and habitat (e.g. bats are shaped like birds but textured like mammals). In the absence of sensory access, structured appearance knowledge is acquired through inference.