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Jules Davidoff, Julie Goldstein, Ian Tharp, Elley Wakui, Joel Fagot; Binary Division Constrains Human but not Baboon Categorical Judgements within Perceptual (colour) Continua. Journal of Vision 2010;10(7):1208. doi: 10.1167/10.7.1208.
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In Experiment 1, two human populations (Westerners and Himba) and old-world monkeys (baboons: Papio papio) were given matching-to-sample colour tasks. We report a similar strong tendency to divide the range of coloured stimuli into two equal groups in Westerners and in the remote population (Himba), but not in baboons. When matching the range of colours to the two samples, both human groups produced a boundary at the midpoint of the range and it was at this point where there was most uncertainty of the best match. The boundary depended on the range of stimuli and hence overrode established colour categories. However, range differences did not affect the names given to the colours by either Western or Himba observers. In Experiment 2, we showed that a distinctive stimulus (focal colour) in the range affected the equal division though observers again made a boundary. Experiment 3 employed an implicit task (visual search) to assess colour categorization (Categorical Perception), and it was only in this task that categorization was immune to range effects and observed only at the established colour boundary. Nevertheless, prior exposure to the range of colours did affect naming producing binary division for a restricted range of colours. Thus, irrespective of whether colour categories are taken to be universal (Berlin & Kay, 1969) or language induced (Davidoff, Davies & Roberson, 1999), they are overridden in colour decision tasks by this stronger human tendency to divide continua into two. It is argued that binary division is the basic human mechanism whereby labels are used to establish colour categories.
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