How the Blind “See” Colour

Abstract

We live in a world where colour pervades every facet of our lives, yet we cannot hear, smell, taste, or touch it. We can only see it.With this in mind, we asked three questions: (1) what conceptions of colour do the congenitally blind hold and how are they constructed? (2) What notions of colour remain in the adventitiously blind? And (3) what influence does language have on the performance of colour deficient individuals in colour categorisation? Multidimensional scaling (MDS) offers a unique vantage point into the cognitive processes involved in subjective judgements between stimuli. By quantifying (dis)similarity judgements, MDS produces a perceptual map (or configuration) fitted with dimensions from which inferences can be made as to how stimuli are being distinguished from one another. A component of MDS known as Individual differences scaling can then illustrate the extent to which observers are employing each dimension. While some studies employing MDS have provided evidence indicating that the congenitally blind have a limited understanding of colour order, others have shown that the congenitally blind have a sophisticated understanding of colour order, one that highly resembles that of trichromatic observers; this thesis was partially inspired by these inconsistent findings. Studies exploring colour categorisation in the adventitiously blind have shown that memory of colour order is well preserved, allowing for the adventitiously blind to appropriately categorise colour terms. Studies involving colour deficient individuals have shown that simultaneously presentation of colour terms and corresponding colours does have an effect on categorical judgements, indicating that language influences cognition. By employing non-metric MDS this thesis first explored the cognitive structure of basic colour categories in samples of congenitally and adventitiously blind individuals. Both groups yielded two-dimensional MDS configurations approximating the Newtonian colour circle. A semantic differential application demonstrated that the congenitally blind can learn both concrete and arbitrary associations of colours, these associations also correlated with the dimensions of their MDS configuration. The second study presented descriptive (or non-) basic colour terms to the same groups. Their MDS configurations again revealed an appropriate categorisation colour terms. These findings indicate that the congenitally blind are not only able to apprehend the order of colours, but can learn colour associations via linguistic properties such as metaphors, metonyms, and similes. The findings also demonstrate that the adventitiously blind maintain their colour memory despite of being blind for decades. The influence of language on cognition consequently led to the third study. Severe dichromatic observers (protanopes and deuteranopes) were presented with four sets of colour stimuli: (1) colour cards, (2) colour cards with the corresponding colour term printed on it, (3) colour terms presented verbally, and (4) descriptive colour terms mapping onto basic colours initially presented. As expected, their MDS configuration collapsed on dimension-two (red–green opponent-channels) for the first condition. Yet, an immediate expansion of dimension-two is observed when colour terms are made available in the second condition; demonstrating that semantic knowledge of colours has influenced their subjective judgements. No significant difference was found between the dichromatic and trichromatic MDS configurations in the remaining two conditions. The implications of the results of this thesis are considered in the context of cognitive linguistics, embodied cognition, perceptual symbols, mental imagery, and philosophy.