Parallel and sequential processing in visual discrimination of simple geometrical patterns

Alkhateeb, W.; Bromley, J. M.; Ibbotsen, V.; Javadnia, A.; Ruddock, K. H. and Terry, A. (1989). Parallel and sequential processing in visual discrimination of simple geometrical patterns. In: Kulikowski, J. J.; Dickinson, C. M. and Murray, I. J. eds. Seeing Contour and Colour: Proceeedings of the Third Symposium of the Northern Eye Instiute, Manchester, UK, 9-13 August 1987. Vision and Visual Health Care (3). Oxford: Pergamon Press, p. 419.


This paper describes an experimental investigation of pattern discrimination by the human visual system. Observers were asked to detect a single target element, embedded in a random array of identical reference elements, and in this study, the target was differentiated from the reference elements by orientation or magnification. The dependence of the response time for detection f the target on the number, N, of reference elements provided a measure of the extent to which the target parameters could be discriminated by parallel operations, without sequential scanning of the elements. The results establish that, with the exception of certain classes of elements, response times are essentially independent of N, that is, the targets can be discriminated without sequential scanning of the field. The exceptions occur when the elements are structurally ill-defined. It is shown that a subject with visual form agnosia suffers a severe loss of capacity for parallel discrimination.

In a second set of experiments, the elements were differentiated from the background field by colour and/or luminance. It is shown that normal capacities for the discrimination of magnification or orientation are retained when the elements area at equi-luminance with the background, and are distinguished from it only by colour contrast. Data for a subject with a congenital red-green colour vision defect establish tat under these conditions, the responses are dependent on the physiological mechanisms of colour vision.

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