Texture Segmentation and Visual Search in Deaf and Hearing Subjects: Evidence for Compensation?

Abstract

Do deaf people develop capacities of their remaining senses that exceed those of hearing individuals? Are the compensatory effects due to attention-dependent strategies? We investigated these questions, using texture segmentation and visual search tasks. The advantage of these tasks is that they contain attention-dependent and attention-independent components. We investigated 8 hearing adult observers, and 99 hearing and 89 deaf subjects aged between 6 and 20 years. The subject's task was to search for a discrepant stimulus among a number of distracting items. We used four different visual search tasks (circles with and without a 90° gap; circles with and without an added vertical line; pairs of convergent and parallel lines; tilted and vertical single lines) and oriented textures containing either a single line or a group of 16 discrepant lines. Visual search and texture segmentation tasks were randomly intermingled. Each subject participated in eight experimental runs, on two consecutive days. Both groups of subjects showed consistent learning effects for all tasks. In both groups, reaction times for all tasks decreased with age and reached an optimum at about 16 – 18 years. However, statistical comparisons do not indicate compensatory effects for deafness: reaction times and error rates of the deaf subjects were higher than those of the age-matched hearing subjects, for both the serial and the parallel tasks. These results were independent of the age and gender of the subjects and occurred for all etiologies for deafness. These results suggest deficiencies in the visual processing capacity of deaf subjects in tasks with and without attentional load.