| Although it is widely believed that the deaf "see" better and have more "alert" vision, few empirical studies have addressed this claim. The purpose of the following dissertation was to examine motion sensitivity and visual attention in deaf subjects. Two sources of influence were hypothesized to alter visual sensitivity and attention in deaf subjects: auditory deprivation and sign language experience.;If sign language experience alters visual sensitivity, then this influence will occur within the range of visual properties contained in the sign language signal, and not outside this range. In order to test visual sensitivity within this range, Study 1 aimed at quantifying eccentricity, spatial frequency, and movement speed of the hands.;In three experiments that follow, thresholds and reaction times were obtained in a direction-of-motion discrimination task. To separate the influences of auditory deprivation vs. sign language experience upon task performance, three groups of subjects were tested: deaf signers, hearing signers, and hearing non-signers. Performance under various conditions of attentional demand was assessed by manipulating spatial certainty about target location.;Studies 2 and 3 demonstrated similar performance for all subject groups, hence, motion sensitivity is not altered in deaf signers. In Study 2 and 4, visual field asymmetries due to perceptual and attentional factors were investigated. Results suggest that auditory deprivation may enhance sensitivity in the periphery, relative to central vision, and in the inferior visual field, relative to the superior visual field. In addition, a robust right visual field advantage was found in hearing and deaf signers, indicating a left hemisphere advantage for motion processing that is related to sign language experience. These asymmetries appear to be due to sensory, and not attentional, factors, since attentional manipulations did not alter the pattern of asymmetries.;In Study 3, three aspects of attention were compared across subject groups: attentional orienting towards the periphery, divided attention amongst multiple stimuli, and selective attention of a target amongst distractors. Although no evidence of enhanced divided attention in deaf subjects was found, deaf individuals may have a superior ability to orient attention toward moving targets and to selectively process a target while ignoring distractors. |
