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Face Processing in Deaf and Hearing Individuals
AuthorGroesbeck, Elizabeth Ashley
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Deaf individuals may possess enhanced visual processing abilities, particularly in the periphery. Deaf individuals may also be more accurate at discriminating between faces, compared to their hearing counterparts. We examined deaf and hearing subjects’ ability to discriminate between faces, in either the central or peripheral visual fields, using behavioral measures and EEG. In a delayed matching task, subjects were presented with a 'target' face and after a delay were required to identify which of two 'test' faces matched the target. In separate conditions, images were presented centrally and in the periphery. Thresholds were measured using a forced-choice, staircase procedure and were estimated using Weibull functions to determine the level of similarity between test images associated with 80% correct performance. Overall deaf subjects were more accurate than hearing subjects and this difference was most evident in the periphery. Neurophysiological responses to these images were then assessed using EEG and an oddball paradigm. In this paradigm facial images are presented at a base frequency (6 Hz) and within the sequence a different ‘oddball’ face is presented at a lower frequency (1.2 Hz). The presence of significant responses at the oddball frequency indicates the difference between the faces has been detected. In separate trials we presented subjects with base and oddball images that were more or less similar to each other. Across trials these images were presented either centrally or in the periphery. Both subject groups showed similar reductions in amplitude at the oddball frequency for images that were more similar to each other. However, compared to hearing subjects, deaf subjects showed a larger decrease in amplitude when images were presented in the periphery compared to centrally. Results of the behavioral experiment support earlier findings that deaf individuals may possess enhanced face discrimination abilities and further extend them by showing that these effects may be more prominent in the periphery. Furthermore, our results from the EEG experiment suggest that the enhanced processing ability in deaf for peripherally presented faces is not necessarily related to higher amounts of neurophysiological activity at the level of face coding. This discrepancy between the two experiments in the present study may be due to differences in the task demands, with the behavioral experiment reflecting more local feature discrimination, while the EEG experiment may reflect more holistic face coding.