Abstract
Prosopagnosia is a selective loss of the ability to recognize faces as a result of brain damage. A well-accepted explanation for this disability is the loss of a mechanism involved in visual configural processing. A seemingly related visual process is the ability to allocate attention to the global aspect of an object. The relationship between these two processes was tested with an individual with prosopagnosia. It was predicted that if these two processes are one and the same then a prosopagnosic should be impaired at global processing. Normal control participants were also tested. Navon-type figures were presented in an undirected attention task in which a 2 or a 5 occurred at either the global or local level. The task was to identify which of these numbers was present during a trial. Size of the figures was also varied (3, 6, 9 and 12 deg. of visual angle). Contrary to the prediction, the prosopagnosic demonstrated superior global processing relative to local processing at all stimulus sizes. More interesting was the fact that as the stimuli increased in size, local processing worsened. In contrast, normal control participants demonstrated a well known interaction under these conditions; global processing was superior when stimuli were small in size and local processing was superior when stimuli were large in size. These results fail to support the notion that configural processing is global processing and introduce some new notions of the deficit underlying prosopagnosia.
This study was funded by grants from the Natural Sciences and Engineering Research Council of Canada and the Human Frontiers Science Program.