DEFICITS IN COMPLEX VISUAL-PERCEPTION FOLLOWING UNILATERAL TEMPORAL LOBECTOMY

Although human temporal cortex is known to be important for short- and long-term memory, its role in visual perception is not well understoo d. In this study, we compared the performance of three patients with u nilateral temporal lobectomies to that of normal controls on both ''si mple'' and ''complex'' visual discriminations that did not involve exp licit memory components. Two types of complex tasks were tested that i nvolved discriminations secondary to texture segmentation. These were contrasted with simple discriminations using luminance-defined stimuli . Patients showed impaired thresholds only on tasks involving texture segmentation, performing as well as controls when the targets were def ined by luminance rather than texture. The minimum stimulus presentati on times for threshold performance were also measured for all tasks an d found to be elevated in temporal lobectomy patients relative to cont rols. Although the magnitude of the deficits observed was substantial, loss was equivalent in ipsi- and contra-lesional regions of the visua l field. Additional control experiments showed that the patients' perc eptual deficits were not due, even in part, to disturbances of basic v isual capacities such as acuity and contrast sensitivity. Our results indicate that temporal lobe damage disrupts complex, but not simple, v isual discriminations throughout the visual field.