HEMIFIELD-SPECIFIC VISUAL RECOGNITION MEMORY IMPAIRMENTS IN PATIENTS WITH UNILATERAL TEMPORAL-LOBE REMOVALS

Recent evidence on visual neglect suggests that each hemisphere mainta ins a retinotopically organized representation of the visual world con tralateral to the current fixation point and that this representation is based not only on analysis of the current retinal input but, equall y importantly, on information retrieved from memory. This idea predict s that unilateral damage to memory systems should produce a lateralize d impairment of memory for the retinotopically contralateral visual wo rld. To test this prediction we examined visual recognition memory per formance in the left and right visual hemifields of patients who had u ndergone partial unilateral temporal lobe removals for the relief of e pilepsy, either in the left hemisphere (n=5) or the right (n=5). The p atients were given complex artificial scenes to remember, constructed of independent left and right halves, and were then tested for recogni tion of the left and the right halves separately. Stimuli were exposed tachistoscally throughout and fixation was maintained on a central po sition. Patients made significantly more errors with half-scenes in th e hemifield contralateral to their removal than in the ipsilateral hem ifield, an increase of 50% in the error rate on average. The effect wa s seen equally in patients with left and right removals. This finding supports the idea that visual memory retrieval is retinotopically orga nized. (C) 1997 Elsevier Science Ltd.