VERBAL RECALL AND RECOGNITION AS A FUNCTION OF DEPTH OF ENCODING IN PATIENTS WITH UNILATERAL TEMPORAL LOBECTOMY

The hypothesis that impairment in cognitive organization is a signific ant causal Factor in the verbal memory impairment known to follow left anterior temporal (LT) lobectomy was tested by assessing verbal recal l and recognition as a function of depth of encoding in 20 patients wi th LT lobectomy (19 in the recognition condition), 20 patients with ri ght temporal lobectomy and 20 normal control subjects. Subjects first made decisions regarding either the physical, phonemic or semantic asp ects of 48 words. After the encoding phase, a free recall test was giv en, followed by a recognition test. As expected, the verbal memory of the LT group was impaired in both the recall and recognition condition s. However, the LT group followed the pattern of the other two groups in recalling and recognizing more words which had been subjected to se mantic analysis. These findings do not support the hypothesis that a d isruption in the normal relationship between cognitive organization an d memory contributes to the memory impairment following LT lobectomy. In contrast, the verbal recall of the LT group failed to follow the pa ttern of the other two groups in that it did not benefit from phonemic encoding. Taken together, these findings support the notion that left anterior temporal-lobe cortical structures are more specialized For t he evocation of the sound of a word than for those processes that unde rlie the recall of semantically encoded verbal material.