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 significant causal factor in the verbal memory impairment known to follow left anterior temporal (LT) lobectomy was tested by assessing verbal recall and recognition as a function of depth of encoding in 20 patients with LT lobectomy (19 in the recognition condition), 20 patients with right temporal lobectomy and 20 normal control subjects. Subjects first made decisions regarding either the physical, phonemic or semantic aspects of 48 words. After the encoding phase, a free recall test was given, followed by a recognition test. As expected, the verbal memory of the LT group was impaired in both the recall and recognition conditions. However, the LT group followed the pattern of the other two groups in recalling and recognizing more words which had been subjected to semantic analysis. These findings do not support the hypothesis that a disruption in the normal relationship between cognitive organization and memory contributes to the memory impairment following LT lobectomy. In contrast the verbal recall of the LT group failed to follow the pattern 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 the evocation of the sound of a word than for those processes that underlie the recall of semantically encoded verbal material.