Abstracts

Memory dysfunction is a known consequence of anterior temporal lobectomy (ATL). The memory loss pattern has been reported to differ between patients with surgery in the language dominant versus the non-language dominant hemisphere, though the factors underlying lateralized memory differences continue to be debated. A left hemisphere deficit for memory for familiar verbal material (such as real words) has been well-demonstrated, and though less consistent, a right hemisphere deficit for memory for unfamiliar nonverbal material (such as unfamiliar faces) has also been shown. It is unclear from these results whether apparent lateralization is a function of the [italic]verbalizability[/italic] of the to-be-learned information or whether it is due to exposure or [italic]familiarity[/italic] of the information prior to learning.
To assess the effects of verbalizability and familiarity on memory, a completely crossed design used four types of materials; familiar verbal stimuli consisted of real abstract English nouns, unfamiliar verbal stimuli consisted of pronounceable pseudowords (PWs), familiar nonverbal stimuli consisted of photographs of familiar but unnamable people taken from the popular media, and unfamiliar nonverbal stimuli consisted of photographs of unknown people. LATL and RATL patients who were left hemisphere language dominant and healthy controls completed four paired-associate learning followed by yes-no recognition memory tests.
Significant lateralized effects of verbalizability were found on memory accuracy discrimination. LATL patients were impaired for both real words and PWs compared to other groups. RATL and LATL groups were equally impaired compared to controls for familiar and unfamiliar faces. There were no hemispheric differences in familiarity of the to-be-learned information in memory discrimination, nor were there effects of familiarity for discrimination of verbal and nonverbal materials. With respect to response bias, or the strategy that was adopted in conditions of response uncertainty, RATL patients and controls showed more liberal response bias for unfamiliar compared to familiar information, while LATL patients[rsquo] response bias was more liberal for familiar information, especially real words.
These results support a partial material-specific account of memory lateralization. There was clear left hemisphere superiority for verbal discrimination (words and PWs) and involvement of both left and right hemispheres in nonverbal face memory processing. Familiarity did not play a role in lateralization of memory accuracy. Response bias, on the other hand, was related to prior familiarity with to-be-learned information and was selectively affected by LATL lesion. Thus, three factors were identified as underlying lateralization of memory functions in temporal lobectomy patients; verbalizability of the to-be-learned material, prior familiarity with the material, and response strategies.