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Abnormally slow processing of language may be a factor contributing to the poor verbal memory seen in many patients with lesions of the anterior temporal region in the left hemisphere. This possibility was examined by comparing the performance of 12 patients with left temporal-lobe resections (LT), 10 patients with similar lesions in the right hemisphere (RT) and 13 normal control (NC) subjects on a lexical-decision task, a sentence-plausibility-judgement task, and a story-recall task. Stimuli were presented aurally, and, in the latter two tasks, at 5 different speech rates ranging from 125 words per minute (wpm) to 325 wpm. Recall of stories by LT subjects was not abnormally sensitive to the effect of increasing rate, although it was inferior to that by NC subjects at all speeds. LT patients presented aurally but not visually (Frisk and Milner, 1991), suggesting that the left anterior temporal region plays a special role in the processing of speech sounds.

In Part I of this thesis, recognition of natural scenes was tested in 72 patients with unilateral frontal- or temporal-lobe excisions and 32 normal control subjects (NC). The occurrence of a novel scene in the midst of a series of other scenes normally induces forgetting of the scene that had preceded the novel one. This phenomenon was not observed following right frontal- and right temporal-lobe lesions, and was only partially present after left temporal-lobe excisions that included the hippocampus (LTH). These brain regions were thus seen as part of a circuit that codes novel stimuli. In Part 2, recall of lists of words was examined in 77 patients and 12 normal control subjects. Both the left frontal-lobe (LF) and LTH groups recalled fewer words overall than the other groups; their performance was normal, however, when the words were pre-organized into categories and when category labels were supplied during test. In another experiment it was demonstrated that the LF group was impaired when category exemplars were provided together with the category labels, the LTH group being unaffected in this condition. It was concluded that left frontal-lobe lesions may affect retrieval mechanisms.

In Part I, recall of spatial location was studied in an incidental-learning situation, where patients with unilateral brain lesions, the amnesic patient, H. M., and normal control subjects were asked to estimate the prices of objects in an array. All patient groups could encode location normally, but patients with right temporal-lobe lesions that included extensive hippocampal removal showed abnormally rapid forgetting. For all groups, and for H. M., location-recall did not differ under automatic and under effortful encoding conditions. It is argued that these results point to the importance of hippocampal-ceocortical interactions in spatial memory. In Part II, patients with frontal-lobe lesions were shown to be impaired in judging the frequency with which words or designs occurred in a list. With words, the deficits were demonstrable for both examiner-provided and self-generated stimuli. This impairment may be attributable either to a disorderly search process or to a deficit in cognitive estimation, or both.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2008. / Härtill 4 uppsatser.

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