2000 Volume 20 Issue 3 Pages 251-259
To clarify the nature of deficits in verbal short-term memory in brain-damaged patients, weexamined two patients with mild aphasia. Case 1 had transcortical aphasia after damage to the Broca's area and case 2 had conduction aphasia after temporo-parietal lesion. Both patients showed almost the same performances in the forward digit span task and various subtasks for single words in the Standard Language Test of Aphasia (SLTA).
The following four tasks were used : a serial word repetition task, a serial pointing task from auditorily presented words, a serial oral recall task, and a serial pointing task from visually presented words. Case 1 exhibited graver impairment in the serial pointing task than in the serial word repetition task from auditorily presented words. She also showed impairments in the two tasks in which stimuli were presented visually. By contrast, case 2 demonstrated no differences among all the four tasks.
These results indicate that impaired processes in verbal short-term memory are different between case 1 and case 2. Case 1, who had damage to the left frontal lobe, may have impairments in the semantic storing system or in translating plural stimuli from the phonological short-term store to the semantic storing system, as well as in phonological recoding from the visual short-term store. The impairments of case 2, who had damage to the left temporo-parietal lobe, may reflect reduced capacity of the phonological short-term store, despite ability to translate phonological information to the semantic storing system.
We propose a model in which there exist two parallel storing systems for verbal information in the human brain : a phonological loop and a semantic short-term store.
