They were normal in reporting the number of briefly presented scattered dots, performing accurately with arrays of up to six items. Remarkably, the patients’ impairment was specific to verbal symbolic material and did not extend to spatial arrays of dots. Kinsbourne & Warrington dismissed any primary “perceptual” or “attentional” explanation of these effects since it did not appear to matter whether the stimuli were large or small or whether they were horizontally or vertically aligned. The impairment of this type of visual short-term memory has since been replicated in other patients (J.D.C., Warrington & Shallice, 1980 M.L., Shallice & Saffran, 1986). The patients claimed that they could not recall a second item and made errors of omission and substitution. However, when pairs of stimuli were presented, the patients could only report one of the items. These patients were able to report single geometric shapes, silhouettes, and letters shown for 160 ms. Kinsbourne & Warrington (1962b) investigated four patients who had particular difficulty in reporting more than one briefly presented visual stimulus. Under these conditions normal subjects can report between four and five items. The use of such brief exposure durations prevents subjects from “recoding” stimuli into a spoken form. Visual span for symbolic or otherwise meaningful stimuli can be tested by using brief exposure durations of stimulus arrays (of the order of 100–200 ms). Two main classes of material have been investigated-visual–verbal and visual–spatial. Furthermore (as was the case with auditory span), the deficit may be specific to particular types of material. Selective impairments of visual short-term memory have also been documented. In such cases the retention of visually presented material may be relatively spared. The evidence discussed so far has focused on impairments in retaining auditory material. Warrington, in Cognitive Neuropsychology, 1990 Visual Short-Term Memory
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