Short-term memory scan in normal individuals and individuals with aphasia

Ten matched pairs of normal adults and adults with aphasia participated in a short-term memory, visual recognition paradigm wherein each determined whether or not a probe digit appeared in a subset of digits previously presented. Reaction times, measured in milliseconds from onset of probe digits until completion of visual-motor responses, were analyzed as a function of increasing subset size (two, four, and six digits) and the positive versus the negative response condition. Reaction times were significantly slower for the subjects with aphasia. Both groups of subjects demonstrated linear increases in reaction time across levels of subset size. For both groups, increases in reaction time were similar in the positive vs the negative-response conditions. Resulting parallel slopes suggested that both groups of subjects used a serial exhaustive scan of short-time memory. Results from this study did not support results obtained by others in previous studies which may have been confounded by group differences in visual retention spans.