Abstract
The storage capacity of visual short-term memory (VSTM) for simple objects is known to be severely restricted and to vary considerably across individuals. These individual differences in capacity have often been proposed to be due to variability in memory storage space. However, it is also possible that much of the variability stems from the efficiency of attentional control mechanisms that restrict access to VSTM. In previous experiments, we have found that low capacity subjects are poorer at keeping irrelevant items from being stored in VSTM than high capacity subjects. In the present study, we extend these findings by examining individual differences in the initial allocation of spatial attention towards target and distractor onsets. Here we found that when targets were presented in isolation or with task-irrelevant distractors, all subjects showed equivalent attentional modulations of the P1/N1 ERP components. However, when the target was accompanied by task-relevant (contingent) distractors, large differences across individuals were observed; while high capacity subjects maintained a tight focus upon the target location, the low capacity subjects involuntarily reallocated attentional focus to also include the distractor locations. These results suggest that individual differences in VSTM may stem from variability in resisting attentional capture by the initial onsets of contingent distractors.