The relationship between time of arrival of nontargets and their spatial location: evidence for asymmetries in visual attentional processing.

Abstract

A brief advance of the presentation of distant nontargets has previously been shown to secure them an analysis, suggesting that even stimuli beyond the putative 'spotlight' of attention are analysed. In the present experiment nontargets were presented near to fixation or peripherally (at 0.6 or 1.9 deg of visual angle) for a duration of 17, 33, or 67 ms before being masked. After a subsequent period (SOA) of 0, 20, 40, 60, or 80 ms the target was presented at fixation. The results from the shortest nontarget duration show a time lag in the development of the effect of far nontargets on response to the target. At durations of 33 and 67 ms the identity of far nontargets has been established before masking takes place, since their effect is observable at zero SOA. However, while this effect remains relatively constant over SOAs of 20 to 80 ms it increases with SOA in the near condition, suggesting that, although both near and far nontargets have been identified, it is only the near nontargets which are subject to further processing during the interval between nontarget and target presentations. The results favour a model of attention in which stimuli are passively selected and subject to additional processing on the basis of their spatial location rather than that the location or representation of distractor items are actively suppressed.