Categorization and Identification of Simultaneous Targets (Categorisatie en Identificatie Van Simultaan Aangeboden Targets)
INSTITUTE FOR PERCEPTION RVO-TNO SOESTERBERG (NETHERLANDS)
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Studies on visual attention are concerned with human limits in identifying simultaneously presented stimuli. Several studies have shown that the time to detect whether a single target categorically different from non- targets is present or not, is relatively independent of the number of non- targets in the display. Invariance of performance with display size is taken as evidence in favor of late-selection theories claiming unlimited-capacity, spatially parallel processing of all items in the display. As an extension of previous studies, in the present study two categorically different targets were presented simultaneously among a variable number of non-target. Subjects were shown brief displays of two target letters among either 2, 4 or 6 non-target digits. Subjects responded same when the two letters were identical and different otherwise. Since the same-different response reflects the combined outcome of the simultaneous targets, late-selection theory predicts that the time to match the target letters is independent of the number of non-target digits. Alternatively, early-selection theory predicts a linear increase of reaction time with display size since the presence of more than one target disrupts parallel pre-attentive processing, leading to a serial search through all items in the display. The results provide evidence for the early-selection view since reaction time increased linearly with the number of categorically different non-targets. Netherlands.