Abstract
pAttentional capture produced by a task-irrelevant color singleton is assumed to reflect stimulus-driven processing, completely governed by bottom-up factors. Results from two converging paradigms – search reaction time and free letter report – support the conclusion that singleton capture is fully determined by (top-down) expectation. The first series of experiments resulted in strong expectation-based capture when the color singleton is expected in a given location (or color) but is not actually presented. For example, when participants are presented with a sequence of trials with a red singleton (among green items) randomly switching among four positions, attention ends up being captured by red stimuli within a non-singleton (four color) display (red, green, blue and yellow) presented unexpectedly. In the second series of experiments we eliminated singleton expectation by embedding singleton displays with visually similar but non-singleton displays. For example, participants were presented with nine letter circular displays with all possible combinations of red and white letters, of which a fourth of the trials were singleton displays (one red letter among eight white letters, or one white letter among eight red letters). In this condition singleton capture was completely eliminated (i.e. did not exceed chance - calculated separately for each participant). We conclude that singlet on capture is a top-down phenomenon originated from pervasive mental programs that direct the attentional system to seek out unique items in the visual field irrespective of task demands. We speculate that the rationale for such programs may derive from the fact that whereas processing several identical non-singleton items is redundant, processing the singleton, which is statistically most likely to be missed (one vs. many), provides important unique information.
Meeting abstract presented at VSS 2015