An analysis of the time course of visual marking
Humphreys G., Jung-Stallmann B., Olivers C.
In the real world, visual search operates across time as well as space. Visual search over time has been studied in the laboratory using the 'preview' search procedure, where there is staggered presentation of distractors over time. Using this procedure it has been found that there is prioritised selection of new stimuli, a result attributed in part to top-down inhibition of irrelevant old information ('visual marking'). We used a probe dot detection paradigm to measure attentional allocation in preview search, varying the time at which the probe appeared. A distinct time course to probe detection was observed. Relative to when probes fell at 'neutral' areas of the display, there was initially good detection of probes falling on 'old' stimuli followed by impaired detection at old locations, after previews had been shown for longer periods. This time course is consistent with participants initially attending to old stimuli before inhibiting them in order to prioritise selection of the new displays. We discuss (i) the implications of the results for understanding visual selection over time and (ii) the relations between the data and studies showing dual task interference with preview search.