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Kevin Dent, Jason Braithwaite, Harriet Allen, Glyn Humphreys; Selective conjunctive suppression in visual search for motion – form conjunctions. Journal of Vision 2010;10(7):1297. doi: 10.1167/10.7.1297.
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© ARVO (1962-2015); The Authors (2016-present)
Three experiments investigated the mechanism underlying efficient visual search for conjunctions of motion and form (e.g. McLeod, Driver, & Crisp, 1988) using a probe-dot procedure (e.g. Klein, 1988). In Experiment 1 participants completed 3 conditions: 1) conjunction (moving X target amongst moving Os and static Xs), 2) moving feature (moving X target amongst moving Os), and 3) static feature (static X in static Os). Following the search response (target present or absent) all items stopped moving and (after 60 ms) a probe-dot appeared on a distractor, or on the blank background. Probe-dots on static distractors in the conjunction condition were located most slowly, slower than probes on moving distractors, and slower than probes on static distractors in the static feature condition. In contrast a second group who viewed the stimuli passively before locating the dot showed a different pattern: a cost for probe-dots on moving items. In Experiment 2 we investigated whether suppression applied to all static items regardless of form by adding static Os to the conjunction displays. The results showed that the suppression was specific to distractors sharing the target form (e.g. static Xs) and did not apply to static Os. Experiment 3 investigated the time-course of suppression when searching for a moving X (conjunction condition of Experiment 2). Stimuli moved for between 100 and 925 ms before the probe-dot appeared (60 ms later). The results revealed that the selective suppression of static X distractors was fast-acting, being fully in place after 100 ms of stimulus motion. The results are difficult to account for in terms of feature based guidance of attention, and suggest instead, a mechanism of selective tuning or biasing of competition in the form system by signals from the motion system.
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