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Jelmer de Vries, Ignace Hooge, Frans Verstraten; Saccadic target selection and crowding. Journal of Vision 2009;9(8):1208. doi: 10.1167/9.8.1208.
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© ARVO (1962-2015); The Authors (2016-present)
Camouflage is a well-known practice to avoid detection. Similar surroundings impair the recognition of an object, a phenomenon called crowding. However, knowledge about camouflage is often common ground and an observer could search first among similar surroundings, even though an object is more difficult to distinguish there. Here we ask how visual information surrounding search elements affects selection of locations through eye movements.
Our search stimulus consisted of a vertical Gabor (target) and 11 slightly tilted Gabors (distractors) on a hexagonal grid. Each of these Gabors is flanked by 4 Gabors, rotated 45°, resulting in a display with 12 individual clusters. In two experiments we used color and spatial frequency, respectively, to vary similarity between target and flankers.
In the first experiment the target was a red Gabor, either flanked by red or green Gabors. The spacing between clusters was such that the target could not be distinguished peripherally. Search times were shorter when a red target was placed among red flankers than when it was placed among green flankers. Fixation data showed that locations with red flankers were selected far more frequently than locations with green flankers, explaining the difference in search times.
In the second experiment we showed that saccadic selection differs when the target is not completely masked. A vertical low spatial frequency target Gabor was placed among high or low spatial frequency flankers. In this experiment contrasting results were found. Search times were now shorter when a low spatial frequency target was located among high spatial frequency Gabors.
These results suggest that saccadic target selection is the outcome of a combination of two factors. Surroundings similar to the target impair its peripheral recognition, but can also attract eye movements, as more of the target property is present at the location.
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