Object-Based Attention is Impervious to Nearby Targets During Visual Search

Abstract

Recent studies on the representational basis of attention have suggested that uncertainty of either the target location (Shomstein & Yantis, 2002, 2004) or the target-defining feature (Greenberg, 2009) promotes object-based selection, whereas target certainty promotes space-based selection. Here, we examined the effects of visual search strategy on the magnitude of object-based attention. Displays contained a single rectangular object among gray (parallel search condition) or multicolored (serial search condition) distracters, which appeared 300 ms after an exogenous cue at one end of the rectangle. Subjects searched for a green target (or orange, for half the subjects) positioned at one of four locations relative to the cue: (1) valid location on the object, (2) invalid location, far end of the object, (3) an equidistant invalid location not on the object, or (4) random background location. In Experiment 1, search slopes for background targets were positive when distracters were multicolored and flat when distracters were gray, confirming that subjects employed serial and parallel search, respectively. Robust same object advantage values were observed during both search strategies, presumably because the target location was uncertain in both conditions. However, serial search produced a significantly larger same object advantage than parallel search, suggesting that object-based selection may be modulated by the seriality of the transmission of selected information. We ran two additional experiments during which the invalid, off-object target was moved closer to the object by a distance of ~1/2 (Expt. 2) or ~3/4 (Expt. 3), creating a spatial advantage for this location compared to the invalid, on-object target. Unexpectedly, neither of these manipulations produced a significant reversal of the same object advantage. This suggests that proximal locations not on the selected object are prioritized lower than distal locations on the object. Object-based selection, therefore, is surprisingly resistant to distraction during conditions of target spatial uncertainty. Meeting abstract presented at VSS 2012