The gradual emergence of spatially selective target processing in visual search: From feature-specific to object-based attentional control.

Abstract

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Category-based guidance of spatial attention during visual search for feature conjunctions.

“…4 While the early phase of the N2pc was equal in size for targets and summed partially matching nontargets on competition trials, the target N2pc started to become larger than the summed contribution of the two partially matching nontargets at about 210 -220 ms after search display onset. The emergence of a superadditive target N2pc, which was also observed in our previous study of color/shape conjunction search (Eimer & Grubert, 2014a), could mark the point in time when attentional guidance mechanisms no longer operate in a strictly independent feature-based fashion, and information about target-matching features begins to be integrated across different feature dimensions. At this point, top-down control processes begin to facilitate the focal attentional processing of target objects above and beyond the spatial bias that was previously triggered in parallel by independent feature-based guidance.…”

“…Color seems to be a more effective selection attribute than either shape (e.g., Eimer & Grubert, 2014a) or alphanumerical category (Experiment 1 of the current study), and thus tends to dominate parallel feature-based attentional selection processes. In contrast, as suggested by the results of Experiment 2, shape and alphanumerical category appear to be similar in their ability to guide the allocation of attention during visual search.…”

“…The task design employed in the present experiments was analogous to the design of a recent N2pc study where targets were defined by a specific combination of color and shape (Eimer & Grubert, 2014a). Search displays always contained four objects.…”

“…Eimer & Grubert, 2014a), but also by category-matching nontargets. If color-based and category-based attentional control processes operate independently and in parallel at different locations in the visual field during the early phase of attentional target selection, the sum of the two N2pc components to color-matching and category-matching nontargets should initially equal the N2pc to target objects on competition trials.…”

“…To find out whether alphanumerical category can guide the allocation of attention even when another visual feature is simultaneously task-relevant and when multiple items with target-matching attributes can be present in the same search display, we ran two experiments that used the same procedures as our previous color/shape conjunction search study (Eimer & Grubert, 2014a), except that one of the two target-defining attributes was now alphanumerical category (letter versus digit). Because sixteen participants were included in this previous study, the same sample size was used in the current experiments, to allow for direct comparison between the N2pc results obtained in these two studies.…”