Rapid guidance of visual search by object categories.

Abstract

Visual search is often controlled by attentional templates that represent specific target items or target features, but can also be directed toward object categories. We studied the relationship between item-based and category-guided attentional control during visual search for one specific item (e.g., the letter C), two or three items (e.g., the letters C, F, and X), or categorically defined targets (e.g., any letter). To assess the efficiency of visual search for single, multiple, or category-defined targets, we measured the N2pc component as an electrophysiological marker of attentional target selection. In Experiment 1, where targets were presented among distractors from a different category (e.g., letters among digits), a category-based selection strategy was available. Category-based attentional control triggered spatially selective modulations of visual-perceptual processing that emerged within less than 200 ms after stimulus onset and preceded the effects of item-specific attentional templates. In Experiment 2, where letter targets appeared among letter distractors, target detection could no longer be guided by categorical top-down task sets. Search efficiency decreased as the target set size increased, in line with capacity limitations for item-specific attentional templates. Results demonstrate that category-based attentional guidance can be used rapidly and efficiently during visual search for alphanumeric targets.

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

“…Previous electrophysiological studies (Wu et al, 2013;Nako et al, 2014aNako et al, , 2014b have shown that reliable N2pc components are elicited during the selection of search targets that are defined by their category, demonstrating that category-based attentional control processes can operate at relatively early visual-perceptual processing stages.…”

“…This suggests that when the deployment of attention has to be guided by search templates for object categories, target objects can still be selected rapidly, at relatively early stages during the processing of visual input. Importantly, when observers searched for a particular item, nontarget objects that matched the category of the current target (e.g., the letter A during search for the letter P) also triggered N2pc components (Nako et al, 2014a). Although this "foil" N2pc was smaller than the N2pc to targets, it was already reliably present during the 180-200 ms post-stimulus interval.…”

“…In all previous N2pc studies that provided evidence for the guidance of attentional selection processes in visual search by category (Wu et al, 2013;Nako et al, 2014aNako et al, , 2014b, category-defined target objects were always accompanied by multiple distractor objects that belonged to a different task-irrelevant category (e.g., one target letter among digits during letter search, or one kitchen object among items of clothing during search for kitchen utensils). In other words, target objects were category singletons in the sense that they were the only category-matching item in the search displays.…”

“…In our studies of feature-based and category-based attentional selection processes (Wu et al, 2013;Nako et al, 2014a), N2pc components were elicited not only by targets that were defined at the item level, but also by category-defined targets. This suggests that when the deployment of attention has to be guided by search templates for object categories, target objects can still be selected rapidly, at relatively early stages during the processing of visual input.…”

The neural basis of attentional control in visual search

“…Target detection is strongly impaired when targets are immediately replaced by another visual stimulus, and therefore can no longer be addressed by recurrent feedback signals. The existence of fast recurrent pathways from categoryselective areas to visual cortex [85] can also explain why category-guided object selection is often remarkably rapid [89]. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 candidate target objects at particular locations in the visual field can be effectively routed back to spatially corresponding regions of visual cortex [18].…”