Memory-based attention capture when multiple items are maintained in visual working memory

Abstract

Efficient visual search requires that attention is guided strategically to relevant objects, and most theories of visual search implement this function by means of a target template maintained in visual working memory (VWM). However, there is currently debate over the architecture of VWM-based attentional guidance. We contrasted a single-item-template hypothesis with a multiple-item-template hypothesis, which differ in their claims about structural limits on the interaction between VWM representations and perceptual selection. Recent evidence from van Moorselaar, Theeuwes, and Olivers (2014) indicated that memory-based capture during search, an index of VWM guidance, is not observed when memory set size is increased beyond a single item, suggesting that multiple items in VWM do not guide attention. In the present study, we maximized the overlap between multiple colors held in VWM and the colors of distractors in a search array. Reliable capture was observed when 2 colors were held in VWM and both colors were present as distractors, using both the original van Moorselaar et al. singleton-shape search task and a search task that required focal attention to array elements (gap location in outline square stimuli). In the latter task, memory-based capture was consistent with the simultaneous guidance of attention by multiple VWM representations. (PsycINFO Database Record

Figure 1

A) Gap-location search task. Participants began the trial by repeating aloud a set of four randomly chosen digits (not pictured) to suppress verbal encoding. After pressing a pacing button, there was a delay of 500 ms, followed by the depicted events. One or two color squares (1.32° X 1.32°) were presented in the memory sample display, with the first color location chosen randomly on a 2.34°-radius virtual circle and the second (if present) displayed opposite the first. The search array consisted of eight squares with one side missing (0.88° X 0.88°, 0.15° line width), distributed evenly on a virtual circle (radius 3.66°) with a random angular offset. Participants reported the gap location of the target (left/right) among distractors (top/bottom). The memory test contained two colored square alternatives (1.10° X 1.10°) presented 0.73° to the left and right of the original location of the corresponding memory square. B) Illustration of the seven conditions created by the combination of memory set size and distractor color match. C) Singleton-shape search task. The search array consisted of one outlined diamond (2.93° X 2.93°, 0.11° line width) and seven outlined circles (2.77° diameter, 0.11° line width) distributed evenly on a virtual circle (radius 5.22°) with a random angular offset. A horizontal or vertical white bar (0.18° X 1.28°) was presented in the center of each object, and participants reported the bar orientation for the target diamond

Figure 2

Mean correct reaction time for the gap-location search task as a function of memory set size and distractor match condition (* p < .05, ** p < .01, *** p < .001). Error bars are condition-specific, within-subject 95% confidence intervals (Morey, 2008).

Figure 3

Mean correct reaction time for the singleton-shape search task as a function of memory set size and distractor match condition (* p < .05, ** p < .01, *** p < .001). Error bars are condition-specific, within-subject 95% confidence intervals (Morey, 2008).