Multiple representations in visual working memory simultaneously guide attention: The type of memory-matching representation matters

Whether multiple visual working memory (VWM) representations can simultaneously become active templates to guide attention is controversial. The single-item-template hypothesis argues that only one VWM representation can be active at a time, whereas the multiple-item-template hypothesis argues that multiple VWM templates can simultaneously guide attention. The present study examined the two hypotheses in three (out of four) experiments, using three different types of memory objects: Experiment 1: shapes; Experiment 2: colors; and Experiment 3: colored shapes. Participants were required to hold one (memory-1) or two objects (memory 2) in VWM while performing a tilted line search task. Zero (match-0), one (match-1), or two (match-2) memory stimuli reappeared as distracters in the search array. Guidance effects were found for each type of memory stimuli. More importantly, the guidance effect for memory-2/match-2 trials was significantly larger than that for memory-2/match-1 and memory-1/match-1 trials when holding two colors or two colored shapes in VWM, which is in line with the multiple-item-template hypothesis. However, the pattern of simultaneous guidance effect is not perfectly found for two memory shapes, which may indicate that a reliable simultaneous guidance effect from two representations in VWM can be observed only when the memory-matching stimuli is more effective in guiding attention. Experiment 4 directly compared the guidance effect induced by feature-based matches (partial matching) with the guidance effect induced object-based matches (complete matching) in memory-set-size 2. Reliable guidance effects in match-1 and match-2 trials for object-based matches but not for feature-based matches confirmed the crucial role of the type of memory-matching stimuli in guiding attention.