An extensive amount of research indicates that repeating target and distractor features facilitates pop-out search while switching these features slows the search. Following the seminal study by Maljkovic and Nakayama (1994), this “priming of pop-out” effect (PoP) has been widely described as an automatic bottom-up process that is independent of the observers’ expectations. At the same time, numerous studies highlight the crucial role of expectations in visual attention deployment. Our experiment shows that in contrast to previous claims, PoP in a classic color singleton search task is a mix of automatic processing and expectations. Participants searched for a uniquely colored diamond among 2 same-colored distractors. Target color sequences were either predictable (e.g., 2 red-target-green-distractors trials, followed by 2 green-target-red-distractors trials, and so on) or random. Responses were faster in predictable color sequences than randomly changing ones with equal number of repetitions of target colors on preceding trials. Analyses of observers’ eye movements showed that predictability of target color affected both latency and accuracy of the first saccade during a search trial. Our results support the idea that PoP is governed not only by automatic effects from previous target or distractor features but also by top-down expectations.
Prevailing theories of visual working memory assume that each encoded item is stored or forgotten as a separate unit independent from other items. Here, we show that items are not independent, and that the recalled orientation of an individual item is strongly influenced by the summary statistical representation of all items (ensemble representation). We find that not only is memory for an individual orientation substantially biased towards the mean orientation, but the precision of memory for an individual item also closely tracks the precision with which people store the mean orientation (which is, in turn, correlated with the physical range of orientations). Thus, individual items are reported more precisely when items on a trial are more similar. Moreover, the narrower the range of orientations present on a trial, the more participants appear to rely on the mean orientation as representative of all individuals. This can be observed not only when the range is carefully controlled, but also shown even in randomly generated, unstructured displays, and after accounting for the possibility of location-based ‘swap’ errors. Our results suggest that the information about a set of items is represented hierarchically, and that ensemble information can be an important source of information to constrain uncertain information about individuals.
The heterogeneity of our visual environment typically reduces the speed with which a singleton target can be found. Visual search theories explain this via nontarget similarities and dissimilarities that affect grouping, perceptual noise, etc. Here, we show that increasing the heterogeneity of a display can facilitate rather than inhibit visual search for size and orientation singletons when heterogeneous features smoothly fill the transition between highly distinguishable nontargets. We suggest that this smooth transition reduce the “segmentability” of dissimilar items to otherwise separate subsets making the visual system to treat them as a near-homogenous sets opposing to a singleton.
During difficult foraging tasks, humans rarely switch between target categories, but switch frequently during easier foraging. Does this reflect fundamental limits on visual working memory (VWM) capacity or simply strategic choice due to effort? Our participants performed time-limited or unlimited foraging tasks where they tapped stimuli from 2 target categories while avoiding items from 2 distractor categories. These time limits should have no effect if capacity imposes limits on VWM representations but more flexible VWM could allow observers to use VWM according to task demands in each case. We found that with time limits, participants switched more frequently and switch-costs became much smaller than during unlimited foraging. Observers can therefore switch between complex (conjunction) target categories when needed. We propose that while maintaining many complex templates in working memory is effortful and observers avoid this, they can do so if this fits task demands, showing the flexibility of working memory representations used for visual exploration. This is in contrast with recent proposals, and we discuss the implications of these findings for theoretical accounts of working memory.