Visual foraging and executive functions: A developmental perspective

In the past few years, interest in visual foraging, where participants search for multiple targets at a time, has increased, as such tasks may provide a richer picture of visual attention than traditional single-target visual search tasks. Little is known about visual foraging in childhood, so we tested 67 6th grade Icelandic children (mean age = 11.80 years, SD = 0.30 years; 36 girls) on a foraging task involving multiple targets of different types, also measuring three subdomains of executive functioning: inhibition, attentional flexibility, and working memory. The foraging results were then compared to findings from a previous study on younger children (66 children aged 4-7 years). The results show that foraging ability improves dramatically between the preschool and middle school years, and that this improvement reflects greater ease with switching between target types. The older children showed foraging patterns previously seen for adults: randomly switching between target templates during feature foraging, but exhaustively foraging for a single target type before switching during conjunction foraging. Younger children, conversely, tended to stick with the same target type for long runs during feature foraging. Switch costs were also much lower for the older children, resulting in faster and more efficient foraging. Lastly, a connection was established between foraging ability and both working memory and attentional flexibility, but not inhibition. Our study shows that foraging is a promising field of study to further our knowledge of visual attention, how it changes throughout the lifespan, and how it is connected to other cognitive functions.

Visual Search: How Do We Find What We Are Looking For?

In visual search tasks, observers look for targets among distractors. In the lab, this often takes the form of multiple searches for a simple shape that may or may not be present among other items scattered at random on a computer screen (e.g., Find a red T among other letters that are either black or red.). In the real world, observers may search for multiple classes of target in complex scenes that occur only once (e.g., As I emerge from the subway, can I find lunch, my friend, and a street sign in the scene before me?). This article reviews work on how search is guided intelligently. I ask how serial and parallel processes collaborate in visual search, describe the distinction between search templates in working memory and target templates in long-term memory, and consider how searches are terminated.

Preparatory Template Activation during Search for Alternating Targets

Visual search is guided by representations of target-defining features (attentional templates). We tracked the time course of template activation processes during the preparation for search in a task where the identity of color-defined search targets switched across successive trials (ABAB). Task-irrelevant color probes that matched either the upcoming relevant target color or the previous now-irrelevant target color were presented every 200 msec during the interval between search displays. N2pc components (markers of attentional capture) were measured for both types of probes at each time point. A reliable probe N2pc indicates that the corresponding color template is active at the time when the probe appears. N2pcs of equal size emerged from 1000 msec before search display onset for both relevant-color and irrelevant-color probes, demonstrating that both color templates were activated concurrently. Evidence for color-selective attentional control was found only immediately before the arrival of the search display, where N2pcs were larger for relevant-color probes. These results reveal important limitations in the executive control of search preparation in tasks where two targets alternate across trials. Although the identity of the upcoming target is fully predictable, both task-relevant and task-irrelevant target templates are coactivated. Knowledge about target identity selectively biases these template activation processes in a temporally discrete fashion, guided by temporal expectations about when the target template will become relevant.

Oscillatory Mechanisms of Preparing for Visual Distraction

Evidence shows that observers preactivate a target representation in preparation of a visual selection task. In this study, we addressed the question if and how preparing to ignore an anticipated distractor differs from preparing for an anticipated target. We measured EEG while participants memorized a laterally presented color, which was cued to be either a target or a distractor in two subsequent visual search tasks. Decoding the location of items in the search display from EOG channels revealed that, initially, the anticipated distractor attracted attention and could only be ignored later during the trial. This suggests that distractors could not be suppressed in advance but were represented in an active, attention-guiding format. Consistent with this, lateralized posterior alpha power did not dissociate between target and distractor templates during the delay periods, suggesting similar encoding and maintenance. However, distractor preparation did lead to relatively enhanced nonlateralized posterior alpha power, which appeared to gate sensory processing at search display onset to prevent attentional capture in general. Finally, anticipating distractors also led to enhanced midfrontal theta power during the delay period, a signal that was predictive of how strongly both target and distractor were represented in the search display. Together, our results speak against a distractor-specific advance inhibitory template, thus contrary to the preactivation of specific target templates. Rather, we demonstrate a general selection suppression mechanism, which serves to prevent initial involuntary capture by anticipated distracting input.