Inhibitory tagging in an interrupted visual search

Interruption in visual search: a systematic review

Visual search, the process of trying to find a target presented among distractors, is a much-studied cognitive task. Less well-studied is the condition in which the search task is interrupted before the target is found. The consequences of such interruptions in visual search have been investigated across various disciplines, which has resulted in diverse and at times contradictory findings. The aim of this systematic review is to provide a more cohesive understanding of the effects of interruptions in visual search. For this purpose, we identified 28 studies that met our inclusion criteria. To facilitate a more organized and comprehensive analysis, we grouped the studies based on three dimensions: the search environment, the interruption aftermath, and the type of the interrupting event. While interruptions in visual search are variable and manifest differently across studies, our review provides a foundational scheme for a more cohesive understanding of the subject. This categorization serves as a starting point for exploring potential future directions, which we delineate in our conclusions.

Attentional Strategies and the Transition From Subitizing to Estimation in Numerosity Perception

The common view of the transition between subitizing and numerosity estimation regimes is that there is a hard bound on the subitizing range, and beyond this range, people estimate. However, this view does not adequately address the behavioral signatures of enumeration under conditions of attentional load or in the immediate post-subitizing range. The possibility that there might exist a numerosity range where both processes of subitizing and estimation operate in conjunction has so far been ignored. Here, we investigate this new proposal, that people strategically combine the processes of subitizing and estimation to maximize accuracy and precision, given time or attentional constraints. We present a process-level account of how subitizing and estimation can be combined through strategic deployment of attention to maximize the precision of perceived numerosity given time constraints. We then describe a computational model of this account and apply it in two experimental simulations to demonstrate how it can explain key findings in prior enumeration research. While recent modeling work has argued that the behavioral signatures of enumeration can best be explained through a single numerosity system with a single form of representation, we argue that our model demonstrates how the traditional two-systems view of numerical representation accounts for behavioral data through coordination with a unified attentional mechanism, rather than a unified representation.

Inhibition of return as a foraging facilitator in visual search: Evidence from long-term training

Inhibition of return (IOR) discourages visual attention from returning to previously attended locations, and has been theorized as a mechanism to facilitate foraging in visual search by inhibitory tagging of inspected items. Previous studies using visual search and probe-detection tasks (i.e., the probe-following-search paradigm) found longer reaction times (RTs) for probes appearing at the searched locations than probes appearing at novel locations. This IOR effect was stronger in serial than parallel search, favoring the foraging facilitator hypothesis. However, evidence for this hypothesis was still lacking because no attempt was made to study how IOR would change when search efficiency gradually improves. The current study employed the probe-following-search paradigm and long-term training to examine how IOR varied following search efficiency improvements across training days. According to the foraging facilitator hypothesis, inhibitory tagging is an after-effect of attentional engagement. Therefore, when attentional engagement in a visual search task is reduced via long-term training, the strength of inhibitory tagging decreases, thus predicting a reduced IOR effect. Consistent with this prediction, two experiments consistently showed that IOR decreased while search efficiency improved through training, although IOR reached the floor more quickly than search efficiency. These findings support the notion that IOR facilitates search performance via stronger inhibitory tagging in more difficult visual search.

Between the Scenes

We constantly move our eyes to new information while inspecting a scene, but these patterns of eye movements change based on the task and goals of the observer. Inhibition of return (IOR) may facilitate visual search by reducing the likelihood of revisiting previously attended locations. However, IOR may present in any visual task, or it may be search-specific. We investigated the presence of IOR in foraging, memorization, change detection, and two versions of visual search. One version of search used a static search array that remained stable throughout the trial, but the second used a scene flickering paradigm similar to the change detection task. IOR was observed in both versions of visual search, memorization, and foraging, but not in change detection. Visual search and change detection both had temporal nonscene components, and we observed that IOR could be maintained despite the scene removal but only for search. Although IOR is maintained in scene coordinates, short disruptions to this scene are insufficient to completely remove the inhibitory tags. Finally, we compare return saccades in trials without a probe and observe fewer return saccades in tasks for which IOR was observed, providing further evidence that IOR might serve as a novelty drive.

A target contrast signal theory of parallel processing in goal-directed search

Feature Integration Theory (FIT) set out the groundwork for much of the work in visual cognition since its publication. One of the most important legacies of this theory has been the emphasis on feature-specific processing. Nowadays, visual features are thought of as a sort of currency of visual attention (e.g., features can be attended, processing of attended features is enhanced), and attended features are thought to guide attention towards likely targets in a scene. Here we propose an alternative theory - the Target Contrast Signal Theory - based on the idea that when we search for a specific target, it is not the target-specific features that guide our attention towards the target; rather, what determines behavior is the result of an active comparison between the target template in mind and every element present in the scene. This comparison occurs in parallel and is aimed at rejecting from consideration items that peripheral vision can confidently reject as being non-targets. The speed at which each item is evaluated is determined by the overall contrast between that item and the target template. We present computational simulations to demonstrate the workings of the theory as well as eye-movement data that support core predictions of the theory. The theory is discussed in the context of FIT and other important theories of visual search.

Post-search IOR: Searching for inhibition of return after search

Previous research has indicated that Inhibition of return (IOR) supports visual search by discouraging the re-inspection of recently inspected items during search. However, it is not clear whether IOR persists after a search is completed or whether this depends on the presence of a further search in the same display. To investigate this issue, we had participants search consecutively twice in the same display (Experiment 1). Immediately after the end of the first search and after the end of the second search we probed an item which had been recently inspected or not in the previous search. The results showed that IOR as measured by the saccadic latency to the probed items was absent after the end of each of the two successive searches. In Experiment 2, we measured both saccadic latencies and manual responses in a single-search paradigm. We found that IOR during and after the search was present for saccadic responses but absent for manual responses. This suggests that IOR during and after a visual search depends on the modality of the response and the number of required searches.

Environment- and eye-centered inhibitory cueing effects are both observed after a methodological confound is eliminated

Inhibition of return (IOR), typically explored in cueing paradigms, is a performance cost associated with previously attended locations and has been suggested as a crucial attentional mechanism that biases orientation towards novelty. In their seminal IOR paper, Posner and Cohen (1984) showed that IOR is coded in spatiotopic or environment-centered coordinates. Recent studies, however, have consistently reported IOR effects in both spatiotopic and retinotopic (eye-centered) coordinates. One overlooked methodological confound of all previous studies is that the spatial gradient of IOR is not considered when selecting the baseline for estimating IOR effects. This methodological issue makes it difficult to tell if the IOR effects reported in previous studies were coded in retinotopic or spatiotopic coordinates, or in both. The present study addresses this issue with the incorporation of no-cue trials to a modified cueing paradigm in which the cue and target are always intervened by a gaze-shift. The results revealed that a) IOR is indeed coded in both spatiotopic and retinotopic coordinates, and b) the methodology of previous work may have underestimated spatiotopic and retinotopic IOR effects.

Allocating Attention to Distractor Locations is Based on Top-Down Expectations

Failures of selective attention may be explained by the attentional white bear (AWB) hypothesis maintaining that prior knowledge of distractor location causes attentional allocation to it. The AWB is demonstrated by embedding infrequent trials of two simultaneous dots among flanker trials. The dot at the expected distractor location is perceived as appearing before the dot at the expected empty location, indicating attentional allocation to expected distractor locations. A major requirement of the AWB hypothesis is that it occurs in a top-down manner due to expectations. We devised a variation of the original AWB experiment, which enabled us to differentiate between the top-down and bottom-up contributions. The results show that top-down expectancies, which are a critical part of the AWB characterization, occur independently of bottom-up contributions.

Effects of display complexity on location and feature inhibition

Inhibition of return refers to the lengthening of reaction times (RTs) to a target when a preceding stimulus has occupied the same location in space. Recently, we observed a robust inhibitory effect for color and shape in moderately complex displays: It is more difficult to detect a target with a particular nonspatial attribute if a stimulus with the same attribute was recently the focus of attention. Such nonspatial inhibitory effects have not generally been found in simpler displays. In the present study, we test how location-based and nonspatial inhibitory effects vary as a function of display complexity (eight, six, four, and two locations). The results demonstrated that (1) location-based inhibition effects were much stronger in more complex displays, whereas the nonspatial inhibition was only slightly stronger in more complex displays; (2) nonspatial inhibitory effects emerged at longer stimulus onset asynchronies than did location-based effects; and (3) nonspatial inhibition appeared only when cues and targets occurred in the same locations, confirming that pure feature repetition does not produce a cost. Taken together, the results are consistent with perceptual processes based on object files that are organized by spatial location. Using somewhat more complex displays than are most commonly employed provides a more sensitive method for observing the role of inhibitory processes in facilitating visual search. In addition, using a relatively wide set of cue-target timing relationships is necessary in order to clearly see how inhibitory effects operate.

Dissociable spatial and temporal effects of inhibition of return

Inhibition of return (IOR) refers to the relative suppression of processing at locations that have recently been attended. It is frequently explored using a spatial cueing paradigm and is characterized by slower responses to cued than to uncued locations. The current study investigates the impact of IOR on overt visual orienting involving saccadic eye movements. Using a spatial cueing paradigm, our experiments have demonstrated that at a cue-target onset asynchrony (CTOA) of 400 ms saccades to the vicinity of cued locations are not only delayed (temporal cost) but also biased away (spatial effect). Both of these effects are basically no longer present at a CTOA of 1200 ms. At a shorter 200 ms CTOA, the spatial effect becomes stronger while the temporal cost is replaced by a temporal benefit. These findings suggest that IOR has a spatial effect that is dissociable from its temporal effect. Simulations using a neural field model of the superior colliculus (SC) revealed that a theory relying on short-term depression (STD) of the input pathway can explain most, but not all, temporal and spatial effects of IOR.

Neuronal correlates of multiple top-down signals during covert tracking of moving objects in macaque prefrontal cortex

Resistance to distraction is a key component of executive functions and is strongly linked to the prefrontal cortex. Recent evidence suggests that neural mechanisms exist for selective suppression of task-irrelevant information. However, neuronal signals related to selective suppression have not yet been identified, whereas nonselective surround suppression, which results from attentional enhancement for relevant stimuli, has been well documented. This study examined single neuron activities in the lateral PFC when monkeys covertly tracked one of randomly moving objects. Although many neurons responded to the target, we also found a group of neurons that exhibited a selective response to the distractor that was visually identical to the target. Because most neurons were insensitive to an additional distractor that explicitly differed in color from the target, the brain seemed to monitor the distractor only when necessary to maintain internal object segregation. Our results suggest that the lateral PFC might provide at least two top-down signals during covert object tracking: one for enhancement of visual processing for the target and the other for selective suppression of visual processing for the distractor. These signals might work together to discriminate objects, thereby regulating both the sensitivity and specificity of target choice during covert object tracking.

Inhibition of return in a visual foraging task in non-human subjects

Inhibition of return is thought to help guide visual search by inhibiting the orienting of attention to previously attended locations. We have previously shown that, in a foraging visual search task, the neural responses to objects in parietal cortex are reduced after they have been examined. Here we ask whether the animals' reaction times (RTs) in the same task show a psychophysical correlate of inhibition of return: a slowing of reaction time in response to a probe placed at a previously fixated location. We trained three animals to perform an RT version of the visual foraging task. In the foraging task, subjects visually searched through an array of five identical distractors and five identical potential targets; one of which had a reward linked to it. In the RT variant of the task, subjects had to rapidly respond to a probe if it appeared. We found that RTs were slower for probes presented at locations that contained previously fixated objects, faster to potential targets and between the two for behaviorally irrelevant distractors that had not been fixated. These data show behavioral inhibitory tagging of previously fixated objects and suggest that the suppression of activity seen previously in the same task in parietal cortex could be a neural correlate of this mechanism.