Lifespan changes in attention: The visual search task

There are two popular frameworks for the study of visual attention. Treisman's Feature Integration Theory focuses on the effortful process of binding together the multiple attributes of an object. Posner's Visual Orienting Theory emphasizes the movement of an attentional spotlight across space. Although both aspects are undoubtedly important in any visual search task, it is not clear how each of these aspects changes with age. We tested observers aged 6, 8, 10, 22, and 72 years on visual search tasks designed to isolate these factors. No age-related differences were found in single- or double-feature discrimination, attention movement to a single item, or search for a single-feature target among distractors. Two age-related changes were found: (1) young children were less able than either young adults or seniors to search for targets defined by a conjunction of features, and (2) both children and seniors were less able than young adults to move attention voluntarily from item to item. This implies that feature integration and voluntary movement of attention have different trajectories over the lifespan.     

Attention demands of visual search

The relation between attention demand and the number of items in the array (array size) was investigated by engaging subjects in a primary search task and measuring spare capacity at different points in time, with a secondary tone task that occurred randomly on half of the trials. The major variables in both tasks were array size 14, 8, or 12 letters and stimulus onset asynchrony (SOA: ?400, ?200, 0, 200, 400, and 600 msec. Subjects were able to perform the tasks quite independently, and me, st of the interference that resulted from nonindependence appeared in tone-task performance. Theamount of interference (i.e., maximum tone reaction time) was independent of array size, but theduration of interference (li.e., the number of SOAs at which tone reaction time was elevated) increased with array size. The findings were interpreted as supporting unlimited-capacity models of visual search performance.     

Dimension- and space-based intertrial effects in visual pop-out search: modulation by task demands for focal-attentional processing

Two experiments compared reaction times (RTs) in visual search for singleton feature targets defined, variably across trials, in either the color or the orientation dimension. Experiment 1 required observers to simply discern target presence versus absence (simple-detection task); Experiment 2 required them to respond to a detection-irrelevant form attribute of the target (compound-search task). Experiment 1 revealed a marked dimensional intertrial effect of 34 ms for an target defined in a changed versus a repeated dimension, and an intertrial target distance effect, with an 4-ms increase in RTs (per unit of distance) as the separation of the current relative to the preceding target increased. Conversely, in Experiment 2, the dimension change effect was markedly reduced (11 ms), while the intertrial target distance effect was markedly increased (11 ms per unit of distance). The results suggest that dimension change/repetition effects are modulated by the amount of attentional focusing required by the task, with space-based attention altering the integration of dimension-specific feature contrast signals at the level of the overall-saliency map.

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Cultural differences in attention: Eye movement evidence from a comparative visual search task

Individual differences in visual attention have been linked to thinking style: analytic thinking (common in individualistic cultures) is thought to promote attention to detail and focus on the most important part of a scene, whereas holistic thinking (common in collectivist cultures) promotes attention to the global structure of a scene and the relationship between its parts. However, this theory is primarily based on relatively simple judgement tasks. We compared groups from Great Britain (an individualist culture) and Saudi Arabia (a collectivist culture) on a more complex comparative visual search task, using simple natural scenes. A higher overall number of fixations for Saudi participants, along with longer search times, indicated less efficient search behaviour than British participants. Furthermore, intra-group comparisons of scan-path for Saudi participants revealed less similarity than within the British group. Together, these findings suggest that there is a positive relationship between an analytic cognitive style and controlled attention.     

The affective consequences of visual attention in preview search

Comparisons of emotional evaluations of abstract stimuli just seen in a two-object visual search task show that prior distractors are devalued, as compared with prior targets or novel items, perhaps as a consequence of persistent attentional inhibition (Raymond, Fenske, & Tavassoli, 2003). To further explore such attention-emotion effects, we measured search response time in a preview search task and emotional evaluations of colorful, complex images just seen therein. On preview trials, the distractors appeared 1,000 msec before the remaining items. On no-preview trials, all the items were presented simultaneously. A single distractor was then rated for its emotional tone. Previewed distractors were consistently devalued, as compared with nonpreviewed distractors, despite longer exposure and being associated with an easier task. This effect was observed only in the participants demonstrating improved search efficiency with preview, but not in others, indicating that the attentional mechanisms underlying the preview benefit have persistent affective consequences in visual search.     

Scanning behaviour in natural scenes is influenced by a preceding unrelated visual search task

Three experiments explored the transference of visual scanning behaviour between two unrelated tasks. Participants first viewed letters presented horizontally, vertically, or as a random array. They then viewed still images (experiments 1 and 2) or video clips (experiment 3) of driving scenes, under varying task conditions. Despite having no relevance to the driving images, layout of stimuli in the letter task influenced scanning behaviour in this subsequent task. In the still images, a vertical letter search increased vertical scanning, and in the dynamic clips, a horizontal letter search decreased vertical scanning. This indicated that (i) models of scanning behaviour should account for the influence of a preceding unrelated task; (ii) carry-over is modulated by demand in the current task; and (iii) in situations where particular scanning strategies are important for primary task performance (eg driving safety), secondary task information should be displayed in a manner likely to produce a congruent scanning strategy.     

Stimulus segmentation in the visual search task

Four experiments were conducted in order to study the segmentation process in a visual search task with relevant stimuli (target and distractors) randomly distributed among textural elements. The basic idea was that a parallel segmentation process of the relevant stimuli would contribute to the overall reaction time independently of the contribution of the number of relevant stimuli. In the first experiment, with relevant stimuli and textural elements that differed in the orientation of their component lines, texture presence interacted with number of relevant stimuli and with target presence. These results were not favorable to the parallel segmentation hypothesis. In the second and third experiments, in which the relevant and the textural stimuli differed in orientation and in the luminance contrast of their component lines, the results support a parallel segmentation process for the higher contrast conditions. In these experiments, the effect of texture presence was greater on target-absent than on target-present trials. Experiment 4 shows that the search can be restricted to the high-contrast relevant stimuli when the number of these stimuli is constant and the number of textural stimuli changes from trial to trial. The present results suggest that the relevant stimuli can be segmented in parallel and then submitted to a restricted analysis, even when they are scattered among textural stimuli.     

Investigating the visual span in comparative search: the effects of task difficulty and divided attention

In three experiments, participants' visual span was measured in a comparative visual search task in which they had to detect a local match or mismatch between two displays presented side by side. Experiment 1 manipulated the difficulty of the comparative visual search task by contrasting a mismatch detection task with a substantially more difficult match detection task. In Experiment 2, participants were tested in a single-task condition involving only the visual task and a dual-task condition in which they concurrently performed an auditory task. Finally, in Experiment 3, participants performed two dual-task conditions, which differed in the difficulty of the concurrent auditory task. Both the comparative search task difficulty (Experiment 1) and the divided attention manipulation (Experiments 2 and 3) produced strong effects on visual span size.     

Differential central resource demands of memory scanning and visual search: The role of consistent and varied mapping

In this paper we compare the effect of mapping on the central resource requirements of two search processes. With consistent mapping of items to the role of either target or distractor, search becomes very efficient; with varied mapping (each item serves as both a target and a distractor in the same experiment), search is less efficient. One interpretation of this effect of manipulating the consistency of mapping is that search under varied mapping requires limited capacity central resources but the requirement for these resources is reduced with consistent mapping. We tested this interpretation by varying the consistency of mapping in memory scanning (Experiments 1 and 2) and in visual search (Experiments 3 and 4) as the second of two tasks in the psychological refractory period (PRP) paradigm. Responses were location based, rather than present/absent judgements, and a target was present on every trial. The results indicated that there was less of a requirement for central resources with consistent mapping than with varied mapping in both memory scanning and in visual search; however, the effect of the mapping manipulation on central resource requirements was different for memory scanning than for visual search. Memory scanning was not done in parallel with a resource-demanding stage of a second task under varied mapping, but was done in parallel with this stage under consistent mapping. Part of visual search under both types of mapping was done in parallel with a resource-demanding stage of a second task and part was not; consistent mapping reduced the duration of the stage of processing that could not be carried out in parallel. We conclude that under consistent mapping, switching among items in memory becomes less controlled and therefore has less of a requirement for central resources than under varied mapping. In visual search, however, consistent mapping improves performance by facilitating the comparison of the target item to items in the search array.     

Modulation of selective attention by sequential effects in visual search tasks

In visual search detection of a target on one display facilitates its subsequent recognition on the next (Rabbitt, Cumming and Vyas, 1977). Experiment I shows that facilitation also occurs when a different display intervenes between two displays containing targets. Two further experiments show that detection of target letters among background letters is also facilitated if the same background letters recur on successive displays. Facilitation is greatest if background letters reappear in identical left-to-right spatial locations, but is also evident when the same background letters recur in different locations on successive displays. The results suggest modifications to models for the ways in which selective attention is continuously modulated by successive events during serial search.     

The contributions of visual and central attention to visual working memory

We investigated the role of two kinds of attention—visual and central attention—for the maintenance of visual representations in working memory (WM). In Experiment 1 we directed attention to individual items in WM by presenting cues during the retention interval of a continuous delayed-estimation task, and instructing participants to think of the cued items. Attending to items improved recall commensurate with the frequency with which items were attended (0, 1, or 2 times). Experiments 1 and 3 further tested which kind of attention—visual or central—was involved in WM maintenance. We assessed the dual-task costs of two types of distractor tasks, one tapping sustained visual attention and one tapping central attention. Only the central attention task yielded substantial dual-task costs, implying that central attention substantially contributes to maintenance of visual information in WM. Experiment 2 confirmed that the visual-attention distractor task was demanding enough to disrupt performance in a task relying on visual attention. We combined the visual-attention and the central-attention distractor tasks with a multiple object tracking (MOT) task. Distracting visual attention, but not central attention, impaired MOT performance. Jointly, the three experiments provide a double dissociation between visual and central attention, and between visual WM and visual object tracking: Whereas tracking multiple targets across the visual filed depends on visual attention, visual WM depends mostly on central attention.     

Serial deployment of attention during visual search

This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks.     

Effects of speed and accuracy instructions on performance in a visual search task by children with good or poor attention

Children rated by teachers as having good or poor attention ability carried out a visual search task in which they were required to find a series of targets in a complex display. Different groups were told to concentrate on either speed or accuracy. Previous studies using this task have consistently shown that children rated as having poor attention make more errors (false alarms to non‐targets in the display), but do not differ in the time to make a correct response; this result was replicated. Though the instructions produced wide differences in speed and error rates in the expected directions, these differences were similar in both attention groups and the differences in error rates between the two groups remained unchanged. It is suggested that these findings are not compatible with the view that children with poor attention make errors primarily due to fast impulsive responding, nor with an explanation in terms of slower processing of the input by such children. An alternative explanation of the high error rates in such children is offered in terms of weak executive function resulting in poor ability to inhibit false alarms to non‐targets.     

Attention capacity and task difficulty in visual search

When a visual search task is very difficult (as when a small feature difference defines the target), even detection of a unique element may be substantially slowed by increases in display set size. This has been attributed to the influence of attentional capacity limits. We examined the influence of attentional capacity limits on three kinds of search task: difficult feature search (with a subtle featural difference), difficult conjunction search, and spatial-configuration search. In all 3 tasks, each trial contained sixteen items, divided into two eight-item sets. The two sets were presented either successively or simultaneously. Comparison of accuracy in successive versus simultaneous presentations revealed that attentional capacity limitations are present only in the case of spatial-configuration search. While the other two types of task were inefficient (as reflected in steep search slopes), no capacity limitations were evident. We conclude that the difficulty of a visual search task affects search efficiency but does not necessarily introduce attentional capacity limits.     

Surprising depth cue captures attention in visual search

A substantial amount of evidence indicates that surprising events capture attention. The present study was primarily intended to investigate whether expectancy discrepant depth information also is able to capture attention immediately and—more specifically—whether cues that are relatively closer or farther differentially modulate behavior. For this purpose, participants had to identify one of two target letters in a search display. Stimulus positions were initially cued by uninformative placeholders. After half of the trials, the cue at the target position was suddenly and unexpectedly (critical trial) displayed closer to or farther from the observer. In line with previous research, both depth cues captured attention on their very first appearance. Performance in the critical trial was superior to the error rates in the trials without depth cue and was even above the performance in subsequent trials that included depth cue. This effect was only observed when the cue preceded the target by 400 ms. Using a shorter cue-stimulus interval of 100 ms, only a delayed improvement was observed, which denotes a typical feature of surprise capture. Moreover, response times were faster in trials comprising a depth cue, and this was already true for the critical trial. Apart from that, no other marked differences between near and far depth cues were observed. Therefore, the present results emphasize that surprising depth information indeed captures attention. However, in contrast to other perceptual tasks, search performance was not considerably influenced by relative position in depth.     

Global statistical learning in a visual search task

Locating a target in a visual search task is facilitated when the target location is repeated on successive trials. Global statistical properties also influence visual search, but have often been confounded with local regularities (i.e., target location repetition). In two experiments, target locations were not repeated for four successive trials, but with a target location bias (i.e., the target appeared on one half of the display twice as often as the other). Participants quickly learned to make more first saccades to the side more likely to contain the target. With item-by-item search first saccades to the target were at chance. With a distributed search strategy first saccades to a target located on the biased side increased above chance. The results confirm that visual search behavior is sensitive to simple global statistics in the absence of trial-to-trial target location repetitions.     

Amount and duration of attentional demands during visual search

Previous research has suggested that, in visual-search tasks, the comparison between target and display items does not require attentional capacity. In the present experiment we used a secondary-task paradigm to distinguish the amount and duration of the attentional demands of visual search. The subjects performed visual search (the primary task) and tone detection (the secondary task) concurrently over the course of five experimental sessions (1,440 trials). For each subject, target-response mapping was either consistent or varied for Days 1-5. The results indicate that the amount of attentional demand, as reflected in secondary-task performance, increased as a function of display size in the search task. Switching from consistent to varied mapping in a sixth experimental session increased both the amount and the duration of the attentional demands of the search. The present results support models of visual-search performance in which the comparison of target and display items requires attentional capacity.     

The role of metacognition in prospective memory: Anticipated task demands influence attention allocation strategies

The present study investigates how individuals distribute their attentional resources between a prospective memory task and an ongoing task. Therefore, metacognitive expectations about the attentional demands of the prospective-memory task were manipulated while the factual demands were held constant. In Experiments 1a and 1b, we found attentional costs from a prospective-memory task with low factual demands to be significantly reduced when information about the low to-be-expected demands were provided, while prospective-memory performance remained largely unaffected. In Experiment 2, attentional monitoring in a more demanding prospective-memory task also varied with information about the to-be-expected demands (high vs. low) and again there were no equivalent changes in prospective-memory performance. These findings suggest that attention–allocation strategies of prospective memory rely on metacognitive expectations about prospective-memory task demands. Furthermore, the results suggest that attentional monitoring is only functional for prospective memory to the extent to which anticipated task demands reflect objective task demands.     

The role of configuration and target discriminability in a visual search task

Ss sorted through decks of cards bearing five-element patterns, separating those in which all five were identical from those in which one of the five was different from the remaining four. Sorting time depended on the configuration and size of the pattern in which the elements were arranged but was independent of the goodness of these patterns. It was concluded that Ss did not attend to the patterns themselves, but just to the elements comprising them in searching for the discrepant element. The differences owing to the patterns appear to be due in part to the compactness of the configurations.