Speed has an effect on multiple-object tracking independently of the number of close encounters between targets and distractors

Multiple-object tracking (MOT) studies have shown that tracking ability declines as object speed increases. However, this might be attributed solely to the increased number of times that target and distractor objects usually pass close to each other (“close encounters”) when speed is increased, resulting in more target–distractor confusions. The present study investigates whether speed itself affects MOT ability by using displays in which the number of close encounters is held constant across speeds. Observers viewed several pairs of disks, and each pair rotated about the pair’s midpoint and, also, about the center of the display at varying speeds. Results showed that even with the number of close encounters held constant across speeds, increased speed impairs tracking performance, and the effect of speed is greater when the number of targets to be tracked is large. Moreover, neither the effect of number of distractors nor the effect of target–distractor distance was dependent on speed, when speed was isolated from the typical concomitant increase in close encounters. These results imply that increased speed does not impair tracking solely by increasing close encounters. Rather, they support the view that speed affects MOT capacity by requiring more attentional resources to track at higher speeds.     

What is learned about nontarget items in simple visual search?

Human sensitivity to correlational structure between nontargets and likelihood of target presence in a visual letter-search task were studied in two experiments. In each of these experiments, the performance of subjects for whom the nontarget information was altered in the final trial block was compared with the performance of subjects for whom the nontarget information did not change. When stimulus strings were presented individually on a computer screen and subjects were required to make a yes-no decision about target presence (Experiment 1), the change in nontarget structure resulted in increased reaction times for target-absent trials. When subjects searched simultaneously for three possible targets (Experiment 2), the change in nontarget structure produced increased error rates and increased reaction times for both target-absent and target-present trials. Correlations between the amount of predictive information in individual stimulus strings and reaction times also showed that both switching and nonswitching subjects were sensitive to the nontarget context. However, neither self-reports of strategy nor postexperiment choices between context-consistent and -inconsistent letter strings indicated any explicit knowledge of the predictive information in the nontarget stimuli. Subjects can thus acquire and benefit from, apparently without awareness, information about subtle correlational structure in nontarget elements in simple visual search.     

Response-based strengthening in task shifting: evidence from shift effects produced by errors

The hypothesis is introduced that 1 source of shift costs is the strengthening of task-related associations occurring whenever an overt response is produced. The authors tested this account by examining shift effects following errors and error compensation processes. The authors predicted that following a specific type of error, called task confusion, shift benefits instead of shift costs should result. A series of 3 experiments confirmed this prediction showing that task confusions produce shift benefits in subsequent trials (Experiment 1), even when the error is detected (Experiment 2). Moreover, only posterror processes that imply an error correction response produce shift costs (Experiment 3). These results additionally suggest that error detection cannot prevent errors from affecting subsequent performance.     

The mechanism of priming: episodic retrieval or priming of pop-out?

Previous studies indicate that priming affects attentional processes, facilitating processes of target detection and selection on repetition trials. However, the results are so far compatible with two different attentional views that propose entirely different mechanisms to account for priming. The priming of pop-out hypothesis explains priming by feature weighting processes that lead to more frequent selections of nontarget items on switch trials. According to the episodic retrieval account, switch trials conversely lead to temporal delays in retrieving priority rules that specify the target. The results from two eye tracking experiments clearly favour the priming of pop-out hypothesis: Switching the target and nontarget features leads to more frequent selection of nontargets, without affecting the time-course of saccades to a great extent. The results from two more control experiments demonstrate that the same results can be obtained in a visual search task that allows only covert attention shifts. This indicates that eye movements can reliably indicate covert attention shifts in visual search.     

Proactive control and episodic binding in context processing effects

Decision making often involves using prior contextual information to evaluate relevant events. A laboratory equivalent of context processing situations, the AX-Continuous Performance Task (AX-CPT), yields errors when a target probe appears in a nontarget context, or when a nontarget probe appears in a target context. According to goal-driven accounts, context information is used for top-down preparation towards processing of context-appropriate information. Performance costs in nontarget trials are attributed to inefficient cognitive control. In contrast, the episodic binding account predicts that prior experiences with combinations of a context, probe, and response are bound in episodic memory and thus bias future actions. Performance costs in this view are caused by the need to overrule prepotent associations. The current experiments tested the relative importance of proactive cognitive control versus episodic learning of appropriate stimulus-response relations for CPT performance. Support was obtained for both contributions.     

Effects of task-irrelevant grouping on visual selection in partial report

Perceptual grouping modulates performance in attention tasks such as partial report and change detection. Specifically, grouping of search items according to a task-relevant feature improves the efficiency of visual selection. However, the role of task-irrelevant feature grouping is not clearly understood. In the present study, we investigated whether grouping of targets by a task-irrelevant feature influences performance in a partial-report task. In this task, participants must report as many target letters as possible from a briefly presented circular display. The crucial manipulation concerned the color of the elements in these trials. In the sorted-color condition, the color of the display elements was arranged according to the selection criterion, and in the unsorted-color condition, colors were randomly assigned. The distractor cost was inferred by subtracting performance in partial-report trials from performance in a control condition that had no distractors in the display. Across five experiments, we manipulated trial order, selection criterion, and exposure duration, and found that attentional selectivity was improved in sorted-color trials when the exposure duration was 200 ms and the selection criterion was luminance. This effect was accompanied by impaired selectivity in unsorted-color trials. Overall, the results suggest that the benefit of task-irrelevant color grouping of targets is contingent on the processing locus of the selection criterion.     

Hue distinctiveness overrides category in determining performance in multiple object tracking

The visual distinctiveness between targets and distractors can significantly facilitate performance in multiple object tracking (MOT), in which color is a feature that has been commonly used. However, the processing of color can be more than “visual.” Color is continuous in chromaticity, while it is commonly grouped into discrete categories (e.g., red, green). Evidence from color perception suggested that color categories may have a unique role in visual tasks independent of its chromatic appearance. Previous MOT studies have not examined the effect of chromatic and categorical distinctiveness on tracking separately. The current study aimed to reveal how chromatic (hue) and categorical distinctiveness of color between the targets and distractors affects tracking performance. With four experiments, we showed that tracking performance was largely facilitated by the increasing hue distance between the target set and the distractor set, suggesting that perceptual grouping was formed based on hue distinctiveness to aid tracking. However, we found no color categorical effect, because tracking performance was not significantly different when the targets and distractors were from the same or different categories. It was concluded that the chromatic distinctiveness of color overrides category in determining tracking performance, suggesting a dominant role of perceptual feature in MOT.     

Syllables and spelling units affect feature integration in words

Three experiments showed that syllables and spelling patterns function as higher order units in word perception. Subjects were required to identify the color of a target letter in briefly presented words composed of different-colored letters. In Experiment 1, subjects incorrectly reported the color of a nontarget letter (conjunction error) more often in one-syllable words containing few spelling units than in two-syllable words containing many spelling units. Experiment 2 showed that subjects made more conjunction errors in one-syllable words than in two-syllable words when the number of spelling patterns was controlled. Experiment 3 showed that conjunction errors decreased as spelling units increased when the number of syllables was held constant. Experiments 1 and 3 also showed that more conjunction errors occurred within syllabic and spelling units than between these units. These findings are discussed in light of previous research on syllable and spelling pattern effects.     

Understanding priming of color-singleton search: Roles of attention at encoding and “retrieval”

We investigated how the performance of a color-singleton search (the search for a single odd-colored item among homogeneously colored distractors) left a persistent memory trace (lasting up to six intervening trials or ～17 sec) that facilitated a subsequent color-singleton search (when the same targetdistractor color combination was repeated). Specifically, we investigated the roles of attention in the encoding and “retrieval” stages of this priming effect by intermixing trials in which the target location was precued by an onset cue. We found that the encoding of both target and distractor colors was automatic in that whether or not observers had to use color in locating the target in the preceding trial did not substantially affect priming. However, priming required that the color-singleton item be attended in the preceding trial. Once a color singleton display was encoded, our results indicated that priming facilitated the direction of attention to the color-singleton target on a subsequent trial. In short, when a color-singleton item happened to be a critical item to be attended in one situation, another color-singleton item defined by the same color combination tended to attract attention in subsequent encounters.     

Understanding priming of color-singleton search: roles of attention at encoding and "retrieval"

We investigated how the performance of a color-singleton search (the search for a single odd-colored item among homogeneously colored distractors) left a persistent memory trace (lasting up to six intervening trials or approximately 17 sec) that facilitated a subsequent color-singleton search (when the same target-distractor color combination was repeated). Specifically, we investigated the roles of attention in the encoding and "retrieval" stages of this priming effect by intermixing trials in which the target location was precued by an onset cue. We found that the encoding of both target and distractor colors was automatic in that whether or not observers had to use color in locating the target in the preceding trial did not substantially affect priming. However, priming required that the color-singleton item be attended in the preceding trial. Once a color singleton display was encoded, our results indicated that priming facilitated the direction of attention to the color-singleton target on a subsequent trial. In short, when a color-singleton item happened to be a critical item to be attended in one situation, another color-singleton item defined by the same color combination tended to attract attention in subsequent encounters.     

Auditory, tactile, and multisensory cues facilitate search for dynamic visual stimuli

Presenting an auditory or tactile cue in temporal synchrony with a change in the color of a visual target can facilitate participants’ visual search performance. In the present study, we compared the magnitude of unimodal auditory, vibrotactile, and bimodal (i.e., multisensory) cuing benefits when the nonvisual cues were presented in temporal synchrony with the changing of the target’s color (Experiments 1 and 2). The target (a horizontal or vertical line segment) was presented among a number of distractors (tilted line segments) that also changed color at various times. In Experiments 3 and 4, the cues were also made spatially informative with regard to the location of the visual target. The unimodal and bimodal cues gave rise to an equivalent (significant) facilitation of participants’ visual search performance relative to a no-cue baseline condition. Making the unimodal auditory and vibrotactile cues spatially informative produced further performance improvements (on validly cued trials), as compared with cues that were spatially uninformative or otherwise spatially invalid. A final experiment was conducted in order to determine whether cue location (close to versus far from the visual display) would influence participants’ visual search performance. Auditory cues presented close to the visual search display were found to produce significantly better performance than cues presented over headphones. Taken together, these results have implications for the design of nonvisual and multisensory warning signals used in complex visual displays.     

An attentional blink for nontargets?

In a typical attentional blink experiment, viewers try to detect two target items among distractors in a Rapid Serial Visual Presentation (RSVP): processing of the first target impairs participants' ability to recall a subsequent target at short stimulus onset asynchronies (SOAs). However, little is known about whether target detection interferes with memory for nontarget items. To answer this question, in two experiments, we employed a novel dual-task procedure: participants searched for a word target (e.g., "a four-footed animal") and then were tested for recognition of nontarget words. Detection of the target word, which was present on half the trials, produced a standard attentional blink effect on memory for nontarget words, with lag 1 sparing followed by an attentional blink at longer lags. This result shows that target processing has a generalized effect on processing of later events, not only other targets.     

Preferential processing of target features in texture segmentation

In five experiments, observers were required to detect a texture target and/or identify the orientation of elements composing target and nontarget regions. They were significantly worse at discerning the orientation of nontarget regions than at detecting target presence (Experiment 1). On the other hand, accuracy of identifying target orientation was found to be near 100% (Experiment 2). When observers were required only to identify surround orientation (Experiment 3), accuracy was diminished on target-present trials relative to that on target-absent trials. The superiority of target processing and the interference produced by target presence on surround processing were demonstrated in unpracticed observers (Experiment 4). In Experiment 5, it was found that information regarding target presence is available before information regarding feature values of the target. These findings are consistent with a model of visual attention and search that incorporates a fast generalized difference operator and a slower feature comparison process.     

Evidence that short-term memory is not the limiting factor in the tachistoscopic full-report procedure

An experiment was conducted to determine whether acoustic short-term memory is the factor which limits performance in the tachistoscopic full-report paradigm. Many Es have demonstrated the existence of phonemic encoding in short-term memory. The confusion errors from a tachistoscopic full-report task were, therefore, analyzed for the presence of acoustic confusions. Absolutely no evidence for acoustic confusions was found; visual confusions, however, were abundant. It was concluded that acoustic short-term memory is not the limiting factor in the full-report paradigm.     

Simply shapely: Relative, not absolute shapes are primed in pop-out search

Visual search is typically faster when the target from the previous trial is repeated than when it changes. This priming effect is commonly attributed to a selection bias for the target feature value or against the nontarget feature value that carries over to the next trial. By contrast, according to a relational account, what is primed in visual search is the target–nontarget relationship—namely, the feature that the target has in relation to the features in the nontarget context (e.g., larger, darker, redder)—and switch costs occur only when the target–nontarget relations reverse across trials. Here, the relational account was tested against current feature-based views in three eye movement experiments that used different shape search tasks (e.g., geometrical figures varying in the number of corners). For all tested shapes, reversing the target–nontarget relationships produced switch costs of the same magnitude as directly switching the target and nontarget features across trials (“full-switch”). In particular, changing only the nontargets produced large switch costs, even when the target feature was always repeated across trials. By contrast, no switch costs were observed when both the target and nontarget features changed, such that the coarse target–nontarget relations remained constant across trials. These results support the relational account over feature-based accounts of priming and indicate that a target’s shape can be encoded relative to the shapes in the nontarget context.     

When does repeated search in scenes involve memory? Looking at versus looking for objects in scenes

One might assume that familiarity with a scene or previous encounters with objects embedded in a scene would benefit subsequent search for those items. However, in a series of experiments we show that this is not the case: When participants were asked to subsequently search for multiple objects in the same scene, search performance remained essentially unchanged over the course of searches despite increasing scene familiarity. Similarly, looking at target objects during previews, which included letter search, 30 seconds of free viewing, or even 30 seconds of memorizing a scene, also did not benefit search for the same objects later on. However, when the same object was searched for again memory for the previous search was capable of producing very substantial speeding of search despite many different intervening searches. This was especially the case when the previous search engagement had been active rather than supported by a cue. While these search benefits speak to the strength of memory-guided search when the same search target is repeated, the lack of memory guidance during initial object searches-despite previous encounters with the target objects-demonstrates the dominance of guidance by generic scene knowledge in real-world search.     

Not all triads are created equal: further support for the importance of visual and semantic proximity in object identification

Identification deficits were investigated in ELM, a temporal lobe stroke patient with category-specific deficits. We replicated previous work done on FS, a patient with category specific deficits as a result of herpes viral encephalitis. ELM was tested using novel, computer generated shapes that were paired with artifact labels. We paired semantically close or disparate labels to shapes and ELM attempted to learn these pairings. Overall, ELM's shape-label confusions were most detrimentally affected when we used labels that referred to objects that were visually and semantically close. However, as with FS, ELM had as many errors when shapes were paired with the labels "donut," "tire," and "washer" as he did when they were paired with visually and semantically close artifact labels. Two explanations are put forth to account for the anomalous performance by both patients on the triad of donut-tire-washer.     

Tracking objects that move where they are headed

Previous work has demonstrated that the ability to keep track of moving objects is improved when the objects have unique visual features, such as color or shape. In the present study, we investigated how orientation information is used during the tracking of objects. Orientation is an interesting feature to explore in moving objects because it is directional and is often informative of the direction of motion. Most objects move forward, in the direction they are oriented. In the present experiments, participants tracked a subset of moving isosceles triangles whose orientations were constant, related, or unrelated to the direction of motion. In the standard multiple object tracking (MOT) task, tracking performance improved when orientations were unique and remained constant, but not when orientation and direction of motion were aligned. In the target recovery task, in which MOT was interrupted by a brief blanking of the display, performance did improve when orientation and direction were aligned. In the final experiment, results showed that orientation was not used before the blank to predict future target locations, but was instead used after the blank. We concluded that people use orientation to compare a stored representation to target position for recovery of lost targets.     

Fortune and reversals of fortune in visual search: Reward contingencies for pop-out targets affect search efficiency and target repetition effects

Rewards have long been known to modulate overt behavior. But their possible impact on attentional and perceptual processes is less well documented. Here, we study whether the (changeable) reward level associated with two different pop-out targets might affect visual search and trial-to-trial target repetition effects (see Maljkovic & Nakayama, 1994). Observers searched for a target diamond shape with a singleton color among distractor diamond shapes of another color (e.g., green among red or vice versa) and then judged whether the target had a notch at its top or bottom. Correct judgments led to reward, with symbolic feedback indicating this immediately; actual rewards accumulated for receipt at study end. One particular target color led to a higher (10:1) reward for 75% of its correct judgments, whereas the other singleton target color (counterbalanced over participants) yielded the higher reward on only 25% of the trials. We measured search performance in terms of inverse efficiency (response time/proportion correct). The reward schedules not only led to better performance overall for the more rewarding target color, but also increased trial-to-trial priming for successively repeated targets in that color. The actual level of reward received on the preceding trial affected this, as did (orthogonally) the likely level. When reward schedules were reversed within blocks, without explicit instruction, corresponding reversal of the impact on search performance emerged within around 6 trials, asymptoting at around 15 trials, apparently without the observers’ explicit knowledge of the contingency. These results establish that pop-out search and target repetition effects can be influenced by target reward levels, with search performance and repetition effects dynamically tracking changes in reward contingency.     

Target localization after saccades and at fixation: Nontargets both facilitate and bias responses

ABSTRACT

The image on our retina changes every time we make an eye movement. To maintain visual stability after saccades, specifically to locate visual targets, we may use nontarget objects as “landmarks”. In the current study, we compared how the presence of nontargets affects target localization after saccades and during sustained fixation. Participants fixated a target object, which either maintained its location on the screen (sustained-fixation trials), or displaced to trigger a saccade (saccade trials). After the target disappeared, participants reported the most recent target location with a mouse click. We found that the presence of nontargets decreased response error magnitude and variability. However, this nontarget facilitation effect was not larger for saccade trials than sustained-fixation trials, indicating that nontarget facilitation might be a general effect for target localization, rather than of particular importance to post-saccadic stability. Additionally, participants’ responses were biased towards the nontarget locations, particularly when the nontarget-target relationships were preserved in relative coordinates across the saccade. This nontarget bias interacted with biases from other spatial references, e.g., eye movement paths, possibly in a way that emphasized non-redundant information. In summary, the presence of nontargets is one of several sources of reference that combine to influence (both facilitate and bias) target localization.