Context and competition in the capture of visual attention

Competition-based models of visual attention propose that perceptual ambiguity is resolved through inhibition, which is stronger when objects share a greater number of neural receptive fields (RFs). According to this theory, the misallocation of attention to a salient distractor--that is, the capture of attention--can be indexed in RF-scaled interference costs. We used this pattern to investigate distractor-related costs in visual search across several manipulations of temporal context. Distractor costs are generally larger under circumstances in which the distractor can be defined by features that have recently characterised the target, suggesting that capture occurs in these trials. However, our results show that search for a target in the presence of a salient distractor also produces RF-scaled costs when the features defining the target and distractor do not vary from trial to trial. Contextual differences in distractor costs appear to reflect something other than capture, perhaps a qualitative difference in the type of attentional mechanism deployed to the distractor.     

Cross-dimensional interference and cross-trial inhibition

In two experiments, we examined whether one source of cross-dimensional interference in visual search involves cross-trial position priming. In Experiment 1, we demonstrated cross-dimensional interference in search for an orientation-defined target: Search for a left-tilted target among right-tilted non-targets was disrupted by the presence of a singleton color distractor. In all conditions, search was facilitated when a target was presented at the same position as a target in the previous trial (positive position priming). In addition, there were negative effects of position priming on orientation targets that fell on the same side as singleton distractors on the previous trial. In Experiment 2, to examine the impact of negative position priming on cross-dimensional interference, trials with and without singleton distractors were presented in a single trial block. The chance of a singleton distractor's being present on a preceding trial was then equated across displays when the distractor was and when it was not subsequently present. Cross-dimensional interference was eliminated under this mixed presentation condition, suggesting that the cost of cross-dimensional interference was not determined by the stimulus-driven factors in the current trial, at least when a limited number of target and distractor locations was used. We conclude that top-down selection is possible during visual search, and this leads to inhibition of the location of salient distractors. The cost of this is slowed detection of targets at inhibited locations on subsequent trials.     

Target uncertainty does not lead to more distraction by singletons: intertrial priming does

In two experiments, we examined why a singleton distractor has a stronger interfering effect in visual search when the target identity is uncertain. When participants searched for a shape, a color singleton distractor had a larger slowing effect in a mixed block, in which the target shape could change from trial to trial, than in a pure block, in which the target shape remained the same. Importantly, this increased singleton distractor effect could be traced back entirely to intertrial priming, since the increased costs occurred only on trials in which the target and the singleton distractor swapped identity (Experiment 1, allowing for priming between targets and singleton distractors) or on trials in which the target alone changed identity while the singleton distractor remained constant (Experiment 2, allowing for priming between targets only). This suggests that target uncertainty itself does not lead to strategic changes in the attentional selection of singletons. Instead, selection is affected by relatively automatic priming mechanisms that may be enhanced by competition for attention.     

The influence of a salient distractor in object-substitution masking

It remains unclear whether a salient distractor directly affects performance accuracy and the perceptual resolution of a target. In order to investigate this issue, the present study employed object substitution masking (OSM) to index perceptual hypothesis testing of a target. Trailing-mask duration of the four-dot mask was varied to investigate how the representation of the masked target decayed over time. Participants responded to the presence of a vertical line on a target ring that was isolated by a four-dot mask while an irrelevant salient distractor was presented in a subset of trials. The results revealed that the salient distractor only impacted performance when the mask and target offset concurrently (Experiment 1) or at short mask durations (Experiment 2). At longer mask durations performance in the distractor present condition was identical to performance in the distractor absent condition, suggesting that involuntary capture of attention did not affect OSM. These results show that the perceptual resolution of a masked target can operate independently of involuntary attentional selection.     

Can the location negative priming process operate in a proactive manner?

The location negative priming (NP) effect refers to the fact that the processing of a current target stimulus (probe trial) is delayed when it appears at a location that has recently contained a distractor event (prime trial), relative to when it occurs at a previously unoccupied position. One view is that the process causing the NP effect involves the inhibition of the internal representation of the prime-distractor event, and that the future processing of target stimuli that involve this event are prolonged because this distractor inhibition is persistent. In this study, we examined the possibility that the NP process (inhibition) could act proactively; specifically asking whether inhibition could be allocated to a location merely predicted to hold a future distractor event. To do this, we cued the probe distractor's location using an otherwise traditional location NP paradigm. No evidence of a proactive NP process was obtained. Probe-trial target latency was the same whether it appeared at the cued distractor location or at a new location, but was delayed when it occupied the prime-distractor location (NP effect). The location NP process is seemingly a reactive one, applying inhibition only when an actual distractor is present, much as past theories have implied.     

Negative priming and perceptual fluency: More than what meets the eye

In two priming experiments, we manipulated the perceptual quality of the target or the distractor on the prime trial; the stimuli were repeated or novel. Negative priming was found to be contingent on stimulus repetition, because it was obtained with repeated items but not with novel items. Prime trial perceptual degradation modulated negative priming for repeated items but had no effect on priming in ignored repetition conditions using novel stimuli. These patterns were obtained even when the effect of perceptual degradation was (1) greater than the effect of stimulus repetition and (2) greater for novel words than for repeated words. Although stimulus repetition increases perceptual fluency, the activation of perceptual representations by itself is not sufficient to produce negative priming. Instead, we suggest that negative priming is a manifestation of an activation-sensitive inhibitory mechanism that functions to reduce response competition.     

Negative priming and perceptual fluency: more than what meets the eye

In two priming experiments, we manipulated the perceptual quality of the target or the distractor on the prime trial; the stimuli were repeated or novel. Negative priming was found to be contingent on stimulus repetition, because it was obtained with repeated items but not with novel items. Prime trial perceptual degradation modulated negative priming for repeated items but had no effect on priming in ignored repetition conditions using novel stimuli. These patterns were obtained even when the effect of perceptual degradation was (1) greater than the effect of stimulus repetition and (2) greater for novel words than for repeated words. Although stimulus repetition increases perceptual fluency, the activation of perceptual representations by itself is not sufficient to produce negative priming. Instead, we suggest that negative priming is a manifestation of an activation-sensitive inhibitory mechanism that functions to reduce response competition.     

Does a salient distractor capture attention early in processing?

Kim and Cave (1999) used spatial probes in order to measure the effects of bottom-up and top-down factors on the allocation of spatial attention over time. Subjects searched for a target with a unique shape, with a uniquely colored distractor present on each trial. The singleton distractor captured attention early in processing, whereas attention homed in on the target’s location later on. Kim and Cave (1999) concluded that top–down factors cannot prevent the presence of a salient distractor from delaying target selection. The present study tested the idea that such results were obtained only because subjects adopted the strategy of searching for the most salient item. Kim and Cave’s (1999) finding was replicated in Experiment 1. In Experiment 2, instead of a feature search, subjects performed a conjunction search—that is, a task that could not be performed using a salience–based strategy. Probe response times were longest at the salient distractor’s location at both the short and the long stimulus onset asynchronies. These results suggest that, early in processing, top–down factors can exert their influence and prevent the capture of attention by a salient distractor.     

Trial-by-trial adjustments of top-down set modulate oculomotor capture

The role of top-down control in visual search has been a subject of much debate. Recent research has focused on whether attentional and oculomotor capture by irrelevant salient distractors can be modulated through top-down control, and if so, whether top-down control can be rapidly initiated based on current task goals. In the present study, participants searched for a unique shape in an array containing otherwise homogeneous shapes. A cue prior to each trial indicated the probability that an irrelevant color singleton distractor would appear on that trial. Initial saccades were less likely to land on the target and participants took longer to initiate a saccade to the target when a color distractor was present than when it was absent; this cost was greatly reduced on trials in which the probability that a distractor would appear was high, as compared to when the probability was low. These results suggest that top-down control can modulate oculomotor capture in visual search, even in a singleton search task in which distractors are known to readily capture both attention and the eyes. Furthermore, the results show that top-down distractor suppression mechanisms can be initiated quickly in anticipation of irrelevant salient distractors and can be adjusted on a trial-by-trial basis.     

Response inhibition in motor and oculomotor conflict tasks: Different mechanisms,different dynamics?

Previous research has shown that the appearance of task-irrelevant abrupt onsets influences saccadic eye movements during visual search and may slow down manual reactions to target stimuli. Analysis of reaction time distributions in the present study offers evidence suggesting that top-down inhibition processes actively suppress oculomotor or motor responses elicited by a salient distractor, in order to resolve the conflict that arises when reflex-like and deliberate responses are in opposition. Twenty-six participants carried out a variation of the oculomotor capture task. They were instructed to respond with either a saccade toward or with a button press at the side of the hemifield in which a target color singleton appeared. A distractor stimulus could appear either in the same or in the opposite hemifield. Delta plots revealed competition between reflex-like and deliberate response activation, and highlighted selective inhibition of automatic responses: While participants generally responded more slowly in incongruent compared to congruent situations, this effect diminished and even reversed in the slowest speed quantiles. These effects were present in both the oculomotor and motor response-mode conditions.     

Attentional repulsion effect despite a colour-based control set

A salient distractor can have a twofold effect on concurrent visual processes; it can both reduce the processing efficiency of the relevant target (e.g., increasing response time) and distort the spatial representation of the display (e.g., misperception of a target location). Previous work has shown that knowledge of the key feature of visual targets can eliminate the effect of salient distractors on processing efficiency. For instance, knowing that the target of interest is red (i.e., having an attentional control set for red) can eliminate the cost of green distractors on the speed of response to the target. The present study shows that the second mark of irrelevant salient distractors, i.e., distortions in spatial representation, is resistant to such top-down control. Using the attentional repulsion effect, we examined the influence of salient distractors on target localization. Observers had a colour-based control set and the distractors either matched or mismatched with the control set. In the first two experiments, we found systematic mislocalization of targets away from the peripheral distractors (i.e., an attentional repulsion effect). Critically, the effect was caused by distractors that both matched and mismatched the control set. A third experiment, using the same stimuli, found that processing efficiency was perfectly resistant to distractors that did not match the control set, consistent with previous work. Together, the present findings suggest that although top-down control can eliminate the cost of a salient distractor on processing efficiency, it does so without eliminating the distractor's influence on the spatial representation of the display.     

Spatiotemporal competition and task-relevance shape the spatial distribution of emotional interference during rapid visual processing: Evidence from gaze-contingent eye-tracking

People’s ability to perceive rapidly presented targets can be disrupted both by voluntary encoding of a preceding target and by spontaneous attention to salient distractors. Distinctions between these sources of interference can be found when people search for a target in multiple rapid streams instead of a single stream: voluntary encoding of a preceding target often elicits subsequent perceptual lapses across the visual field, whereas spontaneous attention to emotionally salient distractors appears to elicit a spatially localized lapse, giving rise to a theoretical account suggesting that emotional distractors and subsequent targets compete spatiotemporally during rapid serial visual processing. We used gaze-contingent eye-tracking to probe the roles of spatiotemporal competition and memory encoding on the spatial distribution of interference caused by emotional distractors, while also ruling out the role of eye-gaze in driving differences in spatial distribution. Spontaneous target perception impairments caused by emotional distractors were localized to the distractor location regardless of where participants fixated. But when emotional distractors were task-relevant, perceptual lapses occurred across both streams while remaining strongest at the distractor location. These results suggest that spatiotemporal competition and memory encoding reflect a dual-route impact of emotional stimuli on target perception during rapid visual processing.     

Extinction-like effects in normals: independence of localization and response selection

An extinction-like effect in normal subjects was previously elicited when a low-salience target in the left was simultaneously presented with a highly salient distractor in the right visual hemifield, but not vice versa (Pollmann, 1996). We investigated in four experiments whether this extinction-like effect depends on (a) explicit localization and (b) response competition. It was found that the extinction-like effect could be replicated in the absence of both. In contradistinction to our previous results, low-salience distractors had no effect on pop-out target search. This showed that explicit spatial localization demands lead to low-salience distractor interference on pop-out search.     

奖赏预期调节局部注意干扰效应

局部注意干扰效应(Localized attentional interference, LAI)是指在视觉搜索任务中同时搜索在空间上分离的两个目标时, 或者目标周围存在一个无关奇异项时, 这两个关键刺激相距较近时产生的干扰现象。本实验采用视觉搜索范式, 探讨了奖赏预期对局部注意干扰效应的影响。实验1采用双目标搜索任务, 要求被试判断搜索画面中两个奇异项刺激的形状是否相同。结果显示奖赏条件和无奖赏条件都表现出显著的距离主效应, 随着目标间距离增大, 被试的正确率提高, 反应时下降。同时, 在远距离时, 奖赏条件下的正确率高于无奖赏条件, 而在近距离时, 奖赏条件下的正确率反而低于无奖赏条件, 即, 奖赏条件下局部注意干扰效应反而增大。高动机状态增强了两个目标的表征, 反而不利于解决局部注意干扰效应。实验2采用单目标搜索任务, 要求被试判断特定目标的方位并忽略另一无关奇异项刺激。与实验1不同的是, 实验2仅在无奖赏条件下观察到显著的距离主效应, 即被试行为表现在远距离时更好; 而在奖赏条件下, 被试在近距离和远距离的表现一样好, 即没有局部注意干扰效应。这说明在奖赏预期条件, 个体可以有效抑制分心物刺激的干扰, 将注意集中于目标刺激的加工, 从而对局部注意干扰效应产生调节。整个研究表明, 奖赏整体上能够提高对任务相关刺激的表征, 并抑制任务无关刺激, 虽然这并不总是能够提高任务表现。     

Does response interference depend on the subjective visibility of flanker distractors?

Response interference (or response conflict) refers to the phenomenon whereby response times to a target stimulus are longer in the presence of distractor stimuli that indicate contrary motor responses. Response interference has been observed even when the distractor stimuli cannot be discriminated above chance levels. These results raise the question of whether response interference might be driven automatically by the physical distractor stimuli, independently of one??s subjective perception of the distractors. Using a modified version of the Eriksen flanker task, we applied metacontrast masks to the flanker stimuli and measured their subjective visibility after each trial. We found converging lines of evidence that the subjective perception of flankers contributed to response interference, over and above the contribution of automatic processing of the stimulus itself. A factorial analysis revealed that the objective, physical congruency of target and flankers and the subjective, perceptual congruency of target and flankers make additive, noninteracting contributions to target response interference, suggesting that the two interference effects originate from independent levels or stages of cognitive processing.     

Selective target processing: perceptual load or distractor salience?

Perceptual load theory (Lavie, 1995) states that participants cannot engage in focused attention when shown displays containing a low perceptual load, because attentional resources are not exhausted, whereas in high-load displays attention is always focused, because attentional resources are exhausted. An alternative "salience" hypothesis holds that the salience of distractors and not perceptual load per se determines selective attention. Three experiments were conducted to investigate the influence that target and distractor onsets and offsets have on selective processing in a standard interference task. Perceptual load theory predicts that, regardless of target or distractor presentation (onset or offset), interference from ignored distractors should occur in low-load displays only. In contrast, the salience hypothesis predicts that interference should occur when the distractor appears as an onset and would occur for distractor offsets only when the target was also an offset. Interference may even occur in highload displays if the distractor is more salient. The results supported the salience hypothesis.     

The role of probe trial distractors in the production/removal of the spatial negative priming effect

When a current (probe trial) target arises at a location formerly occupied by a distractor event (prime trial; ignored-repetition trial), its reaction time is slower than when it occurs at a previously empty location (control trial), revealing a spatial negative priming (SNP) effect. Here, we examined the influence of prime- and probe trial distractor identity similarity on the retrieval of the stored representations of prime trial processing (i.e., indexed by SNP production), in a context where the prevention of the SNP phenomenon had been motivated (via low probability of probe distractor presence—.25). Two results were important. One, the SNP effect was evident when the prime–probe distractor identities fully matched, but not when they partially or totally mismatched, showing a retrieval role for the probe distractor. Two, target-repeat trial latency facilitation showed the same pattern, indicating that representations of prime target and distractor processing are retrieved together, indicative of an episodic storage format. Since target identity remained fixed, the role of a matching probe distractor identity in SNP production was to presumably complete the triggering requirement (i.e., full event identity matching) for accessing the episodically stored representations.     

Identity and semantic negative priming in rapid serial visual presentation streams

In selective attention tasks, the efficiency of processing concurrently presented target and distractor stimuli in a given display is often influenced by the relationship these stimuli have with those in the previous display. When a to-be-attended target on a current trial (the probe trial) matches the ignored, non-target distractor on a previous trial (the prime trial), a response to the target is typically delayed compared with when the two stimuli are not associated. This negative priming (NP) phenomenon has been observed in numerous studies with traditional NP tasks presenting the target and distractor simultaneously in both the prime and probe trial couplets. Here, however, in four experiments using a mixture of stimulus types (letters, digits, English number words, and logographic Chinese number words), target and distractor stimuli were temporally separated in two rapid serial visual presentation (RSVP) streams instead of concurrently presented. The findings provide a conceptual replication and substantial extension of a recent study by Wong (Plos One, 7, e37023, 2012), and suggest that active suppression of irrelevant distracting information is a more ubiquitous form of cognitive control than previously thought.     

Limitations in attending to a feature value for overriding stimulus-driven interference

Six experiments were conducted to examine the effect of knowledge of a target for overriding stimulus-driven interference in simple search tasks (Experiments 1-3) and compound search tasks (Experiments 4-6). In simple search when the target differed from nontargets in orientation, a singleton distractor that had an orientation equivalent to that of a target interfered with search for the target. When the singleton distractor was less salient than the target with respect to the target-defining feature, it still caused interference. Such within-dimensional, nonsaliency-based interference also occurred in compound search tasks. In contrast, no interference occurred when a singleton distractor was defined in cross-dimension in a simple search task. When a compound search task was used, the salient distractor interfered with the search for a less salient target. These results are discussed in terms of their applicability to existing models and the limitations of top-down penetrability of a feature processing stage.     

Negative priming for spatial location?

The term negative priming has been used to describe the deleterious consequences for performance when the current target shares properties with an ignored distractor from the previous trial. Location-based negative priming was first reported by Tipper, Brehaut, and Driver (1990) who used a prime-probe procedure wherein the task was to localize targets defined by their identity (shape). Design imbalances in this seminal study, and others, are illustrated and it is indicated how these might have contaminated the reported effects. The findings, from three experiments using an unbiased design, suggest that negative priming in the spatial location procedure may be more closely related to inhibition of return (IOR), or to the automatic attraction of attention by new objects, than to the concepts of distractor inhibition, episodic retrieval, and feature mismatch, which have traditionally been used to explain negative priming for spatial location.