Task-dependent modulation of target-flanker lateral interactions in vision

Visibility of a central target Gabor element often improves in the presence of collinear flankers. Such lateral interactions may reflect fundamental mechanisms underlying the perceptual integration of contours in early vision. We recently reported (Freeman, Sagi, & Driver, 2001) attentional modulation of these interactions. Here, we test whether this modulation is task dependent. Subjects had to detect a near-threshold central target while performing a secondary discrimination task on one pair of flankers that could appear with another distractor pair (one pair collinear with the target, the other orthogonal). Central target thresholds were lowered when collinear flankers were judged for the secondary task, but only when this task concerned the global spatial relationship between these flankers (discrimination of their Vernier offset or global orientation). Other secondary tasks involving discriminating the local orientations, contrasts, or colors of the relevant flanker pair produced no such attentional modulation. However, this task-dependent modulation was observed only when two flanker pairs were present, not for displays with only a single flanker pair. Top-down modulation of lateral interactions may function to select between overlapping potential contours whenever the global spatial properties of one are task relevant.     

Collinear masking effect in visual search is independent of perceptual salience

Searching for a target in a salient region should be easier than looking for one in a nonsalient region. However, we previously discovered a contradictory phenomenon in which a local target in a salient structure was more difficult to find than one in the background. The salient structure was constructed of orientation singletons aligned to each other to form a collinear structure. In the present study, we undertake to determine whether such a masking effect was a result of salience competition between a global structure and the local target. In the first 3 experiments, we increased the salience value of the local target with the hope of adding to its competitive advantage and eventually eliminating the masking effect; nevertheless, the masking effect persisted. In an additional 2 experiments, we reduced salience of the global collinear structure by altering the orientation of the background bars and the masking effect still emerged. Our salience manipulations were validated by a controlled condition in which the global structure was grouped noncollinearly. In this case, local target salience increase (e.g., onset) or global distractor salience reduction (e.g., randomized flanking orientations) effectively removed the facilitation effect of the noncollinear structure. Our data suggest that salience competition is unlikely to explain the collinear masking effect, and other mechanisms such as contour integration, border formation, or the crowding effect may be prospective candidates for further investigation.     

Object-based attention: sensory modulation or priority setting?

The detection of an invalidly cued target is faster when it appears within a cued object than when it appears in an uncued object equally distant from the cued location; this is a manifestation of object based attention. Five experiments are reported in which it was investigated whether early sensory enhancement (in which attention "spreads" within an attended object but stops at its borders) or a later attentional prioritization mechanism best accounts for these effects. In Experiments 1-4, subjects identified a centrally located target with a buttonpress while attempting to ignore flanking distractors that were mapped to either a compatible or an incompatible response. The flankers appeared either within the object occupied by the target or in a different object but at the same distance from the target. The well-known effect of distance between the target and the flankers on the magnitude of the compatibility effect was replicated. However, whether the target and the flankers were in the same or different objects had no effect on the magnitude of the compatibility effect. In Experiment 5, when attention could not be narrowly focused in advance, object-based modulation of the flanker effect was observed. These results suggest that object-based selection may reflect an object-specific attentional prioritization strategy, rather than object-based attentional modulation of an early sensory representation.     

抑制控制能力衰退对知觉组织老年化的影响

通过比较注意线索对老年人和年轻人共线性和相似性知觉组织的影响,探讨了知觉组织老年化的原因。研究发现,注意线索对年轻人的助益更大,对老年人的助益较小,符合抑制控制理论的研究假设,同时本文还对加工速度、基本感觉能力等可能引起认知老年化的因素进行了分析。此外,还发现了知觉组织中与阅读习惯一致的方向偏好,无论在有无注意线索的条件下,135°方向上的知觉组织都快于45°方向上的知觉组织。     

Attentional bias during emotional processing: evidence from an emotional flanker task using IAPS

Attention is biased towards threat-related stimuli. In three experiments, we investigated the mechanisms, processes, and time course of this processing bias. An emotional flanker task simultaneously presented affective or neutral pictures from the international affective picture system database either as central response-relevant stimuli or surrounding response-uninformative flankers. Participants’ response times to central stimuli was measured. The attentional bias was observed when stimuli were presented either for 1500?ms (Experiment 1) or 500?ms (Experiment 2). The threat-related attentional bias held regardless of the stimuli competing for attention even when presentation time was further reduced to 200?ms (Experiment 3). The results indicate that automatic and controlled mechanisms may interact to modulate the orientation of attention to threat. The data presented here shed new light on the mechanisms, processes, and time course of this long investigated by still largely unknown processing bias.     

Perceptual load modulates attentional capture by abrupt onsets

The abrupt appearance of a new object captures attention, even when the object is task irrelevant. These findings suggest that abrupt onsets capture attention in a stimulus-driven manner and are not susceptible to top-down influences on attentional control. However, previous studies examining the ability of abrupt onsets to capture attention have used search displays that lacked significant complexity. Because attention is a limited capacity mechanism, it is possible that increasing the complexity, or perceptual load, of the search arrays may modulate capture by abrupt onsets. We used a flanker task to examine the effect of perceptual load on attentional capture by abruptly appearing objects. Subjects searched for a target letter through low-load (set size=1) and high-load (set size=6) displays. On each trial, irrelevant flankers also appeared, one as an onset and the other as an offset. Onset flankers affected search in low-load but not high-load displays. This modulation of attentional capture was not caused by generalized slowing when subjects searched through high-load displays; search for a single perceptually degraded target slowed response times but did not affect attentional capture. These findings demonstrate that attentional capture by an abrupt onset is attenuated when people search through high-load scenes.     

Attentional capture by emotional faces is contingent on attentional control settings

Attentional capture by schematic emotional faces was investigated in two experiments using the flanker task devised by Eriksen and Eriksen (1974). In Experiment 1, participants were presented with a central target (a schematic face that was either positive or negative) flanked by two identical distractors, one on either side (schematic faces that were positive, negative, or neutral). The objective was to identify the central target as quickly as possible. The impact of the flankers depended on their emotional expression. Consistent with a threat advantage hypothesis (negative faces are processed faster and attract more processing resources), responses to positive faces were slower when these were flanked by (response incompatible) negative faces as compared with positive or neutral faces, whereas responses to negative faces were unaffected by the identity of the flankers. Experiment 2 was a standard flanker task with letter stimuli except that the task-neutral flankers were schematic faces that were either positive, negative, or emotionally neutral. In this case, in which faces and emotional expressions were to be ignored, performance seemed entirely unaffected by the faces. This result suggests that attentional capture by emotional faces is contingent on attentional control settings.     

Attentional capture by emotional faces is contingent on attentional control settings

Attentional capture by schematic emotional faces was investigated in two experiments using the flanker task devised by Eriksen and Eriksen (1974). In Experiment 1, participants were presented with a central target (a schematic face that was either positive or negative) flanked by two identical distractors, one on either side (schematic faces that were positive, negative, or neutral). The objective was to identify the central target as quickly as possible. The impact of the flankers depended on their emotional expression. Consistent with a threat advantage hypothesis (negative faces are processed faster and attract more processing resources), responses to positive faces were slower when these were flanked by (response incompatible) negative faces as compared with positive or neutral faces, whereas responses to negative faces were unaffected by the identity of the flankers. Experiment 2 was a standard flanker task with letter stimuli except that the task-neutral flankers were schematic faces that were either positive, negative, or emotionally neutral. In this case, in which faces and emotional expressions were to be ignored, performance seemed entirely unaffected by the faces. This result suggests that attentional capture by emotional faces is contingent on attentional control settings.     

Attentional scanning in the selection of central targets from multi-symbol strings

Abstract

Subjects responded to five-symbol strings consisting of a central target, one or two compatible or incompatible flankers, and neutral symbols in the remaining positions. Performance strongly depended on the position of compatible or incompatible flankers. With normal letters, left-side flankers had a much larger impact than right-side flankers. This left-side asymmetry of the flanker compatibility effect disappeared with strings composed of spaced letters or of tiny pictures and tended to turn into a right-side asymmetry with vertically mirrored letters. These results seem to indicate the operation of attentional scanning processes. Flankers may be scanned either automatically, due to a reading-like habit, or strategically, in attempting to localize the target.     

Time course of visual attention across perceptual levels and objects

Theories of shifts of visual attention based on attentional blink or dwell time do not directly address shifts of attention across different levels (global or local) involving multiple objects. Two experiments were conducted employing the attentional dwell time paradigm to investigate the shifts of visual attention between objects selected at same or different levels. Participants were instructed to identify two successive compound stimuli at a pre-specified level (global or local) presented at two different locations with variable SOA. The initial pair of locations in which the stimulus was presented was fixed in Experiment 1 but not in Experiment 2. Experiment 1 results showed very little impairment for second target identification when both the targets were at the global level. Attentional shift was better with both targets at the same level compared to different levels. Experiment 2 results showed that local followed by global target identification is difficult at short SOAs compared to other conditions. The results indicate that scope of attention affects the time course of visual attention. Global processing could be performed with very little capacity limitation simultaneously with distributed attention. The default mode of attention might be distributed and attention becomes focused for target identification. Different mechanisms may underlie shifts in focused attention between different locations and changes in attentional set required by changes in perceptual levels.     

Local and global orientation in visual search

Six experiments investigated the role of global (shape) and local (contour) orientation in visual search for an orientation target. Experiment 1 demonstrated thatsearch for a conjunction of local contours with a distinct global orientation was less efficient than search for a target featurally distinct in terms of both global and local contour orientation. However, Experiments 2 and 4 demonstrated that the presence of a unique line contour was neither sufficient nor necessary to allow efficient search. Experiment 5 found thatsearch for a local orientation difference was strongly impeded by irrelevant variation in global orientation, arguing for a preeminent role for global orientation. Finally, Experiment 6 demonstrated that the orientation search asymmetry holds for the global orientation of stimuli. Taken together, the results are consistent with visual search processes guided predominately by a representation of global orientation.     

Coactivation, pop-out, and symmetry affect line discrimination

17 college students discriminated between vertical and horizontal target lines flanked by vertical and horizontal distractors. Large displays with 3.0-cm lines and small displays half this size were used. The distractors were positioned above and below the target or to the left and right of it, forming vertical and horizontal global orientations. The number of flankers sharing the target's orientation was varied. Vertical targets and small display sizes were processed more quickly. Speed of responding did not differ for the two global orientations. There was no advantage for target lines consistent with global orientation. The results were replicated in Exp. 2 with diagonal flankers. This supports an explanation using stimulus compatibility, since diagonal lines do not correspond to either of the response options and cannot induce a tendency to respond more to one target than another. Displays with multiple symmetry were responded to faster than those with a single symmetry which were faster than asymmetrical displays, supporting the idea that symmetrical axes parallel and perpendicular to the target orientation provide a facilitative frame of reference. Coactivation from same-oriented flankers, pop-out from differences in orientation, and symmetry all influenced responding in these patterns.     

Collinearity,curvature interpolation,and the power of perceptual integration

In three experiments, participants determined the orientation of a global triangle formed by three Gabor patches of a target spatial frequency in a field of distracters. The orientation of the target patches and their proximity were varied between conditions. When all the target patches had the same orientation this facilitated the response compared to random orientations. This effect occurred only when the patches were in close proximity. When the orientations of the target patches were different but aligned to the global triangle, facilitation occurred regardless of proximity. These contrasting types of facilitation were attributed to different early perceptual integration mechanisms that enable the perception of holistic structure.     

Anxious mood narrows attention in feature space

Spatial attention can operate like a spotlight whose scope can vary depending on task demands. Emotional states contribute to the spatial extent of attentional selection, with the spotlight focused more narrowly during anxious moods and more broadly during happy moods. In addition to visual space, attention can also operate over features, and we show here that mood states may also influence attentional scope in feature space. After anxious or happy mood inductions, participants focused their attention to identify a central target while ignoring flanking items. Flankers were sometimes coloured differently than targets, so focusing attention on target colour should lead to relatively less interference. Compared to happy and neutral moods, when anxious, participants showed reduced interference when colour isolated targets from flankers, but showed more interference when flankers and targets were the same colour. This pattern reveals that the anxious mood caused these individuals to attend to the irrelevant feature in both cases, regardless of its benefit or detriment. In contrast, participants showed no effect of colour on interference when happy, suggesting that positive mood did not influence attention in feature space. These mood effects on feature-based attention provide a theoretical bridge between previous findings concerning spatial and conceptual attention.     

Conflict adaptation in time: Foreperiods as contextual cues for attentional adjustment

Interference evoked by distractor stimulus information, such as flankers in the Eriksen task, is reduced when the proportion of conflicting stimuli is increased. This modulation is sensitive to contextual cues such as stimulus location or color, suggesting attentional adjustment to conflict contingencies on the basis of context information. In the present study, we explored whether conflict adjustment is modulated by temporal variation of conflict likelihood. To this end, we associated low and high proportions of conflict stimuli with foreperiods of different lengths. Flanker interference was higher with foreperiods associated with low conflict proportions, suggesting that participants use the foreperiod as a contextual cue for attentional adjustment. We conjecture that participants initially adopt the strategy useful for conflict contingencies associated with short foreperiods, and then readjust during the trial, in the absence of any additional exogenous cue, when the imperative stimulus has not occurred during a certain time interval.     

Negative triangles: simple geometric shapes convey emotional valence

It has been suggested that downward pointing triangles convey negative valence, perhaps because they mimic an underlying primitive feature present in negative facial expressions (Larson, Aronoff, and Stearns, 2007). Here, we test this proposition using a flanker interference paradigm in which participants indicated the valence of a central face target, presented between two adjacent distracters. Experiment 1 showed that, compared with face flankers, downward pointing triangles had little influence on responses to face targets. However, in Experiment 2, when attentional competition was increased between target and flankers, downward pointing triangles slowed responses to positively valenced face targets, and speeded them to negatively valenced targets, consistent with valence-based flanker compatibility effects. These findings provide converging evidence that simple geometric shapes may convey emotional valence.     

Valuable orientations capture attention

Visual attention has long been known to be drawn to stimuli that are physically salient or congruent with task-specific goals. Several recent studies have shown that attention is also captured by stimuli that are neither salient nor task relevant, but that are rendered in a colour that has previously been associated with reward. We investigated whether another feature dimension—orientation—can be associated with reward via learning and thereby elicit value-driven attentional capture. In a training phase, participants received a monetary reward for identifying the colour of Gabor patches exhibiting one of two target orientations. A subsequent test phase in which no reward was delivered required participants to search for Gabor patches exhibiting one of two spatial frequencies (orientation was now irrelevant to the task). Previously rewarded orientations robustly captured attention. We conclude that reward learning can imbue features other than colour—in this case, specific orientations—with persistent value.     

Directional harmonic theory: a computational Gestalt model to account for illusory contour and vertex formation

Visual illusions and perceptual grouping phenomena offer an invaluable tool for probing the computational mechanism of low-level visual processing. Some illusions, like the Kanizsa figure, reveal illusory contours that form edges collinear with the inducing stimulus. This kind of illusory contour has been modeled by neural network models by way of cells equipped with elongated spatial receptive fields designed to detect and complete the collinear alignment. There are, however, other illusory groupings which are not so easy to account for in neural network terms. The Ehrenstein illusion exhibits an illusory contour that forms a contour orthogonal to the stimulus instead of collinear with it. Other perceptual grouping effects reveal illusory contours that exhibit a sharp corner or vertex, and still others take the form of vertices defined by the intersection of three, four, or more illusory contours that meet at a point. A direct extension of the collinear completion models to account for these phenomena tends towards a combinatorial explosion, because it would suggest cells with specialized receptive fields configured to perform each of those completion types, each of which would have to be replicated at every location and every orientation across the visual field. These phenomena therefore challenge the adequacy of the neural network approach to account for these diverse perceptual phenomena. I have proposed elsewhere an alternative paradigm of neurocomputation in the harmonic resonance theory (Lehar 1999, see website), whereby pattern recognition and completion are performed by spatial standing waves across the neural substrate. The standing waves perform a computational function analogous to that of the spatial receptive fields of the neural network approach, except that, unlike that paradigm, a single resonance mechanism performs a function equivalent to a whole array of spatial receptive fields of different spatial configurations and of different orientations, and thereby avoids the combinatorial explosion inherent in the older paradigm. The present paper presents the directional harmonic model, a more specific development of the harmonic resonance theory, designed to account for specific perceptual grouping phenomena. Computer simulations of the directional harmonic model show that it can account for collinear contours as observed in the Kanizsa figure, orthogonal contours as seen in the Ehrenstein illusion, and a number of illusory vertex percepts composed of two, three, or more illusory contours that meet in a variety of configurations.     

The effect of betel nut chewing on contour and object masking

The betel nut is a common stimulant in many Asian countries. We employed the masking task developed by Enns and Di Lollo (Trends in Cognitive Sciences, 4, 345-352, 1997) to investigate the effects of betel nuts on sensory and attentional processing. In the masking task, participants needed to identify a target that was masked by either a contour mask or an object mask. Sensory processing was assessed by examining target identification in the contour mask condition when the target was presented only centrally, whereas attentional processing was assessed by examining target identification in the object mask condition when the target was presented randomly in either a central or a parafoveal location. The results showed that chewing betel nut and chewing gum produced significant contour masking with a large effect size, similar to the pure control condition, in which participants chewed nothing, and the placebo control condition, in which what participants chewed was disguised. This suggests that neither betel nut nor gum affects sensory processing. Alternatively, betel nut chewing could produce a reduction in object masking for the habitual chewers and the nonchewers, suggesting an effect of betel nut on attentional processing. This concentrated attention was also observed in the placebo control condition; thus, it cannot be exclusively driven by the expectation effect. Also, chewing per se reduced the attentional distribution foveally.     

The effect of repetitive saccade execution on the attention network test: Enhancing executive function with a flick of the eyes

The simple act of repeatedly looking left and right can enhance subsequent cognition, including divergent thinking, detection of matching letters from visual arrays, and memory retrieval. One hypothesis is that saccade execution enhances subsequent cognition by altering attentional control. To test this hypothesis, we compared performance following repetitive bilateral saccades or central fixation on the revised attention network test, which measures the operation of three distinct attentional networks: alerting, orienting, and executive function. The primary finding was that saccade execution increased the subsequent operation of the executive function network, which encompasses attentional control. Specifically, saccade execution decreased response time to target stimuli in the presence of response-incongruent flankers. A secondary finding was that saccade execution decreased response time to targets when an invalid location was cued prior to target onset. These findings suggest that saccades are an effective means of improving attentional control. Of greater theoretical importance, the study establishes attentional enhancement as a potential mechanism by which saccades enhance other aspects of cognition. Although some saccade execution effects have been found to depend on consistency of handedness (i.e., the consistency with which an individual uses one hand over the other), saccade-induced enhancement of attentional control occurred independently of handedness consistency.