The role of perceptual load in processing distractor faces

It has been established that successful ignoring of irrelevant distractors depends on the extent to which the current task loads attention. However, the previous load studies have typically employed neutral distractor stimuli (e.g., letters). In the experiments reported here, we examined whether the perception of irrelevant distractor faces would show the same effects. We manipulated attentional load in a relevant task of name search by varying the search set size and found that whereas congruency effects from meaningful nonface distractors were eliminated by higher search load, interference from distractor faces was entirely unaffected by search load. These results support the idea that face processing may be mandatory and generalize the load theory to the processing of meaningful and more complex nonface distractors.     

A bottleneck in face identification: repetition priming from flanker images

There is evidence that face processing is capacity-limited in distractor interference tasks and in tasks requiring overt recognition memory. We examined whether capacity limits for faces can be observed with a more sensitive measure of visual processing, by measuring repetition priming of flanker faces that were presented alongside a face or a nonface target. In Experiment 1, we found identity priming for face flankers, by measuring repetition priming across a change in image, during task-relevant nonface processing, but not during the processing of a concurrently-presented face target. Experiment 2 showed perceptual priming of the flanker faces, across identical images at prime and test, when they were presented alongside a face target. In a third Experiment, all of these effects were replicated by measuring identity priming and perceptual priming within the same task. Overall, these results imply that face processing is capacity limited, such that only a single face can be identified at one time. Merely attending to a target face appears sufficient to trigger these capacity limits, thereby extinguishing identification of a second face in the display, although our results demonstrate that the additional face remains at least subject to superficial image processing.     

The entry point of face recognition: evidence for face expertise.

Previous studies have shown that experts (e.g., birdwatchers) are as fast to recognize objects at subordinate levels of abstraction (e.g., robin) as they are to recognize the same object at the basic level (e.g., bird). As a test of face expertise, the current study found that adults identify faces more frequently (Experiment 1) and as quickly (Experiment 2) at the subordinate level (e.g., Bill Clinton) as at the basic level (e.g., human). Whereas brief presentation (75 ms) impaired subordinate-level recognition of nonface objects, it did not impair the subordinate level recognition of faces (Experiment 3). Finally, in an identity-matching task, subordinate-level primes facilitated the matching responses of faces but not nonface objects (Experiment 4). Collectively, these results indicate that face expertise, like expert object expertise, promotes a downward shift in recognition to more subordinate levels of abstraction.     

Attentional set interacts with perceptual load in visual search

In the present study, we examined the hypothesis that perceptual load is the primary factor that determines the efficiency of attentional selection. Participants performed a visual search task under conditions of high- and low-load. In line with the perceptual load hypothesis, presenting conditions of highand low-load in separate blocks of trials resulted in processing of to-be-ignored stimuli only in the lowload condition (Experiment 1). However when high- and low-load conditions were randomly mixed in blocks of trials, the participants showed processing of to-be-ignored stimuli in both conditions, suggesting that high perceptual load is not necessarily sufficient to obtain perceptual selectivity (Experiment 2). An analysis of intertrial transition effects showed that on high-load trials, processing of to-be-ignored stimuli occurred only when the previous trial was a low-load trial. The results suggest that low perceptual load can engender broad attentional processing. On the other hand, when a high-load trial was preceded by another high-load trial, little processing of task-irrelevant stimuli was observed. The present results are discussed in terms of the interaction between expectancies and bottom-up factors in the efficiency of attentional selection.     

Face value: testing the utility of contextual face cues for face recognition

The presence of multiple faces during a crime may provide a naturally-occurring contextual cue to support eyewitness recognition for those faces later. Across two experiments, we sought to investigate mechanisms underlying previously-reported cued recognition effects, and to determine whether such effects extended to encoding conditions involving more than two faces. Participants studied sets of individual faces, pairs of faces, or groups of four faces. At test, participants in the single-face condition were tested only on those individual faces without cues. Participants in the two and four-face conditions were tested using no cues, correct cues (a face previously studied with the target test face), or incorrect cues (a never-before-seen face). In Experiment 2, associative encoding was promoted by a rating task. Neither hit rates nor false-alarm rates were significantly affected by cue type or face encoding condition in Experiment 1, but cuing of any kind (correct or incorrect) in Experiment 2 appeared to provide a protective buffer to reduce false-alarm rates through a less liberal response bias. Results provide some evidence that cued recognition techniques could be useful to reduce false recognition, but only when associative encoding is strong.     

Long-term effects of covert face recognition

Covert face recognition has previously been thought to produce only very short-lasting effects. In this study we demonstrate that manipulating subjects' attentional load affects explicit, but not implicit memory for faces, and that implicit effects can persist over much longer intervals than is normally reported. Subjects performed letter-string tasks of high vs. low perceptual load (Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Perfomance. 21, 451-468.), while ignoring task-irrelevant celebrity faces. Memory for the faces was then assessed using (a) a surprise recognition test for the celebrities' names, and (b) repetition priming in a face familiarity task. The load manipulation strongly influenced explicit recognition memory, but had no effect on repetition priming from the same items. Moreover, faces from the high load condition produced the same amount of priming whether they were explicitly remembered or not. This result resolves a long-standing anomaly in the face recognition literature, and is discussed in relation to covert processing in prosopagnosia.     

Effects of concurrent spatial and verbal memory loads on serial position functions of laterally presented letter strings

In this study the influence of visuospatial and verbal memory loads on the identification of laterally presented letter strings was investigated. In the asymmetry task without concurrent loads, a clear right visual field advantage for letter identification was obtained. Hemisphere-specific effects due to concurrent loads were particularly observed when the difficulty of the load tasks was increased. The effects of visuospatial loads were found to be sex related, suggesting that under heavy load conditions mental rotation selectively overloads the processing capacity of the right hemisphere in males, while in females capacity limitations were observed in both hemispheres. Concurrent visuospatial loads produced more facilitation (or less interference) for letters in the outermost positions of each visual field than for letters in the innermost positions of each visual field. The results of the verbal memory load tasks revealed that an easy verbal load task facilitated performance which was particularly manifest for the right-most letter of both the left visual field and the right visual field. A difficult verbal memory load task interfered with recognition accuracy of letters which was most marked for the center letter in the right visual field. Letter position effects obtained in this study were interpreted in terms of various processing mechanisms influencing the serial position curves.     

Similarity modulates the face-capturing effect in change detection

We investigated whether similarity among faces could modulate the face-capturing effect in change detection. In Experiment 1, a singleton search task was used to demonstrate that a face stimulus captures attention and the odd-one-out hypothesis cannot account for the results. Searching for a face target was faster than searching for a nonface target no matter whether distractor–distractor similarity was low or high. The fast search, however, did not lead to a face-detection advantage in Experiment 2 when the pre- and postchange faces were highly similar. When participants in Experiment 3 had to divide their attention between two faces in stimulus displays for change detection, detection performance was worse than performance in detecting nonface changes. The face-capturing effect alone is insufficient to produce the face-detection advantage. Face processing is efficient but its effect on performance depends on the stimulus–task context.     

Perceptual asymmetries in face recognition

Four experiments were carried out to investigate perceptual asymmetries in face recognition. Perceptual asymmetries favoring the half-face on the observer's left were found under free viewing conditions for both unfamiliar faces (Experiment 1) and famous faces (Experiment 3). For unfamiliar faces, this asymmetry was not obtained when fixation was controlled by presenting faces tachistoscopically (Experiment 2). For famous faces, the perceptual asymmetry favoring the half-face normally seen on the left did not appear to be retained in memory (Experiments 3 and 4). Asymmetries in face perception have been explained in terms of a direct access model of laterally effects. However, these results raise the possibility that asymmetric scanning or attentional factors may be important.     

Blur detection is unaffected by cognitive load

Blur detection is affected by retinal eccentricity, but is it also affected by attentional resources? Research showing effects of selective attention on acuity and contrast sensitivity suggests that allocating attention should increase blur detection. However, research showing that blur affects selection of saccade targets suggests that blur detection may be pre-attentive. To investigate this question, we carried out experiments in which viewers detected blur in real-world scenes under varying levels of cognitive load manipulated by the N-back task. We used adaptive threshold estimation to measure blur detection thresholds at 0°, 3°, 6°, and 9° eccentricity. Participants carried out blur detection as a single task, a single task with to-be-ignored letters, or an N-back task with four levels of cognitive load (0, 1, 2, or 3-back). In Experiment 1, blur was presented gaze-contingently for occasional single eye fixations while participants viewed scenes in preparation for an easy picture recognition memory task, and the N-back stimuli were presented auditorily. The results for three participants showed a large effect of retinal eccentricity on blur thresholds, significant effects of N-back level on N-back performance, scene recognition memory, and gaze dispersion, but no effect of N-back level on blur thresholds. In Experiment 2, we replicated Experiment 1 but presented the images tachistoscopically for 200 ms (half with, half without blur), to determine whether gaze-contingent blur presentation in Experiment 1 had produced attentional capture by blur onset during a fixation, thus eliminating any effect of cognitive load on blur detection. The results with three new participants replicated those of Experiment 1, indicating that the use of gaze-contingent blur presentation could not explain the lack of effect of cognitive load on blur detection. Thus, apparently blur detection in real-world scene images is unaffected by attentional resources, as manipulated by the cognitive load produced by the N-back task.     

On the construction and maintenance of expectancies

Reaction time techniques were used to examine the role of attention in the construction and maintenance of expectancies. In Experiment I, a primed letter matching task, expectancies were observed through a delay (cost) in responding to misprimed letter arrays. A secondary probe task was interpolated between prime and array letters on some of the trials, with attentional demands inferred from delayed responding to probes. By varying the amount of time between onset of the prime and either a probe or letter array, it was found that there is attentional involvement (as reflected in probe inhibition) prior to the observation of expectancies (as reflected in letter matching cost). It was also found that the interpolation of an attention-demanding probe task did not entirely disrupt primed expectancies. Experiment II found that an expectancy persists even when an interpolated distractor task signals that the expectancy is no longer valid. These expectancies were found to decay as a function of time. The implications of these results for attention allocation and memory activation views of expectancy were discussed.     

Social anxiety and attentional biases: A top-down contribution?

Selective attention toward threatening facial expressions has been found to precipitate and maintain symptoms of social anxiety. However, the automaticity of this bias is under debate. In the present study, we aimed to test whether top-down (controlled) engagement and disengagement of attention toward threatening faces is associated with social anxiety. This was examined by testing the impact of a secondary working memory (WM) load on attentional biases. In a variation of the dot-probe task, participants’ attention was initially cued to the left or right of fixation before an upright face paired with an inverted face was presented (displaying a disgust or neutral expression), and participants responded to a subsequently presented probe. The task was performed under no-load, low-load (one-digit memory task), and high-load (six-digit memory task) conditions. Social anxiety was not found to be associated with delayed disengagement from threat. However, surprisingly, high social anxiety was associated with an engagement bias away from threat, whereas low social anxiety was associated with a bias toward threat. These results were unaffected by the WM load manipulation. This indicates that engagement with threatening facial expressions has minimal contributions from top-down mechanisms, since it is likely that orienting to facial expressions occurs relatively automatically.     

Effects of divided attention and social categorization on the own-race bias in face recognition

Perceivers remember own-race faces more accurately than other-race faces (i.e., Own-Race Bias). In the current experiments, we manipulated participants' attentional resources and social group membership to explore their influence on own and other-race face recognition memory. In Experiment 1, Chinese participants viewed own-race and Caucasian faces, and between-subjects we manipulated whether participants attention was divided during face encoding. We found that divided attention eliminated the Own-Race Bias in memory due to a reduction of memory accuracy for own-race faces, implicating that attention allocation plays a role in creating the bias. In Experiment 2, Chinese participants completed an ostensible personality test. Some participants were informed that their personality traits were most commonly found in Caucasian (i.e., other-race) individuals, resulting in these participants sharing a group membership with other-race targets. In contrast, other participants were not told anything about the personality test, resulting in the default own-race group membership. The participants encoded the faces for a subsequent recognition memory test either with or without performing a concurrent arithmetic distracting task. Results showed that other-race group membership and reducing attention during encoding independently eliminated the typical Own-Race Bias in face memory. The implications of these findings on perceptual-expertise and social-categorization models are discussed.     

The role of attention in binding visual features in working memory: Evidence from cognitive ageing

Two experiments were conducted to assess the costs of attentional load during a feature (colour–shape) binding task in younger and older adults. Experiment 1 showed that a demanding backwards counting task, which draws upon central executive/general attentional resources, reduced binding to a greater extent than individual feature memory, but the effect was no greater in older than in younger adults. Experiment 2 showed that presenting memory items sequentially rather than simultaneously, such that items are required to be maintained while new representations are created, selectively affects binding performance in both age groups. Although this experiment exhibited an age-related binding deficit overall, both age groups were affected by the attention manipulation to an equal extent. While a role for attentional processes in colour–shape binding was apparent across both experiments, manipulations of attention exerted equal effects in both age groups. We therefore conclude that age-related binding deficits neither emerge nor are exacerbated under conditions of high attentional load. Implications for theories of visual working memory and cognitive ageing are discussed.     

Trait anxiety and perceptual load as determinants of emotion processing in a fear conditioning paradigm

The impact of trait anxiety and perceptual load on selective attention was examined in a fear conditioning paradigm. A fear-conditioned angry face (CS+), an unconditioned angry face (CS-), or an unconditioned face with a neutral or happy expression were used in distractor interference and attentional probe tasks. In Experiments 1 and 2, participants classified centrally presented letters under two conditions of perceptual load. When perceptual load was high, distractors had no effect on selective attention, even with aversive conditioning. However, when perceptual load was low, strong response interference effects for CS+ face distractors were found for low trait-anxious participants. Across both experiments, this enhanced distractor interference reversed to strong facilitation effects for those reporting high trait anxiety. Thus, high trait-anxious participants were faster, rather than slower, when ignoring CS+ distractors. Using an attentional probe task in Experiment 3, it was found that fear conditioning resulted in strong attentional avoidance in a high trait-anxious group, which contrasted with enhanced vigilance in a low trait-anxious group. These results demonstrate that the impact of fear conditioning on attention is modulated by individual variation in trait anxiety when perceptual load is low. Fear conditioning elicits an avoidance of threat-relevant stimuli in high trait-anxious participants.     

Automatic letter priming in an alphabetic decision task

An alphabetic decision task was used to study effects of form priming on letter recognition at very short prime durations (20 to 80 msec). The task required subjects to decide whether a stimulus was a letter or a nonletter. Experiment 1 showed clear facilitatory effects of primes being either physically or nominally identical to the targets, with a stable advantage for the former. Experiment 2 demonstrated that uppercase letters are classified more rapidly as letters (vs. non-letters) when they are preceded by a briefly exposed, forward- and backward-masked, visually similar uppercase letter than when they are preceded by a visually dissimilar uppercase letter. Finally, Experiment 3 demonstrated that nominally identical and visually similar primes facilitate processing more than do nominally identical, visually dissimilar primes. The alphabetic decision task proved to produce sensitive and stable priming effects at the feature, letter, and response-choice level. The present results on letter-letter priming thus constitute a solid data base against which to evaluate other priming effects, such as word-letter priming. The results are discussed in light of current activation models of letter and word recognition and are compared with data simulated by the interactive activation model (McClelland & Rumelhart, 1981).     

注意瞬脱范式中的知觉负载对情绪面孔加工的影响

情绪性刺激的加工是否受注意影响目前尚存争论。基于许多操纵空间注意焦点的研究未能在注意资源的分配上进行精确的调节, 本实验将时间维度的注意瞬脱范式与负载理论相结合, 通过调节注意瞬脱中T1刺激物知觉负载水平的高低(箭头朝向相同与否), 观察被试在四种时间延迟条件下(延迟2, 延迟3, 延迟5, 延迟8)T2目标侦测任务恐惧和中性面孔的反应正确率, 从而对情绪性刺激的加工特征进行研究。实验发现：对恐惧面孔侦测的正确率在高知觉负载条件下显著降低, 而中性面孔则不受知觉负载水平影响, 并且这种高知觉负载对恐惧面孔加工的抑制作用仅发生在注意瞬脱中的短延迟条件下。说明在知觉加工资源和注意调节作用同时受限的情况下恐惧面孔的优势加工受到限制, 提示情绪性刺激的加工与中性刺激相比消耗的加工资源较少, 并依赖于注意的调控。     

Task- and location-switching effects on visual attention

In two experiments, we examined the effects of task and location switching on the accuracy of reporting target characters in an attentional blink (AB) paradigm. Single-character streams were presented at a rate of 100 msec per character in Experiment 1, and successive pairs of characters on either side of fixation were presented in Experiment 2. On each trial, two targets appeared that were either white letters or black digits embedded in a stream of black letter distractors, and they were separated by between zero and five items in the stream (lags 1-6). Experiment 1 showed that report of the first target was least accurate if it immediately preceded the second target and if the two targets were either both letters or both digits (task repetition cost). Report of the second target was least accurate if one or two distractors intervened between the two targets (the U-shaped AB lag effect) and if one target was a letter and the other a digit (task switch cost). Experiment 2 added location uncertainty as a factor and showed similar effects as Experiment 1, with one exception. Lag 1 sparing (the preserved accuracy in reporting the second of two targets if the second immediately follows the first) was completely eliminated when the task required attention switching across locations. Two-way additive effects were found between task switching and location switching in the AB paradigm. These results suggests separate loci for their attentional effects. It is likely that the AB deficit is due mainly to central memory limitations, whereas location-switching costs occur at early visual levels. Task-switching costs occur at an intermediate visual level, since the present task switch involved encoding differences without changes in stimulus-response mapping rules (i.e., the task was character identification for both letters and digits).