视觉注意瞬脱实验范式述评

视觉注意瞬脱是指在很短时间内(约500 ms)序列呈现两个目标刺激时,被试对第二个目标正确报告率显著下降的现象。近年来国外注意瞬脱实验研究渐成选择性注意研究领域的热点, 其实验范式疏理为两大类-- 单刺激序列RSVP范式和多刺激序列RSVP范式。综述对两类范式的诸多变式进行了分析与评估, 提出了影响注意瞬脱实验范式发展的四项实验因素和今后视觉注意瞬脱实验范式发展的五种趋势。     

The meaning of the mask matters: evidence of conceptual interference in the attentional blink

The rapid serial visual presentation (RSVP) experiment reported here investigated the role of conceptual interference in the attentional blink (AB). Subjects were presented with RSVP streams that contained five stimuli: Target 1, a distractor, Target 2, a second distractor, and a symbol mask. Target 1 was a green letter, Target 2 was a red letter, and the distractors were either white letters or white digits. The stimuli were presented in a font typically seen on the face of a digital watch. Thus, "S" and "O" were identical to "5" and "0," respectively. This allowed us to present streams that were conceptually different even though featurally identical: The two letter targets were followed by distractors that were recognized either as "5" and "0" or as "S" and "O." The AB was substantially attenuated when subjects were told the distractors were digits rather than letters. This result indicates that conceptual interference plays a role in the AB.     

Two noncontiguous locations can be attended concurrently: Evidence from the attentional blink

When two targets (T1 and T2) are inserted in a rapid stream of visual distractors (RSVP), detection/ identification accuracy of T2 is impaired at intertarget lags shorter than about 500 msec. This phenomenon, the attentional blink (AB), has been regarded as a hallmark of the inability of the visual system to process multiple items. Yet, paradoxically, the AB is much reduced when T2 is presented directly after T1 (known aslag-1 sparing). Because lag-1 sparing is said to depend on observers’ spatial attention being set to process the first target, we predicted that if observers are set to monitor two RSVP streams, they could process more than two items; that is, two instances of lag-1 sparing would be obtained concurrently. The results of three experiments indicated that this was the case. When observers searched for two targets in each of two synchronized RSVP streams, lag-1 sparing occurred concurrently in both streams. These results suggest that the visual system can handle up to four items at one moment under RSVP circumstances.     

RSVP in orbit: Identification of single and dual targets in motion

Three experiments using rapid serial visual presentation (RSVP) tested participants' ability to detect targets in streams that are in motion. These experiments compared the ability to identify moving versus stationary RSVP targets and examined the attentional blink with pairs of targets that were moving or stationary. One condition presented RSVP streams in the center of the screen; a second condition used an RSVP that was orbiting in a circle, with participants instructed to follow the stream with their eyes; and a third condition had participants fixate in the middle while observing a circling RSVP stream. Relative to performance in stationary RSVP streams, participants were not markedly impaired in detecting single targets in RSVP streams that were moving, either with or without instructions to pursue the motion. In streams with two targets, a normal attentional blink effect was observed when participants were instructed to pursue the moving stream. When participants had to maintain central fixation as the RSVP stream moved, the attentional blink was nearly absent even when a trailing mask was added. We suggest that the reduction of the attentional blink for moving RSVP streams may reflect a reduced ability to perceive the temporal boundaries of the individual items.     

Dividing attention between two different categories and locations in rapid serial visual presentations

When two targets are embedded in a rapid serial visual presentation (RSVP) stream of distractors, perception of the second target is impaired if the intertarget lag is relatively short (less than 500 msec). This phenomenon, called attentional blink, has been attributed to a temporal inability of attentional resources. Nevertheless, a recent study found that observers could monitor two RSVP streams concurrently for up to four items presented in close succession, suggesting a much larger visual capacity limit. However, such high-capacity performance could be obtained by a rapid shift of attention, rather than concurrent monitoring of multiple locations. Therefore, the present study examined these alternatives. Results from six experiments indicate that observers can concurrently monitor two noncontiguous locations, even when targets and distractors are from different categories, such as digits, English alphabet letters, Japanese characters, and pseudocharacters. These results can be explained in terms of a modified input-filtering model in which a multidimensional attentional set can be flexibly configured at different spatial locations.     

Sources of interference in the attentional blink: target-distractor similarity revisited

Observers monitored streams of words or letters (10 items/sec) for one or two targets. An attentional blink (AB) effect was observed in which identification of the first target temporarily impaired identification of the second target. Target identification was impaired when the distractors were composed of either letters or false-font characters (cf. Maki, Couture, Frigen, & Lien, 1997). An asymmetrical AB effect was observed with letters and mathematical symbols; the AB effect was largest for symbol targets and letter distractors. The characters used in these experiments were rated on their meaningfulness, familiarity, and other stimulus properties. The rating data showed that pixel density best accounted for the asymmetrical target-distractor similarity effects. Modulation of the AB effect by target-distractor similarity appears to result partly from low-level masking. But masking effects may be reduced by attentional capture by target features.     

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.     

Repetition blindness and repetition priming: Effects of featural differences between targets and distractors on RSVP dual-target search

In six experiments, we investigated the influence of featural differences between targets and distractors on the detection and identification of dissimilar and repeated targets in conditions that typically produce an attentional blink and repetition blindness (when a target is repeated). Rapid serial visual presentation streams were presented that contained letter targets and distractors that were either letters or digits. The targets and the distractors were either the same color or a different color and were presented either in the same font or in a differentfont. Dual-target performance on nonrepeat trials was strongly enhanced when the targets were colored. In addition, when subjects used either the color or the font cues to select the targets, there was benefit of repetition on dual-target report, instead of repetition blindness. The results suggest that featural differences between targets and distractors play an important role in registering stimuli as distinct objects.     

Different attentional blink tasks reflect distinct information processing limitations: an individual differences approach

To study the temporal dynamics and capacity-limits of attentional selection and encoding, researchers often employ the attentional blink (AB) phenomenon: subjects' impaired ability to report the second of two targets in a rapid serial visual presentation (RSVP) stream that appear within 200-500 ms of one another. The AB has now been the subject of hundreds of scientific investigations, and a variety of different dual-target RSVP paradigms have been employed to study this failure of consciousness. The three most common are those where targets are defined categorically from distractors; those where target definition is based on featural information; and those where there is a set switch between T1 and T2, with the first target typically being featurally defined and T2 requiring a detection or discrimination judgment (probe task). An almost universally held assumption across all AB theories is that these three tasks measure the same deficit; however here, using an individual differences approach, we demonstrate that AB magnitude is only related across categorical and featural tasks. Thus, these paradigms appear to reflect a distinct cognitive limitation from that observed under set-switch conditions.     

Rapid serial visual distraction: task-irrelevant items can produce an attentional blink

When two sequential targets (T1 and T2) are presented within about 600 msec, perception of the second target is impaired. This attentional blink (AB) has been studied by means of two paradigms: rapid serial visual presentation (RSVP), in which targets are embedded in a stream of central distractors, and the two-target paradigm, in which targets are presented eccentrically without distractors. We examined the role of distractors in the AB, using a modified two-target paradigm with a central stream of task-irrelevant distractors. In six experiments, the RSVP stream of distractors substantially impaired identification of both T1 and T2, but only when the distractors shared common characteristics with the targets. Without such commonalities, the distractors had no effect on performance. This points to the subjects' attentional control setting as an important factor in the AB deficit and suggests a conceptual link between the AB and a form of nonspatial contingent capture attributable to distractor processing.     

The attentional blink: A review of data and theory

Under conditions of rapid serial visual presentation, subjects display a reduced ability to report the second of two targets(Target2; T2) in a stream of distractors if it appearswithin200-500 msec of Target 1 (Tl). This effect. known as the attentional blink(AB),has been central in characterizing the limits of humans’ ability to consciously perceive stimuli distributed across time. Here, we review theoretical accounts of the AB and examine how they explain key findings in the literature. We conclude that the AB arises from attentional demands of Tl for selection, working memory encoding, episodic registration,and response selection, which prevents this high-level central resource from being applied to T2 at shortT1-T2 lags. Tl processing also transiently impairs the redeployment of these attentional resources to subsequent targets and the inhibition of distractors that appear in close temporal proximity to T2. Although these findings are consistent with a multifactorial account of the AB,they can also be largely explained by assuming that the activation of these multiple processes depends on a common capacity-limited attentional process for selecting behaviorally relevant events presented among temporally distributed distractors. Thus, at its core, the attentional blink may ultimately reveal the temporal limits of the deployment of selective attention.     

An attentional blink for sequentially presented targets: Evidence in favor of resource depletion accounts

Several accounts of the attentional blink (AB) have postulated that this dual-target deficit occurs because of limited-capacity attentional resources being devoted to processing the first target at the expense of the second (resource depletion accounts; e.g., Chun & Potter, 1995). Recent accounts have challenged this model (e.g., Di Lollo, Kawahara, Ghorashi, & Enns, 2005; Olivers, van der Stigchel, & Hulleman, 2007), proposing instead that the AB occurs because of subjects’ inability to maintain appropriate levels of attentional control when targets are separated by distractors. Accordingly, the AB is eliminated when three targets from the same attentional set are presented sequentially in a rapid serial visual presentation (RSVP) stream. However, under such conditions poorer identification of the first target is typically observed, hinting at a potential trade-off between the first and subsequent target performances. Consistent with this hypothesis, the present study shows that an AB is observed for successive targets from the same attentional set in an RSVP stream when the first target powerfully captures attention. These results suggest that resource depletion contributes significantly to the AB.     

On the failure of distractor inhibition in the attentional blink

We investigated whether a failure of distractor inhibition contributes to the magnitude of theattentional blink (AB). Subjects viewed dual-targetrapid serial visual presentation (RSVP) streams, where the distractors that directly preceded and succeeded Target 2 (T2−1, T2+1) were either identical to each other or different. Previously, Dux, Coltheart, and Harris (2006) found enhanced target report in RSVP due to repetition of distractors around Target 1, which was interpreted as evidence of distractor inhibition. Here, distractor repetition again attenuated the AB, but only at lag 2, the Target 2 position where T2−1 would have undergone attentive processing. Our results demonstrate that the distractor repetition effect is dependent on attention, and that a failure to inhibit distractors contributes to the AB.     

Target enhancement and distractor inhibition affect transitory surround suppression in dual tasks using multiple rapid serial visual presentation streams

Few studies have investigated the interaction between temporal and spatial dimensions on selective attention using dual tasks in the multiple rapid serial visual presentation (RSVP) paradigm. A phenomenon that the surround suppression in space changes over time (termed transitory surround suppression, TSS, in the present study) has been observed, suggesting the existence of this time–space interaction. However, it is still unclear whether target enhancement or distractor inhibition modulates TSS. Four behavioural experiments were conducted to investigate the mechanism of TSS by manipulating the temporal lag and spatial distance factors between two targets embedded in six RSVP streams. The TSS effect was replicated in a study that eliminated confounds of perceptual effects and attentional switch (Experiment 1). However, the TSS disappeared when two targets shared the same colour in a between-subjects design (Experiment 2a) and a within-subject design (Experiment 2b), suggesting the impact of target enhancement on TSS. Moreover, the TSS was larger for within-category than for between-category distractors (Experiment 3), indicating the impact of distractor inhibition on TSS. These two influences on TSS under different processing demands of target and distractor processing were further confirmed in a skeletal design (Experiment 4). Overall, combinative effects of target enhancement and distractor suppression contribute to the mechanisms of time–space interaction in selective attention during visual search.     

Capturing and holding attention: The impact of emotional words in rapid serial visual presentation

When two masked, to-be-attended targets are presented within approximately 500 msec of each other, accurate report of the second target (T2) suffers more than when targets are presented farther apart in time--an attentional blink (AB). In the present study, the AB was found to be larger when taboo words were presented as a first target (T1), as compared with the AB found when emotionally neutral, negative, or positive words were presented as T1, suggesting that taboo words received preferential attentional processing. Comparable results were also obtained when taboo words were presented as to-be-ignored distractors in single-target rapid serial visual presentation (RSVP). Arousal, but not valence, ratings of the emotional words predicted accuracy on subsequent targets in both dual- and single-task RSVP. Recognition memory for taboo words accounted fully for the negative relationships between arousal ratings and accuracy on subsequent targets, suggesting that arousal-triggered changes in attentional allocation influenced encoding of taboo words at the time they were encountered.     

Attentional capture triggers an attentional blink

Two experiments examined the possibility that attention directed to a distractor during rapid serial visual presentation (RSVP) can produce an attentional blink (AB). A to-be-ignored distractor (D1) preceded a target word (T2) by a variable lag in RSVP streams of black false-font distractors. D1 was highlighted by color and was a word, a string of consonants, a string of digits, or a string of false-font characters. Recall of T2 was significantly suppressed at short D1-T2 lags (the AB) but only when D1 contained letters; the AB was completely absent when D1 was composed of digits or false-font characters. Thus, the AB can be triggered by a highlighted distractor if the distractor shares features with a target.     

Phonological encoding in the attentional blink paradigm

The attentional blink refers to a deficit in reporting a second target that follows a first target within a few hundred milliseconds, when both targets occur in a sequence of distractors shown serially at rates of about 10 items per second. In four experiments, phonological similarity of post-Target 1 distractors impaired dual target report within the interval in which the attentional blink occurs. Similarity of letter targets had a smaller, less reliable effect on performance. Phonological similarity of letter distractors did not affect single target identification (Experiment 3), but it continued to impair dual target report (Experiment 5), even when the targets belonged to a different category—namely, digits. The results demonstrated that, not only targets, but also distractors are encoded phonologically, despite the fact that distractors are irrelevant and never have to be reported.     

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).     

Task-set reconfiguration suspends perceptual processing: evidence from semantic priming during the attentional blink

When two visual targets, Target 1 (T1) and Target 2 (T2), are presented among a rapid sequence of distractors, processing of T1 produces an attentional blink. Typically, processing of T2 is markedly impaired, except when T1 and T2 are adjacent (Lag 1 sparing). However, if a shift of task set--a change in task requirements from T1 to T2--occurs, this sparing is reduced substantially. With a semantic priming technique, in which T1 could be either related or unrelated to T2, the priming of T2 by T1 diminished markedly at Lag 1, when the transition between T1 and T2 involved a switch in either location (Experiments 1 and 2) or task (Experiment 3), but remained unaffected at other lags. These results suggest that perceptual processing of T2 cannot be carried out in parallel with task-set reconfiguration.     

Relationships between attentional blink magnitude, RSVP target accuracy, and performance on other cognitive tasks

When two masked, to-be-attended targets are presented within approximately half a second of each other, performance on the second target (T2) suffers, relative to when the targets are presented further apart in time or when the first target (T1) can be ignored. This pattern of results is known as the attentional blink (AB). Typically, participants differ with respect to the magnitude of their AB and their overall target accuracy. Despite investigations as to what participant characteristics may influence AB performance (e.g., age, brain damage, or mood state), there has been no focused examination of whether individual differences in cognitive performance measures predict the magnitude of the AB or overall rapid serial visual presentation(RSVP) target accuracy. Our university studentparticipants performed single-target and dual-target RSVP tasks, as well as a selection of cognitive tasks that did not use RSVP presentations, with color, letter, digit, and object stimuli. Overall performance on each of the RSVP targets (T1, T2, and single target) was predicted by speeded manual and vocal identification times to isolated stimuli and by performance with other RSVP targets. However, the magnitude of the AB was predicted only by T1 accuracy, not by any other performance measures. The results suggest that individual differences in AB magnitude do not result from differences in effective RSVP target encoding and are not well explained by varied information-processing abilities.