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.     

The role of attention in subitizing: Is the magical number 1?

Subitizing, the fast and accurate enumeration of up to about 3 or 4 objects, has often been thought to be dependent on limited-capacity preattentive mechanisms. We used an attentional blink paradigm to investigate the extent to which subitizing requires attentional resources. On each trial, subjects identified a target letter in an RSVP stream and then enumerated dots presented in the stream that were either simultaneous with the target letter or followed it by up to 400 ms. For numerosities from 2 to 9, evidence of an attentional blink was observed; only enumeration of 0 or 1 elements was independent of lag. Thus, even enumeration of 2–3 objects, which is within the traditional subitizing range, appears to require attentional resources. The relation of this work to studies on the attentional requirements of detecting a unique item among distractors, a supposedly preattentive discrimination, is briefly discussed.     

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.     

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.     

Transient suppression of processing during rapid serial visual presentation: Acquired distinctiveness of probes modulates the attentional blink

The attentional blink is revealed in studies of rapid serial visual processing, in which observers view a stream of letters presented sequentially at the same location in a visual display. Reporting the identity of a specially marked letter (the target) amidst distractors causes a transient loss of accuracy for detection of another prespecified symbol (the probe). In two experiments, observers viewed lists of letters, identified a randomly selected letter as a target, and detected the presence of a probe from a different category (a digit or a Greek letter). After several days of training, probe detection following a target had improved markedly. Posttarget probe detection was again impaired when the distractor set included members of the probe set. These results are compatible with an explanation of the attentional blink as an act of suppression aimed at the current set of distractors, but additional mechanisms are needed to account for the effects of training.     

Perception of temporal order is impaired during the time course of the attentional blink

Identification accuracy for the second of two target (T2) is impaired when presented shortly after the first (T1). Does this attentional blink (AB) also impair the perception of the order of presentation? In four experiments, three letter targets (T1, T2, T3) were inserted in a stream of digit distractors displayed in rapid serial visual presentation (RSVP), with T3 always presented directly after T2. The T1-T2 lag was varied to assess the perception of T2-T3 temporal order throughout the period of the AB. Factorial manipulation of the presence or absence of distractors before T1 and between T1 and T2 had similar effects on accuracy and on perception of temporal order. It is important to note that perception of temporal order suffered even when accuracy was unimpaired. This pattern of results is consistent with prior-entry theories of the perception of temporal order but not with episodic-integration theories. Simulations based on the Episodic Simultaneous Type, Serial Token (eSTST) model (Wyble, Bowman, & Nieuwenstein, 2009) provided excellent fits to the data except for the condition in which no distractors were presented in the RSVP stream.     

Synergy of stimulus-driven salience and goal-directed prioritization: Evidence from the spatial blink

In the spatial blink paradigm, participants search for a target of a designated color in a rapidly presented stream of letters at fixation. Target identification is typically impaired if a peripheral distractor appears shortly before the target, inducing a spatial blink, but impairment is observed only when the distractor also shares the sought-for color. Such results reveal an important top-down influence on the capture of attention. In the present experiments, we examined the influence of the bottom-up transients associated with the appearance and disappearance of distractors in the spatial blink paradigm. Onsets and offsets alone are incapable of inducing a spatial blink, but we found that the presence of such transients did enhance the effects of target-color-matched distractors. The results reveal important synergistic interactions between top-down and bottom-up factors involved in attentional capture.     

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).     

The influence of temporal selection on spatial selection and distractor interference: an attentional blink study.

Both spatial and temporal selection require focused attention. The authors examine how temporal attention affects spatial selection. In a dual-task rapid serial visual presentation paradigm, temporal selection of a target (T1) impairs processing of a second target (T2) that follows T1 within 500 ms. This process is the attentional blink (AB). To test the effects of withdrawing temporal attention, the authors measured concurrent distractor interference on T2 when the distractors were presented during and outside of the AB. Perceptual interference was manipulated by the similarity in color between T2 and concurrent distractors, and response interference was manipulated by the flanker congruency task. Results showed that perceptual interference was larger during the AB. Response interference also increased during the AB, but only when perceptual interference was high. The authors conclude that temporal selection and spatial selection rely on a common attentional process.     

Behavioral Goals Constrain the Selection of Visual Information

Although there is agreement that attentional processes are limited, the necessary conditions for such limitation have not been determined. We investigated whether behavioral goals are sufficient to constrain the selection of visual information. In two tasks, subjects were presented with targets and distractors that varied on two dimensions (e.g., color and letter). In separate conditions, the subjects' goal was to identify only one dimension of the target while ignoring the second dimension and ignoring the distractors. In both tasks, peripheral distractors interfered with target selection only when the targets and distractors differed on the goal-relevant dimension. When the goal was changed, the pattern of interference from the same stimuli was reversed, so that distractors affected target selection only according to the new goal. These results suggest that behavioral goals constrain the selection of visual information to a greater extent than the physical characteristics of the visual information.     

Temporal limits of selection and memory encoding: A comparison of whole versus partial report in rapid serial visual presentation

People often fail to recall the second of two visual targets presented within 500 ms in rapid serial visual presentation (RSVP). This effect is called the attentional blink. One explanation of the attentional blink is that processes involved in encoding the first target into memory are slow and capacity limited. Here, however, we show that the attentional blink should be ascribed to attentional selection, not consolidation of the first target. Rapid sequences of six letters were presented, and observers had to report either all the letters (whole-report condition) or a subset of the letters (partial-report condition). Selection in partial report was based on color (e.g., report the two red letters) or identity (i.e., report all letters from a particular letter onward). In both cases, recall of letters presented shortly after the first selected letter was impaired, whereas recall of the corresponding letters was relatively accurate with whole report.     

Attentional capture by emotional stimuli is modulated by semantic processing

The attentional blink paradigm was used to examine whether emotional stimuli always capture attention. The processing requirement for emotional stimuli in a rapid sequential visual presentation stream was manipulated to investigate the circumstances under which emotional distractors capture attention, as reflected in an enhanced attentional blink effect. Emotional distractors did not cause more interference than neutral distractors on target identification when perceptual or phonological processing of stimuli was required, showing that emotional processing is not as automatic as previously hypothesized. Only when semantic processing of stimuli was required did emotional distractors capture more attention than neutral distractors and increase attentional blink magnitude. Combining the results from 5 experiments, the authors conclude that semantic processing can modulate the attentional capture effect of emotional stimuli.     

Both exogenous and endogenous target salience manipulations support resource depletion accounts of the attentional blink: A reply to Olivers, Spalek, Kawahara, and Di Lollo (2009)

Input control theories of the attentional blink (AB) suggest that this deficit results from impaired attentional selection caused by the post-Target 1 (T1) distractor (Di Lollo, Kawahara, Ghorashi, & Enns, 2005; Olivers, van der Stigchel, & Hulleman, 2007). Accordingly, these theories predict that there should be no AB when no distractors intervene between the targets. Contrary to these hypotheses, Dux, Asplund, and Marois (2008) observed an AB (T3 deficit) when three targets, from the same attentional set, were presented successively in a rapid stream of distractors, if subjects increased the resources they devoted to T1 processing. This result is consistent with resource depletion accounts of the AB. However, Olivers, Spalek, Kawahara, and Di Lollo (2009) argue that Dux et al.’s results can be better explained by the relationship between T1 and T2, and by target discriminability effects, rather than by the relationship between T1 and T3. Here, we find that manipulating the resources subjects devote to T1, either exogenously (target perceptual salience) or endogenously (target task relevance), affects T3 performance, even when T2 and target discriminability differences are controlled for. These results support Dux et al.’s conclusion that T1 resource depletion underlies the AB.     

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.     

Spreading the sparing: against a limited-capacity account of the attentional blink

The identification of the second of two targets presented in close succession is often impaired—a phenomenon referred to as the attentional blink. Extending earlier work (Di Lollo, Kawahara, Ghorashi, and Enns, in Psychological Research 69:191–200, 2005), the present study shows that increasing the number of targets in the stream can lead to remarkable improvements as long as there are no intervening distractors. In addition, items may even recover from an already induced blink whenever they are preceded by another target. It is shown that limited memory resources contribute to overall performance, but independent of the attentional blink. The findings argue against a limited-capacity account of the blink and suggest a strong role for attentional control processes that may be overzealously applied.     

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.     

Beyond similarity: Masking of the target is sufficient to cause the attentional blink

When subjects are asked to identify a letter target embedded in a rapid serial visual presentation stream, the detection of a subsequent letter probe is briefly impaired. This transient deficit in probe detection, termed the “attentional blink,” depends on the type of item that immediately follows the letter target (Raymond, Shapiro, & Arnell, 1995). Two models have been proposed to account for this effect. The interference model of the attentional blink predicts that visual similarity between the probe and item immediately following the target (+1 item) causes the attentional blink, whereas the two-stage model is based on the notion that increased time needed to process the target letter causes the attentional blink. In order to test between these two possibilities, the masking properties of the +1 item and its similarity to the probe were varied. We found the attentional blink when the +1 item acted as a mask of the target, even though the +1 item and the probe were visually dissimilar. This pattern of results supports the two-stage model of the attentional blink.     

Faster target selection in preview visual search depends on luminance onsets: behavioral and electrophysiological evidence

To investigate how target detection in visual search is modulated when a subset of distractors is presented in advance (preview search), we measured search performance and the N2pc component as an electrophysiological marker of attentional target selection. Targets defined by a color/shape conjunction were detected faster and the N2pc emerged earlier in preview search relative to a condition in which all items were presented simultaneously. Behavioral and electrophysiological preview benefits disappeared when stimuli were equiluminant with their background, in spite of the fact that targets were feature singletons among the new items in preview search. The results demonstrate that previewing distractors expedites the spatial selection of targets at early sensory-perceptual stages, and that these preview benefits depend on rapid attentional capture by luminance onsets.     

Alerting enhances target identification but does not affect the magnitude of the attentional blink

Identification of the second of two targets is impaired when presented less than about 500 ms after the first. The magnitude of this attentional blink (AB) is known to be modulated by tonic factors (e.g., observer's state of relaxation). The present work examined the effects of a phasic change in observer's state brought about by an alerting stimulus (an aggregate of faint rings) presented in temporal proximity to either letter-target inserted in a temporal stream (RSVP) of digit distractors. In four experiments, identification accuracy of each target was substantially improved by presenting the alerting stimulus either in the target's frame or in the preceding RSVP frame. However, alerting did not modulate the magnitude of the AB. The appearance of an alerting effect on the AB in Experiment 1 was ascribed to a ceiling effect in Experiment 2. Experiment 3 ruled out endogenous temporal cueing effects; Experiment 4 examined the temporal gradient of alerting. Independence of the alerting and AB effects suggests that the alerting stimuli and the letter targets may be processed along distinct visual pathways.     

No commonality between attentional capture and attentional blink

Visual search for a unique target is impaired when a salient distractor is presented (attentional capture). This phenomenon is said to occur because attention is diverted to a distractor before it reaches the target. Similarly, perception of the second of two targets embedded in a rapid stream of nontargets is impaired, suggesting attentional deprivation due to the processing of the first target (attentional blink). We examined whether these phenomena emerge from a common underlying attentional mechanism by using correlation studies. If these phenomena share a common foundation, the magnitude of these deficits should show within-subject correlations. Participants (N = 135) revealed significant attentional deficits during spatial and temporal capture and the attentional blink tasks. However, no significant correlation was found among these tasks. Experiment 2 (N = 95) replicated this finding using the same procedure as that used in Experiment 1 but included another attentional blink task that required spatial switching between the two targets. Strong correlations emerged only between the two attentional blink tasks (with/without spatial switching). The present results suggest that attentional deficits during spatial and temporal capture and the attentional blink tasks reflect different aspects of attention.