What factors influence the switch from unitary to divided attention?

The focus of attention can be either unitary or divided and can transition from unitary to divided while performing a task. In Experiment 1, we investigated whether alerting hastens the transition from unitary to divided attention. To this end, we employed a dual-RSVP-stream Attentional Blink task (AB; impaired perception of the second of two rapidly sequential targets) with two pairs of letter targets (T1-pair and T2-pair). One component of the AB known as Lag-1 sparing (unimpaired perception of the T2-pair when it is presented directly after the T1-pair) occurs only when the T2-pair falls in an attended location. When the T2-pair falls in an unattended location, the converse pattern occurs (Lag-1 deficit). Accordingly, we used the incidence of Lag-1 sparing/deficit to index whether a location was attended or unattended. We found that presenting a brief brightening flash of the screen (alerting) just before the T1-pair hastened the transition from the initial unitary focus to a divided focus. In Experiment 2, we pitted the hastening account against an alternative hypothesis that the flash triggers phasic activation of the Locus Coeruleus-norepinephrine neuromodulatory system, thus resetting the underlying neural networks that mediate the distribution of attention, triggering a switch from unitary to divided attention. The results of Experiment 2 were incompatible with the hastening account, but consistent with the network-reset account.

Sudden Events Change Old Visual Objects Into New Ones: A Possible Role for Phasic Activation of Locus Coeruleus.

We report a novel visual phenomenon called the rejuvenation effect. It causes an "old" object that has been on view for some time to acquire the properties of a suddenly appearing new object. In each experiment, a square outline was displayed continuously on one side of fixation. The target (an asterisk) was presented either inside the square or on the opposite side of fixation. On half of the trials, a transient visual or auditory event preceded the target. In Experiment 1a ( N = 139), response times were faster when the target appeared inside the square, but only when it was preceded by a transient event, consistent with the network-reset theory of locus coeruleus-norepinephrine (LC-NE) phasic activation. Three further experiments confirmed the predictions of network-reset theory, including the absence of rejuvenation in participants with atypical LC-NE functioning (individuals with symptoms of autism spectrum disorder). These findings provide new perspectives on what causes a visual object to be perceived as new.

The exogenous and endogenous control of attentional focusing.

Selective visual attention involves prioritizing both the location (orienting) and distribution (focusing) of processing. To date, much more research has examined attentional orienting than focusing. One of the most well-established findings is that orienting can be exogenous, as when a unique change in luminance draws attention to a spatial location (e.g., Theeuwes in Atten Percept Psychophys 51:599-606, 1992; Yantis and Jonides in J Exp Psychol Hum Percept Perform 10:601, 1984), and endogenous, as when a red distractor shape diverts attention when one is looking for a red target (e.g., Bacon and Egeth in Percept Psychophys 55:485-496, 1994; Folk et al. in J Exp Psychol Hum Percept Perform 18:1030, 1992). Here we ask whether attentional focusing-the broadening and contracting of prioritized processing-is influenced by the same two factors. Our methodology involved a dual-stream attentional blink task; participants monitored two spatially separated streams of items for two targets that could appear unpredictably either in the same stream or in opposite streams. The spatial distribution of attention was assessed by examining second-target accuracy in relation to inter-target lag and target location (same or opposite streams). In Experiment 1, we found that attentional contracting was more rapid when the targets differed in luminance from the distractor items. In Experiments 2 and 3, we found that the rate of attentional contracting was slower when there were task-relevant distractors in the stream opposite the first target. These results indicate that the rate of attentional focusing, like orienting, can be modulated by both exogenous and endogenous mechanisms.

The attentional blink: why does Lag-1 sparing occur when the dependent measure is accuracy, but Lag-1 deficit when it is RT?

Perception of the second of two targets (T1, T2) displayed in rapid sequence is impaired if it comes shortly after the first (attentional blink, AB). In an exception, known as Lag-1 sparing, T2 is virtually unimpaired if it is presented directly after T1. Three experiments examined the seemingly inconsistent findings that Lag-1 sparing occurs in accuracy but Lag-1 deficit occurs in RT. Experiment 1 pointed to masking of T2 as the critical factor. When T2 was not masked, the results replicated the conventional findings. The novel finding was that Lag-1 sparing occurred in RT, provided that T2 was masked. An account was provided by a psychological refractory period-based model in which processing was said to occur in two broadly sequential stages: stimulus selection and response planning. Experiments 2 and 3 tested predictions from the PRP-based model regarding Lag-1 sparing/Lag-1 deficit. In Experiment 2, we increased T2 salience, notionally reducing the duration of the T2 selection stage, with corresponding reduction in Lag-1 sparing. In Experiment 3, we manipulated the compatibility between the T1 stimulus and the response to notionally decrease/increase the duration of the T1 response-planning stage with corresponding increment/decrement in Lag-1 sparing. The results of both experiments confirmed predictions from the PRP-based model.

Attention is a sterile concept; iterative reentry is a fertile substitute.

Attention has been defined as a filter, a limited resource, a spotlight, a zoom lens, and even as a glue that binds disconnected visual features into a coherent object. Here, I claim that all of these metaphor-based explanations are circular. As such, they fail to provide adequate accounts of the phenomena they are purported to explain. In contrast, those very phenomena can be explained on the idea that perceptions emerge from iterative exchanges between cortical regions linked by two-way pathways. Processing can occur in one of two modes: feed-forward and reentrant. In feed-forward mode, the system is configured optimally for the expected input, and perception occurs on the feed-forward sweep. This form of processing corresponds to what is commonly referred to as "preattentive". If the system cannot be configured appropriately, perceptions emerge from iterative reentrant processing, which is slower, and corresponds to what is commonly referred to as "attentive".

On the time course of attentional focusing in older adults.

Many sensory and cognitive changes accompany normal ageing, including changes to visual attention. Several studies have investigated age-related changes in the control of attention to specific locations (spatial orienting), but it is unknown whether control over the distribution or breadth of attention (spatial focus) also changes with age. In the present study, we employed a dual-stream attentional blink task and assessed changes to the spatial distribution of attention through the joint consequences of temporal lag and spatial separation on second-target accuracy. Experiment 1 compared the rate at which attention narrows in younger (mean age 22.6, SD 4.25) and older (mean age 66.8, SD 4.36) adults. The results showed that whereas young adults can narrow attention to one stream within 133 ms, older adults were unable to do the same within this time period. Experiment 2 showed that older adults can narrow their attention to one stream when given more time (266 ms). Experiment 3 confirmed that age-related changes in retinal illuminance did not account for delayed attentional narrowing in older adults. Considered together, these experiments demonstrate that older adults can narrow their attentional focus, but that they are delayed in initiating this process compared to younger adults. This finding adds to previously reported reductions in attentional dynamics, deficits in inhibitory processes, and reductions in posterior parietal cortex function that accompany normal ageing.

Need for cross-level iterative re-entry in models of visual processing.

Two main hypotheses regarding the directional flow of visual information processing in the brain have been proposed: feed-forward (bottom-up) and re-entrant (top-down). Early theories espoused feed-forward principles in which processing was said to advance from simple to increasingly complex attributes terminating at a higher area where conscious perceptions occur. That view is disconfirmed by advances in neuroanatomy and neurophysiology, which implicate re-entrant two-way signaling as the predominant form of communication between brain regions. With some notable exceptions, the notion of re-entrant processing has had a relatively modest effect on computational models of perception and cognition, which continue to be predominantly based on feed-forward or within-level re-entrant principles. In the present work we describe five sets of empirical findings that defy interpretation in terms of feed-forward or within-level re-entrant principles. We conclude by urging the adoption of psychophysical, biological, and computational models based on cross-level iterative re-entrant principles.

Relative blindsight arises from a criterion confound in metacontrast masking: implications for theories of consciousness.

Relative blindsight is said to occur when different levels of subjective awareness are obtained at equality of objective performance. Using metacontrast masking, Lau and Passingham (2006) reported relative blindsight in normal observers at the shorter of two stimulus-onset asynchronies (SOAs) between target and mask. Experiment 1 replicated the critical asymmetry in subjective awareness at equality of objective performance. We argue that this asymmetry cannot be regarded as evidence for relative blindsight because the observers' responses were based on different attributes of the stimuli (criterion contents) at the two SOAs. With an invariant criterion content (Experiment 2), there was no asymmetry in subjective awareness across the two SOAs even though objective performance was the same. Experiment 3 examined the effect of criterion level on estimates of relative blindsight. Collectively, the present results question whether metacontrast masking is a suitable paradigm for establishing relative blindsight. Implications for theories of consciousness are discussed.

Alerting effects occur in simple-But not in compound-Visual search tasks.

Alerting (e.g., a brief brightening of the screen just before a target display) is known to facilitate visual search in simple tasks that involve the single step of detecting a pop-out item within a stimulus array. What is not known is whether alerting facilitates performance also in compound search tasks which involve two steps: First, locate the pop-out item, then identify a detail of that item. In a series of five experiments, we show that alerting facilitates performance of each component of a compound task when tested separately, (Experiments 2a and 2b) but not when the components are combined in a compound task (Experiment 1). Yet, alerting does facilitate performance in a compound task when the pop-out item is displayed in the same location on successive trials (Experiment 3). We hypothesized that such spatial repetition allows attention to linger at that location, thus allowing the first component (locate the pop-out item) to be bypassed. In practice, this turns the compound task into a simple task. That hypothesis was confirmed in Experiment 4 using a reorienting cue to shift the focus of attention to another location. An overall account of the absence of alerting effects in compound search tasks is proposed in terms of the temporal relationship between a period of enhancement rendered as an ex-Gaussian function and the hypothesized sequence of processing stages in visual search. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Metacontrast masking reduces the estimated duration of visible persistence.

A brief visual display can give rise to a sensation that outlasts the duration of the physical stimulus. The duration of this visible persistence has been estimated with paradigms that require the temporal integration of two brief sequential displays (frames) separated by a blank temporal gap. Temporal integration is said to occur when the visible persistence generated by the first frame is sufficiently long to bridge the inter-frame temporal gap. The longest gap at which integration still occurs is taken as an estimate of the duration of visible persistence. In the present work, we show that the duration of visible persistence has been underestimated in at least some of the experiments involving the temporal integration of successive displays. This is because the trailing frame can act as a metacontrast mask that foreshortens the visibility of the leading frame. Specifically, we show that operations that reduce the strength of metacontrast masking yield longer estimates of visible persistence. The relationship between metacontrast masking and visible persistence had been mentioned in some individual studies, but a comprehensive examination of that relationship is currently unavailable. Finally, we show that estimates based on single displays (e.g., the Sperling paradigm) also fail to provide untainted estimates because, in single displays, visible persistence is confounded with informational persistence.

T1 difficulty does not modulate the magnitude of the attentional blink.

When the visual system is busy processing one stimulus, it has problems processing a subsequent stimulus if it arrives soon after the first. Laboratory studies of this second-stimulus impairment-known as attentional blink (AB)-have employed two targets (T1, T2) presented in rapid sequence, and have found identification accuracy to be nearly perfect for T1, but impaired for T2. It is commonly believed that the magnitude of the AB is related directly to the difficulty of T1: the greater the T1 difficulty, the larger the AB. A survey of the experimental literature disconfirms that belief showing it to have arisen from artificial constraints imposed by the 100% limit of the response scale. Removal of that constraint, either using reaction time (RT) instead of accuracy as the dependent measure, or in experiments in which the functions of T2 accuracy over lags do not converge to the limit of the response scale, reveals parallel functions for the easy-T1 and the hard-T1 conditions, consistent with the idea that T1 difficulty does not modulate AB magnitude. This finding is problematic for all, but the Boost and Bounce (B&B) and the Locus Coeruleus-Norepinephrine (LC-NE) theories in which T1 acts merely as a trigger for an eventual refractory period that leads to the failure to process T2, rendering T1 difficulty and its relationship to the AB an irrelevant consideration.

Spatial selection and target identification are separable processes in visual search.

Visual search involves deciding both where to look (spatial selection) and whether any given object is a target or a non-target (identification). The aim of the present study was to determine whether these two functions are separable in performance. Spatial selection was manipulated by an exogenous cue and identification was manipulated by whether a second target appeared after a short or long delay following a first target (the attentional blink, AB). Experiment 1 indicated an additive relation between non-informative spatial cueing and the AB, pointing to independent spatial and identification processes. Experiment 2 tested an informative spatial cue with similar results. Experiment 3 also showed an additive relationship, using a response measure that avoided possible floor effects. We interpret the separability of spatial selection and identification as reflecting the independent operation of dorsal and ventral visual pathways, respectively, at least at the early stages of processing.

Are the inverse-duration and inverse-proximity effects in temporal integration subserved by independent mechanisms?

Displays shorter than about 100 ms are normally seen as lasting longer than their physical duration. This visible persistence can bridge a temporal gap between two sequential stimuli causing them to be temporally integrated into a single percept. We investigated two findings in the temporal-integration literature: the inverse duration effect (temporal integration is progressively impaired as the duration of the first stimulus is increased) and the inverse proximity effect (temporal integration is progressively impaired as the spatial proximity between the stimuli is increased). In two experiments we asked whether the two effects are separable (i.e., whether they are subserved by independent mechanisms) or interact with one another. To estimate the duration of visible persistence we used the missing element paradigm in Experiment 1 and directional stroboscopic motion between two lines in Experiment 2. In both experiments we manipulated the duration of the leading stimulus and the spatial gap between the elements of the two sequential displays. Additive-factors logic was employed to examine the separability of the effects of duration and proximity. Independence (separability) of the two factors would be evidenced in a graph in which the functions of duration over proximity are parallel. The results pointed uniformly to separability. A plausible mechanism for the inverse duration effect is the burst of processing activity time-locked to stimulus onset. A plausible mechanism for the inverse proximity effect is lateral inhibition that acts to reduce the visible persistence of the leading stimulus.

Linear changes in the spatial extent of the focus of attention across time.

This research examined changes in the spatial extent of focal attention over time. The Attentional Blink (impaired perception of the second of two targets) and Lag-1 sparing (the seemingly paradoxical finding that second-target accuracy is high when the second target immediately follows the first) were employed in a dual-stream paradigm to index spatiotemporal changes in focal attention. Lag-1 sparing occurs to targets in different streams if the second target falls within the focus of attention. Focal attention is assumed to initially encompass both streams but to shrink rapidly to the first-target stream, thus withdrawing from the second target if it appears in the opposite stream. The time available for the focus to shrink before second target onset was manipulated by varying the stimulus-onset asynchrony (SOA) between successive items in the stream. There was a progressive transition from Lag-1 sparing to its converse (Lag-1 deficit) as the SOA was increased. This transition was related linearly to SOA, which suggests that the spatial extent of focal attention varies linearly over time.

The attentional blink: increasing target salience provides no evidence for resource depletion. A commentary on Dux, Asplund, and Marois (2008).

The authors have argued elsewhere that the attentional blink (AB; i.e., reduced target detection shortly after presentation of an earlier target) arises from blocked or disrupted perceptual input in response to distractors presented between the targets. When targets replace the intervening distractors, so that three targets (T1, T2, and T3) are presented sequentially, performance on T2 and T3 improves. Dux, Asplund, and Marois (2008) argued that T3 performance improves at the expense of T1, and thus provides evidence for resource depletion. They showed that when T1 is made more salient (and presumably draws more resources), an AB for T3 appears to reemerge. These findings can be better explained, however, by (1) the relationship between T1 and T2 (not T1 and T3) and (2) differential salience for T3 in the long-lag condition of Dux et al.'s study. In conclusion, the Dux et al. study does not present a severe challenge to input control theories of the AB.

Attentional capture by a salient distractor in visual search: the effect of target-distractor similarity.

Models of attentional selection are based on either stimulus-driven or goal-directed processes. Support for the latter comes from a study showing that a salient singleton in a search display can be ignored when the target has a different defining feature (Kumada, 1999). We show that this finding holds only when the target and the nonsalient distractors are highly dissimilar from one another. When the target and the distractors are made more similar, whilst ensuring that the target still pops out of the display, the salient distractor can no longer be ignored. This outcome is consistent with predictions from stimulus-driven accounts.

Visual search is postponed during the attentional blink until the system is suitably reconfigured.

J. S. Joseph, M. M. Chun, and K. Nakayama (1997) found that pop-out visual search was impaired as a function of intertarget lag in an attentional blink (AB) paradigm in which the 1st target was a letter and the 2nd target was a search display. In 4 experiments, the present authors tested the implication that search efficiency should be similarly impaired (steeper search slopes at shorter lags). A conventional AB deficit was found, but, contrary to expectations, search slopes were invariant with lag. These results suggest that no search can be carried out during the period of the AB. Instead, the search is postponed until after the 1st target has been processed. The authors conclude that efficient visual search cannot be carried out unless the visual system is configured appropriately for the search task. If the initial configuration is inappropriate, processing of the 2nd target is held in abeyance until the system has been suitably reconfigured.

The time required for perceptual (nonmotoric) processing in IOR.

In an inhibition of return (IOR) paradigm, we used a threshold-tracking procedure combined with backward masking to measure the speed of perceptual processing in IOR independent of motoric factors. Instead of the conventional reaction time measure, this procedure yielded the critical exposure duration (DURc) that is required in order for a target to be identified reliably before the onset of a trailing mask. In Experiment 1, the facilitation effects conventionally found at short cue-target onset asynchrony (CTOA) were evidenced by shorter values of DURc at cued relative to uncued locations. Conversely, the retardation effects conventionally found at long CTOA were evidenced by correspondingly longer values of DURc. In Experiment 2, the DURc results strongly suggest that the directional reading bias previously observed in IOR studies is due, at least in part, to perceptual rather than motoric factors.

Deployment of spatial attention to a structural framework: exogenous (alerting) and endogenous (goal-directed) factors.

The main question examined in the present work was whether spatial attention can be deployed to an appropriate structural framework not only endogenously when the framework is displayed continuously, as in previous work, but also exogenously, when it is displayed transiently 100 ms before the target. The results of five experiments answered that question in the negative. We found that the onset transient triggered by a brief presentation of the structural framework did enhance the response to the upcoming target. That enhancement, however, was due not to the framework itself but to the alerting effect produced by its sudden onset, witness the finding that the same enhancement was produced by an onset transient triggered by a featureless stimulus (i.e., by a brief dimming of the entire screen, in the absence of a structural framework). We conclude that spatial attention can be deployed to the region demarcated by a structural framework when it is deployed endogenously but not when it is deployed exogenously. A theoretical account of the results is proposed in terms of the temporal dynamics of the locus cœruleus/norepinephrine neuromodulatory system.

The attentional blink is governed by a temporary loss of control.

Identification of the second of two brief targets is impaired at intertarget lags of less than about 500 msec. We compared two accounts of this attentional blink (AB) by manipulating the number of digit distractors--and hence the lag--inserted among three letter targets in a rapid serial visual presentation stream of digit distractors. On the resource-depletion hypothesis, longer lags provide more time for processing the leading target, thus releasing resources for the trailing target. On the temporary-loss-of-control (TLC) hypothesis, intervening distractors disrupt the current attentional set, producing a trailing-target deficit. Identification accuracy for trailing targets was unimpaired not only at lag 1 (conventional lag 1 sparing) but also at later lags, if preceded by another target. The results supported the TLC hypothesis but not the resource-depletion hypothesis. We conclude that the AB is caused by a disruption in attentional set when a distractor is presented while the central executive is busy processing a leading target.