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.

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

(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.

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.

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 ()-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.

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).

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).

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 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.

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.

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.

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.

Perception of temporal order during the attentional blink: Using stimulus salience to modulate prior entry.

When multiple targets are presented in rapid sequence, observers frequently confuse the order in which they were presented. The probability of order reversals is known to vary throughout the period of the attentional blink (AB), which refers to impairment in the perception of the second of two targets when it is presented within approximately 500 ms from the first. Our objective was to examine the principle of prior entry (in which perception of temporal order is said to be affected by the relative latency at which each target is processed) as a determinant of the perception of temporal order throughout the AB.

Visual search is postponed during the period of the AB: An event-related potential study.

In the phenomenon known as the attentional blink (AB), perception of the second of two rapidly sequential targets (T2) is impaired when presented shortly after the first (T1). Studies in which T2 consisted of a pop-out search array provided evidence suggesting that visual search is postponed during the AB. In the present work, we used behavioral and electrophysiological measures to test this postponement hypothesis.

Individual differences in rate of encoding predict estimates of visual short-term memory capacity (K).

The capacity of visual short-term memory (VSTM) is commonly estimated by K scores obtained with a change-detection task. Contrary to common belief, K may be influenced not only by capacity but also by the rate at which stimuli are encoded into VSTM. Experiment 1 showed that, contrary to earlier conclusions, estimates of VSTM capacity obtained with a change-detection task are constrained by temporal limitations.

Is pop-out visual search attentive or preattentive? Yes!

Is the efficiency of "pop-out" visual search impaired when attention is preempted by another task? This question has been raised in earlier experiments but has not received a satisfactory answer. To constrain the availability of attention, those experiments employed an attentional blink (AB) paradigm in which report of the second of 2 targets (T2) is impaired when it is presented shortly after the first (T1). In those experiments, T2 was a pop-out search display that remained on view until response.

Escape from temporal-integration masking: the roles of visible persistence and input filtering.

A brief target embedded in—and coterminating with—a noise mask is identified easily when the duration of the mask is long but not when it is short (Di Lollo, 1980; inverse-duration effect). Identification has been said to be mediated by the visible persistence of the target, which outlasted that of the mask. We tested an alternative account based on input filtering triggered by the onset and offset of the target, relative to those of the mask, without recourse to visible persistence.

When can spatial attention be deployed in the form of an annulus?

Can spatial attention be deployed as an annulus? Some studies have answered this question in the positive, others in the negative. We tested the hypothesis that annular deployment depends on the presence of a suitable structural framework to which attention can be anchored. To this end, we added a structural framework to the displays of a study that failed to find an annular distribution of attention.

Reentrant processing mediates object substitution masking: comment on Põder (2013).

Object-substitution masking (OSM) occurs when a target stimulus and a surrounding mask are displayed briefly together, and the display then continues with the mask alone. Target identification is accurate when the stimuli co-terminate but is progressively impaired as the duration of the trailing mask is increased. In reentrant accounts, OSM is said to arise from iterative exchanges between brain regions connected by two-way pathways.

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.

The flexible focus: whether spatial attention is unitary or divided depends on observer goals.

The distribution of visual attention has been the topic of much investigation, and various theories have posited that attention is allocated either as a single unitary focus or as multiple independent foci. In the present experiment, we demonstrate that attention can be flexibly deployed as either a unitary or a divided focus in the same experimental task, depending on the observer's goals. To assess the distribution of attention, we used a dual-stream Attentional Blink (AB) paradigm and 2 target pairs.

A novel paradigm reveals the role of reentrant visual processes in object substitution masking.

Object substitution masking (OSM) occurs when an initial display of a target and mask continues with the mask alone, creating a mismatch between the reentrant hypothesis, triggered by the initial display, and the ongoing low-level activity. We tested the proposition that the critical factor in OSM is not whether the mask remains in view after target offset, but whether the representation of the mask is sufficiently stronger than that of the target when the reentrant signal arrives. In Experiment 1, a variable interstimulus interval (ISI) was inserted between the initial display and the mask alone.

On the electrophysiological evidence for the capture of visual attention.

The presence of a salient distractor interferes with visual search. According to the salience-driven selection hypothesis, this interference is because of an initial deployment of attention to the distractor. Three event-related potential (ERP) findings have been regarded as evidence for this hypothesis: (a) salient distractors were found to elicit an ERP component called N2pc, which reflects attentional selection; (b) with target and distractor on opposite sides, a distractor N2pc was reported to precede the target N2pc (N2pc flip); (c) the distractor N2pc on slow-response trials was reported to occur particularly early, suggesting that the fastest shifts of attention were driven by salience.

The root cause of the attentional blink: first-target processing or disruption of input control?

Identification of the second of two targets (T2) is impaired when presented shortly after the first (T1). T1-based theories ascribe this attentional blink (AB) to a T1-initiated period of inattention. Distractor-based theories ascribe it to a disruption of input control caused by post-T1 distractors.

The feature-binding problem is an ill-posed problem.

The binding problem arises when visual features (colour, orientation), said to be coded in independent brain modules, are to be integrated into unitary percepts. I argue that binding is an ill-posed problem, because those modules are now known to code jointly for multiple features, rendering the feature-binding issue moot. A hierarchical reentrant system explains the emergence of coherent visual objects from primitive features.

The attentional blink is not affected by backward masking of T2, T2-mask SOA, or level of T2 impoverishment.

Identification of the second of two targets (T2) is impaired when presented shortly after the first (T1). This attentional blink (AB) is thought to arise from a delay in T2 processing during which T2 is vulnerable to masking. Conventional studies have measured T2 accuracy which is constrained by the 100% ceiling.