Evidence for split foci of attention in a priming paradigm

Crowding expands and is less sensitive to target-flanker differences during a shift of visual attention

Target-flanker similarity and critical spacing control visual crowding when attention is pre-allocated, but these have not been studied when attention shifts. Flanked target Gabors appeared 8° left and right of central fixation throughout each 1.5 s trial. Subjects reported target Gabor tilt. In Expt. 1, target blinks increased accuracy, and flanker blinks decreased it, but only when attention shifted left or right from a central RSVP cue, hardly before it, indicating an exogenous/endogenous synergy. Whether parallel or orthogonal, flankers of the same wavelength as the target crowded substantially. Parallel half-wavelength flankers also crowded, but orthogonal half-wavelength ones did not. In Expt. 2, crowding when attention shifts was the same for targets and flankers within Bouma's bound (2.5° apart) as outside it (5.0° apart.) In Expt. 3, Bouma's bound was restored when attention was focused continuously on the target. We conclude that crowding temporarily expands and becomes less discriminative when attention shifts.

Flexible attention system: Appearance time of split attention changes in accordance with the task difficulty level

Although it is often assumed that spatial attention exists in the form of a unitary focus, the split-attention hypothesis proposes that attention can be simultaneously divided into two spatially noncontiguous positions and that the space in between can be ignored. However, whether split attention occurs directly based on the generation of attentional benefit or whether it requires a gradual divide from a unitary focus over time has not been clarified. In the present study, by using two spatial salient cues to direct the attention allocation of participants, we aimed to investigate whether attention requires time to divide from a unitary focus and whether the appearance time of split attention varies when the task difficulty level increases between experiments. The results showed that attention required time to divide from a unitary focus, and the position between the two cued positions was not excluded by attention when the stimulus-onset asynchrony (SOA) was 60 ms. However, as the task difficulty increased between experiments, the appearance time of split attention was earlier. These findings suggest that the appearance time of split attention has a certain flexibility and can be changed according to the task requirement, thus implying that split attention and unitary attention present some common attention mechanisms and that a split or unitary mode can be flexibly selected for an attention system.

Spatial Separation and Working Memory Capacity Affect Selective Visual Attention in the Periphery

The current study aimed to examine the effects of spatial separation and working memory capacity on selective visual attention. We investigated differences in the ability to identify the two covertly attended stimuli that appeared either along one of the meridians (e.g., both along the horizontal) or along two of the meridians (e.g., one along the horizontal and one along the vertical) in the attention-window task. Two visual stimuli in the periphery could be perceived along wider extents of the attentional focus’ meridians (horizontal, vertical, and diagonal) when they were located along the same meridian (e.g., horizontal) compared to two different ones (e.g., horizontal and vertical). Subjects with high working memory capacity outperformed subjects with lower working memory capacity in both conditions and stimuli presented on two meridians were less accurately perceived. The findings support the proposal that individual differences in working memory capacity are important for selective spatial visual attention.

Spatial distribution of attentional bias in visuo-spatial working memory following multiple cues

When attention is focused on one location, its spatial distribution depends on many factors, such as the distance between the attended location and the target location, the presence of visual meridians in between them, and the way, endogenous or exogenous, by which attention is oriented. However, it is not well known how attention distributes when more than one location is endogenously or exogenously cued, which was the focus of the current study. Furthermore, the distribution of attention has been manly investigated in perception. In the present study we faced this issue from a different perspective, by examining the spatial distribution of the attentional bias in visuo-spatial working memory (VSWM), when attention is oriented either exogenously or endogenously, i.e., after two peripheral vs. central symbolic cues (also manipulating cue-target predictability). Results indicated a systematic difference between endogenous and exogenous attention regarding the distribution of the attentional bias over VSWM. In fact, attentional bias following endogenous cues was affected by the presence of visual meridians and by the split of the attentional focus, converging in a unipolar attentional distribution, independently of cue-target predictability. On the other hand, when pulled by exogenous cues, attention distributed uni-modally or multi-modally depending on the distance between the cued locations, with larger effects for highly predictive cues. Results are discussed in terms of space-based, object-based and perceptual grouping mechanisms.

Fixation strategy influences the ability to focus attention on two spatially separate objects

The ability to devote attention simultaneously to multiple visual objects plays an important role in domains ranging from everyday activities to the workplace. Yet, no studies have systematically explored the fixation strategies that optimize attention to two spatially distinct objects. Assuming the two objects require attention nearly simultaneously, subjects either could fixate one object or they could fixate between the objects. Studies measuring the breadth of attention have focused almost exclusively on the former strategy, by having subjects simultaneously perform one attention-demanding task at fixation and another in the periphery. We compared performance when one object was at fixation and the other was in the periphery to a condition in which both objects were in the periphery and subjects fixated between them. Performance was better with two peripheral stimuli than with one central and one peripheral stimulus, meaning that a strategy of fixating between stimuli permitted greater attention breadth. Consistent with the idea that both measures tap attention breadth, sport experts consistently outperformed novices with both fixation strategies. Our findings suggest a way to improve performance when observers must pay attention to multiple objects across spatial regions. We discuss possible explanations for this performance advantage.

A mixture distribution of spatial attention

Although it may seem paradoxical, the unified-focus and multiple-foci theories of spatial selective attention are both well supported by experimental evidence. However, the apparent contradiction is illusory and the two competing views may be reconciled by a closer examination of the spatial mechanisms involved. We propose that the deployment of attention may be modeled as a mixture of individual distributions of attention and we tested this hypothesis in two experiments. Participants had to identify targets among distractors, with the targets presented at various distances from the cued locations. Experiment 1 confirmed that the distribution of attention may be described by a mixture of individual distributions, each centered at a cued location. Experiment 2 showed that cue separation is an important determinant of whether spatial attention is divided or not.

At the mercy of prior entry: Prior entry induced by invisible primes is not susceptible to current intentions

If one of two events is attended to, it will be perceived earlier than a simultaneously occurring unattended event. Since 150 years, this effect has been ascribed to the facilitating influence of attention, also known as prior entry. Yet, the attentional origin of prior-entry effects(1) has been repeatedly doubted. One criticism is that prior-entry effects might be due to biased decision processes that would mimic a temporal advantage for attended stimuli. Although most obvious biases have already been excluded experimentally (e.g. judgment criteria, response compatibility) and prior-entry effects have shown to persist (Shore, Spence, & Klein, 2001), many other biases are conceivable, which makes it difficult to put the debate to an end. Thus, we approach this problem the other way around by asking whether prior-entry effects can be biased voluntarily. Observers were informed about prior entry and instructed to reduce it as far as possible. For this aim they received continuous feedback about the correctness of their temporal judgments. If elicited by invisible primes the effect could not be reduced at all and only by 12 ms if elicited by visible cues. This challenges decision biases as primary source of prior-entry effects - at least if attention is oriented exogenously.

Top-down contingent feature-specific orienting with and without awareness of the visual input

In the present article, the role of endogenous feature-specific orienting for conscious and unconscious vision is reviewed. We start with an overview of orienting. We proceed with a review of masking research, and the definition of the criteria of experimental protocols that demonstrate endogenous and exogenous orienting, respectively. Against this background of criteria, we assess studies of unconscious orienting and come to the conclusion that so far studies of unconscious orienting demonstrated endogenous feature-specific orienting. The review closes with a discussion of the role of unconscious orienting in action control.

Distinguishing between parallel and serial accounts of multiple object tracking

Humans can track multiple moving objects. Is this accomplished by attending to all the objects at the same time or do we attend to each object in turn? We addressed this question using a novel application of the classic simultaneous-sequential paradigm. We considered a display in which objects moved for only part of the time. In one condition, the objects moved sequentially, whereas in the other condition they all moved and paused simultaneously. A parallel model would predict that the targets are tracked independently, so the tracking of one target should not be influenced by the movement of another target. Thus, one would expect equal performance in the two conditions. Conversely, a simple serial account of object tracking would predict that an observer's accuracy should be greater in the sequential condition because in that condition, at any one time, fewer targets are moving and thus need to be attended. In fact, in our experiments we observed performance in the simultaneous condition to be equal to or greater than the performance in the sequential condition. This occurred regardless of the number of targets or how the targets were positioned in the visual field. These results are more directly in line with a parallel account of multiple object tracking.

Bilateral field advantage in visual crowding

Thirty randomly oriented T's were presented in a circle around fixation at an eccentricity of 11 degrees such that each T was crowded by its neighbors. Two locations within the same hemifield (unilateral condition) or one location in each hemifield (bilateral condition) were precued for subsequent probing. Observers were then asked to report the orientation of a target T at one of these locations. A bilateral field advantage was found: target identification was better when the two precued targets were in different hemifields than when they were within the same hemifield. This bilateral advantage was absent when only targets were presented, without any distracters. Further controls showed that this advantage could not be attributed to differences between horizontal and vertical target alignments or to visual field anisotropies. A similar bilateral advantage has been reported for multiple object tracking (Alvarez, G. A., & Cavanagh, P. (2005). Independent resources for attentional tracking in the left and right visual fields. Psychological Science 16(8), 637-643) and other attentional tasks. Our results suggest that crowding also demonstrates separate attentional resources in the left and right hemifields. There was a cost to attending to two targets presented unilaterally over attending to a single target. However, this cost was reduced when the two crowded targets were in separate hemifields.

Attentional guidance relies on a winner-take-all mechanism

The finding that attention can encompass several non-contiguous items at once challenges the current models of visual search based on a winner-take-all mechanism assuming the selection of a single object. It has been proposed instead that attentional guidance involves mechanisms selecting all relevant items simultaneously. In order to test this hypothesis, we studied attentional allocation during various visual search tasks. We confirmed that attention can indeed select several items concurrently but on the basis of their spatial relation, not relevance. This finding corroborates the view that during visual search, attentional guidance is based on a winner-take-all mechanism.

Características atentivas reveladas por dicas múltiplas locais e globais

As características do foco atentivo foram investigadas por meio do efeito de dicas locais múltiplas e globais, múltipla e unitária, sobre o desempenho em uma tarefa de busca visual. Os resultados mostram um ganho no desempenho de provas com dicas locais múltiplas válidas; o ganho é proporcional ao tamanho da área na qual os estímulos são apresentados. Nas provas com dica local válida para área existe ganho quando os estímulos são apresentados na área maior e custo na área menor. Dicas globais não proporcionam ganho em provas com dicas válidas, mas são acompanhadas de custo nas provas com dicas inválidas. Também existe custo nas provas em que o foco atentivo deve ser expandido ou contraído. Os resultados sugerem que o modelo de focos atentivos múltiplos é mais adequado para explicar o desempenho em tarefas com dicas locais múltiplas.

Perceptual latency priming: A measure of attentional facilitation

The present paper reviews recent research on perceptual latency priming (PLP). PLP is the relative latency advantage-earlier perception-of a visual stimulus that is preceded by another, masked stimulus at its location. The first stimulus attracts attention which accelerates perception of the second stimulus. This facilitation arises even if the first stimulus is visually backward-masked by the second one. The paper summarises research on temporal and spatial properties of PLP and the question whether intentions mediate shifts of attention to external events. Possible sources of PLP besides visuo-spatial attention are discussed. Finally, I give a review of feedforward and reentrant models of PLP and compare them to the empirical evidence.