Attention In Visual Space Research Articles

An ERP study of sustained spatial attention to stimulus eccentricity

Effects of attention on event-related brain potentials (ERPs) were measured when subjects kept sustained attention focused on ring-shaped regions of visual space to detect infrequently presented targets at a given eccentricity. In line with a previous study that employed a trial-by-trial cueing paradigm, no modulations of sensory-evoked P1 and N1 components were found. This suggests that attentional selectivity in complex spatial selection tasks is primarily located at post-perceptual processing levels. Enhanced negativities for attended as compared to unattended stimuli were present between 220 and 380 ms post-stimulus and were followed by an enlarged positivity for attended stimuli in the P3 time range. These effects reflected the distribution of attention in visual space, in part consistent with ‘attentional gradient’ and ‘zoom-lens’ models. However, ERPs also suggested the presence of selective mechanisms that exclude irrelevant stimuli located between two simultaneously attended areas.

Shifting attention in visual space: Tests of moving-spotlight models versus an activity-distribution model.

Participants were induced to concentrate preparatory attention at a central location, to identify a letter there, to identify a 2nd letter to the extreme left or right of a central horizontal range of 5 locations, and then to identify a 3rd letter at 1 of the central 5 locations. Analog and discrete versions of the moving-spotlight model predict that response times to the 3rd letter will be most rapid at the location of the 2nd letter, whereas an activity-distribution model predicts that the most rapid responses to the 3rd letter will be at the central location, where preparatory attention is strongest. The data from 3 experiments, taken together, are inconsistent with the moving-spotlight models and are consistent with the activity-distribution model.

Shifting attention in visual space: tests of moving-spotlight models versus an activity-distribution model.

Participants were induced to concentrate preparatory attention at a central location, to identify a letter there, to identify a 2nd letter to the extreme left or right of a central horizontal range of 5 locations, and then to identify a 3rd letter at 1 of the central 5 locations. Analog and discrete versions of the moving-spotlight model predict that response times to the 3rd letter will be most rapid at the location of the 2nd letter, whereas an activity-distribution model predicts that the most rapid responses to the 3rd letter will be at the central location, where preparatory attention is strongest. The data from 3 experiments, taken together, are inconsistent with the moving-spotlight models and are consistent with the activity-distribution model.

Orienting of spatial attention – its reflexive, compensatory, and voluntary mechanisms

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion – line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side when attention was captured to that side of the line by a preceding visual cue stimulus. This effect was due to acceleration of visual information processing at the locus of attention. The motion illusion was produced by both stimulus-induced (bottom-up) and voluntary (top-down) attention, which suggested that the two kinds of attention act on relatively early stages of visual processing. The objective of this study was to examine how various modes of spatial attention might be represented and reorganized in the brain. Using the induction of illusory line motion as a measure we found that: (1) once attention is captured by a moving object, it follows the object as it moves; and (2) attention moves with a saccade in the retinal coordinates such that its focus remains fixed in space. We then asked whether attention acts across different sensory modalities. We found that both auditory and somatosensory cues induced focal visual attention in space where the cue was presented. Based on these findings we propose a model which would allow (1) matching of visual spatial information obtained across saccades, and (2) matching of spatial information obtained in different sensory modalities.

Shifting attention in visual space: the effects of peripheral cueing on brain cortical potentials.

The effects of attentional shifts following peripheral cues were studied in humans using event-related potentials (ERPs) and reaction times. Subjects released a key following the presentation of a target preceded by a predictive cue in the same (valid) or the opposite (invalid) visual field, or a bilateral, non-predictive cue. The stimulus onset asynchrony (SOA) separating cue and target was either 200 or 600 ms. Subjects were faster and more accurate when responding to validly cued targets. Attentional modulation of the ERP was manifested as an enhancement of P1-N1 amplitude at posterior electrode sites following a validly cued target. Furthermore, the latencies of P1, N1 and P3 were significantly shorter in valid trials than in invalid trials. These results only reached significance with the longer SOA, since ERP refractoriness distorted the response evoked by the target when the SOA was only 200 ms. The findings are discussed in the context of previous behavioral and ERP cueing studies.

Overt orienting in the rat: parametric studies of cued detection of visual targets.

Covert shifts of visual attention in space have been quantified by measuring the effects of visual cues on the detection of visual targets in humans and monkeys maintaining visual fixation. These observations of "covert orienting" have provided important information regarding the neurobiology of visual attention in primates. This article describes a cued spatial target detection task for physically unrestrained rats. Valid cues (spatially contiguous with the target) enhanced target detection, and invalid cues (spatially discontiguous with the target) degraded target detection. Both visual and auditory cues were effective. These validity effects could not be explained by stimulus additivity or response preparation mechanisms, whereas a cue-independent "alerting effect" appeared to reflect response preparation. The effects compare favorably with primate work and suggest that this method may enable assessment of visual attention shifts in rats.

Reflexive and voluntary orienting of visual attention: Time course of activation and resistance to interruption.

To study the mechanisms underlying covert orienting of attention in visual space, subjects were given advance cues indicating the probable locations of targets that they had to discriminate and localize. Direct peripheral cues (brightening of one of four boxes in peripheral vision) and symbolic central cues (an arrow at the fixation point indicating a probable peripheral box) were compared. Peripheral and central cues are believed to activate different reflexive and voluntary modes of orienting (Jonides, 1981; Posner, 1980). Experiment 1 showed that the time courses of facilitation and inhibition from peripheral and central cues were characteristic and different. Experiment 2 showed that voluntary orienting in response to symbolic central cues is interrupted by reflexive orienting to random peripheral flashes. Experiment 3 showed that irrelevant peripheral flashes also compete with relevant peripheral cues. The amount of interference varied systematically with the interval between the onset of the relevant cue and of the distracting flash (cue-flash onset asynchrony) and with the cuing condition. Taken together, these effects support a model for spatial attention with distinct but interacting reflexive and voluntary orienting mechanisms.

Learning where to look: Electrophysiological and behavioral indices of visual search in young and old subjects

The present investigation explores the way young and elderly subjects use regularities in target location in a visual display to guide search for targets. Although both young and old subjects show efficient use of search strategies, slight but reliable differences in reaction times suggest decreased ability in the elderly to use complex cues. Event-related potentials were very different for the young and the old. In the young, P3 amplitudes were larger on trials where the rule that governed the location of the target became evident; this was interpreted as an effect of memory updating. Enhanced positive Slow Wave amplitude indicated uncertainty in random search conditions. Elderly subjects' P3 and SW, however, seemed unrelated to behavioral performance, and they showed a large negative Slow Wave at central and parietal sites to randomly located targets. The latter finding was tentatively interpreted as a sign of increased effort in the elderly to allocate attention in visual space. This pattern of behavioral and ERP results suggests that age-related differences in search tasks can be understood in terms of changes in the strategy of allocating visual attention.