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Biomedical subjects

J Driver

Publications and source records attributed to J Driver.

At least 91 records · Page 5Linked to original sources
PubMed1994

Shifting visual attention between objects and locations: evidence from normal and parietal lesion subjects.

Space- and object-based attention components were examined in neurologically normal and parietal-lesion subjects, who detected a luminance change at 1 of 4 ends of 2 outline rectangles. One rectangle end was precued (75% valid); on invalid-cue trials, the target appeared at the other end of the cued rectangle or at 1 end of the uncued rectangle. For normals, the cost for invalid cues was greater for targets in the uncued rectangle, indicating an object-based component. Both right- and left-hemisphere patients showed costs that were greater for contralesional targets. For right-hemisphere patients, the object cost was equivalent for contralesional and ipsilesional targets, indicating a spatial deficit, whereas the object cost for left-hemisphere patients was larger for contralesional targets, indicating an object deficit.

Adult↗
PubMed1993

Visual attention and objects: evidence for hierarchical coding of location.

In 5 experiments, it was found that judging the relative location of 2 contours was more difficult when they belonged to 2 objects rather than 1. This was observed even when the 1- and 2-object displays were physically identical, with perceptual set determining how many objects they were seen to contain. Such a 2-object cost is consistent with object-based views of attention and with a hierarchical scheme for position coding, whereby object parts are located relative to the position of their parent object. In further experiments, it was shown that in accord with this hierarchical scheme, the relative location of objects could disrupt judgments of the relative location of object parts, but the reverse did not occur. This was found even when the relative position of the parts could be judged more quickly than that of the objects.

Adult↗
PubMed1992

Preserved figure-ground segregation and symmetry perception in visual neglect.

A central controversy in current research on visual attention is whether figures are segregated from their background preattentively, or whether attention is first directed to unstructured regions of the image. Here we present neurological evidence for the former view from studies of a brain-injured patient with visual neglect. His attentional impairment arises after normal segmentation of the image into figures and background has taken place. Our results indicate that information which is neglected and unavailable to higher levels of visual processing can nevertheless be processed by earlier stages in the visual system concerned with segmentation.

Aged↗
PubMed1992

Levels of processing for visual stimuli in an "extinguished" field.

Volpe et al. (Nature 282, 722, 1979 [19]) described an experimental study of four patients with parietal tumours who were able to judge whether two simultaneous stimuli were identical or different, even when they were unable to name the stimulus contralateral to their brain injury. We report the case of another patient, E.M., in whom we have investigated this phenomenon further. E.M. had undergone a right temporal lobectomy to prevent recurrent seizures. She could correctly name photographs of objects presented in isolation to either the left or right visual field, at 150 msec exposure (although she was impaired for single objects on the left at 10 msec exposures). She was able to judge correctly whether two simultaneous objects on the left and right had the same or different names, even though she was often unable to name the object on the left. These judgements remained above chance when same-name pairs of stimuli showed the same object but seen from two different viewpoints, or even when they showed visually dissimilar exemplars of the same name category. This implies that the patient based her same-different judgements on categorical information about the pair of objects, even though she was often unable to name the contralateral object.

Adult↗
PubMed1992

The neurobiology of selective attention.

Research in the field of selective visual attention has recently seen substantial progress in several areas. Neuroimaging and electrical recording results have indicated that selective attention amplifies neural activity in prestriate areas concerned with basic visual processing. Imaging and cellular studies are delineating the networks of anatomical areas that serve as the source of attentional modulation and have suggested that these networks are anatomically distinct from the sites of the resulting amplifications. Cognitive studies of visual search have explored the role of these amplified computations in the integration of visual features into objects. Attentional effects in normal subjects, and their disruption following brain injury, have revealed the mental representations upon which attention operates.

Animals↗
PubMed1992

Movement and proximity constrain miscombinations of colour and form.

A relatively frequent error when reporting brief visual displays is to combine presented features incorrectly. It has been proposed that Gestalt grouping constrains such errors so that miscombined features tend to come from the same perceptual group. In three experiments it was examined whether this principle applies to grouping by motion, and to grouping by proximity. Miscombinations of colour and form were more likely to consist of a colour and form that had moved in the same direction than features which had moved in opposite directions. Miscombinations were also more likely for adjacent items. The implications of these results for the mechanisms of feature integration are discussed.

Adult↗
PubMed1992

Are direction and speed coded independently by the visual system? Evidence from visual search.

Three visual search experiments examined whether motion is coded as two separate features, speed and direction. Increasing the heterogeneity of the directions in which stimuli moved disrupted detection of a target defined by speed (fast among medium and slow nontargets), suggesting that speed is coded integrally with direction. However, heterogeneity in speed did not disrupt detection of a target moving in a particular direction among nontargets with different directions. This suggests that direction is coded independently of speed. The apparent paradox raised by these contrasting conclusions is consistent with neurophysiological and computational models of motion-detection, which suggest that low-levels of the visual system contain direction-detectors insensitive to speed, while speed is coded at higher levels by detectors which are also sensitive to direction. Evidence consistent with the existence of the latter conjunction detectors was obtained in a final experiment which found search for a conjunction of speed and direction to be parallel.

Adult↗
PubMed1992

Motion coherence and conjunction search: implications for guided search theory.

Feature integration theory has recently been revised with two proposals that visual conjunction search can be parallel under some circumstances--either because items with nontarget features are inhibited, or because items with target features are excited. We examined whether excitatory or inhibitory guidance controlled conjunction search for an X oscillating in one direction among Os oscillating in that direction and Xs oscillating in another. Search was affected by whether items oscillated in phase with each other, and it was exceptionally difficult when items with target motion moved out of phase with each other and items with nontarget motion moved out of phase. The results suggest that conjunction search can be guided both by excitation of target features and by inhibition of nontarget features.

Adolescent↗
PubMed1992

Visual parsing and response competition: the effect of grouping factors.

When the task is to categorize a target letter at a known location, subjects show more interference from incongruent distractors that are relatively close (B. A. Eriksen & C. W. Eriksen, 1974) or that share common motion with the target (Driver & Baylis, 1989). In eight experiments, we examined whether static factors other than proximity can affect the amount of interference. When distractors and the target letter were in the same color, the distractors interfered more than they did when they were in a different color, even when the latter were closer to the target. Good continuation between the target and distractors also led to more interference. These results suggest that the efficiency of selection is determined by several aspects of the relation between targets and distractors in addition to their proximity, and thus that visual attention is not directed on the basis of position information alone.

Adult↗
PubMed1991

Target--distractor separation and feature integration in visual attention to letters.

The interference produced by distractor letters diminishes with increasing distance from a target letter, as if the distractors fall outside an attentional spotlight focussed on the target (Eriksen and Eriksen 1974). We examine Hagenaar and Van der Heijden's (1986) claim that this distance effect is an acuity artefact. Feature integration theory (Treisman 1986) predicts that even when acuity is controlled for, distance effects should be found when interference is produced by conjoined distractor features (e.g. letter-identities), but not when interference arises from isolated distractor features (e.g. letter-strokes). The opposite pattern of results is found. A model is proposed in which both letter-strokes and letter-identities are derived in parallel. The location of letter-strokes can also be coded in parallel, but locating letter-identities may require the operation of attention.

Attention↗
PubMed1991

Filtering by movement in visual search.

Search for a target defined by a conjunction of movement and form (e.g., an X moving up in a display of intermingled Os moving up and stationary Xs) is parallel. This result is also found if (a) the moving Os and target X move in unpredictable directions so that the moving stimuli do not form a clear perceptual group or (b) the nontarget Xs also move but in a known, different direction from the Os and target X. In contrast, search is slow and serial if the target may be unpredictably among either moving or stationary stimuli. These results suggest that a component of the visual system operates as a movement filter that can direct attention to stimuli with a common movement characteristic. The filtering cue can be moving (vs. stationary), or movement in 1 particular direction. The results do not support the view that attention can only be directed to groups defined by common fate.

Adult↗
PubMed1991

Object-centred inhibition of return of visual attention.

Our response to visual events can be delayed at positions we have recently examined attentively. Such inhibition could organize visual search through static scenes by suppressing those loci already searched, but this mechanism would fail in moving scenes as objects' locations then change during search. We cued attention to a moving object and found subsequent inhibition at the locus the object later occupied. This implies that previously examined objects are suppressed. Such object-centred inhibition would be highly adaptive, but would require a sophisticated neural implementation for a mechanism held to be sub-cortical.

Adult↗
PubMed1990

Selection of moving and static objects for the control of spatially directed action.

Research studying visual selective attention has largely examined filtering tasks in which stationary targets are selected from stationary distractors by a physical cue such as location and identity is the reported attribute. During many interactions with the visual environment however, target stimuli are selected by what they are, whereas action is controlled by where the stimulus is located. This study demonstrates that the interference and negative priming effects observed in standard filtering tasks, which suggest that distractors are analyzed and subsequently inhibited during selection, are also observed when targets are selected on the basis of identity and spatial location is the reported attribute. Furthermore, experimental results suggest that inhibition associated with distracting objects in this new task is object-centered, so that if the object is moving through space, inhibition moves with it.

Adult↗
PubMed1989

Selective deficit of visual search in moving displays after extrastriate damage.

A visual cue that is often associated with significant stimuli, such as those provided by prey and predators, is movement relative to the observer. An efficient visual system should be able to direct attention to those parts of the visual field that contain such stimuli. What is needed is a system that can filter by movement difference. This could direct attention to a moving item among stationary items, or an item moving in one direction against a background moving in a different direction. Visual search experiments have shown that people are indeed able to filter by movement; that is, they can attend to just the moving items in arrays of moving and stationary stimuli. Single-cell recordings from monkey visual cortex show that the medial temporal cortical area (MT) has some of the properties required to filter by movement. We have now linked these two observations by showing that a patient with bilateral lesions to the presumed human homologue of MT cannot restrict visual attention to the moving items in arrays of both moving and stationary items. This suggests that MT is the site of a movement filter used in normal visual processing.

Animals↗
PubMed1989

Movement and visual attention: the spotlight metaphor breaks down.

The interfering effects of distractor letters are known to diminish with increasing distance from the target letter (Eriksen & Eriksen, 1974). This result is held to support spotlight models in which visual attention can only be assigned to contiguous regions of the visual field. However, the result is also consistent with the rival claim that attention is assigned to perceptual groups. Four experiments show that grouping of target and distractors by common motion can have more influence than their proximity. Distant distractor letters that move with a target letter produce more interference than static distractors that are nearer the target. Near distractors are equally ineffective if the target is static while they move. These results imply that attention is directed to perceptual groups whose components may be spatially dispersed. The spotlight metaphor seems inappropriate for visual attention in a dynamic environment.

Adult↗
PubMed1988

Visual search for a conjunction of movement and form is parallel.

Treisman has proposed when a human subject performs a visual search, the search is parallel for targets defined by a single feature, and serial for targets defined by a conjunction of features. Here we report that this is not true for targets defined by a conjunction of the features movement and form. Detection of a moving X among randomly distributed moving Os and static Xs is parallel. Search is uninfluenced by the stationary stimuli despite their spatial intermingling with the moving items. Thus, attention can be restricted to a spatially dispersed perceptual group, defined by common movement. This contradicts previous conclusions from visual search experiments that attention can only be assigned to contiguous regions of visual space. The search process first segregates the array into moving and stationary items, and then examines the moving group for the target form. Cells in the middle temporal region (cortical area MT) have the properties required to perform these operations.

Color Perception↗