Grouping Influences in Unilateral Visual Neglect

Authors:

• Lynn C. Robertson

• Mirjam Eglin

• Robert T. Knight

Date: 2003

PubMed: 12916644

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Abstract:

Effects of grouping on unilateral neglect were investigated in 8 neurological patients with right hemisphere damage. It is well documented that arranging items to form a group spanning the midline decreases the magnitude of neglect. In the present study we examined how clusters of groups within the left or right visual field affect neglect and whether isolated groups within the neglected field deflect attention from right-sided displays. We orthogonally varied the strength of grouping on the right and left sides of a display and measured the time to find a predesignated target in one of those groups. Groups on the neglected left side did not affect right-sided target detection any more than an empty left page. However, strength of grouping did affect left sided target detection. These findings are discussed as they relate to attention and preattention in unilateral visual neglect.

Search deficits in neglect patients are dependent on size of the visual scene.

Authors:

• Mirjam Eglin

• Lynn C. Robertson

• Robert T. Knight

• Peter Brugger

Date: 1994

DOI: 10.1037/0894-4105.8.3.451

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Abstract:

Patients with hemispatial neglect are impaired at moving their attention to a target on the contralesional display side. In the present study, visual display area was varied independently of the number of items displayed within the area. Patients searched for the absence of a simple visual feature in displays that produce serial search performance in normals (R. Klein, 1988; A. Treisman & J. Souther, 1985; J. M. Wolfe & C. W. Pokorny, 1990). The contralesional delay was enhanced for stimulus arrays that were distributed over a larger display area, which suggests that neglect is more severe when attention has to be moved over a larger distance. The directional disengage deficit in neglect (M. I. Posner, J. A. Walker, F. A. Friedrich, & R. D. Rafal, 1984, 1987) therefore depends on the target's relative position within a display, the number of ipsilesional items competing for attention (M. Eglin, L. C. Robertson, & R. T. Knight, 1989), and the distance of the contralesional attention movements.

Cortical substrates supporting visual search in humans

Authors:

• Mirjam Eglin

• Lynn C. Robertson

• Robert T. Knight

Date: 1991

PubMed: 1822736

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Abstract:

Serial and parallel visual search tasks were presented to patients with focal lesions in dorsolateral frontal, lateral parietal, or temporal-parietal cortex. In the unilateral display conditions, search efficiency in all patient groups was similar to the normal control group for stimuli both on the ipsi- and on the contralesional side of the displays. In contrast, in the bilateral display conditions, all patient groups showed a marked delay in initiating search on the side contralateral to the lesion as compared to normal controls. This delay was more pronounced when attention demands on the ipsilateral side increased, either by making target-distractor discrimination more difficult (serial search task), or by increasing the number of ipsilateral distractor items. The contralateral deficit was evident in all patient groups, supporting the notion that dorsolateral frontal as well as posterior parietal and temporal-parietal cortex plays a critical role in visual spatial attention.

Visual search performance in the neglect syndrome

Authors:

• Mirjam Eglin

• Lynn C. Robertson

• Robert T. Knight

Date: 1989

DOI: 10.1162/jocn.1989.1.4.372

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Abstract:

Patients with hemispatial neglect fail to respond to stimuli on one side of space. We assessed to what extent the complexity and number of visual stimuli on both sides determine the severity of neglect. Patients with neglect were required to find specified targets in a cluttered visual field. Two sets of stimuli were used. One set produced effortless and parallel search performance in normal controls; the other set was more complex and produced serial search performance in normal controls. Both sets of stimuli resulted in a serial performance pattern in the patients. Their baseline search performance on both sides was similar when all stimulus items were restricted to one side. A pronounced difference between the two sides was evident when stimuli appeared on both sides. Search for targets on the intact side of space was unaffected by distractors on the neglected side, whereas search for targets on the neglected side was slowed disproportionately by distractors on the intact side. The slowing on the neglected side was more severe during the more demanding search task and when more items were present on the intact side. The results indicate that neglect is associated with an inability to move attention from objects on the intact side to items on the neglected side.