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.

Cognitive neuropsychology is more than single-case studies

Authors:

• Lynn C. Robertson

• Robert T. Knight

• Robert Rafal

• Arthur P. Shimamura

Date: 1993

PubMed: 8347215

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Abstract:

S. M. Sokol et al. (1991) claim that "The Cognitive Neuropsychology Approach" (p. 355) is limited to the single-case study design. The present article takes issue with this claim. Contrary to the beliefs of Sokol et al., we argue (a) that cognitive modularity is best studied by group design, (b) that the possibility of neural reorganization in patients should be tested through converging evidence from different populations using various methods, and (c) that cognitive neuropsychology can benefit from being a part of cognitive neuroscience where both neural and cognitive mechanisms underlying normal cognition are relevant.

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.

Normal global-local analysis in patients with dorsolateral frontal lobe lesions

Authors:

• Lynn C. Robertson

• Michele Lazzara

• Robert T. Knight

Date: 1991

PubMed: 1762675

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Abstract:

The role of prefrontal cortex in the analysis of global and local levels of a visual stimulus was assessed by measuring reaction time to identify a target at one level or the other. Unlike patients with temporal-parietal lesions (STG), there were no global-local performance deficits in right or left prefrontal groups (RFL or LFL). Reallocation of attention to global and local levels was measured by examining changes in performance when the probability of a target appearing at one level or the other varied. While patients with lateral parietal lesions (IPL) have been shown to have deficits in these conditions, both RFL and LFL showed normal changes in performance. In sum, the performance of prefrontal groups differed from both IPL and STG groups but not from normal controls. These results strengthen previous arguments that posterior association cortex is crucial in responding to global and local levels of a pattern.

Effects of unilateral temporal-parietal lesions on interference between global and local levels in a divided attention task

Authors:

• M. Lamb

• Lynn C. Robertson

• Robert T. Knight

Date: 1990

Posterior/Anterior contributions in responding to global and local levels of visual stimuli

Authors:

• Lynn C. Robertson

• M. Lamb

• Robert T. Knight

Date: 1990

Component Mechanisms Underlying the Processing of Hierarchically Organized Patterns: Inferences From Patients With Unilateral Cortical Lesions

Authors:

• Michele Lazzara

• Lynn C. Robertson

• Robert T. Knight

Date: 1990

PubMed: 2140405

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Abstract:

Subjects identified target letters that occurred randomly at the local or global level in a divided attention task. The visual angle of the stimuli was varied. Neurologically intact controls showed a reaction time advantage for local targets which increased as visual angle increased. Patients with lesions centered in the posterior superior temporal gyms (STG) showed a larger local advantage than controls if the lesion was on the right and a global advantage if the lesion was on the left. STG patients were no more influenced by visual angle than were controls. Control subjects also showed the usual interference of global distractors on responding to local targets. STG patients showed little evidence of interference. Control patients with lesions centered in the rostral inferior parietal lobe performed normally. The findings suggest that several component mechanisms are involved in the processing of hierarchical levels of structure, each linked to specific anatomical regions.

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.

Effects of Lesions of Temporal-Parietal Junction on Perceptual and Attentional Processing in Humans

Authors:

• Lynn C. Robertson

• Michele Lazzara

• Robert T. Knight

Date: 1988

PubMed: 3193178

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Abstract:

When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.

Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans

ABSTRACT

When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.

AUTHORS

• Lynn C. Robertson

• Marvin R. Lamb

• Robert T. Knight

Date: 1988

DOI: 10.1523/JNEUROSCI.08-10-03757.1988

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Attention and interference in the processing of global and local information: effects of unilateral temporal-parietal junction lesions

Authors:

• Michele Lazzara

• Lynn C. Robertson

• Robert T. Knight

Date: 1988

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Abstract:

The processing of hierarchical stimuli was examined in patients with lesions in the temporal-parietal junction. In separate blocks of trials, subjects were instructed to identify the letter at the local or the global level of a hierarchical stimulus. Consistent with previous findings, reaction times for controls were faster in the globally than in the locally directed condition and reaction times to the local level were longer when the letters at the two levels were different (e.g. local "S"s forming a global "H") than when they were the same (e.g. local "S"s forming a global "S"). In other words, controls exhibited interference when locally directed. Patients with lesions centered in the rostral inferior parietal lobe (IPL) showed interference effects similar to controls. In contrast, patients with lesions centered in the posterior superior temporal gyrus and adjacent caudal inferior parietal lobe (STG) showed no interference. The data suggest that the posterior superior temporal plane and adjacent caudal inferior parietal lobe plays an important role in the integration of and/or attention to local and global level information.