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Biomedical subjects

L C Robertson

Publications and source records attributed to L C Robertson.

46 records · Page 3Linked to original sources
PubMed1987

Reference frames in mental rotation.

Four experiments are reported that investigate whether images or reference frames are transformed during a mental rotation task. In all experiments a display of four identical letters (P1) was presented at either +90 degrees or -90 degrees from upright, and subjects had to decide whether the letters were normal or mirror-image reflections. A single letter (P2) was then presented 100 ms later in a variable orientation with the same task instructions. Reaction times to P2 were assessed to determine whether an image of P2 was rotated to upright or whether an internal reference frame was rotated into congruence with P2 from the orientation of P1. The results as a whole suggest that transformations of P2 can be initiated either relative to upright or relative to the orientation of P1. They further indicate that the probability of using each reference orientation can be changed by procedural variations. The findings are most parsimoniously interpreted as suggesting that mental rotation involves the transformation of reference frames rather than the transformation of template-like representations.

Attention↗
PubMed1987

Effect of acute alcohol on attention and the processing of hierarchical patterns.

Subjects received 100-msec exposures of hierarchical patterns consisting of a large "global" letter composed of several smaller "local" letters. Subjects were to respond whether a target letter was present at the global or at the local level. In the Neutral Bias condition target letters occurred randomly and equally often at the global and local levels. In the Global Bias condition, 79% of the targets occurred at the global and 21% at the local level. In the Local Bias condition, 79% of the targets occurred at the local and 21% at the global level. Subjects indicated by pressing a key which of two target letters had appeared on that trial. Subjects received either a placebo drink, a drink containing 0.7 ml of Alcohol per kg body weight, or a drink containing 1 ml of Alcohol per kg body weight. Placebo subjects were better at detecting letters at the global than at the local level in the Global Bias condition, better at local than global in the Local Bias condition, and about equally good at both levels in the Neutral Bias condition. Alcohol had no effect on detection of letters at the local level in any of the bias conditions but reduced detection of letters at the global level except when subjects were biased globally. The data suggest that alcohol does not affect attentional capacity. Instead, alcohol seems to affect either how attentional capacity is allocated or the global processing mechanism itself.

Adult↗
PubMed1986

'Part-whole' processing in unilateral brain-damaged patients: dysfunction of hierarchical organization.

Visuospatial processing in unilateral brain-damaged patients was investigated by aligning two elements along different axes of an equilateral triangle and asking subjects to report the direction the triangle appeared to point when first observed. Left brain-damaged patients were more affected by the alignment than right brain-damaged patients, with controls performing in between the two brain-damaged groups. The implications of these findings for hemispheric differentiation in visuospatial processing are discussed.

Brain↗
PubMed1986

Hemispheric specialization of memory for visual hierarchical stimuli.

Unilateral brain-damaged patients and normal control subjects were asked to remember visual hierarchical stimuli consisting of larger forms constructed from smaller forms. The right-hemisphere damaged patients made more errors in remembering the larger forms relative to the smaller forms, whereas the left-hemisphere damaged patients made more errors in remembering the smaller forms relative to the larger forms. These findings are discussed as they relate to hemispheric specialization for visuospatial processing.

Cerebrovascular Disorders↗
PubMed1985

The effect of alcohol abuse on perceptual reference frames.

Visuospatial processing in alcoholics was investigated by aligning two elements along different axes of an equilateral triangle and asking subjects to report the direction the triangle appeared to point when first observed. Alcoholics were not as affected as controls by alignment of the elements. The implications of these findings are discussed.

Adult↗
PubMed1983

Holistic processes in the perception and transformation of disoriented figures.

Two experiments tested whether mental rotation of complex, hierarchical stimuli occurs holistically or separately at global and local levels of structure. Large (global) letters were constructed from spatial arrangements of small (local) letters. Reflection conditions (normal vs. reflected) were produced by varying the two levels independently. The task was structured so that subjects could rotate one level of the stimulus in some conditions but had to rotate both levels in other conditions. Experiment 1 showed that rotation rate was not affected by the number of levels that had to be rotated to make a reflection decision. This result implies that the rotation of global and local levels occurred together rather than sequentially. Experiment 2 showed that the rotation of the two levels was holistic as opposed to parallel and independent. The results also demonstrate that global information is processed faster than local information regardless of whether or not a rotation is performed. These findings are discussed in relation to theories of mental rotation and global precedence.

Adolescent↗
PubMed1983

The breakdown and rehabilitation of visuospatial dysfunction in brain-injured patients.

Neuropsychological studies on visuospatial dysfunction are reviewed and a model is described that characterizes hemispheric specialization of this function. It is proposed that the right hemisphere is dominant for configural processing and the left hemisphere for detail processing. Past efforts of visuospatial rehabilitation, which have focused primarily on one type of impairment, "left-neglect", are discussed. Future directions for rehabilitation of visuospatial dysfunction associated with both right- and left-hemisphere pathology are suggested.

Brain Diseases↗
PubMedDate not supplied

Cortical substrates supporting visual search in humans.

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.

Aged↗