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Biomedical subjects

V W Mark

Publications and source records attributed to V W Mark.

15 recordsLinked to original sources
PubMed1998

Diagonal spatial neglect.

OBJECTIVE: To determine whether stroke patients with diagonal neglect on cancellation may show diagonal neglect on line bisection, and hence to indicate whether diagonal neglect may be related solely to the type of test used or whether instead it may reflect a fundamental spatial disorder. METHODS: Nine patients with subacute right hemispheric stroke who neglected targets primarily in the near left direction on line cancellation bisected diagonal lines of two opposing orientations: near left to far right and far left to near right. The errors were assessed to determine whether line orientation significantly affected bisection error. RESULTS: Eight patients had significant bisection errors. One of these showed no effect of line orientation on error, consistent with lateral neglect. The remaining seven patients had a line orientation effect, indicating a net diagonal spatial bias. For the group, cancellation errors were significantly correlated with the line orientation effect on bisection errors. CONCLUSIONS: A significant diagonal bias on two tests of spatial attention may appear in stroke patients, although the directions of the biases may differ within individual patients. None the less, diagonal neglect may be a fundamental spatial attentional disturbance of right hemispheric stroke. Greater severity of stroke deficit as indicated by cancellation error score may be associated with a greater degree of diagonal neglect on line bisection.

Aged↗
PubMed1997

Two-dimensional cancellation neglect a review and suggested method of analysis.

Directional bias on cancellation has thus far not been standardized. While cancellation tasks are primarily used to assess lateral performance asymmetries, they may also reveal two-dimensional (i.e., combined lateral and radial) neglect patterns. We propose a method to evaluate and report cancellation neglect regardless of whether the neglect pattern is strictly unilateral or two-dimensional. Our method establishes the location of the geographic center of all neglected stimuli relative to the page center by averaging their Cartesian coordinates. This "neglect center" is reported in polar coordinates to indicate its distance and direction from the page center. We apply our method to published examples of two-dimensional neglect. We find that neglect centers from different cancellation performances may not be statistically distinct even though they may occupy different quadrants. In addition, the net direction of neglect found by the coordinate method may differ from that inferred from measuring differences in quadrant omission totals. The suitability of the coordinate vs. the quadrant method will depend on the mechanism hypothesized for visuospatial exploration under particular test conditions. Using both approaches may detect different attentional biases operating during the same task. The coordinate method is appropriate for conventional cancellation testing. By incorporating the precise locations of all neglected stimuli and determining the net neglect direction in two dimensions, the technique may stimulate more comprehensive explanations for directional bias.

Attention↗
PubMed1997

The effects of gender, menstrual phase and practice on the perceived location of the midsagittal plane.

Women show menstrual phase-related cognitive changes that suggest altered hemispheric activation for a particular task, such that they demonstrate the greatest lateral performance differences on prototypical left hemisphere tasks during the luteal phase and on prototypical right hemisphere tasks during menstruation. Additionally, menstrual phase may alter total cerebral responsiveness, such that response times and performance accuracy for many tasks are best during the luteal phase and most impaired during the menstrual phase. We evaluated the effect of menstrual phase on spatial bisection (a perceptuospatial task) to help further understand hormonally-mediated changes in interhemispheric dynamics. Healthy young adult women and men blindly pointed to their midsagittal plane with either hand. Women were repeatedly tested according to menstrual phase, and men were tested at similar intervals. The mean pointing error in the luteal phase differed significantly from that of all other phases and did not differ significantly from those of men, who pointed significantly to the left across test sessions. These findings suggest that, in space bisection tasks, women are more likely to have asymmetric hemispheric activation during the luteal phase than during the menstrual phase. Thus, space bisection did not resemble other prototypical right hemisphere behaviors. The luteal phase may have nonspecifically activated both hemispheres on this task instead of suppressing right hemisphere function, and a slight functional asymmetry favoring the right hemisphere may have been promoted. In addition, intermanual pointing discrepancies in both subject groups decreased over repeated sessions. This suggests that, while practice alters an internal kinesthetic reference, it does not influence an imaginal extrapersonal spatial reference.

Adolescent↗
PubMed1997

Diagonal neglect on cancellation.

Patients with right hemisphere injury frequently neglect to cancel targets primarily in the left part of the page nearest the body. Since this region is diagonally opposite the area from where such patients usually begin cancelling, near left ('diagonal') neglect may be consequent to stimulus order effects ('fatigue'). We evaluated the persistence of near left neglect in nine stroke patients when they had to cancel either the near or the far half of the page before proceeding to the other half. Our results showed that near left neglect on the page was largely unaffected by cancellation order. Furthermore, a near left gradient of omissions was established within both radial (near and far) halves of the page, as well as for the entire page. Our findings suggest that diagonal cancellation neglect is unrelated to fatigue and reflects a consistent, two-dimensional disorder of spatial attention. Such neglect may be related to the extent of the visible stimulus array, as well as to the array's location in egocentric space.

Attention↗
PubMed1990

Bodily neglect and orientational biases in unilateral neglect syndrome and normal subjects.

Patients with neglect erred toward the right when attempting to locate the intercepts of their midsagittal planes with a horizontal line placed in front of them. When control subjects could not see their bodies, they also pointed to the right. While control subjects improved when they were able to see their bodies, neglect subjects did not. When the horizontal line was moved toward the right, both neglect and control subjects increased their rightward pointing errors. However, patients with neglect made greater errors than did controls. When the line was in far left hemispace, controls pointed accurately to their midsagittal planes. The neglect subjects, in contrast, erred toward the left. Our results suggest that patients with neglect from right hemisphere lesions are not only inattentive to their bodies, but are also distracted by extracorporeal stimuli, especially on the right. Our results also suggest that normal subjects have a propensity to orient to or be distracted by stimuli in right hemispace.

Cerebral Hemorrhage↗
PubMed1988

An experimental analysis of factors underlying neglect in line bisection.

The finding that patients with neglect make larger errors when bisecting longer lines could be due to failure to disengage attention from a segment of the line on the ipsilesional side, or to a reduced ability to direct attention and/or action contralaterally. The findings are reported from a patient with left-sided neglect who set the midpoint further away from the right end of lines as their length increased, a finding consistent with the latter interpretation. His errors were significantly related to length and lateral extent of lines presented in left hemispace, but only to length of lines presented in right hemispace.

Aged↗
PubMed1988

Hemispatial neglect affected by non-neglected stimuli.

Patients with hemispatial neglect fail to cancel lines distributed on one side of a piece of paper. This defect is thought to be induced by a deficit in the neuronal systems that mediate attention, intention, and exploration toward and in the hemispace contralateral to the lesion. However, an alternate (but not mutually exclusive) interpretation is that the patients are either strongly attracted to or impaired in disengaging from the stimuli occupying the other, non-neglected hemispace. We tested ten patients with neglect on two versions of a cancellation test. In the control test they cancelled lines by drawing over them, and in the experimental test they erased lines. There were significantly more omissions in the drawing-over task than in the erasing task. The improved performance when lines were cancelled by removal instead of by marking them suggests that hemispatial neglect is influenced by the presence of stimuli in the non-neglected hemispace.

Adult↗