Neuropsycholoyia. Printed in Great
Vol. 29, No. 7, pp. 619-628, Britain.
MODULATION OF VISUO-SPATIAL A CASE STUDY
0028-3932/91 S3.00+0.00 1991 Pergamon Press plc
PETERW. HALLEAN* and JOHN C. MARSHALLt$ *Rivermead Rehabilitation Centre, Oxford OX1 4XD, U.K.; and tNeuropsychology Unit, University Department of Clinical Neurology, The Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, U.K. (Received 15 January 1991; accepted 26 February 1991) Abstract-We report a case of severe left visuo-spatial neglect consequent upon right-hemisphere stroke. In Experiment 1, horizontal and vertical (radial) line bisection is performed; the patient displays left neglect and “altitudinal” (radial) neglect, placing his transections too far to the right and to the top, respectively. In Experiment 2, the patient is required to place a dot at the centre of squares and circles, the horizontal and vertical extents of which are identical to the length of the lines employed in Experiment 1. Performance is now extremely accurate. In Experiment 3, the height of the rectangular or elliptical figure whose midpoint is to be estimated is held constant whilst length varies. In Experiment 4, the length of the figure is held constant whilst height is varied. Both manipulations exert a profound, lawful influence on the patient’s estimate of each figure’s midpoint. We provide some preliminary hypotheses concerning how configurational constraints may affect perceptual and attentional processes in visual neglect.
INTRODUCTION PATIENTSwith left visuo-spatial neglect bisect horizontal lines significantly to the right of the true centre . Descriptively at least, the typical pattern of performance is well-known. There is a linear relationship between stimulus line length and the magnitude of transection displacement [ll, 141; the slope of the regression is such that, at small line lengths, transections often “cross-over” to give leftwards displacements indicative of a change from left to apparent “right” neglect [6, 181. Studies of line bisection in orientations other than the horizontal are comparatively rare. BENDERand TEUBER , however, reported two cases of shrapnel injury to the right hemisphere in which the patients bisected vertically-presented lines too high. This phenomenon of “altitudinal” neglect has subsequently been confirmed in cases of bilateral parieto-occipital infarction , and of closed head injury with bilateral damage to the dorsal portion of the occipital lobes [S]. The opposite effect, vertical lines bisected too low, has been reported in a patient with bilateral infarction of the inferior temporal lobes and the occipital lobes [ 171. Another study has presented lines in the transverse plane at orientations through a full 360” [lo] to a patient with unilateral infarction of the right parietal region (and some encroachment into the superior and lateral aspect of the right temporal lobe); the patient showed maximal left neglect in the horizontal orientation, some “lower” (near)
SCorrespondence Clinical Neurology,
to be addressed to: Dr John C. Marshall, Neuropsychology Unit, University The Radcliffe Infirmary, Woodstock Road, Oxford OX2 6HE, U.K. 619
P. W. HALLIGANand J. C. MARSHALL
neglect in the vertical (radial) condition, and there was a smooth psychophysical function that related displacement to angular orientation across the full range of stimuli. In the current paper, we report a new patient with left neglect consequent upon unilateral right-hemisphere damage. The patient’s performance is examined first on horizontal and “vertical” (radial) line bisection. In subsequent experiments, we investigate his ability to estimate the centre of closed, two-dimensional figures. The initial question posed is this: can the patient’s performance on two-dimensional figures be extrapolated from performance in the two discrete one-dimensional conditions? Alternatively, do configurational (“gestalt”) factors determine spatial judgements when multi-dimensional stimuli are employed?
CASE REPORT T.R. is a 54 year-old, right-handed, man. He sustained a right-hemisphere stroke with left hemiplegia and left homonymous hemianopia on 15 May 1990. C.T. scan, performed on 7 November 1990, showed an area of well defined low density in the medial aspect of the right occipital lobe, extending into the inferior temporal region. The posterior limb of the right internal capsule is also affected. The appearance is consistent with a right posterior cerebral distribution infarct. On neuropsychological examination (6 June 1990) the outstanding symptom was left visuo-spatial neglect. Examined on the Behavioural Inattention Test f211. T.R. obtained a score of 941146. This BIT aggregate is based upon peformance on: line crossing, letter and star cancellation, figure copying, line bisection and-representational drawing. The cut-off score for normality is 130/146. Inspection of T.R.‘s performance on cancellation tasks revealed a larger number of omissions in lower left space. On a letter-cancellation task, dividing the stimulus array into quadrants revealed the following distribution of omissions: upper left = 25%, lower left = lOO%, upper right = 33%, and lower right =O%. The experimental studies that follow were conducted over the course of 4 weeks.
The purpose of the present experiment is to obtain a quantitative accuracy on both horizontal and “vertical” (radial) line bisection.
Method Lines ofextent IO mm, 30 mm, 60 mm, 90 mm, 120 mm, 150 mm and 180 mm were drawn in black ink on sheets ofwhite A4 paper (298 x 208 mm), one line per sheet. The width ofeach line was 1 mm. The lines were centred on the page, both horizontally and vertically. Lines were presented for bisection in two blocks, one horizontal and one vertical; for horizontal bisection each stimulus sheet was oriented such that its longest side was horizontal; for vertical presentation, the longest side was vertically oriented. Each stimulus sheet was placed on the desk top immediately in front of the patient and was always centred on the midsagittal plane of the patient’s head and trunk. Within a block (horizontal or vertical) all stimulus lengths were presented IO times in one session, with order of presentation pseudo-randomized across all lengths. T.R. bisected these lines with a fine pen held in the right hand. All stimuli were displayed in free vision, without restraint on head or eye movements.
Results Transection accuracy was measured to the closest mm and expressed as positive (+ ) for rightwards or upwards displacements and negative (-) for leftwards or downwards displacements. The data are given in Table 1, where we display the mean signed displacements (and their respective standard deviations and ranges) for all lengths in the two respective orientations (horizontal and “vertical”). The best-fitting regression equation for horizontal bisection was - 7.03 + (0.229 x line length), with 95% of the variance accounted for (P