Visual and Tactile Size Distortion in a Patient with Right Neglect

School of Psychology, University of St Andrews, St Andrews, UK.
Neurocase (Impact Factor: 1.12). 02/2001; 7(5):391-6. DOI: 10.1076/neur.7.5.391.16246
Source: PubMed


One typical feature of the neglect syndrome in patients with right hemisphere damage is that they bisect horizontal lines to the right of centre. It has been argued that to a large extent these bisection errors can be attributed to a perceptual change whereby the patient experiences the left half of a line as shorter than the right half, causing them to set the midpoint of the line towards the right. We describe here a patient with a left hemisphere lesion and rightward neglect, who consequently makes bisection errors in a leftward direction. We carried out a series of tests which confirmed that he shows a subjective visual distortion in the converse direction, i.e. a perception of horizontal extents on the right as shorter than extents on the left. We also found that he shows a similar distortion in his tactile perception. The association of visual and tactile distortions in this patient is compatible with the view that the distortion effects have a rather high-level origin. Multiple single-case studies will, however, be required to establish whether this association of deficits is typical, or whether visual and tactile size distortions are separable symptoms associated with neglect.

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    • "It has been hypothesised that these phenomena are due to a distortion of space perception and representation in neglect (Halligan and Marshall 1991; Milner et al. 1993; Bisiach et al. 1994; Ishiai et al. 1994). Consistent with this claim is the finding that an analogous perceptual distortion can also be observed in tactile size evaluation (Pritchard et al. 2001). Bisiach and colleagues (Bisiach et al. 1994, 1996, 2002) hypothesised that such a distortion in neglect might be due to an anisometric medium for space representation progressively relaxed proceeding from the ipsilesional towards the contralesional space. "
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    ABSTRACT: Patients with visuospatial neglect tend to underestimate horizontal magnitudes in contralesional space. It has been recently hypothesised that this behaviour might be due to anisometry of space perception, by which horizontal stimuli would be progressively underestimated proceeding from the ipsi towards the contralesional side of space. We investigated the effects of modulating space perception through the Oppel-Kundt illusion (i.e. a filled space is perceived as more expanded than an empty space) on the behaviour of 28 neglect patients and 28 normal subjects. The two groups bisected lines on backgrounds of vertical lines evenly spaced or unevenly spaced, with distances which decreased progressively from one side of the page to the other. On the same backgrounds, they extended segments to the left or to the right so as to double them. Patients also had to cancel targets, the density of which was evenly distributed or horizontally increased from one side of the page to the other. Both groups were prone to the illusion. Neglect bias was modulated by the illusion in the expected direction. It was reduced when the illusion induced a perceptual distortion opposite to that thought to underlie neglect. On bisection and cancellation tasks, illusory effects were greater in patients with higher values of response bias on the Milner Landmark task. These findings, taken together with patients' anatomical data, suggest that a modulation of neglect through a visual illusion can normally be induced in patients with relatively intact visual input processes.
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    • "Several authors have shown that hemispatial neglect impairs the ability to plan and initiate visually guided leftward limb movements [3] [22] and eye movements [4] [19] [29]. For example, Ro et al. [30] found an ipsilesional bias in saccadic eye movements associated with hemispatial neglect that could not be attributed to deficient visual perception. "
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