Bimanual coordination and perceptual grouping in a patient with motor neglect

Abstract

Motor neglect refers to the underutilisation of a limb contralateral to a brain lesion in the absence of primary motor and sensory deficits. The related problem of motor extinction refers to a contralesional motor deficit that worsens or only becomes apparent when bilateral actions are required. We present a single case (MM) of a patient with motor neglect who also demonstrates a form of motor extinction that is influenced by visual grouping between stimuli. The comparisons of unimanual and bimanual reach to grasp movements towards one or two objects in Experiment 1 showed that MM made relatively normal unimanual contralesional movements but impaired contralesional movements under bimanual action conditions. Experiment 2 demonstrated that motor extinction was improved by asking MM to make bimanual movements towards a single object. In Experiment 3, the effects of object coding on bimanual movement were replicated across conditions that varied the distance between end points for the movements. MM did not show overt visual extinction. We suggest that MM demonstrates a late-acting attentional bias that is expressed in terms of competitive motor activity. Normally, the contralesional limb “loses” the competition for action, but this can be modulated by visual grouping between targets.

Acknowledgments

This work was supported by grants from The Stroke Association to all three authors, and by grants from the MRC and Wellcome Trust to Jane Riddoch and Glyn Humphreys. We gratefully acknowledge this support. We thank MM for her participation.

Notes

Significance level at.025 to correct for Bonferroni Type I error.

Significance level at.017 to correct for Bonferroni Type I error.