Does the midsagittal plane play any privileged role in “left” neglect?

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Abstract
We report two studies of a star cancellation task performed by patients with left neglect consequent upon unilateral right hemisphere stroke. In the first experiment, 24 patients performed the task once; in the second, 3 patients were tested repeatedly over the post-stroke period. Rather than dichotomise the data (accuracy on the right versus the left half of the test) we report the results in terms of percent omissions from 6 laterally ordered columns. We find that, for most patients, there is an “attentional boundary” beyond which sustained attention cannot be further directed leftwards. The spatial position of this boundary is not intrinsically linked to the midsagittal plane; its position is rather a function of the overall severity of the patient's deficit on the task. We conclude that “unilateral visuospatial agnosia” is better conceptualised as “ipsilateral capture” than as “contralateral neglect”.