Perceptual and response-related components of unilateral neglect may evolve independently of one another: evidence from five single-case studies.

The Milner Landmark Task allows the disentanglement of perceptual and response-related components of unilateral neglect. If these two components reflect separate functional systems, then cases should be observed in which the two components evolve differently across time. To test this hypothesis we surveyed a continuous series of 21 right hemisphere stroke patients. Five patients from the sample were affected by unilateral neglect at the outset and could be submitted to repeated administrations of the Landmark task in the first weeks post stroke. Two versions of the task were used, Landmark-Manual and Landmark-Verbal, differing in the type of response required. Two patients showed independent changes in the perceptual and the response-related component of neglect, hence confirming the view of separate functional systems underlying them. Dissociations between the task versions were found, witnessing a role of the type of response. Unexpectedly, one patient showed an initial leftward deviation of the subjective midpoint of the stimulus line, which later reversed to a classical rightward deviation. We interpreted such a pattern in terms of co-existing "productive" and "negative" components of perceptual neglect.