Summary:Patient GY was tested on a cued target detection response time task in six sessions over a period of a year and a half following a right sub-cortical cerebrovascular accident (CVA). In the initial sessions, over a period of 2 months, GY showed a marked asymmetry in speed of target detection in the two visual fields. The asymmetry was significant even when standard clinical assessment showed no clinical evidence of visual neglect or extinction, demonstrating the greater sensitivity of the response time measure. Of particular interest is the fluctuation in the degree of left-right asymmetry across testing sessions.