Effects of left parietal injury on covert orienting of attention

Objective: To assess the effects of left parietal injury on covert visual attention during a detection task and a pointing task. Methods: The Posner's paradigm was given to a patient who was found at the age of 74 to have spent all his life without the left parietal lobe as a result of a congenital perinatal insult and to a control subject. In one session subjects were required to provide an arbitrary response at stimulus appearance (key press). In another session subjects were required to point to the stimulus. Results: The patient was able to disengage covert attention from a cued position when the task was to provide an arbitrary key press response in a similar fashion to a control subject with no neurological deficits. By contrast, he was impaired in disengaging attention from a cued position when the task was to reprogramme an overt pointing action. Conclusions: Response to cued information is differentially available depending on task. It is suggested that mechanisms concerned with the attention for action systems are located within the left parietal lobe.