Directed and divided attention during hierarchical processing in patients with visuo-spatial neglect and matched healthy volunteers

Hierarchically organized figures (for example, a large E made up of smaller N's) are frequently used to investigate directed and divided attention. Investigations of neurological and psychiatric patients, and also tachistoscopic and functional neuroimaging studies on healthy subjects, typically find the right hemisphere to be specialized for the processing of global stimuli and the left hemisphere to be specialized for the processing of local stimuli. In the current study, a group of 12 patients with visuo-spatial neglect (NP) after right hemisphere lesions and 12 age and sex-matched control subjects (CO) performed a directed and a divided attention task with hierarchically organized letters. As expected, faster reaction times were found for control subjects than for neglect patients, especially for the directed global attention task. Lower error rates were found for CO and NP for local than for global targets during the divided attention condition. Local on global interference was found for both groups in reaction times. These local processing advantages for older healthy adults have been reported previously. Additionally, an impairment in the divided attention task was found in both groups, but especially for global targets in NP. This impairment is consistent with other evidence of difficulty in disengaging attention shown by patients with visuo-spatial neglect.