Visual hemispatial inattention: stimulus parameters and exploratory strategies.

Patients with unilateral hemispheric lesions were given visual target cancellation tasks. As expected, marked contralateral and less severe ipsilateral visual inattention were observed in patients with right-sided cerebral lesions whereas those with left-sided lesions showed only mild contralateral neglect. Stimulus material (shapes vs letters) and array (random vs structured) interacted in a complex manner to influence target detection only in patients with right-sided lesions. Furthermore, the search strategy of these patients tended to be erratic, particularly when the stimuli were in an unstructured array. A structured array prompted a more systematic and efficient search. It appears, therefore, that stimulus content and spatial array affect neglect behaviour in patients with right-sided lesions and that a lack of systematic visual exploration within the extrapersonal space is one factor that contributes to visual hemispatial inattention.