Manual responses and saccades in chronic and recovered hemispatial neglect: a study using visual search

Hemispatial neglect affects both the ability to respond to targets on the contralesional side of space and to programme saccades to such targets. In the current study, we looked in detail at saccade programming and manual reaction times (RTs) in a range of visual search tasks, in which task difficulty was systematically increased by changing the nature of the distracters. In condition 1, the target was presented with no distracters. In the other conditions, displays contained three distracters that were changed across conditions to manipulate similarity to the target and so task difficulty. We tested two neglect patients, one chronic, one recovered along with two RCVA control patients and 12 age-matched controls. Both neglect patients studied could successfully execute saccades into the neglected field when the target was presented alone. However, a dissociation emerged between the two patients when the target was presented with distracter items. Patient ERs first saccade to target performance in the three search conditions revealed clear effects of distracter type. In contrast for the recovered patient AF, the left/right difference was present for all search displays and appeared to be constant regardless of distracter type. This differential pattern of behaviour may reflect the different underlying neural causes of the neglect in these patients. In the current study, the measurement of saccades allowed the task to be fractionated, and thus, reveal the action of multiple mechanisms controlling saccades in search. (C) 2002 Elsevier Science Ltd. All rights reserved.