Compensatory strategies following visual search training in patients with homonymous hemianopia: an eye movement study

Abstract

A total of 29 patients with homonymous visual field defects without neglect practised visual search in 20 daily sessions, over a period of 4 weeks. Patients searched for a single randomly positioned target amongst distractors displayed for 3 s. After training patients demonstrated significantly shorter reaction times for search stimuli (Pambakian et al. in J Neurol Neurosurg Psychiatry 75:1443-1448, 2004). In this study, patients achieved improved search efficiency after training by altering their oculomotor behaviour in the following ways: (1) patients directed a higher proportion of fixations into the hemispace containing the target, (2) patients were quicker to saccade into the hemifield containing the target if the initial saccade had been made into the opposite hemifield, (3) patients made fewer transitions from one hemifield to another before locating the target, (4) patients made a larger initial saccade, although the direction of the initial saccade did not change as a result of training, (5) patients acquired a larger visual lobe in their blind hemifield after training. Patients also required fewer saccades to locate the target after training reflecting improved search efficiency. All these changes were confined to the training period and maintained at follow-up. Taken together these results suggest that visual training facilitates the development of specific compensatory eye movement strategies in patients with homonymous visual field defects.

Fig. 1

Effect of training on fixation search parameters in four sessions each 1 month apart (1 baseline, 2 second baseline immediately preceding training, 3 immediately following 1 month training, 4 1 month after cessation of training. a The percentage of fixations made in the hemifield containing the target increased after training. b The number of fixations initially made in the hemifield not containing the target decreased after training. c The number of hemifield switches made before locating the target decreased after training. d Total number of fixations made during search decreased after training. Filled circles denote target in the blind hemifield and white squares denote target in the seeing hemifield. Error bars show 1 SEM

Fig. 2

Effect of training on fixation search parameters in four sessions each 1 month apart (1 baseline, 2 second baseline immediately preceding training, 3 immediately following 1 month training, 4 1 month after cessation of training. a The mean amplitude of the initial saccade increased after training. b The mean area of the intact visual lobe—the area within the seeing field in which the patient can fixate the target in the following saccade—remained unchanged after training. c The mean area of the hemianopic visual lobe—the area within the hemianopic field in which the patient can fixate the target in the following saccade—increased after training. Filled circles denote target in the blind hemifield and white squares denote target in the seeing hemifield. Error bars show 1 SEM