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

Mannan, Sabira K.; Pambakian, Alidz L. M.; Kennard, Christopher · 2010 · Crossref

DOI: 10.1007/s00415-010-5615-3

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Summary

This study investigates the specific oculomotor compensatory strategies developed by patients with homonymous hemianopia (HH) following visual search training. While previous research established that such training improves search efficiency and reaction times, it remained unclear whether these improvements resulted from adaptive changes in eye movement strategies or from perceptual learning and neuronal plasticity. The authors aimed to characterize the precise alterations in scanning behavior that facilitate improved target detection in patients with visual field defects. The study included 29 patients with HH caused by post-chiasmatic lesions, who underwent 20 daily sessions of visual search training over four weeks. During training, patients searched for a single target among distractors on a monitor without prescribed scanning strategies. Eye movements were recorded using a binocular infrared system during testing sessions conducted before and after training. The experimental design included baseline visits to control for spontaneous recovery or practice effects, allowing the researchers to isolate the specific impact of the training regimen on oculomotor parameters such as fixation duration, saccade amplitude, and visual lobe size. The results demonstrated that training induced specific, sustained changes in oculomotor behavior. Patients directed a higher proportion of fixations into the hemispace containing the target and made fewer transitions between hemifields before locating it. When patients initially saccaded into the incorrect hemifield, they switched to the correct field more rapidly after training, evidenced by fewer fixations in the wrong area and shorter fixation durations in the intact hemispace when the target was located there. Additionally, patients made larger initial saccades and exhibited an enlarged visual lobe in their blind hemifield, indicating an increased ability to fixate targets within the blind field in a single saccade. These changes were specific to the training period and were maintained one month after training ceased. The findings suggest that visual search training facilitates the development of efficient, adaptive eye movement strategies rather than relying solely on perceptual learning or cortical restitution. By optimizing scanning patterns—specifically by reducing unnecessary hemifield switches and expanding the effective search area in the blind field—patients achieve improved search efficiency. This supports the efficacy of visual search training as a rehabilitation method that helps patients compensate for visual field loss through learned oculomotor adaptations, with benefits persisting after the training concludes.

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