The effectiveness of compensatory eye movement strategies in cortically blind humans - a virtual reality study

Abstract

Unilateral damage to the primary visual cortex causes extensive, homonymous, loss of vision in the contra-lateral visual hemifield, referred to as partial cortical blindness. When stationary, those afflicted display a compensatory eye movement strategy that places most relevant visual information in their intact visual hemifield. However, cortically blind patients complain of difficulties navigating and avoiding obstacles during ambulation. This prompted our hypothesis that their compensatory gaze strategies may not be maintained when navigating. To test this hypothesis, we used a head-mounted display with intra-helmet eye tracking to measure fixations, navigation accuracy and visual detection performance in seven patients with cortical blindness and ten visually intact controls immersed in a naturalistic, virtual representation of Penn Station. Our results confirmed prior observations that cortically blind patients place most of their fixations in their blind hemifield when stationary and maintain this bias under ambulatory conditions. However, this strategy only allows for good detection of peripherally presented, moving objects when stationary. Ambulation widened both head movements and horizontal fixation distribution in controls, but only head movements in cortically blind patients. While their narrower fixation distribution likely allowed blind subjects to maintain good navigation accuracy, their ability to detect peripherally presented moving objects while walking was significantly impaired. Our findings suggest that compensatory gaze strategies developed spontaneously by cortically blind patients optimize heading performance, but do so at the expense of detecting peripheral targets. By understanding the nature of this trade-off, it may be possible to develop more effective rehabilitation strategies for cortical blindness.

Acknowledgments

Supported by an unrestricted grant from the Research to Prevent Blindness Foundation to the Flaum Eye Institute, NEI core grant P30EY0131 to the Center for Visual Science, the Pfeiffer Foundation, The Schmitt Foundation.