Is the origin of the hemianopic line bisection error purely visual? Evidence from eye movements in simulated hemianopia.

It is still unclear whether the contralateral line bisection error in unilateral homonymous hemianopia is caused by the visual field defect, strategic oculomotor adaptation or by additional extrastriate brain injury. We therefore simulated hemianopia in healthy participants using a gaze-contingent display paradigm and investigated its effects on manual and ocular line bisection performance and eye-movements. Although simulated hemianopia impaired line bisection and induced the adaptive oculomotor eye-movement pattern of hemianopic patients, it did not induce the contralateral bisection error, suggesting that neither the visual field defect nor oculomotor adaptation to it are the primary causes of the hemianopic bisection error.