We investigated whether retinis pigmentosa (RP) patients with residual visual field of <10° could perceive heading
from optic flow
Four RP patients and four age-matched normally sighted control subjects viewed displays simulating an observer walking over a ground. In experiment 1, subjects viewed either the entire display with free fixation (full-field condition) or through an aperture with a fixation point at the center (aperture condition). In experiment 2, patients viewed displays of different durations.
RP patients’ performance was comparable to that of the age-matched control subjects: heading
judgment was better in the full-field condition than in the aperture condition. Increasing display duration from 0.5 s to 1 s improved patients’ heading
performance, but giving them more time (3 s) to gather more visual information did not consistently further improve their performance.
RP patients use active scanning eye movements to compensate for their visual field loss in heading
perception; they might be able to gather sufficient optic flow
information for heading
perception in about 1 s.