Temporal characteristics of extraretinal signals during voluntary saccades and head roll in the dark
Purpose. An afterimage (AI) is perceived to move during voluntary saccades in the dark, which is attributed to the information from extraretinal eye-movement signals. The perceived AI displacement decreases with the frequency of equal-amplitude saccades, suggesting that the extraretinal signals for saccades are a temporally low-pass filtered version of the physical eye motion (Gruesser et al., Vision Res., 1987). Because retinal image motion results from head as well as eye movements, the goal of this study was to assess the extraretinal signals for voluntary head roll and compare the temporal-frequency dependence of these extraretinal signals to those associated with saccades.
Methods. Six normal observers synchronized voluntary horizontal saccades or shoulder-to-shoulder head roll in darkness to a metronome at frequencies from 0.5 to 1.7 Hz. During each trial, the observer represented the perceived change in AI direction during saccades or AI orientation during head roll using a hand-held rod. Eye movements were recorded by a ViewPoint Eye Tracker. Head movements and settings of perceived AI displacement or orientation change were recorded on video tape. (Abstract shortened by UMI.)