Target selection in torsional pursuit eye movements

Abstract

Purpose: Torsional eye movements can be controlled voluntarily with training (Balliet & Nakayama 1978, Invest Ophthalmol Vis Sci. 17(4):303–14). This study addressed whether attention to one or another torsion stimulus can modify visually-driven torsion. Methods: The stimuli were two annular bands of filtered spatial noise that rotated sinusoidally about a common center. The central disk diameter was 3 deg, the inner annulus diameter was 9 deg and the outer annulus diameter was 30 deg. Peak velocity was 128 degrees per second and frequency was 0.25 Hz for one annulus and 0.50 Hz for the other. Subjects were instructed to attend to one annulus and ignore the other, to follow its torsional motion without head movement, all while maintaining fixation on the center of the pattern. Eye torsion was measured with a video system (Arrington Research) with a resolution of 0.5 degrees. Head stability was monitored by the experimenter during recordings. Tracking amplitude at each frequency was determined by Fourier analysis. Results: Four subjects (three authors and one naïve) all showed a strong bias to make torsional responses to the attended pattern. Three of the four subjects showed some residual response to ignored patterns, while the fourth was able to track the attended pattern exclusively. This fourth subject also has the ability to produce torsion on command without a stimulus to follow. Torsion amplitude at the attended frequency was about 5 deg (peak to peak) for two subjects, about 2 deg for the third subject and about 14 deg for the fourth. Conclusions: Torsional pursuit movements are strongly modified by attention to one or another stimulus. This voluntary aspect of torsion does not require any training.