Abstract
Purpose: :
When two eyes view discordant monocular stimuli, alternating periods of monocular suppression and dominance occur; this is the well–know phenomenon of binocular rivalry (BR). BR has been studied intensively using subjective methods, but not objective methods. This study investigated the temporal course of suppression during BR using ocular following responses (OFR) eye movements.
Methods: :
Dichoptic stimuli were presented using a mirror haploscope with two computer monitors subtending 40x30 deg at 47 cm from each eye. Experiment 1. A stationary horizontal grating pattern was presented to the right eye and vertical grating to left eye to induce BR. The subjects were required to press a button as soon as he/she perceived one of the alternating patterns. The interval between subjective alternation was recorded with an infrared eye tracking system and measured with custom software offline. Experiment 2. The same orthogonal patterns were presented to each eye dichoptically. Subjects pressed a button to start horizontal movement of the vertical grating pattern as soon as he/she perceived one of patterns. Eye movements were recoded during both psychophysical suppression and non–suppression phase. The movement of the vertical grating started with various delays and lasted for 1.5 seconds. Early ocular following responses (OFR) were recorded and measured in both open and closed loop windows.
Results: :
Experiment 1. The time interval between each alternation averaged about 1000 ms, consistent with a Gamma distribution previously reported. Experiment 2. The velocity of initial OFR was slower with short presentation delays, and increased progressively with longer delays, reaching a maximum level after 600 ms.
Conclusions: :
Early OFR was largely suppressed during the psychophysical suppressed phase of binocular rivalry, but the suppression recovered gradually over the suppression phase. This implies that suppression of binocular rivalry is a dynamic process.
Keywords: eye movements • temporal vision • binocular vision/stereopsis