Sensory eye dominance.

BACKGROUND: Sensory eye dominance is revealed in tasks like the Red Lens test and binocular rivalry. To understand its neural basis, we used a new protocol based on binocular rivalry to quantify its consequent interocular imbalance. Then we investigated whether the extent or sign of interocular imbalance is correlated with the difference in monocular contrast responses at threshold and suprathreshold and with the observer's motor eye dominance. METHODS: To evaluate sensory eye dominance, the stimulus intensity in each eye during rivalry was adjusted to achieve equal predominance. The difference in stimulus intensity constitutes the interocular imbalance. Standard procedures were used to measure monocular spatial contrast sensitivity, suprathreshold brightness judgment, and motor eye dominance. RESULTS: There was no positive correlation between interocular imbalance (sensory eye dominance) and motor eye dominance. No systematic correlation was found between interocular imbalance and monocular contrast sensitivities at 1 and 3 cycles/degree. Correlation coefficient between interocular imbalance and monocular suprathreshold brightness judgment was close to significant, suggesting that a difference in monocular brightness percept might (in part) account for interocular imbalance. But this explanation is only partial, since the difference in the monocular brightness percept was too small to account for the interocular imbalance. CONCLUSIONS: Interocular imbalance is a sensory eye dominance that cannot be equated with motor eye dominance. It manifests largely as a binocular phenomenon, which bears little relationship with the monocular neural mechanisms of contrast detection and brightness perception.