Temporal Frequency Modulation of Binocular Balance in Normal and Amblyopic Vision.

Purpose: To investigate how temporal frequency modulates binocular balance in normally sighted and amblyopic adults.

Methods: Twenty-three controls and 13 amblyopes participated in this study. The effects of temporal frequency differences and monocularly directed attention on binocular balance were measured using an onset binocular rivalry task with sinusoidally flickering gratings at varying temporal frequencies and static gratings with monocular attentional cues. For the flickering gratings, different combinations of temporal frequencies (2, 4, or 10 Hz in one eye vs. 2, 3, 4, 6, 10, 15, or 20 Hz in the other) were presented. Their effects were then compared, and their relationship was analyzed.

Results: There was no relationship between the shifts in balance from temporal frequency and monocularly directed attention in both controls and amblyopes. Intermediate temporal frequencies (8.9 ± 1.4 Hz) in one eye maximized its perceptual dominance, with a larger shift due to temporal frequency in amblyopes than in controls. While normally sighted observers experienced similar degrees of shift in balance from temporal frequency and attentional (active and passive) modulations, amblyopic observers experienced a larger shift from temporal frequency than from monocularly focused passive (but not active) attention.

Conclusions: Intermediate temporal frequencies in one eye, rather than a specific temporal frequency difference between both eyes, maximized its perceptual dominance in both normally sighted and amblyopic observers. This balance shift from temporal frequency modulation was larger in amblyopes than in controls. Finally, the effect of temporal frequency on balance was larger than that of monocularly directed passive attention in amblyopes.