Abstract
Purpose :
A nasalward bias in motion coherence thresholds has been reported in individuals with a history of monocular deprivation. However, the mechanism behind this bias is unclear. Here we investigated whether the locus of such asymmetry lies within the early visual areas, such as V1, or further downstream within the extrastriate cortex.
Methods :
In individuals with normal vision (n = 14), we measured motion coherence (MT+/V5) and contrast-detection (V1) thresholds for random dot kinematograms (100 dots, 6 deg/sec) in one eye after adaptation of the fellow eye to visual noise. To measure the motion coherence threshold, the contrast of the dots was maintained at 100% and coherence was varied. To measure detection thresholds, coherence was fixed at 100% and contrast was varied. Within separate sessions, thresholds were measured monocularly with and without adaptation of the fellow eye. Adaptation involved 60s viewing a random-dot-kinematogram with an equal number of black and white dots with varying speed and contrast, followed by 15 s periods of top up adaptation after every 10 trials.
Results :
Only motion coherence thresholds following noise adaptation exhibited a robust naso-temporal asymmetry in favor of nasalward motion (mean nasal MCT: 8 ± 2.25% vs mean temporal MCT: 14 ± 2%). When compared to the non-adapted condition, noise-adapted motion coherence thresholds were significantly worse only for temporalward motion post adaptation (noise-adapted 14 ± 2% vs. non-adapted 8 ± 1.92%). Contrast detection thresholds did not show any naso-temporal asymmetry for any condition.
Conclusions :
We were able to simulate the monocular nasal temporal MCT asymmetry we have previously observed in individuals with monocular deprivation using monocular noise adaptation of one eye. The presence of such asymmetry only in the global motion, but not in the contrast-detection task, suggests that MT+/V5 could be a potential site for this asymmetry.
This is a 2021 ARVO Annual Meeting abstract.