Angular motion discrimination thresholds in amblyopic non-human primates and their implications for motion decoding
53.322, Tuesday, May 14, 8:30 am - 12:30 pm, Royal Ballroom 6-8
Michael Caruso1, Najib Majaj1, Lynne Kiorpes1; 1Center for Neural Science, New York University
Goal: Amblyopia is a developmental vision disorder characterized by a loss of monocular spatial acuity. In addition to acuity deficits, amblyopes show decreased sensitivity to visual motion in random dot kinematogram (RDK) displays. Previous studies from our lab show particular impairment for fine spatial and long temporal offsets slow speeds on a 180-degree left-right direction discrimination. Physiological data from area MT in amblyopic macaques show that neuronal motion encoding deficits do not fully account for these impairments, suggesting a deficit in motion decoding. Coherence thresholds for different angular motion discriminations can be used to elucidate visual motion decoding. Small changes in coherence threshold as discrimination angle decreases suggest optimal decoding, whereas large increases in coherence threshold at fine discrimination angles reflect inefficiencies in decoding. Methods: To explore amblyopic motion decoding deficits, we used a two-AFC direction discrimination task with 3-5 test angles ranging from 10 to 90 degrees from vertical. For a single patch RDK, the animals task was to indicate whether motion was to the right or left of vertical on each trial. A coherence threshold was measured for each test angle for each eye of seven amblyopic macaque monkeys (3 strabismic, 3 anisometropic, 1 unknown etiology). Results: Across the range of test angles, threshold coherence was elevated for the amblyopic eye relative to the fellow eye. This effect was less pronounced amongst our anisometropic amblyopes. While threshold coherence increased at fine discrimination angles, there was no evidence of a difference in the rate of increase between the two eyes. Conclusion: This pattern of deficits argues against, but does not completely rule out, a specific motion decoding deficit. Alternatively, these results can be explained by input deficiencies and/or increased neural noise downstream.