Visual Tracking in Amblyopia: A Continuous Psychophysical Approach

Abstract

Purpose This study aimed to explore the underlying mechanisms of the observed visuomotor deficit in amblyopia. Methods Twenty-four amblyopic (25.8 ± 3.8 years; 15 males) and 22 normal participants (25.8 ± 2.1 years; 8 males) took part in the study. The participants were instructed to continuously track a randomly moving Gaussian target on a computer screen using a mouse. In experiment 1, the participants performed the tracking task at six different target sizes. In experiments 2 and 3, they were asked to track a target with the contrast adjusted to individual's threshold. The tracking performance was represented by the kernel function calculated as the cross-correlation between the target and mouse displacements. The peak, latency, and width of the kernel were extracted and compared between the two groups. Results In experiment 1, target size had a significant effect on the kernel peak ( F (1.649, 46.170) = 200.958, P = 4.420 × 10 −22 ). At the smallest target size, the peak in the amblyopic group was significantly lower than that in the normal group (0.089 ± 0.023 vs. 0.107 ± 0.020, t (28) = −2.390, P = 0.024) and correlated with the contrast sensitivity function ( r = 0.739, P = 0.002) in the amblyopic eyes. In experiments 2 and 3, with equally visible stimuli, there were still differences in the kernel between the two groups (all P s < 0.05). Conclusions When stimulus visibility was compensated, amblyopic participants still showed significantly poorer tracking performance.