Abstract
Purpose: Individuals with central field loss (CFL) have impaired acuity, contrast sensitivity and stereopsis. However, their ability to judge heading direction does not appear to be impaired in the absence of noise (Odom et al. ARVO 2010). Consistent with this finding, our recent study shows that speed and direction discrimination in this group are comparable to age-matched controls (Shanidze & Verghese OSAFV 2018). Here, we aim to investigate whether motion perception depends on the location, extent and eccentricity of the missing information.
Methods: Observers performed a 2AFC task on patches of dots on the left and right of fixation, while viewing binocularly. The dots moved in an oblique direction at reference speeds of 5, 10, 20/s (in separate blocks). For speed discrimination, participants judged which side had the faster speed, while for direction discrimination, they judged which side had a more vertical direction of motion. Participants included 7 individuals with CFL (57-91, 3F), 6 age-matched controls (60-77, 4F) and 6 young controls,(26-48, 5F). For CFL participants, we analyzed the pattern of errors on each side and compared it to that individual’s scotoma measured with binocular perimetry using an eye tracker. To determine whether the extent and eccentricity of the stimulus impacts discrimination we also tested the young control group on a variant of the task with thin strips of dots at different eccentricities whose width was scaled for cortical magnification.
Results: For the CFL group, 3 participants showed a bias with lower proportion correct on the right. These data points are numbered in the first column of Figure 1, which shows proportion correct responses on the right vs. left for speed (A) and direction (B) discrimination (error bars: 95% CI). However, this biased performance is unrelated to scotoma location or size (last column). In the young control group, we found no difference in thresholds for direction or speed discrimination between the full field stimulus (2A) and limited stimulation at a given eccentricity (2B) of 5, 10 or 15 (Fig 2, error bars: SEM).
Conclusions: Under high visibility conditions, CFL does not impair speed and direction discrimination performance. Furthermore, restricting motion information to narrow bands in the periphery did not impact motion perception. These results suggest that motion perception in the periphery is intact for a majority of individuals with CFL.