Abstract
Spatial frequency (SF) encoding in the human visual system is influenced by amblyopia. Amblyopic individuals struggle with low-contrast, high-SF stimuli, especially when presented monocularly to their amblyopic (suppressed) eye. To assess the neuronal underpinning of this phenomenon, we compared the amblyopia impact on SF preference in V2/V3 thick and thin stripes. These mesoscale sites are known to be involved in SF encoding (Tootell and Nasr, 2017). However, the amblyopia impact on their function remains largely unknown. Six strabismic and five anisometropic (best-corrected visual acuity in the amblyopic eye between 20/60 to 20/300) individuals, aged 19-55 years old, participated in this study. Using high-resolution fMRI (7T; voxel size = 1 mm isotropic), we localized their iso-eccentric (3˚<r<10˚) thin and thick stripes across V2 and V3 (Tootell and Nasr, 2021). Then, we measured the activity within these stripes as subjects were presented with low- vs. high-contrast gratings of 0.1 – 5.8 cycle/deg., monocularly. When high-contrast stimuli were presented, iso-eccentric thin and thick stripes showed a stronger preference for high- and low-SF stimuli, respectively. This difference in SF preference between thin vs. thick stripes is consistent with our previous study in individuals with normal vision (Tootell and Nasr, 2017). For high-contrast stimuli, the activity evoked by stimulation of amblyopic- vs. fellow-eye remained equivalent. When low-contrast stimuli were presented, we found a significantly weaker response to higher (but not lower) SF in both stripes, in the amblyopic- vs. fellow-eye stimulation (p<0.01). In thin (but not thick) stripes, this effect led to a shift in response preference to lower SF values. These effects were detected in both strabismic and anisometropic individuals, ruling out the possibility that they are due to an interocular difference in uncorrected visual acuity. Thus, amblyopia has a stronger impact on low-contrast SF preference of thin (compared to thick) stripes.