Are visual deficits in amblyopia driven by spatial frequency tuning?

Amblyopia is characterized by visual deficits at high spatial frequencies. Prior work has demonstrated individuals with amblyopia have larger population receptive field (pRF) sizes in early visual areas, but how this increased RF size is linked to changes in spatial frequency tuning has yet to be determined. Model-based functional neuroimaging provides a method to map and interrogate how population spatial frequency tuning (pSFT) may differ in individuals with amblyopia. Here, we compared pSFT estimates to pRF maps in early visual cortex (V1–V3) in individuals with amblyopia and normally-sighted control participants. Monocular voxel-wise pRF and pSFT estimates were acquired in separate scanning sessions. We then compared pRF and pSFT estimates between eyes (amblyopic/non-dominant vs fellow/dominant eye) and between subject groups (amblyopia vs control). Across all individuals, RF size increased with eccentricity, and amblyopes had larger RF sizes compared to controls (p < 0.001), supporting previous findings. Moreover, spatial frequency preferences were higher and broader in amblyopes across V1–V3, and the amblyopic eye had broader bandwidths compared to the fellow eye. To compare pSFT and pRF estimates, we calculated a Scale Invariance metric, taking a ratio of preferred spatial frequency over pRF size (cycles per RF). The amblyopic eye showed fewer cycles per RF in central vision compared to the fellow eye and normally-sighted controls, consistent with deficits in the sampling of SF information in amblyopia. Together, our data suggest that differences in both RF size and spatial frequency tuning contribute to visual deficits observed in individuals with amblyopia.