Examining the retinotopic organization of the visual hierarchy in autistic and neurotypical individuals

As information ascends the visual hierarchy, smaller receptive fields that are selective for simple visual features combine to form larger ones that are selective for more complex features. Previous research demonstrates different receptive field sizes in lower levels of the autism visual hierarchy, which vary with symptom severity (Schwarzkopf et al., 2014). In this study, we examined whether such group differences propagate to the category-selective levels atop the visual hierarchy. We used population receptive field (pRF) analysis to test whether pRF sizes are atypical in both lower (early visual cortex, EVC) and higher levels (parahippocampal place area, PPA; occipital place area, OPA) of the visual hierarchy in individuals with autism spectrum conditions (ASC; n=6) compared to neurotypical controls (n=17). fMRI participants viewed traversing bar stimuli of scene fragments (4 orientations x 2 directions, each 36s, diameter=11.4°) and a traditional category localizer rapidly presenting blocks of scene, face, and object images. In both groups, pRF sizes grew with eccentricity in the EVC (one-way ANOVA, ASC p<0.001, Con p<0.001) with no interaction (Diagnosis*Eccentricity p>0.05). From EVC to category-selective areas, pRF sizes increased in both groups. In both groups, the size of pRFs in PPA was larger than those in EVC (two-sample t-test, ASC t(10)=-4.43, p<0.01, Con t(32)=-9.06, p<0.001). However, in both PPA and OPA (permutation-test, p<0.05) the ASC group had a smaller pRF size than that of controls, when comparable in EVC. These results show that the fine-grained visual architecture in autism differs from that of controls in category-selective areas. Specifically, we observe smaller pRFs in category-selective scene areas. Future work should explore pRF sizes in other category-selective areas, and how these relate to autistic sensory and cognitive traits.