Our visual system can recognize patterns across many spatial scales. A fundamental assumption in visual neuroscience is that this ability relies on the putative scale-invariant properties of receptive fields in early vision, whereby the spatial area over which a visual neuron responds is proportional to the spatial scale of information it can encode (i.e. spatial frequency). In other words, the resolution of spatial sampling of a receptive field is assumed to be constant in visual cortex. However, this assumption has gone untested in human visual cortex. To address this, we leveraged model-based fMRI techniques that characterize the spatial tuning and spatial frequency preferences of cortical subpopulations sampled within a voxel across eight participants (five female, three male). We find that the voxel-wise ratio between peak spatial frequency tuning and receptive field size — expressed as "cycles per receptive field" (CPF) — remains constant across visual areas V1, V2, and V3, suggesting that, at the population-level, spatial frequency preferences are inversely proportional to receptive field size, a tenet of scale invariance in early human vision. Significance Statement The human visual system interprets patterns across a range of spatial scales, a capability thought to rely on scale-invariant properties of receptive fields. Although widely assumed, this principle had not been directly tested in the human brain. Using model-based fMRI, we measured how population receptive field size and spatial frequency tuning vary across the visual field. We use a novel metric, cycles per receptive field (CPF), to reveal that spatial frequency preferences scale inversely with receptive field size across early visual areas (V1–V3). This provides the first direct evidence of scale invariance in the human visual cortex and offers a new framework for characterizing how spatial information is sampled and represented in early vision.
Wiecek et al. (Mon,) studied this question.