Coarse-Scale Biases for Spirals and Orientation in Human Visual Cortex

Abstract

Multivariate decoding analyses are widely applied to functional magnetic resonance imaging (fMRI) data, but there is controversy over their interpretation. Orientation decoding in primary visual cortex (V1) reflects coarse-scale biases, including an over-representation of radial orientations. But fMRI responses to clockwise and counter-clockwise spirals can also be decoded. Because these stimuli are matched for radial orientation, while differing in local orientation, it has been argued that fine-scale columnar selectivity for orientation contributes to orientation decoding. We measured fMRI responses in human V1 to both oriented gratings and spirals. Responses to oriented gratings exhibited a complex topography, including a radial bias that was most pronounced in the peripheral representation, and a near-vertical bias that was most pronounced near the foveal representation. Responses to clockwise and counter-clockwise spirals also exhibited coarse-scale organization, at the scale of entire visual quadrants. The preference of each voxel for clockwise or counterclockwise spirals was predicted from the preferences of that voxel for orientation and spatial position (i.e., within the retinotopic map). Our results demonstrate a bias for local stimulus orientation that has a coarse spatial scale, is robust across stimulus classes (spirals and gratings), and suffices to explain decoding from fMRI responses in V1.

Prospective motion correction improves the sensitivity of fMRI pattern decoding

“…Post hoc multiple comparisons also showed that regions with radial bias generates the largest LDC, in line with studies by Freeman et al (2013) and Tong et al (2010) which suggested that decoding in the visual cortex is strongly driven by radial bias rather than more fine‐grained response patterns. There was also a numerical trend that improvements due to PMC were stronger in non‐radial‐bias V1 subregions, where the spatial activation patterns may have been expected to be more fine grained.…”

“…Such fMRI effects may originate in the topography of underlying neuronal population codes. Specifically, neurons responding to radial orientations with respect to the fixation point appear to be more frequent, creating a global areal map of radial orientation frequencies (Freeman, Heeger, & Merriam, 2013; Sasaki et al, 2006). Neurons responding independently of radial bias are organized in a much finer‐grained columnar map of orientation preference (Alink et al, 2013; Swindale, Grinvald, & Shmuel, 2003; Tong et al, 2010).…”

Exploring structure and function of sensory cortex with 7 T MRI

“…The large-scale spatial pattern of the orientation-specific response on the cortical surface appears to be sufficient to allow decoding of stimulus orientation from such visual cortex fMRI measurements (Freeman, Heeger et al 2013). We have not specifically addressed this question in the current study, but the maps in our sample of subjects suggest that the edges of the stimulus annulus may show particularly strong biases that can drive such results (see e.g.…”

Representation of auditory motion directions and sound source locations in the human planum temporale

“…Studies conducted on early visual cortex proposed that classifying orientation preference reflects much larger scale (e.g. retinotopy) rather than columnar organization (Op de Beeck, 2010;Freeman et al, 2011Freeman et al, , 2013. Interestingly, high-field fMRI studies showed that the signal carries information related to both large-and fine-scale (columnar level) biases (Gardumi et al, 2016;Pratte et al, 2016;Sengupta et al, 2017).…”