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At the fovea, face identity recognition preferentially relies on horizontally-oriented face information. Since radially oriented input is privileged in the periphery, along the horizontal meridian (HM) the engagement of face-selective mechanisms is enhanced. We previously showed that subject-level radial bias predicts the speed of saccadic eye movements toward faces. Here, we investigated whether this functional link is due to basic-level face categorization in the periphery being shaped by the radial bias. Thirty-two participants were tested using Fast Periodic Visual Stimulation (FPVS) combined with EEG. Face images were periodically embedded at 1.2 Hz within rapid streams of non-face objects presented at 6 Hz. This frequency-tagging approach allows face categorization responses to be objectively isolated at predefined frequencies with high signal-to-noise ratio. It enables dissociating high-level categorization responses to faces (1.2 Hz, i.e. face oddball frequency) from general visual responses to stimulus sequences (6 Hz, i.e. base frequency). Stimuli were presented at four peripheral locations (left, right, up, down). Neural response to face oddball frequency was localized on occipitotemporal electrodes with a significant right lateralization. This neural marker of face categorization was strongest along the horizontal meridian. It was also stronger in the upper than in the lower visual field in line with past evidence. In contrast, the general visual response at 6 Hz was maximal in the lower visual field, consistent with known low-level visual anisotropies. Together, these results indicate a clear distinction in visual field anisotropy between high-level face categorization responses and low-level visual reponses. Basic-level face categorization in the periphery is most robust along the horizontal meridian, likely reflecting enhanced access to diagnostic horizontal information. These findings indicate that radial bias selectively modulates horizontal–vertical meridian anisotropies at high-level, category-selective stages of visual processing, following a pattern that is qualitatively distinct from low-level visual responses.
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Grandjean, M., Dumont, H., Rossion, B., & Goffaux, V. (2026). Human face categorization is radially-biased: Fast periodic visual stimulation evidence. European Conference on Visual Perception, Bournemouth, UK. https://hdl.handle.net/2078.5/277673