Yaoda Xu¹, Marvin Chun¹; ¹Yale University

An important aspect of understanding primate vision is to determine the key features in visual object coding. In the macaque inferotemporal (IT) cortex, spikiness and animacy are two principal features mediating the coding of a diverse array of objects, with distinctive IT subregions preferring unique combinations of these features (Bao et al., 2020). Similar results, however, were not observed in the human brain. Here, we constructed well-matched spiky and stubby stimuli and reexamined their coding in the human brain with fMRI. Using the output of a convolutional neural network shown to mirror the macaque IT cortex in spiky and stubby object representations, we selected pairs of inanimate spiky and stubby objects matched for semantic category (e.g., tripod vs. camera). The object images were further equated in low-level visual features, including luminance, contrast, and spatial frequency. Across 12 participants, contrasting spiky with stubby objects consistently revealed three areas preferring spiky objects: a small bilateral ventral activation between face- and scene-selective areas (proximal to the location of the macaque’s inanimate-spiky area), a large bilateral lateral activation within a separately localized body-selective area, and a bilateral dorsal activation along superior/anterior intra-parietal sulcus. Meanwhile, no areas were found to prefer stubby objects. The same three spiky areas were also activated when participants viewed matching animate spiky-stubby stimulus pairs (e.g., crane vs. penguin), indicating their spiky-object preference is animacy-independent. Furthermore, within the lateral body-selective area, only the posterior part truly preferred animacy/bodies, as it was activated by both the animate spiky and stubby objects compared to the inanimate ones; the anterior part of the lateral body-selective area prefers spikiness but not animacy/bodies. Together, these results document for the first time a network of human brain areas preferring spiky over stubby objects and highlight the potential importance of spikiness in human visual object perception.

Acknowledgements: This research was supported by NIH grant R01EY030854 to YX.