Boyang Hu¹, Marvin Chun¹, Yaoda Xu¹; ¹Yale University

The hallmark of primate vision is its ability to extract and represent different visual features from the surrounding environment, allowing us to easily recognize and interact with the objects in the natural world. Subregions of the macaque inferotemporal (IT) cortex have been shown to respond differentially to spiky and stubby objects (Bao et al., 2020). Extending this result, we recently unveiled several distinct regions preferring spiky over stubby objects in the human IT cortex for both animate and inanimate stimuli. To understand what is driving this spiky-object preference, we carried out two fMRI experiments to examine how the relative body-to-limb aspect ratio (Experiment 1) and the number of limbs on a body (Experiment 2) affect responses in areas preferring spiky objects. Using the output of a Convolutional Neural Network previously shown to mirror macaque IT’s representations of stubby and spiky objects, in Experiment 1, we collected a set of four-legged mammal stimuli varying in body-to-limb aspect ratio, from stubbier mammals with large bodies and short limbs (e.g., wombat) to spikier mammals with skinny bodies and long legs (e.g., greyhound). Preliminary results showed that in visual areas preferring spiky objects, fMRI responses somewhat tracked the body-to-limb aspect ratio, being greater for greyhounds than wombats, but also high for animals with intermediate ratios, such as puma. In Experiment 2, using images of ceiling fans with 3, 5, 8, or 12 blades to vary the number of limbs on the hub, preliminary results showed that the areas preferring spikiness exhibited a U-shaped response profile, with responses being higher for 3- and 12-blade fans than for 5- and 8-blade ones. Our study constitutes a first step toward a better understanding of what aspects of an object’s shape drive the responses in areas preferring spiky objects in the human visual cortex.

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