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

A central goal in human vision is to identify the key features supporting visual object representation in the human brain. Our recent fMRI work has identified several cortical regions preferring spiky over stubby objects, regardless of animacy, and regions preferring either animate or inanimate objects, independent of shape spikiness. These regions span ventral and lateral occipitotemporal cortex (OTC) and posterior parietal cortex (PPC), raising the question of how spikiness- and animacy-preferring areas relate to category-selective areas. Tool-selective areas are especially pertinent here, as they are typically localized by contrasting responses to tools vs animals, and many tools have elongated or pointed shapes. To investigate the relationship between tool-selective areas and areas modulated by object spikiness and animacy, we conducted an fMRI study in 16 right-handed participants. We identified regions selective for spikiness and animacy while participants viewed images from four stimulus categories, including spiky inanimate objects, stubby inanimate objects, spiky animate objects, and stubby animate objects. We separately localized the tool areas in these participants when they viewed images of tools and animals. We found that the tool-selective area lies exclusively within the intersection area responding to inanimate spiky objects in both OTC and PPC, showing that both animacy and spikiness mediate tool selectivity. This area overlap persisted even when tools were excluded from the inanimate objects, showing that shape, rather than the function of the inanimate object, was relevant here. The same results were obtained when object silhouettes were used to define brain areas, indicating that the effect reflects sensitivity to shape contours rather than surface details. Lastly, the same results were found when elongated spiky objects were excluded, showing that spikiness, rather than elongation, played a more critical role here. Together, these results show that both spikiness and inanimacy mediate tool representation in the human brain.

Acknowledgements: Supported by NIH Grant R01EY030854 to YX.