Megumi Kobayashi¹ (mkobayashi@human.niigata-u.ac.jp); ¹Niigata University

A specialized mechanism for the visual processing of human bodies is well established. One well-known example is the body inversion effect (BIE), in which discrimination performance is poorer for inverted bodies than for upright bodies (e.g., Reed et al., 2003). Recent work, however, has shown that the BIE is markedly reduced for headless bodies (Yovel et al., 2010), suggesting that the head is critical for holistic body representation. Developmental studies have reported the BIE in infancy (e.g., Zieber et al., 2015), and neuroimaging work has demonstrated cortical responses specific to human bodies (Kobayashi et al., 2021). Yet, little is known about how infants represent bodies and the role of the head. The present study examined 5- to 8-month-old infants’ ability to discriminate postures of whole and headless bodies presented upright or inverted. We employed a familiarization/novelty-preference procedure. A pre-test confirmed no spontaneous preference for either posture. Infants were familiarized with a full-color image of a particular posture and then tested for visual preference toward a novel posture as an index of discrimination. In the whole-body condition, infants showed a significant preference for the novel posture in the upright presentation (all ps < .01) but not in the inverted presentation (all ps > .1), demonstrating the BIE. In the headless-body condition, 5- and 6-month-old infants also showed the BIE (p < .05), similar to the whole-body condition. In contrast, 7- and 8-month-old infants did not show the BIE, with no significant discrimination in either orientation (ps > .1). These findings suggest that infants younger than 6 months possess relatively independent holistic representations of bodies and faces, such that removing the head does not disrupt body processing. By 7-8 months, however, infants appear to develop a more integrated, adult-like “whole body” representation in which the head plays a critical role.

Acknowledgements: This study was supported by Grant-in-Aid for Scientific Research from JSPS (19K14492, 23K25752)