Megumi Kobayashi¹ (); ¹Niigata University

It is well known that visual perception and motor ability are interrelated in infants’ development; e.g., optical-flow perception drastically changed just before the emergence of voluntary locomotion (Shirai & Imura, 2013). We report evidence that motor development modulates infants’ face perception. In infancy, face input to infants would shift with their motor development. For instance, infants after rolling over tend to observe more upright or nearly upright faces, whereas infants before rolling over observe from various angles. These changes in visual input with motor development should modulate the development of face processing. In adults, a non-linear relationship between performance and the angle of rotation of faces is shown, which is a significant decline in face recognition between 60° and 90° (e.g., Rossion & Boremanse, 2008). These results imply the difficulty in configural face processing at orientations of faces that are less frequently experienced. We hypothesized that the non-linear relationship between face discrimination and picture-plane rotation in infants may change with motor development. To test this hypothesis, we examined face discrimination ability at various rotation angles (0° to 180°, 4 angles) in 3- to 8-month-old infants. We confirmed that infants showed significant face discrimination when presented upright (0°, p < .05) but not upside-down (180°, p > .05). Also, as shown in adults, they discriminated between faces at 60° (p < .05). At 120°, however, infants before rolling over showed significant discrimination (p < .05), whereas infants after rolling over did not (p = .19). Furthermore, infants after rolling over showed a significant negative correlation between face discrimination at 120° and the number of days from the date of acquisition of rolling over (p < 0.05). These findings suggest that alterations in face input associated with motor development play a pivotal role in the development of face perception.

Acknowledgements: This research was supported by Grant-in-Aid for Scientific Research (B) from JSPS (23H01055/23K25752)