The role of human movement kinematics in internal state inference

Abstract

The kinematics of our movements reflect our internal (mental and affective) states. This thesis tests the hypothesis that these kinematic signals contribute to judgments about others’ internal states through models based on our own actions. Chapter 1 details the theoretical background and previous literature that motivates this hypothesis. Chapter 2 (typical adults) and 3 (typical adolescents) test the hypothesis that we use models of our own action kinematics to make judgments about others’ affective states. Both experiments support the hypothesis by demonstrating that differences in one’s own typical action kinematics determine the perceived intensity of affective states of observed point-light walkers. Chapters 4, 5, and 6 examine the hypothesis that atypical movement kinematics in autism spectrum disorder (autism) contribute to social communication difficulties. Chapters 4 and 5 measure two basic skills required to make internal state judgments from observing others’ actions: visual time perception and sensitivity to kinematic signals that describe ‘natural’ motion. Both studies find no deficits in the autism group compared to the typically developed group – and some enhanced abilities – suggesting that these basic skills are intact. However, Chapter 6 demonstrates that typically developed individuals are impaired at reading mental states from autistic actions, suggesting that atypical movement kinematics may be partly contributing to bi-directional communicative difficulties experienced between individuals with autism and their typical peers. Chapter 7 investigates whether differences in movement kinematics early in development are associated with later social skills in a group of infants at high- or low-risk of developing autism. Indeed, movement kinematics at 10 months of age predicts social abilities at 14 months of age, demonstrating the value of kinematic markers for predicting social functioning and possibly disorder. Chapter 8 summarises the studies presented in this thesis, which show support for the hypothesis that we judge others’ internal states through models based on our own actions