Perception of human actions on the four fundamental dimensions of formidableness, friendliness, intentionality and abduction

We evaluate the actions of other individuals based upon their movements and postures that reveal critical information to guide our decision making and behavioural responses. These signals convey a range of information about the actor, including their goals, intentions and internal mental states. In order to understand the structure of the conceptual space underlying our perception of actions we assessed which action qualities were fundamental, and how individuals perceived actions on these dimensions. We recorded 240 different actions using motion-capture and used these data to animate a volumetric avatar. 230 participants then viewed these actions and rated the extent to which each action demonstrated 23 different action characteristics (e.g., avoiding-approaching, weak-powerful etc.). Exploratory Factor Analysis showed that action space was four-dimensional, with the factors (dimensions) of: friendly-unfriendly, formidable-feeble, intentional-accidental, and abduction-adduction. The first two factors of friendliness and formidableness explained approximately 22% of the variance each, compared to intentionality and abduction, which each explained approximately 7–8% of the variance. We developed an action morphing method that used source actions located at different positions within action space to generate novel actions that lay along the different action dimensions. Morphed actions that varied along each action space dimension were rated as varying monotonically along that dimension. Action discrimination along the action space dimensions was tested using adaptive 2-AFC procedures. We found considerable variation in perceptual thresholds, varying by up to ~1100%; this interindividual variation in action perception could not be explained by autistic traits. Together, our results show that actions are perceived on 4 fundamental quality dimensions. Friendliness and Formidableness appear similar to the principal factors underlying our evaluation of facial traits and emotions, while Intentionality and Abduction appear unique to actions. The isolation of these dimensions allows us to investigate the mechanisms underpinning our conceptual representation of human actions.