Predictive gaze in action observation: social learning in action
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How do we observe other people engaged in activities? Predictive gaze in action observation was first described in 2003 by Flanagan and Johansson who showed that in a block stacking task, observers, like actors, shifted their gaze to locations of upcoming contact events (objects to be grasped and object placement sites) around the same time that a hand movement was initiated. Later studies have shown that even when observers do not know what the actor is going to do next ahead of time, their gaze is still robustly drawn to contact events, typically arriving there before the actor's hand based on extrapolation of the ongoing action. Here I introduce an organizational framework for gaze behavior in action observation in terms of distinct modes of predictive gaze – anticipation, extrapolation, and tracking – and contextual factors shaping observer gaze behavior. These factors include the scene configuration as well as the timing, kinematics, and goals of the actor's movements, but also crucially depend on observers, their knowledge and skills, their perspective on the scene, as well as their own interest and goals. In the three studies presented here we investigate the proposal that observers, like actors, seek to closely monitor object contact events, including object lift-off, in part to learn about and keep track of object properties in the service of guiding future actions. In chapter 2 I describe and quantify social motor learning of object weight. In chapter 3 I show that when observing a demonstrator lift two objects at the same time, participants preferentially shift their gaze towards objects which they expect to subsequently act on themselves. In chapter 4 I describe how knowing the circumstances of an action (object value and distance) translates into predictive gaze behavior in action observation, characterize distinct gaze strategies, and evaluate their visual consequences for the observer. In the final chapter I apply this framework to critically review the current literature – which tends to conflate modes of predictive gaze – revisit the relationship between observer gaze behavior and the mirror neuron system, and review studies into the developmental trajectory of predictive gaze in action observation.