Autism spectrum disorder (ASD) is defined by social impairments (American Psychiatric Association 1994
), but the exact nature of these impairments remains a matter of debate (e.g. Dinstein et al. 2008
). According to a recent hypothesis, individuals with ASD fail to map observed actions onto motor representations of these actions, owing to a dysfunctional mirror neuron system (MNS; Dapretto et al. 2006
). ‘Mirror neurons’, first found in the premotor area (F5) of the macaque, respond both when the animal performs a particular transitive (object-directed) action and when the animal observes another individual perform a similar action (Gallese et al. 1996
). This suggests that mirror neurons constitute a basic link between self and other and, potentially, a dysfunction in the MNS could explain why individuals with ASD often have difficulties understanding other people. This view is supported by studies showing reduced activation in the MNS during observation of actions in ASD compared with controls (e.g. Oberman et al. 2005
; Theoret et al. 2005
). To the authors' knowledge, none of the studies directly supporting the ‘broken mirror’ theory of ASD have used stimuli containing transitive actions. This is noteworthy, given that mirror neurons fire in response to transitive actions, while they do not respond to intransitive actions, or when objects are presented in isolation (Gallese et al. 1996
Electrophysiological data suggest that mirroring is an anticipatory process (Nishitani & Hari 2000
; Kilner et al. 2004
; Aglioti et al. 2008
). Furthermore, behavioural studies of typically developing humans show that strikingly similar predictive eye movements are used both when one executes transitive actions oneself and when one observes similar actions performed by other people (Flanagan & Johansson 2003
), and that predictive gaze during action observation is inhibited by simultaneous execution of simple sequential finger movements, but not by rehearsing sequences of numbers (Cannon & Woodward 2008
). These results indicate that predictive eye movements in action observation reflect an engagement of motor plans in the observer.
Against this background, it was reasoned that if children with ASD have a dysfunctional MNS and consequently use general purpose visual mechanisms in action observation, their gaze is expected to track the actor's hand, and arrive reactively at goal sites. Conversely, if children with ASD use action plans in action observation, gaze should predict upcoming goals by moving to the goal sites ahead of time. These alternative scenarios were evaluated using an eye-tracking method.