Approach and avoidance as action effects.

Numerous studies use arm movements (arm flexion and extension) to investigate the interaction between emotional stimuli and approach/avoidance behaviour. In many experiments, however, these arm movements are ambiguous. Arm flexion can be interpreted either as pulling (approach) or as withdrawing (avoidance). On the contrary, arm extension can be interpreted as reaching (approach) or as pushing (avoidance). This ambiguity can be resolved by regarding approach and avoidance as flexible action plans that are represented in terms of their effects. Approach actions reduce the distance between a stimulus and the self, whereas avoidance actions increase that distance. In this view, action effects are an integral part of the representation of an action. As a result, a neutral action can become an approach or avoidance reaction if it repeatedly results in decreasing or increasing the distance to a valenced stimulus. This hypothesis was tested in the current study. Participants responded to positive and negative words using key-presses. These "neutral" responses (not involving arm flexion or extension) were consistently followed by a stimulus movement toward or away from the participant. Responses to emotional words were faster when the response's effect was congruent with stimulus valence, suggesting that approach/avoidance actions are indeed defined in terms of their outcomes.