The most common explanation for joint-action effects has been the action co-representation account in which observation of another's action is represented within one's own action system. However, recent evidence has shown that the most prominent of these joint-action effects (i.e., the Social Simon effect), can occur when no co-actor is present. In the current work we examined whether another joint-action phenomenon (a movement congruency effect) can be induced when a participant performs their part of the task with a different effector to that of their co-actor and when a co-actor's action is replaced by an attention-capturing luminance signal. Contrary to what is predicted by the action co-representation account, results show that the basic movement congruency effect occurred in both situations. These findings challenge the action co-representation account of this particular effect and suggest instead that it is driven by bottom-up mechanisms.

A growing number of studies have begun to assess how the actions of one individual are represented in an observer. Using a variant of an action observation paradigm, four experiments examined whether one person’s behaviour can influence the subjective decisions and judgements of another. In Experiment 1, two observers sat adjacent to each other and took turns to freely select and reach to one of two locations. Results showed that participants were less likely to make a response to the same location as their partner. In three further experiments observers were asked to decide which of two familiar products they preferred or which of two faces were most attractive. Results showed that participants were less likely to choose the product or face occupying the location of their partner’s previous reaching response. These findings suggest that action observation can influence a range of free choice preferences and decisions. Possible mechanisms through which this influence occurs are discussed.

A number of studies have shown that the motor actions of one individual can affect the attention of an observer. In one notable example, "social inhibition of return," observers are relatively slow to initiate a response to a location where another individual has just responded. In the present article we examine the degree to which this phenomenon can be considered a social effect. We find that unlike the related social, or "joint," Simon effect, social inhibition of return is not influenced by competitive versus cooperative interaction, nor by live versus recorded interaction. We do find however that co-actors need to turn-take in order for the effect to occur. Thus, so-called "social" inhibition of return only reaches a minimal threshold to be considered a social phenomenon.

When two individuals alternate reaching responses to targets located in a visual display, reaction times are longer when responses are directed to where the co-actor just responded. Although an abundance of work has examined the many characteristics of this phenomenon it is not yet known why the effect occurs. In particular, some authors have argued that action representation mechanisms are central to the effect. However, here we present evidence in support of an account in which the representation of action is not necessary. First, the basic effect occurs even when participants cannot see their co-actor's movement but, importantly, have their attention shifted to a target side via an attentional cue. Second, its time course is too short-lasting to function effectively as a component of action planning. Finally, unlike other joint action phenomena, the effect is not modulated by higher order mechanisms concerned with the personal attributes of a co-actor. Taken together, these results suggest that this particular joint action phenomenon is due to attentional rather than action mechanisms.

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