Recently, the Simon effect (SE) has been observed in social contexts when two individuals share a two-choice task. This joint SE (JSE) has been interpreted as evidence that people co-represent their actions. However, it is still not clear if the JSE is driven by social factors or low-level mechanisms. To address this question, we applied a common paradigm to a joint Simon task (Experiments 1 and 4), a standard Simon task (Experiment 2), and a go/no-go task (Experiment 3). The results showed that both the JSE and the SE were modulated by the repetition/non-repetition of task features. Moreover, the JSE was differently modulated by the gender composition of the two individuals involved in the shared task and by their interpersonal relationship. Taken together, our results do not support a pure social explanation of the JSE, nevertheless, they show the independent role of different social factors in modulating the effect.

In stimulus-response compatibility tasks, performance is better when the handle of an object is oriented on the same side of the response than when the handle is oriented on the opposite side. Two major alternative accounts, the motor affordance and spatial accounts, have been proposed to explain this handle-hand compatibility effect. In two experiments, we tested between these two accounts by administering a go/no-go task to right-handed participants. Handled objects presented on a touchscreen were used as stimuli. Half of the participants had to reach-to-touch the stimuli by using their dominant hand, the other half by using their nondominant hand. Liftoff times (LTs), movement times (MTs) and spatial coordinates of the movement endpoints were recorded. Results from the LTs and MTs analyses showed no evidence of handle-hand compatibility effects. In contrast, the analyses of the spatial coordinates revealed that participants' touches were shifted more laterally towards the handle when the handles were oriented on the same side of the responding hand (Experiments 1 and 2). Furthermore, the right-hand touches landed higher (towards the handle) than the left-hand touches, especially when the vertical object dimension was particularly salient (Experiment 1). Overall, these results are in line with the activation of hand motor programs to reach and grasp the object as predicted by the motor account, at least for the right/dominant hand.

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