When sharing a task with another person that requires turn taking, as in doubles games of table tennis, performance on the shared task is similar to performing the whole task alone. This has been taken to indicate that humans co-represent their partner’s task share, as if it were their own. Task co-representation allows prediction of the other’s responses when it is the other’s turn, and leads to response conflict in joint interference tasks. However, data from our lab cast doubt on (...) the view that task co-representation and resulting response conflict are the only or even primary source of effects observed in task sharing. Recent findings furthermore suggest another potential source of interference in joint task performance that has been neglected so far: Self-other discrimination and conflict related to agent identification (i.e., determining whether it is “my” or the other’s turn). Based on these findings we propose that participants might not always co-represent what their partner is supposed to do, but instead co-represent that another agent is responsible for part of the task, and when it is his turn. We call this account the actor co-representation account. (shrink)

A co-actor’s intentionality has been suggested to be a key modulating factor for joint action effects like the joint Simon effect (JSE). However, in previous studies intentionality has often been confounded with agency defined as perceiving the initiator of an action as being the causal source of the action. The aim of the present study was to disentangle the role of agency and intentionality as modulating factors of the JSE. In Experiment 1, participants performed a joint go/nogo Simon task next (...) to a co-actor who either intentionally controlled a response button with own finger movements (agency+/intentionality+) or who passively placed the hand on a response button that moved up and down on its own as triggered by computer signals (agency-/intentionality-). In Experiment 2, we included a condition in which participants believed that the co-actor intentionally controlled the response button with a Brain-Computer Interface while placing the response finger clearly besides the response button, so that the causal relationship between agent and action effect was perceptually disrupted (agency-/intentionality+). As a control condition, the response button was computer controlled while the co-actor placed the response finger besides the response button (agency-/intentionality-). We observed a JSE when the co-actor responded intentionally and the causal relationship between co-actor and action effect could be perceived, but not when the co-actor did not respond intentionally and the causal relationship was disrupted (Experiment 1). When the intentionality of the co-actor was maintained but the perception of the causal relationship between co-actor and action effect destroyed, the JSE was absent (Experiment 2). Our findings clearly indicate a vital role of a co-actor’s agency for the JSE and suggest that the ascription of agency is strongly perceptually grounded. (shrink)

Numerous studies have shown that stimulus-response-compatibility (SRC) effects in the go-nogo version of the Simon task can be elicited as a result of performing the task together with another human or non-human agent (e.g., a Japanese-waving-cat, a working-clock, or a ticking-metronome). A parsimonious explanation for both social and non-social SRC effects is that highlighting the spatial significance of alternative (non-/social) action events makes action selection more difficult. This holds even when action events are task-irrelevant. Recent findings, however, suggest that this (...) explanation holds only for cases of a modality correspondence between the Simon task as such (i.e., auditory or visual) and the alternative (non-/social) action event that needs to be discriminated. However, based on the fact that perception and action are represented by the same kind of codes, an event that makes the go-nogo decision more challenging should impact go-nogo Simon task performance. To tackle this issue, the present study tested if alternative stimulus events that come from a different sensory modality do impact SRC effects in the go-nogo version of the Simon task. This was tested in the presence and absence of alternative action events of a human co-actor. In a multimodal (auditory–visual) go-nogo Simon paradigm, participants responded to their assigned stimulus – e.g., a single auditory stimulus while ignoring the alternative visual stimulus or vice versa – in the presence or absence of a human co-actor (i.e., joint and single go-nogo condition). Results showed reliable SRCs in both, single and joint go-nogo Simon task conditions independent of the modality participants had to respond to. Although a correspondence between stimulus material and attention-grabbing event might be an efficient condition for SRCs to emerge, the driving force underlying the emergence of SRCs rather appears to be whether the attentional focus prevents or facilitates alternative events to be integrated. Thus, under task conditions in which the attentional focus is sufficiently broad to enable the integration and thus cognitive representation of alternative events, go-nogo decisions become more difficult, resulting in reliable SRCs in single and joint go-nogo Simon tasks. (shrink)