TY - JOUR A1 - Stenzel, Anna A1 - Dolk, Thomas A1 - Colzato, Lorenza S. A1 - Sellaro, Roberta A1 - Hommel, Bernhard A1 - Liepelt, Roman T1 - The joint Simon effect depends on perceived agency, but not intentionality, of the alternative action JF - Frontiers in human neuroscienc N2 - 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 (BCI) 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-). Experiment 1 showed that the JSE is present with an intentional co-actor and causality between co-actor and action effect, but absent with an unintentional co-actor and a lack of causality between co-actor and action effect. Experiment 2 showed that the JSE is absent with an intentional co-actor, but no causality between co-actor and action effect. Our findings indicate an important role of the co-actor's agency for the JSE. They also suggest that the attribution of agency has a strong perceptual basis. KW - joint Simon effect KW - joint action KW - social interaction KW - stimulus-response compatibility KW - agency Y1 - 2014 U6 - https://doi.org/10.3389/fnhum.2014.00595 SN - 1662-5161 VL - 8 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Hartmann, Matthias A1 - Fischer, Martin H. A1 - Mast, Fred Walter T1 - Sharing a mental number line across individuals? The role of body position and empathy in joint numerical cognition JF - The quarterly journal of experimental psychology N2 - A growing body of research shows that the human brain acts differently when performing a task together with another person than when performing the same task alone. In this study, we investigated the influence of a co-actor on numerical cognition using a joint random number generation (RNG) task. We found that participants generated relatively smaller numbers when they were located to the left (vs. right) of a co-actor (Experiment 1), as if the two individuals shared a mental number line and predominantly selected numbers corresponding to their relative body position. Moreover, the mere presence of another person on the left or right side or the processing of numbers from loudspeaker on the left or right side had no influence on the magnitude of generated numbers (Experiment 2), suggesting that a bias in RNG only emerged during interpersonal interactions. Interestingly, the effect of relative body position on RNG was driven by participants with high trait empathic concern towards others, pointing towards a mediating role of feelings of sympathy for joint compatibility effects. Finally, the spatial bias emerged only after the co-actors swapped their spatial position, suggesting that joint spatial representations are constructed only after the spatial reference frame became salient. In contrast to previous studies, our findings cannot be explained by action co-representation because the consecutive production of numbers does not involve conflict at the motor response level. Our results therefore suggest that spatial reference coding, rather than motor mirroring, can determine joint compatibility effects. Our results demonstrate how physical properties of interpersonal situations, such as the relative body position, shape seemingly abstract cognition. KW - Mental number line KW - random number generation KW - joint action KW - joint Simon effect KW - empathy KW - Interpersonal Reactivity Index Y1 - 2019 U6 - https://doi.org/10.1177/1747021818809254 SN - 1747-0218 SN - 1747-0226 VL - 72 IS - 7 SP - 1732 EP - 1740 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Sellaro, Roberta A1 - Dolk, Thomas A1 - Colzato, Lorenza S. A1 - Liepelt, Roman A1 - Hommel, Bernhard T1 - Referential Coding Does Not Rely on Location Features: Evidence for a Nonspatial Joint Simon Effect JF - Journal of experimental psychology : Human perception and performance N2 - The joint Simon effect (JSE) shows that the presence of another agent can change one's representation of one's task and/or action. According to the spatial response coding approach, this is because another person in one's peri-personal space automatically induces the spatial coding of one's own action, which in turn invites spatial stimulus-response priming. According to the referential coding approach, the presence of another person or event creates response conflict, which the actor is assumed to solve by emphasizing response features that discriminate between one's own response and that of the other. The 2 approaches often make the same predictions, but the spatial response coding approach considers spatial location as the only dimension that can drive response coding, whereas the referential coding approach allows for other dimensions as well. To compare these approaches, the authors ran 2 experiments to see whether a nonspatial JSE can be demonstrated. Participants responded to the geometrical shape of a central colored stimulus by pressing a left or right button, while wearing gloves of the same or different color as the stimuli. Participants performed the task individually, either by responding to either stimulus shapes (Experiment 1) or by responding to only 1 of the 2 shapes (Experiment 2), and in the presence of a coactor. Congruence between stimulus and glove color affected performance in the 2-choice and the joint tasks but not in the individual go/no-go task. This demonstration of a nonspatial JSE is inconsistent with the spatial response coding approach but supports the referential coding approach. KW - joint Simon effect KW - referential coding KW - spatial response coding KW - dimensional overlap KW - compatibility effect Y1 - 2015 U6 - https://doi.org/10.1037/a0038548 SN - 0096-1523 SN - 1939-1277 VL - 41 IS - 1 SP - 186 EP - 195 PB - American Psychological Association CY - Washington ER -