Joint Simon effects for non-human co-actors.

Social interactions with non-biological agents and interactions with technical devices have become increasingly important over the last years. Recent studies investigating the interactions between humans and non-human agents showed rather inconsistent results. While the joint Simon effect (cSE) was found to be absent for non-human co-actors like virtual wooden hands, other studies showed pronounced cSEs when the co-actor was a real event-producing object. However, an often overlooked difference between these studies is the way these co-actors delivered response events. Studies replacing the co-actor by event-producing objects used a continuous response mode, while in studies using wooden hands, the co-actor always produced action effects in a task-related, turn-taking mode. In a series of four experiments, we systematically tested the effects of the response mode on the size of the cSE. The cSE was larger when the co-actor produced events in a turn-taking response mode than in a continuous response mode. Furthermore, we consistently found reliable cSEs for different kinds of virtual non-human co-actors (including a Japanese waving cat, scrambled patterns, and a wooden hand), and found no difference in the size of the cSE between human and non-human co-actors. We discuss possible mechanisms explaining why a cSE might be present or absent when sharing tasks with virtual non-human co-actors.