Co-actors represent the order of each other's actions

Abstract

Previous research has shown that people represent each other's tasks and actions when acting together. However, less is known about how co-actors represent each other's action sequences. Here, we asked whether co-actors represent the order of each other's actions within an action sequence, or whether they merely represent the intended end state of a joint action together with their own contribution. In the present study, two co-actors concurrently performed action sequences composed of two actions. We predicted that if co-actors represent the order of each other's actions, they should experience interference when the order of their actions differs. Supporting this prediction, the results of six experiments consistently showed that co-actors moved more slowly when performing the same actions in a different order compared to performing the same actions in the same order. In line with findings from bimanual movement tasks, our results indicate that interference can arise due to differences in movement parameters and due to differences in the perceptual characteristics of movement goals. The present findings extend previous research on co-representation, providing evidence that people represent not only the elements of another's task, but also their temporal structure.

Keywords: Action sequence; Bimanual control; Co-representation; Coordination; Joint action; Social cognition.

Fig. 1

Schematic depiction of a joint action situation in which two co-actors perform the same actions in a different order (i.e., B-A vs. A-B), with the joint goal of synchronizing the end state of their action sequences.

Fig. 2

Sketch of experimental setup for Experiments 1–3, with co-actors performing long and short movements either in the same order (A) or in a different order (B). Distances are in cm.

Fig. 3

Four types of blocks in Experiments 1–3. Participants performed sequences of two movements of differing distance, in the order ‘short-long’ or ‘long-short’. The two participants in a pair either performed the same sequence or a different sequence. Note that in the ‘different order’ condition (right column) the labels ‘short-long’/‘long-short’ apply to the order for participant P1 only.

Fig. 4

(A) Displays used in Experiments 1–5 to instruct participants to perform action sequences in the ‘same order’ or in a ‘different order’. ‘Neutral’ refers to the uninformative displays that were presented while co-actors performed the task in Experiments 2–5. (B) The fourth column shows the displays used in the individual baseline.

Fig. 5

Movement times (i.e., times between movement onset at start location and movement offset at final target) for the ‘same order’ and the ‘different order’ condition for Experiments 1–3. The target configurations displayed on the bars serve only as exemplary representations of the two conditions. Participants’ movement times were significantly longer when the co-actor performed her actions in a different order. Error bars indicate Standard Errors. (^*p < .05; ^**p < .01; ^***p < .001).

Fig. 6

Four types of blocks in Experiment 4. Participants performed sequences of two movements to targets of different sizes, in the order ‘big-small’ or ‘small-big’. The two participants in a pair either performed the same sequence or a different sequence. Note that in the ‘different order’ condition (right column) the labels ‘big-small’/‘small-big’ apply to the order for participant P1 only.

Fig. 7

Movement times for the ‘same order’ and the ‘different order’ condition for Experiments 4–6 (where ‘same’/‘different’ corresponds to ‘4 colors’/‘2 colors’ in Exp. 6). In all experiments, participants' movement times were significantly longer when the co-actor performed her actions in a different order. Error bars indicate Standard Errors. (^**p < .01; ^***p < .001).

Fig. 8

Four types of blocks in Experiment 5. Participants performed sequences of two movements to targets of different colors, in the order ‘yellow-brown’ or ‘brown-yellow’. The two participants in a pair either performed the same sequence or a different sequence. Note that in the ‘different order’ condition (right column) the labels ‘yellow-brown’/‘brown-yellow’ apply to the order for participant P1 only.

Fig. 9

Four types of blocks in Experiment 6. Participants performed sequences of two movements to targets of different colors. In blocks of the ‘4 colors’ condition (left column), the target colors were different for the two participants in a pair such that P1’s colors were pink and blue while P2’s colors were green and purple. In blocks of the ‘2 colors’ condition (right column), the two participants shared the same set of brown and yellow targets but the order in which the colors occurred was different (e.g., P1: brown-yellow, P2: yellow-brown).