Visual background information modulates motor contagions in humans

Abstract

Motor contagions refer to implicit effects induced by the observation of actions made by others on one's own actions. A plethora of studies conducted over the last two decades have demonstrated that both observed and predicted actions can induce various kinds of motor contagions in a human observer. However, motor contagions have always been investigated with regard to different features of an observed action, and it remains unclear whether the background environment in which an observed action takes place modulates motor contagions as well. Here, we investigated participant movements in an empirical hand steering task during which the participants were required to move a cursor through a visual channel after being presented with videos of an actor performing the same task. We manipulated the congruency between the actions shown in the video and the background channels and examined whether and how they affected the participants' own movements. We observed a clear interaction between the observed action and its background. The movement time of the participants' actions tended to increase or decrease depending on whether they observed a faster or slower movement, respectively, and these changes were amplified if the background was not congruent with the action contained within it. These results suggest that background information can modulate motor contagions in humans.

Figure 1

The experiments consisted of two types of blocks. (A) In an action block (act block), the participants performed a steering task in a straight channel (${\mathrm{C}}_{\mathrm{const}}$) as quickly as possible. (B) In an observation block (obs block), the participants watched videos of cursor motions implemented by unknown actors, who performed steering tasks with narrowing (${\mathrm{C}}_{\mathrm{nar}}$) or widening (${\mathrm{C}}_{\mathrm{wide}}$) channels. The combination of the actors’ motions and the channels in the observed video was controlled between sessions to create congruent and incongruent conditions (see Table 1). (C) Five act blocks were interspersed with four obs blocks in each session.

Figure 2

The x-velocity of the movement of each actor in each obs block condition (i.e., ${\mathrm{M}}_{\mathrm{wide}}$ and ${\mathrm{M}}_{\mathrm{nar}}$) and the first act block of each participant during the first session (i.e., the movements before the observation period) in Experiment-1. The right panel shows the average velocity values. The left panel shows the velocity observed during the channel passing task at every 10 mm in the x-direction of the channels. The error bars show the standard errors.

Figure 3

The error rates attained in Experiment-1. The left panel shows the error rate produced for each act block under each condition. The right panel shows the differences between the baseline and the average values obtained across blocks 2 to 5 under each condition. The error bars show the standard errors.

Figure 4

The peak distances attained during Experiment-1. The left panel shows the peak distance changes induced during the participants steering tasks conducted across the act blocks under each condition. The right panel shows the differences between the baseline and the average peak values attained across blocks 2 to 5 under each condition. The error bars show the standard errors.

Figure 5

The MTs yielded in Experiment-1. The left panel shows the changes exhibited by the participants’ MTs across the act blocks under each condition. The right panel shows the differences between the baseline and the average values produced across blocks 2 to 5 under each condition. The error bars show the standard errors. $_{}^{\ast }p<0.05$, $_{}^{\ast }_{}^{\ast }p<0.01$, $_{}^{\ast }_{}^{\ast }_{}^{\ast }p<0.001$.

Figure 6

The MTs yielded in Experiment-2. The left panel shows the changes exhibited by the participants’ MTs across the act blocks under each condition. The right panel shows the differences between the baseline and the average values produced across blocks 2 to 5 under each condition. The error bars show the standard errors. Note that the main effect of the presence of movement was significant according to a 2-way ANOVA ($p=0.046$).

Figure 7

The straight channel (upper image) and narrowing channel (lower image) used in the steering task.