# Vocal Synchrony of Robots Boosts Positive Affective Empathy
## 6 Discussion  
The results of the subjective responses consistently indicated that the participants felt stronger affective empathy-related feelings in response to the robot that vocally synchronized with them compared with the robot that did not. These results supported out H1. Moreover, those results are consistent with previous psychological findings such that vocal synchronization enhances empathic communications in humans [25; 29], and they agree with other findings from previous robotics studies [23; 24]. However, because no previous study has investigated the effects of a robot's vocal synchronization on conversations with humans, to the best of our knowledge, the present study provides the first evidence of robot synchronization with a human voice to boost empathic feelings. \begin{table}
\begin{tabular}{l l l l} \hline \hline \multirow{2}{*}{**Measure**} & \multicolumn{3}{c}{**Statistic**} \\ \cline{2-4}  & \(t\) & \(p\) & \(d\) \\ \hline Corrugator supercili EMG & 2.02 & 0.027 & 0.54 \\ Zygomatic major EMG & 1.73 & 0.047 & 0.28 \\ SCL & 1.72 & 0.049 & 0.48 \\ \hline \hline \end{tabular} EMG: electromyography; SCL: skin conductance level.  
\end{table} 
Table 3: Results of one-sample \(t\)-tests for the intra-individual correlation coefficients of the expected subjective physiological concordance across the stimuli. Figure 6: Means with standard error of the facial electromyography from the corrugator supercilii (left image), zygomatic major muscles (middle image), and skin conductance level (right image); \({}^{*}p<0.05\). The participants' physiological responses showed that the synchronization condition induced lower corrugator activity, higher zygomatic activity, and higher SCL. Based on the ample evidence regarding the association between these physiological measures and subjective emotional responses [34; 35], the facial EMG data jointly indicate more positive valence, and the SCL data indicate stronger arousal in response to the robot that vocally synchronized with them compared with the robot that did not. These data complement the subjective ratings and provide objective evidence that a robot that can vocally synchronize with users can enhance empathic responses. These results supported out H2. These findings have practical significance for the development of dialog robots. Specifically, it might be possible to facilitate human-robot rapport by equipping robots with vocal synchrony ability. This can enable robots to gain social value as conversation partners because it will be easier for users to accept active assertions from robots. In turn, users can realize other benefits such as behavior modification or self-reliance support. These results also have theoretical implications for human empathic communication. Although several previous psychological studies of humans have suggested that vocal synchrony can induce empathic feelings [28], other research failed to indicate such an effect [25; 29]. This discrepancy can be attributed at least partially to the difficulty in implementing vocal synchrony in humans while controlling other confounding variables (e.g., volume). Our experiment with the robot clearly shows that vocal synchrony boosts empathic feelings during conversation. Among the participants who favored the de-synchronization condition, no negative opinions toward the scenarios were indicated; however, some impressions toward the voice of the robot were observed. One participant provided the following free descriptions regarding the robot under the synchronization condition: \"The conversation was fast, and I did not get a good impression\"; \"the robot talked to me according to my way of speaking, but it felt like I was concerned, and it was difficult to talk\"; and \"one of the topics was good, but in the other topic, I felt that the robot seemed boring.\" On the basis of these opinions, we determined that in some cases, the de-synchronization condition might lead to better impressions with a participant than that occurring under the synchronization condition.