# Coordinating Entrainment Phenomena: Robot Conversation Strategy for Object Recognition
## 6. Experiment 2
### Discussion
#### 6.3.2 Comparison of Referencing Style  
To compare referencing style between implicit entrainment and explicit request, we investigate (1) the mean number of object attributes and pointing gestures in the references per conversation session and (2) the rate of the redundant reference in the same way as described in Sections 5.2.2 and 5.2.3, respectively. First, we investigate whether the number of object attributes and pointing gestures in the references changed depending on the robot's conversation strategy. Table 3 shows the results. The results of a paired t-test showed that no significant difference existed in the mean number of object attributes (t(25) = 1.677, \(p\) = 0.106, \(d\) = 0.29), but a significant difference was found for the mean number of pointing gestures (t(25) = 4.477, \(p\) < 0.001, \(d\) = 0.19), with the explicit request eliciting more pointing gestures than the implicit entrainment. These results indicate that humans refer to an object by using a similar amount of object information in speech with both the explicit request and the implicit entrainment, and they refer to an object with more pointing gestures in the conversations with the explicit request than with the implicit entrainment. Second, we investigate the rate of the redundant reference per conversation session (ten times object reference conversations). Figure 16 shows the results. The results of a paired \(t\)-test showed that a significant difference existed in the rate of the redundant reference (t(25) = 5.21, \(p\) < 0.001, \(d\) = 1.00). These results indicate that humans use more redundant reference to the robot with explicit request than with implicit entrainment. It is assumed that this significant difference is caused by the significant difference of the number of pointing gestures, because we found no significant difference for the number of object attributes in references. The rate of redundant reference is significantly different between the two strategies; however, the recognition performance is not significantly different between the two strategies (shown in Figure 12). These results seem that both the explicit request and the implicit entrainment strategies elicit sufficient speech and pointing gestures to identify an object with the same level of accuracy at least in our experimental settings. Even in the conversations with the implicit entrainment elicits enough pointing gestures to identify an \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Implicit** & **Explicit** \\ \hline Attributes & 2.5 (0.12) & 2.6 (0.11) \\ Pointing gestures & 0.58 (0.093) & 0.98 (0.016) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of mean number of object attributes and pointing gestures included in references with standard error between explicit request and implicit entrainment strategy. indicated object, and enough object attributes in speech are obtained in each strategy. Therefore, a significant difference of the mean number of pointing gestures exists, and from the viewpoint of the success rate of the recognition, it is considered that there are few substantive differences in the human's reference behaviors. However, in the situation where pointing gestures are important to recognize an indicated object, e.g., robots have no speech recognition function and objects that have similar characteristics are arranged separately if the robots elicit many pointing gestures by making an explicit request, the recognition performance might improve. In Experiment 2, we only used the congestion object arrangement because the recognition performance in the congestion settings is lower than the recognition performance in the sparse set and two groups when the robot did not use the proposed strategy in Experiment 1, and we assumed the congestion arrangement is suitable for comparison between two interactive strategies.