# Subjective Distance Estimates and Sense of Agency in Robotic Wheelchair Control
## 4 General Discussion
In order to corroborate either explanation, we decided to supplement information about the subject's state with a minor EEG study. Importantly, our behavioral study has one serious methodological limitation. It lacked a condition where the wheelchair would move automatically and a participant would be instructed to stop it after the sound. If such a condition had been included, we would have a better understanding of whether the causes of the sound were necessary to produce the effect. In Experiment 2, we tested a reliable indicator of SoA--the N1 component of the auditory ERP. It is known that attention to a sound affects the parameters of the component: its latency and amplitude increase. Voluntary control over the sound, on the contrary, leads to a decrease in the amplitude. We added two control conditions to the procedure, with participants listening to either random sounds (CtrlRand) or self-generated sounds (CtrlSelfgen). These conditions were included to reproduce the classical result for N1-P2 amplitude suppression and to compare the latencies of the component in these conditions to those in the Act and Exp conditions. Ultimately, the N1 suppression in the CtrlSelfgen condition was replicated, and the latencies were significantly smaller in the CtrlSelfgencondition. The amplitudes did not differ much in the Act and Exp conditions, and were even slightly greater in the Exp condition. If attention were to play a critical role in the response to the sound, one would expect significantly higher amplitudes in the Act condition. In addition, the amplitudes in the Act and Exp conditions occupied an intermediate position in magnitude between the amplitudes in the control conditions. However, it should be noted here that comparing the ERP parameters in the conditions with a static wheelchair with the conditions where it is moving is not entirely appropriate. A significant difference between the Act and Exp conditions emerged in the latencies of component N1: the latencies were significantly smaller in the Act condition. This difference is similar to that observed for the control conditions. In sum, the results obtained for the latencies support the fact that participants perceived the sound in the Act condition as self-generated, at least to some extent. This assertion would be more robust if a significant reduction in the N1 amplitude was obtained in the Act condition. Accordingly, we believe it is reasonable to conclude that the difference between the main conditions in Experiment 1 is best explained by the presence of the participant's SoA in the Act condition and its absence in the Exp and Rem conditions. Even if the participants did not think their actions were causing the sound, they nevertheless believed they were in control of the wheelchair in the Act condition. The sense of control scores in respective conditions confirm this thesis, and the EEG study corroborates it further. The effect associated with distance estimates that we identified can potentially be used to assess the involvement of the agent in controlling various means of transportation. In particular, this indicator may provide a way to compare different ways of piloting a vehicle for perceived control. However, this study had several important features that set it apart from similar experiments. It is important that the effect be investigated further, and that it proves to be reproducible under differing conditions. Currently, it is impossible to say exactly why the distance estimation effect was inverted in our design.