＜Abstract＞
A research team from the Vision and Action Laboratory, Visual Perception and Cognition Laboratory, and Cognitive Neurotechnology Unit in the Department of Computer Science and Engineering at Toyohashi University of Technology, led by Associate Professor Hideki Tamura, has demonstrated that, even when an object moves at the same physical speed, its approach is perceived as faster when it comes from behind than when it approaches from the front. Across five experiments using both a real autonomous mobile robot (AMR) and immersive virtual reality (VR), 92% of the participants consistently exhibited this perceptual bias, perceiving approaches from behind as faster than frontal approaches. The results further suggest that this phenomenon is unlikely to be explained by factors such as object appearance or motor noise, but is instead associated with vision-dependent factors that arise when observers turn around to view an approaching object from behind. Furthermore, by incorporating the experimentally observed perceptual bias into a robot navigation model, the researchers simulated a robot overtaking a pedestrian from behind. The simulation suggested that accounting for human perceptual characteristics results in avoidance trajectories that begin earlier while maintaining a greater distance from pedestrians than conventional navigation models.
The study was published in IEEE Robotics and Automation Letters on September 10, 2026.
https://doi.org/10.1109/LRA.2026.3732839
＜Main＞
In recent years, autonomous mobile robots (AMRs) have increasingly been deployed in a wide range of environments shared with humans, including logistics, delivery, and guidance services. To enable robots to navigate safely and naturally in such environments, it is important not only to prevent collisions but also to design robot behavior with consideration for how humans perceive robot motion. Previous studies have shown that people experience greater discomfort and prefer larger interpersonal distances when a robot approaches from behind rather than from the front. However, it has remained unclear whether the perceived speed of an approaching robot itself changes depending on the direction of approach. To address this question, the present study investigated, using psychophysical methods, how humans perceive the speed of objects approaching from the front and from behind.
The study consisted of five experiments. In the first experiment, a real autonomous mobile robot approached participants either from the front or from behind, and participants judged its approach speed. Before each trial, participants memorized two reference speeds (0.5 m/s and 1.0 m/s). They then judged whether a robot approaching at one of seven speeds between 0.5 and 1.0 m/s felt closer to the slower or faster reference speed.
The results showed that, even when moving at the same physical speed, a robot approaching from behind was consistently perceived as faster than one approaching from the front. Subsequent experiments further suggested that this perceptual bias was not attributable to body orientation during learning, the spatial relationship between the observer and the robot, object appearance, or motor noise. Instead, the findings indicate that the bias is associated with vision-dependent factors that arise when observers turn around to view an object approaching from behind.
The researchers then investigated how this perceptual characteristic could influence robot motion design. They incorporated the experimentally observed bias into a robot navigation model and simulated a scenario in which a robot overtakes a pedestrian from behind. Compared with the conventional model, the bias-corrected model initiated avoidance earlier and generated trajectories that maintained a greater distance from the pedestrian. When the largest experimentally observed perceptual bias was applied, the robot passed up to 0.40 m farther away from the pedestrian and initiated avoidance 0.57 s earlier than the baseline model.
Tatsuto Yamauchi, the first author of the study and a second-year Ph.D. student in the Department of Computer Science and Engineering, commented: "Robot speed has traditionally been considered only in terms of its physical value, such as how many meters per second a robot travels. Our findings show that humans perceive the same physical speed differently depending on the direction from which the robot approaches. As AMRs become increasingly common in everyday environments, designing robot motion based not only on physical safety but also on how humans actually perceive robot speed will contribute to safer, more comfortable, and more acceptable human–robot coexistence."
＜Future Directions＞
This study primarily investigated the perception of approach speed itself. Future research is needed to determine how this perceptual bias influences subjective comfort, perceived safety, and actual avoidance behavior during human–robot interactions. In addition, it will be important to examine whether similar perceptual characteristics are observed at speeds outside the range of 0.5–1.0 m/s and for robots with different sizes and shapes.
＜Publication＞
Yamauchi, T., Minami, T., Nakauchi, S., & Tamura, H. (2026). Speed perception bias for objects approaching from behind and its implications for robot motion design. IEEE Robotics and Automation Letters, Early Access: https://doi.org/10.1109/LRA.2026.3732839
＜Acknowledgments＞
This study was based on the results obtained from the JPNP20004 project subsidized by the New Energy and Industrial Technology Development Organization (NEDO). This work was supported by JST Grant Number JPMJPF2502, the Nitto Foundation, and the Foundation of Amano Institute of Technology.
Part of this work was supported by the Tokai Pathways to Global Excellence (T-GEx) program under the MEXT Strategic Professional Development Program for Young Researchers.
