＜Abstract＞
Researchers from the Cognitive Neurotechnology Unit, Vision and Action Laboratory, and Visual Perception and Cognition Laboratory in the Department of Computer Science and Engineering at Toyohashi University of Technology have conducted a psychophysical study using virtual reality (VR) to investigate how humans flexibly use exploratory behaviors—such as changing their viewpoint by moving their head and manipulating objects with their hands—when discriminating the material properties of objects. Participants wore a head-mounted display and freely observed and manipulated virtual objects while judging whether each object appeared more metallic or more glass-like. The results showed that the more ambiguous the material was between metal and glass, the more actively participants explored it by moving their heads and hands. Moreover, individual differences in these exploratory behaviors were associated with a tendency to discriminate material properties more accurately. The researchers also found that participants flexibly switched their exploration strategies depending on the viewing context: they relied more on head movements to change their viewpoint when multiple objects could be compared simultaneously, whereas they relied more on hand movements to manipulate the object when only a single object was available for observation. These findings suggest that human material perception may rely not only on passively seeing an object, but also on actively seeking the visual information needed for material discrimination by moving the head and hands.
The study was published in Journal of Vision on June 8, 2026. https://doi.org/10.1167/jov.26.6.4
＜Main＞
Humans identify the material properties of objects by using visual cues such as surface gloss, transparency, reflections, and distortions of the background. For example, metals reflect the surrounding environment like a mirror, whereas glass transmits and refracts the background. However, depending on the surrounding environment and viewing direction, metal and glass can appear remarkably similar. In such situations, it can be difficult to determine the material from a single frontal view. Just as a gemologist examines a gemstone from different angles, humans may obtain visual information useful for material discrimination by changing their viewpoint or manipulating the object.
To investigate this possibility, we created computer-generated objects whose material appearance varied continuously from metal to glass in a VR environment and examined how participants observed and manipulated these objects while discriminating their materials. Participants sat on a chair wearing a head-mounted display and were free to change their viewpoint by moving their head while translating and rotating virtual objects using handheld controllers. Throughout the experiment, we recorded head position and orientation, object manipulations, and exploration time.
In Experiment 1, the participants freely manipulated a target object and continuously rated whether it appeared more metallic or more glass-like. The results showed that the more ambiguous the material was between metal and glass, the more extensively and frequently participants manipulated the object during observation. Furthermore, individual differences in exploratory behavior were associated with a tendency to discriminate material properties more accurately.
In Experiment 2, we investigated the relative importance of viewpoint changes (moving the head to change one's viewpoint) and object manipulation (moving the object by hand) for material discrimination. To this end, we created four experimental conditions in which viewpoint changes and object manipulation were independently enabled or disabled. Participants compared one target object with two reference objects presented simultaneously and judged whether the target appeared to be metal or glass. The results showed that when multiple objects could be compared simultaneously, changing one's viewpoint by moving the head was more effective for material discrimination than manipulating the object by hand.
In Experiment 3, the reference objects were removed, and participants judged whether a single target object appeared to be metal or glass. In contrast to Experiment 2, the benefit of changing one's viewpoint by moving the head was reduced, whereas manipulating the object by hand became more effective for material discrimination. These findings suggest that humans do not rely on a single exploration strategy but instead flexibly switch between viewpoint changes and object manipulation according to the visual information available in a given situation.
A more detailed analysis of participants' exploratory behaviors further revealed substantial individual differences in exploration strategies, such as bringing the object closer, moving closer to the object, and observing it from above or below. These findings suggest that material perception is not merely a passive process of observing an object from a fixed viewpoint, but rather an active perceptual process in which observers move their head and hands to actively seek the visual information necessary for material discrimination.
The co-first author of the study, Ryu Nomachi, a second-year master's student in the Department of Computer Science and Engineering at Toyohashi University of Technology, commented: "When we look at an object, we are not simply processing the image that reaches our eyes. Whenever it is difficult to make a judgment, we naturally move our head or manipulate the object with our hands to seek the information we need. Our findings suggest that these everyday exploratory behaviors may play an important role in acquiring the visual information necessary for material discrimination."
＜Future Directions＞
In this study, we focused on the visual discrimination of metal and glass based solely on visual information. In the future, we plan to extend our research to a broader range of materials, such as fabric, stone, and plastic, to better understand how humans select exploratory behaviors for different materials and acquire the visual information necessary for material perception. In addition, although participants in the present study were not allowed to use tactile information directly for material discrimination, real-world material perception also relies on haptic cues such as texture, weight, and temperature. By integrating active visual exploration with tactile information, future research is expected to provide a more comprehensive understanding of the mechanisms underlying natural material perception in everyday life.
Furthermore, the concept of active perception demonstrated in this study—that humans actively seek the information they need rather than simply passively observing an object—may contribute to the development of more realistic material rendering in VR/AR, object recognition systems for robots and artificial intelligence that incorporate human-like exploratory behaviors, and human-centered interface designs based on the characteristics of human perception.
＜Publication Information＞
Nomachi, R†., Tamura, H†*., Helgeland, K. A., Morimoto, T., Nakauchi, S., & Minami, T. (2026). Material discrimination relies on context-dependent active sensing strategies. Journal of Vision, 26(6):4, 1–24. https://doi.org/10.1167/jov.26.6.4
(*: Corresponding author, †: These authors contributed equally)
＜Acknowledgments＞
This work was supported by JSPS KAKENHI (Grant Numbers JP25K21323 to H.T., JP25H01141 to S.N., and JP23KK0183 to T.M.) and the Toukai Foundation for 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.
