Tactile motion perception across sensory contexts: from multisensory integration to visual deprivation.

Multisensory integration allows the brain to combine information from different sensory modalities to form a coherent and reliable representation of the environment. Among these interactions, vision and touch play a fundamental role in motion perception, sharing common computational principles and neural mechanisms for encoding orientation and direction. This thesis investigates visuo-tactile integration in motion perception and examines how motion-related information is processed when visual input is available and when it is absent. In the first part of the work, we focus on visuo-tactile integration in sighted individuals. Using the RoMAT robotic platform, we investigated how visual and tactile motion cues interact when presented simultaneously. Specifically, we examined whether motion directions from vision and touch are integrated into a unified percept. Behavioural results show that perceived motion direction reflects a combination of visual and tactile inputs, indicating a flexible and salience-driven integration mechanism across sensory modalities. These findings raised a fundamental question: how is motion perception shaped when visual input is no longer available? To address this issue, the second part of the thesis focuses on tactile motion perception in visually impaired individuals. To enable reliable and accessible assessment of orientation and motion perception in both sighted and blind participants, we developed a novel tactile device, the Tactile Knob (TaK). Using TaK, we demonstrated that tactile-based responses are equivalent to visually guided responses in sighted individuals and that visually impaired participants perform comparably to sighted controls when relying on touch alone. Finally, we investigated tactile motion direction sensitivity in sighted, early-onset blind, and late-onset blind individuals by measuring just noticeable differences (JNDs) across different reference orientations. Results revealed comparable discrimination thresholds across groups, indicating that overall tactile motion sensitivity is not systematically altered by the absence of vision. However, a robust orientation-dependent effect emerged, with enhanced sensitivity for cardinal directions, revealing a tactile oblique effect in motion perception that is independent of visual experience and blindness onset. Together, these findings provide new insights into the shared mechanisms underlying visual and tactile motion perception, highlight the flexibility of multisensory integration processes, and clarify how tactile motion perception is shaped in the absence of vision.