Tactile sensitivity to softness in virtual reality can increase when visual expectation and tactile feedback contradict each other

Objective. The perception of softness plays a key role in interactions with various objects, both in the real world and in virtual/augmented reality (VR/AR) systems. The latter can be enriched with haptic feedback on virtual objects' softness to improve immersivity and realism. In such systems, visual expectation can influence tactile sensitivity to softness, as multisensory integration attempts to create a coherent perceptual experience. Nevertheless, expectation is sometimes reported to attenuate, and other times to enhance, perception. Elucidating how the perception of softness is affected by visual expectation in VR/AR is relevant not only to the neuropsychology and neuroscience of perception, but also to practical applications, such as VR/AR-based training or rehabilitation. Approach. Here, by using novel wearable tactile displays of softness previously described by us, we investigated how the sensitivity to softness in a visuo-tactile VR platform can be influenced by expectation. Twelve subjects were engaged in comparing the softness of pairs of virtual objects, familiar or not, with tactile feedback of softness and visual expectation either conflicting or not. The objects' Young's moduli were initially randomly selected from a large set, spanning two orders of magnitude (0.5, 2, 20, 50 and 100 MPa), and then their difference was iteratively reduced, to reach the just noticeable difference in softness. Main results. For the intermediate modulus, a conflict between tactile feedback and visual expectation caused a statistically significant increase in sensitivity. Significance. This finding supports the theory that there can be conditions in which contradictory stimuli strengthen attention (to resolve conflicting sensory information), which in turn can reverse the sensory silencing effect that expectation may otherwise have on perception.