Investigating the Kappa Effect Elicited Through Concurrent Visual and Tactile Stimulation

The experience of time and space in subjective perception is closely connected. The Kappa effect refers to the phenomenon where the perceived duration of the time interval between stimuli is influenced by the spatial distance between them. In this study, we aimed to explore the Kappa effect from a psychophysical perspective. We investigated participants' perception of temporal duration in the sub-second range by delivering visual and tactile inputs through wearable devices placed on both the palm and the forearm. We compared the impact of unimodal sensory stimulation, involving either visual or tactile stimuli, with different bimodal stimulation conditions. Our results revealed that the illusory effect on inter-stimulus duration perception can be observed in both unimodal conditions, although the distortions were significantly more pronounced in vision. In the multimodal stimulation condition, where visual stimuli were presented at non-equidistant spatial locations, the integration of tactile input did not reduce the Kappa effect, regardless of the spatial location of the tactile stimuli. However, when the visual stimuli were equidistant in space, regardless of the spatial location of the tactile stimuli, the Kappa effect disappeared. These results can shed light on the effect played by multimodality on the perception of space and time.