Peripersonal Space from a multisensory perspective: the distinct effect of the visual and tactile components of Visuo-Tactile stimuli

Behavioural studies on Multisensory Peripersonal Space (PPS) representations are based on seminal findings in single-cell recordings.A classic experimental paradigm used to assess PPS is the Multisensory Integration Paradigm. In this paradigm Visuo-Tactile stimuli are administrated to participants. According to the paradigm, the tactile component vibrates when the visual component, approaching the participant, reaches a specific distance. Participants must detect the tactile component. Reaction times (RTs) are faster with closer visual stimuli. This effect is classically interpreted as a manifestation of PPS representation.However, the Visual and Tactile components are usually targeting at the same body part, and Tactile-Only RTs are considered constant.In this study we formally addressed two research questions: i) whether the Multisensory Visuo-Tactile RTs are independent from Tactile-Only RTs and whether the latter are influenced by time-dependency effects; and ii) whether PPS estimations derived from Multisensory Visuo-Tactile RTs depend on the location of the Visual or Tactile component of the stimuli.We studied 40 right-handed participants, in a repeated-measure design, crossing the position of the Tactile and Visual components of stimuli across the face, the hand and the foot, and 5 distances. Each trial could be Visuo-Tactile, Tactile-Only or a Catch trial.Frequentist and Bayesian analysis demonstrated that Tactile-Only RTs follow a non-monotonic trend, depending on the delay of stimulus administration. Furthermore, according to our findings, Visuo-Tactile RTs were proved to be dependent on Distance and location of the Visual component of the stimulus. Our results lead to the conclusion that Tactile-Only RTs should be removed from Visuo-Tactile RTs and that the Visual and Tactile components of Visuo-Tactile stimuli do not necessarily have to target at the same body part.These results may have an advantageous impact on the study of PPS representations, providing new and important methodological information.