Multisensory interactions between nociception and vision through the looking glass

To efficiently react to a potential threat to protect the body's integrity, it is not only crucial to localize nociceptive stimuli on the body, but also the position of the potentially harmful objects in external space. It is therefore essential to coordinate the representation of the body and that of the surrounding external space. This integrated multisensory representation of the body and its vicinity is conceptualized by the notion of peripersonal space, which would facilitate the processing and integration of somatic and extra-somatic stimuli occurring near the body. The involvement of such reference frames in nociceptive processing is corroborated by findings of interactions between nociceptive and visual stimuli that are presented near the body part on which nociceptive stimuli are applied. Here, we investigated the effect of mismatching visual feedback about the proximity between visual and nociceptive stimuli on these interactions. In three experiments, participants made temporal order judgements on two lateralized visual stimuli, which were preceded by a unilateral nociceptive stimulus applied on one hand. In the main experimental condition, visual stimuli occurred near participants' hands but were visible only indirectly as distant reflections in a mirror positioned in front of them, with the visual feedback indicating that visual stimuli are located farther away from the felt position of the hands on which nociceptive stimuli are applied. This mirror condition was compared to several different control conditions across the three experiments, in which the position of the visual stimuli with regard to the stimulated hands as well as the visual feedback was further varied. The results consistently indicate that, despite the mismatch in visual feedback, visual stimuli were recoded as having a true proximal source near the stimulated hands, allowing the nociceptive stimuli to bias visuospatial perception. This suggests that interactions between nociceptive and near extra-somatic stimuli might indeed rely on a higher-level mental representation of the body and its nearby space, and not solely on low-level visual feedback about the proximity of the somatic and non-somatic stimuli.