Emotion-inducing approaching sounds shape the boundaries of multisensory peripersonal space

Abstract

In order to survive in a complex environment, inhabited by potentially threatening and noxious objects or living beings, we need to constantly monitor our surrounding space, especially in the vicinity of our body. Such a space has been commonly referred to as one's 'peripersonal space' (PPS). In this study we investigated whether emotion-inducing approaching sound sources impact the boundaries of PPS. Previous studies have indeed showed that the boundaries of PPS are not fixed but modulate according to properties of stimuli in the surrounding environment. In Experiment 1, participants performed a simple tactile detection task of targets presented to their right hand. Concurrently, they were presented with intensity-changing task-irrelevant artificial sound sources perceived as approaching toward their body. The physical properties of the sound elicited emotional responses of either neutral or negative valence. Results showed larger PPS when the approaching stimulus had negative as compared to neutral emotional valence. In Experiment 2, we used ecological sounds which content (i.e., psychological associations to the sound producing source), rather than physical properties, elicited emotional responses of negative, positive or neutral valence. In agreement with results from experiment 1, we found larger PPS when the approaching stimuli had negative emotional valence as compared to both neutral and positive ones. Results are discussed within the theoretical framework that conceives PPS as a safety zone around one's body.

What Can Ethobehavioral Studies Tell Us about the Brain's Fear System?

“…In another study [72], a live tarantula was moved closer to participant’s feet while they were restrained in an fMRI machine, which produced similar patterns of neural activity to the AEP experiments and corresponds to similar findings of experiments in rodents [73]. Research on “defensive peripersonal space”, an area in which defensive behaviors scale with distance from the body [74], in human and non-human primates [75, 76] suggests that parieto-frontal interactions also play a role in enhancing defensive reflexes as threats come closer to the body. Incorporating ethological stimuli and situations into human studies will provide a functional understanding of fear across spatial dimensions.…”

On the contribution of overt tactile expectations to visuo-tactile interactions within the peripersonal space

“…That is, even if there is a linearly changing relationship between visual stimulus location and the response time, this method will likely indicate the presence of the boundary. Therefore, we believe that it might be best to reserve this method for body parts where a more vigorous method such as the one used in this study and previous studies has previously demonstrated a multisensory boundary for PPS (Canzoneri et al 2012; Ferri et al 2015; Taffou and Viaud-Delmon 2014). …”

“…That is, PPS neurons respond to stimuli looming towards a body part and to tactile stimuli delivered on that body part. When observers are asked to respond to tactile stimuli, which are delivered at different timepoints during a looming stimulus’s approach, the pattern of response times is found to be sigmoidal in nature (Canzoneri et al 2012; Ferri et al 2015; Noel et al 2016; Taffou and Viaud-Delmon 2014; Teneggi et al 2013). That is, the surmised multisensory summative properties of the PPS neurons would speed up responses (RTs) to tactile stimuli that are delivered when the looming stimulus is within the PPS.…”

Peripersonal space boundaries around the lower limbs

“…This reflects the variability in PPS boundaries (or switch points) within the current sample. Studies have shown that individual differences in brain activity (Ferri et al 2015a) and emotional states such as anxiety (Sambo and Iannetti 2013) or fear (Taffou and Viaud-Delmon 2014;Ferri et al 2015b;de Haan et al 2016), and also anxiety disorders such as claustrophobia (Hunley et al 2017) can contribute to the variability observed in PPS boundaries. Although we did not specifically investigate this, it is possible that individual traits contributed to the large variability in our sample.…”