Effects of looming and static sounds on somatosensory processing: A MEG study

Abstract

The present study aims to assess the mechanisms involved in the processing of potentially threatening stimuli presented within the peri-head space of humans. Magnetic fields evoked by air-puffs presented at the peri-oral area of fifteen participants were recorded by using magnetoencephalography (MEG). Crucially, each air puff was preceded by a sound, which could be either perceived as looming, stationary and close to the body (i.e., within the peri-head space) or stationary and far from the body (i.e., extrapersonal space). The comparison of the time courses of the global field power (GFP) indicated a significant difference in the time window ranging from 70 to 170 ms between the conditions. When the air puff was preceded by a stationary sound located far from the head stronger somatosensory activity was evoked as compared to the conditions where the sounds were located close to the head. No difference could be shown for the looming and the stationary prime stimulus close to the head. Source localization was performed assuming a pair of symmetric dipoles in a spherical head model that was fitted to the MRI images of the individual participants. Results showed sources in primary and secondary somatosensory cortex. Source activities in secondary somatosensory cortex differed between the three conditions, with larger effects evoked by the looming sounds and smaller effects evoked by the far stationary sounds, and the close stationary sounds evoking intermediate effects. Overall, these findings suggest the existence of a system involved in the detection of approaching objects and protecting the body from collisions in humans.