The Effect of Exposure to Aversive Non-verbal Vocalizations on Pain Tolerance

The cold pressor test is among the most common and established methods for studying human reactions to pain and pain tolerance. Participants submerge a hand in cold water (approx. 5°C) and are asked to keep their hand submerged for as long as can (until the sensation is intolerable), up to a maximum of 5 min. The procedure is safe because the hand is removed before adverse effects can occur. The participant will be given a break of 5 min in between trials, and will interchange hands between trials. During this break hand may to be place in warm water (25-35°C) for up to 4 min to normalise hand temperature, which will be measured before and after each trial using a digital thermometer held firmly in the palm of the hand. Each participant will complete no more than three trials (conditions) in a randomised order.

Measurement of the index NOL™: Four sensors, placed non-invasively on one of the four participants' fingers, will make it possible to calculate a dozen physiological parameters converts in real time into a pain index called NOL (for Nociception Level Index).

During the experience, participants are led to listen, via headphones, to aversive non-verbal vocalizations (baby crying). The sound levels used to broadcast the non-verbal vocalisations will be scrupulously measured using approved and certified equipment during the preparation of the experiments. These sound volumes will be chosen so as not to inconvenience participants.

This technique is based on the observation of the dilatation of the pupil during the perception of a nociceptive stimulus in test persons.