The acoustic space of pain: cries as indicators of distress recovering dynamics in preverbal infants

Crying is a vital built-in survival mechanism for the Human baby. Yet both the information carried by cries and the factors driving the perception and reaction of adult listeners remain under-investigated. Here, we contrasted the relevance of psychoacoustic vs. acoustic evaluation for the assessment of distress levels in babies' cries recorded during baths and during an immunization event. Parents asked to rate the level of distress experienced by babies from listening to their cries attributed lower pain ratings to mild discomfort (bath) than to distress (vaccination) cries but failed to discriminate between different putative levels of pain experienced during different vaccination sequences. In contrast, vocal "roughness", a composite acoustic factor characterising the level of aperiodicity of the cries, not only differed between mild discomfort and distress cries but also between the levels of pain experienced during the different vaccination sequences. These observations suggest that acoustic analyses are more powerful than psychoacoustic evaluations for discriminating distress levels in babies’ cries, and opens the way for the design of a tool based on the acoustics of cries for assessing and monitoring pain levels in preverbal infants