Infant and adult pupil dilation in response to unexpected sounds.

Surprisingly occurring sounds outside the focus of attention can involuntarily capture attention. This study focuses on the impact of deviant sounds on the pupil size as a marker of auditory involuntary attention in infants. We presented an oddball paradigm including four types of deviant sounds within a sequence of repeated standard sounds to 14-month-old infants and to adults. Environmental and noise deviant sounds elicited a strong pupil dilation response (PDR) in both age groups. In contrast, moderate frequency deviants elicited a significant PDR in adults only. Moreover, a principal component analysis revealed two components underlying the PDR. Component scores differ, depending on deviant types, between age groups. Results indicate age effects of parasympathetic inhibition and sympathetic activation of the pupil size caused by deviant sounds with a high arousing potential. Results demonstrate that the PDR is a sensitive tool for the investigation of involuntary attention to sounds in preverbal children.