Pupil dilation as an index of listening effort and auditory attention in young children with hearing impairment
Background: There is a general agreement that infants and children are more vulnerable in noisy environments, due to the still ongoing language development and maturation of the auditory pathway in childhood. Noise may particularly disadvantage infants and young children in recognizing and learning from speech. While literature on speech perception in background noise in adult hearing aid and cochlear implant users is abundant, there are only few studies related to listening effort in paediatric populations, with or without hearing impairment. This fact persists, although the most widely used and reliable objective method for assessing listening effort, pupillometry, is thought to be easily administered also in non-communicative populations, including infants and children.
Similar situation can be found in studies on auditory attention. Processing auditory regularities and their violations induces an event-related pupillary dilation response in adults, and studies suggest that this may be a more sensitive attention-capture index than behavioural measures. Auditory attention can be measured with pupillometry also in the paediatric population, as an index of sensitivity to phonological detail, prosodic cues, or unexpected sounds. Albeit possible clinical implications of such a measure, to this date, no studies have been published with hearing impaired adult or paediatric populations.
Methods: I will present two recent studies with preschool children with hearing impairment, in which the listening effort and listening attention were assessed through pupillary dilation response. In the first, we measured pupillary dilation response to speech and music stimuli presented in background noise in 14 children with cochlear implants and 14 normally hearing children. In the second study, involuntary attention to unexpected sounds of various intensities was measured in 44 infants and preschool children with hearing impairment, hearing aids and cochlear implant users.
Results: In the first study children with cochlear implants showed increased pupil response for speech without noise, while music in noise induced larger pupil response in children with normal hearing. In the second study, larger pupil response was measured for unexpected sounds. We furthermore explored the effect of age and hearing status on their responses.
Discussion: We will discuss the possible implications of the observed interaction between presented stimuli and hearing status, as well as the potential clinical applications of the involuntary auditory attention measure in children with hearing impairment.