Sensation level and the pupillary level--response function during passive listening in children with and without hearing loss

This study asked whether the level-response relationship differs between children with and without hearing loss, and whether any difference reflects supra-threshold processing rather than simply reduced audibility. Pupil dilation was recorded during passive listening in children aged 3-47 months, using two paradigms with different participants: one varying presentation order across children, another descending in level by blocks. Each child’s hearing threshold allowed conversion between presentation level and sensation level. In the first paradigm, normal-hearing children showed a negative relationship between level and pupil response, while children with hearing loss showed a weakly positive one—the two groups moved in opposite directions across 40-70 dB. This difference held after adjusting for individual threshold, when comparing children matched on sensation level, and within hearing-device subgroups. A meaningful response to target versus standard sounds appeared only well above each child’s own threshold. Consistency of individual children’s responses across sessions was mixed, while tonic pupil size was reproducible. The pupil’s level-response pattern differs by hearing status, independent of audibility. It is a group-level finding, not yet a reliable individual test, and appears specific to response amplitude rather than discrimination. The response requires a stimulus well above the child’s own threshold, but the present dataset data do not fix that boundary precisely.