Listening effort in young children with cochlear implants

In humans, effortful listening evokes stress and fatigue. In constantly effortful environments (such as classrooms), well-being, learning abilities and academic success are compromised. Such listening environments are much more challenging for severely/profoundly deaf children with cochlear implants. With technological advancement and early implantation, listening skills are thought to have significantly improved. However, it is sometimes difficult to measure listening skills and effort, especially in very young children. Behavioral measures of effort and fatigue cannot be obtained in young/uncooperative children, whereas objective measures are either difficult to assess (cf. EEG) or not reliably correlating with objective behavioral measures (cf. cortisol levels). Recent studies have thus explored pupillometry as a possible objective measure. Available results indicate that pupil dilates in response to effort, which corresponds to pupillary reaction to attention or cognitive load. No study has been, however, done on infants’ or preschool children’s response to various signals and noise levels. The aim of this study is to explore pupillary response to signal in noise in young bilaterally implanted children with congenital hearing loss.

Present study explores pupillary behavior of 14 children (1.5-4-y-old) listening to speech (rhymed verses in their mother tongue, Italian) and music (excerpts from the “Happy song”) at a constant intensity level (60 dB spl) and at various noise levels (babble noise), in an ecological environment (Ambisonics semi-sphere), with one or both cochlear implants switched on. During the session, children watched a repeating excerpt from an animated film.

Preliminary results show that in response to noise, pupil dilates more in noisy conditions (SNR 0 dB) compared to low background noise (SNR 10 dB), but not compared to silence. Possibly, this result reflects the fact that listening in low background noise is the most common everyday experience for these children. Pupil also dilates more in presence of music and speech compared to silence (with low or without background noise), opening the possibility to use pupillometry as a potential measure of auditory signal detection. The overall pupil dilation changes in different cochlear implant configurations (bilateral, left only, right only), increasing significantly when only left implant is turned on. This result may be affected by the sequence of implantation (left implant followed the right one in 13 out of 14 children), or, alternatively, by the general right ear superiority observed in humans. Further research is, however, needed to better understand these results.