Swedish children with moderate hearing loss : on the importance of monitoring auditory and early speech development the first three years

Sammanfattning: The overall aim of this thesis was to investigate the auditory and early speech development in a group of children born with moderate hearing loss (HL) who were fitted with hearing aids (HAs) before the age of 6 months, and to compare their development to a group of children with normal hearing (NH). More specific aims were to examine the impact of auditory variables on the early speech development in the children with HL and to validate a questionnaire of auditory development in the children with NH. This PhD project consisted of four longitudinal studies. Participants included a group of children with moderate HL (n=11) and a reference group of children with NH (n=29). Data was collected at the ages of 10, 18, 34, 30 and 36 months with assessments of early speech development and auditory variables that were compared between groups. In Study I, the Swedish version of the LittlEARS® Auditory Questionnaire (LEAQ) was externally validated in children with NH. In Study II, HA use from first fitting to 36 months of age and the impact of hours of HA use on auditory development and functional performance were investigated. In Study III, consonant production in babbling and early speech at 10 and 18 months and consonant proficiency at 36 months were examined. In Study IV, expressive vocabulary between the ages of 18 to 30 months was investigated and compared between groups. The Swedish version of the LEAQ showed equal validation properties to the original version albeit found to be similar in content to an inventory of vocabulary. The variability in hours of HA use was large and only two children reached full-time HA use at all ages. Auditory development was found similar between the groups but the children with HL presented with lower scores on functional auditory performance in noise at 30 and 36 months of age. The children with HL showed delays in their consonant production in babbling and early speech at 10 and 18 months compared to the children with NH. At 36 months, there was no significant difference between the groups on consonant proficiency. The number of produced words was similar between the groups at 18 months but at 24 months of age there was a gap which increased even further at the age of 30 months, disadvantaging the children with HL. The most prominent auditory variable found to impact the outcomes on the early speech measures was hours of HA use, meanwhile scores on auditory development, functional auditory performance, and aided audibility showed weaker relationships. Despite early fitting with HAs the children with moderate HL showed delays in their early speech development and challenges in auditory functional performance in noise. The findings from this thesis suggest that careful monitoring at specific ages with appropriate methods of early speech development and auditory variables could help professionals to identify children at risk and work in a preventive way. This calls for cross-professional collaboration within the clinical setting. Attention is also needed to make sure that parents and other caregivers outside the clinic (e.g. preschool teachers) receive information so they can use appropriate strategies to reduce the risks of language delays in children with moderate HL. Albeit acknowledging the limitations to generalize the findings from this thesis to a larger population, the results and experiences from the longitudinal project are in line with current research that promotes monitoring of auditory and spoken language development the first three years in children with HL.