Minimal and mild hearing loss in children: Association with auditory perception, cognition, and communication problems

Objectives ‘Minimal’ and ‘mild’ hearing loss are the most common but least understood forms of hearing loss in children. Children with better ear hearing level as low as 30 dB HL have a global language impairment and, according to the World Health Organization, a “disabling level of hearing loss”. We examined in a population of 6 - 11 year olds how hearing level ≤ 40.0 dB HL (1 and 4 kHz pure tone average, PTA, threshold) related to auditory perception, cognition and communication. Design School children (n=1638) were recruited in four centres across the UK. They completed a battery of hearing (audiometry, filter width, temporal envelope, speech-in-noise) and cognitive (IQ, attention, verbal memory, receptive language, reading) tests. Caregivers assessed their children’s communication and listening skills. Children included in this study (702 male; 752 female) had four reliable tone thresholds (1, 4 kHz each ear), and no caregiver reported medical or intellectual disorder. Normal hearing children (n=1124, 77.1%) had all four thresholds and PTA < 15 dB HL. Children with ≥ 15 dB HL for at least one threshold, and PTA < 20 dB (n=245, 16.8%) had Minimal hearing loss. Children with 20 ≤ PTA < 40 dB HL (n=88, 6.0%) had Mild hearing loss. Interaural Asymmetric hearing loss (|Left PTA – Right PTA| ≥ 10 dB) was found in 28.9% of those with Minimal and 39.8% of those with Mild hearing loss. Results Speech perception in noise, indexed by VCV pseudoword repetition in speech modulated noise, was impaired in children with Minimal and Mild hearing loss, relative to Normal hearing children. Effect size was largest (d=0.63) in Asymmetric Mild hearing loss and smallest (d=0.21) in Symmetric Minimal hearing loss. Spectral (filter width) and temporal (backward masking) perception were impaired in children with both forms of hearing loss, but supra-threshold perception generally related only weakly to PTA. Speech-in-noise (nonsense syllables) and language (pseudoword repetition) were also impaired in both forms of hearing loss and correlated more strongly with PTA. Children with Mild hearing loss were additionally impaired in working memory (digit span) and reading, and generally performed more poorly than those with Minimal loss. Asymmetric hearing loss produced as much impairment overall on both auditory and cognitive tasks as Symmetric hearing loss. Nonverbal IQ, attention and caregiver-rated listening and communication were not significantly impaired in children with hearing loss. Modelling suggested that 15 dB HL is objectively an appropriate lower audibility limit for diagnosis of hearing loss. Conclusions Hearing loss between 15 - 30 dB PTA is, at ~20%, much more prevalent in 6-11 y.o. children than most current estimates. Key aspects of auditory and cognitive skills are impaired in both symmetric and asymmetric minimal and mild hearing loss. Hearing loss < 30 dB HL is most closely related to speech perception in noise, and to cognitive abilities underpinning language and reading. The results suggest wider use of speech-in-noise measures to diagnose and assess management of hearing loss and reduction of the clinical hearing loss threshold for children to 15 dB HL.