Variation in the Normal Hearing Threshold Predicts Childhood IQ, Linguistic, and Behavioral Outcomes

Abstract

Childhood hearing level varies considerably within the range considered normal. Four classes of outcome were investigated for associations with hearing thresholds in this range: ability to identify speech in noise, neurocognitive ability, linguistic ability, and behavior. The research was conducted in a general population cohort of 711 children with mean hearing threshold of 15 dB HL or better. Some outcomes: speech in noise, intelligence, and certain linguistic abilities, were predicted in both boys and girls; effects were stronger in girls. In girls only, poorer hearing predicted worse behavior. These effects remained after statistical control for childhood socioeconomic status and otitis media. Variability in normal hearing, due to causes other than otitis media, is associated with the listening, language, and neurocognitive abilities of children, and the behavior of girls. We suggest that these effects may be present for three reasons, cochlear insults, neurodevelopmental factors, and psychological factors. We discuss how these may interact to produce the effects observed. T he conventional cut-off for normal-range hearing in children is 15 dB HL (1); which includes 97% (711/734) of the general population sample assessed here. This includes a wide range of actual hearing abilities, and how it relates to psychosocial consequences in humans is unclear (2). Hitherto, research has concentrated on effects in people with relatively large hearing losses, with little attention paid to the effects of variability within the normal range. We investigated four areas for which we hypothesized effects of hearing level in normally hearing children. Identification of signals in noise.A relation between puretone detection and identification of signals in noise has been demonstrated in minimally hearing-impaired children (3). Variation in normal hearing may be due to vulnerable structures involved in the cochlear active process (4). Children with poorer normal hearing may be less able to identify signals in noise due to slight deterioration in these systems.Neurocognitive ability. Assessment of hearing threshold measures performance on a psychoacoustical task in which general neurocognitive ability might play a part, so variation in threshold might be related to IQ. Furthermore, a body of research has related sensory processing, in terms of inspection time, with IQ (5-7). Thus, there may be a relation between hearing and IQ.Linguistic ability. Children with minimal hearing impairment perform less well on tests of educational performance, particularly in areas related to language (8). Furthermore, those with poor linguistic abilities perform less well on tests of acoustic frequency and temporal resolution (9,10). These findings are with stimuli requiring a high degree of processing (11), however, simple detectability may contribute to the effects shown.Behavior. Little research has investigated behavioral concomitants of variation in hearing in children. In deaf people, there may be effects with depression and interp...

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