Abstract
There is a general consensus that many children and adults with dyslexia and/or specific language impairment display deficits in auditory processing. However, how these deficits are related to developmental disorders of language is uncertain, and at least four categories of model have been proposed: single distal cause models, risk factor models, association models, and consequence models. This study used children with mild to moderate sensorineural hearing loss (MMHL) to investigate the link between auditory processing deficits and language disorders. We examined the auditory processing and language skills of 46, 8–16year-old children with MMHL and 44 age-matched typically developing controls. Auditory processing abilities were assessed using child-friendly psychophysical techniques in order to obtain discrimination thresholds. Stimuli incorporated three different timescales (µs, ms, s) and three different levels of complexity (simple nonspeech tones, complex nonspeech sounds, speech sounds), and tasks required discrimination of frequency or amplitude cues. Language abilities were assessed using a battery of standardised assessments of phonological processing, reading, vocabulary, and grammar. We found evidence that three different auditory processing abilities showed different relationships with language: Deficits in a general auditory processing component were necessary but not sufficient for language difficulties, and were consistent with a risk factor model; Deficits in slow-rate amplitude modulation (envelope) detection were sufficient but not necessary for language difficulties, and were consistent with either a single distal cause or a consequence model; And deficits in the discrimination of a single speech contrast (/bɑ/ vs /dɑ/) were neither necessary nor sufficient for language difficulties, and were consistent with an association model. Our findings suggest that different auditory processing deficits may constitute distinct and independent routes to the development of language difficulties in children.
Highlights
In order to relate our data to the different models shown in Fig. 1, we first asked whether deficits in auditory processing were necessary or sufficient for language deficits in children with mild to moderate sensorineural hearing loss (MMHL) and/or controls
We examined the relationship between auditory processing (AP, amplitude modulation detection (AMD), and speech processing (SP)) and the Language component across groups
In order to identify those who performed poorly on the various tasks we followed Ramus et al (2003), and defined poor performers as children who obtained an AP, AMD, SP, or Language component score that was more than 1.65 SD below the mean for the CA group, calculated after excluding those controls who fell below this criterion
Summary
Specific Language Impairment (SLI) and developmental dyslexia (hereafter dyslexia) are developmental disorders of language and communication that are estimated to affect 7–10% of the population. L.F. Halliday et al / Cognition 166 (2017) 139–151. (Snowling, 2000; Tomblin, Smith, & Zhang, 1997). They are diagnosed when a child experiences extreme delays and/or deviancies in acquiring oral language (SLI), and written language (dyslexia), despite having normal nonverbal ability, an absence of physical, sensory, neurological, or emotional deficits, and adequate opportunity to learn (World Health Organisation, 2010). Despite many decades of research, scientists still do not agree on what causes these disorders
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