| Summary: | INTRODUCTION: Confidence in the reliability and validity of a diagnosis of APD is currently low among clinical and professional groups, principally due to the lack of a gold standard test sensitive to APD, differences in accepted diagnostic criteria and considerable variability in clinical test batteries implemented. Listening difficulties associated with APD are also not exclusive to the disorder, and are frequently observed in individuals with alternative disorders such as specific language impairment, specific reading impairment, and attention deficit disorder. The research undertaken in this thesis attempts to identify subjective and objective measures that differentiate adults diagnosed with clinical-APD from oto-neurologically normal adults with no perceived hearing difficulties using a popular hearing inventory, three speech in-noise tests and the speech-evoked auditory brainstem response test. The Speech, Spatial and Qualities of Hearing Scale (SSQ), presents a rich array of communication environments that reflect the three-dimensional dynamic auditory world humans live in. It comprises three hearing subscales - speech intelligibility, spatial awareness and other qualities of hearing. The three speech-in-noise tests - Who Is Right, the Children’s Coordinate Response Measure with competing male-talker (CCRM1) and the Children’s Coordinate Response Measure with competing speech-shaped noise (CCRM2) assess different aspects of auditory cognition, (i.e., low level auditory processing and auditory attention). In all three speech tests the target signal and competing noise were presented simultaneously and dichotically via headphones, and an automatic adaptive approach was used to adjust the signal-to-noise ratio. The speech-ABR was elicited under monaural and binaural stimulation, with a 40ms /da/ consonantvowel syllable. Several measures can be used to characterise the speech-ABR onset response and frequency following response (FFR) including response timings, responses amplitudes, and stimulus versus response waveform correlation coefficients. METHODOLOGY: Normative data were derived for all three subscales of the SSQ Hearing Scale, for the three behavioural speech tests, and the speech-ABR, following the collection and analysis of data obtained from 52 adults with normal hearing and no reported listening difficulties. Research data for the same outcome measures were obtained from a clinical-APD group (n=21) and two smaller APD subgroups (a developmental-APD group comprising 10 subjects and an acquired- APD group consisting of 8 subjects). SUMMARY OF RESEARCH FINDINGS: SSQ self-reported hearing ability scores were significantly worse for the clinical-APD group (n=21) compared with the normal hearing control group (n=52) for the ‘speech intelligibility’ and ‘other qualities of hearing’ subscales at the 0.01 alpha level. Statistically significant group differences were also observed for CCRM1 and Who Is Right tasks - poorer scores were apparent for the clinical-APD group for both tests, providing some evidence for deficits in auditory attention and auditory processing in these subjects. No statistically significant group differences were observed for all speech-ABR response timings or key features of the FFR. Independent Sample T-tests did suggest that statistically significant group differences were apparent for V-A amplitude, V-A slope and V-A area; however these differences may be attributed to age and gender distribution differences between the two groups. 75% of the acquired-APD subjects failed the CCRM1 task (a test of auditory attention), compared with 30% of the developmental-APD group. 50% of the acquired-APD subjects failed the Who Is Right task (a test of auditory processing) compared with 10% of the developmental- APD group; and 50% of the acquired -APD group failed the CCRM2 task (a test of attentional allocation and/or auditory processing) compared with 10% of the developmental-APD group. Findings for the speech-ABR also revealed evidence for low level central auditory nervous system anomalies for both APD subgroups. Abnormalities in the speech-ABR FFR were observed in 30% of developmental-APD subjects compared with 62.5% of acquired-APD subjects; whilst mild anomalies were present in 20% of developmental-APD subjects compared with 37.5% of acquired-APD subjects for the onset response. Altogether these results provide evidence for the deficits in auditory cognition for both APD-groups. Although this test battery demonstrates low sensitivity overall for the developmental-APD group, it does show better sensitivity for the acquired-APD subjects who exhibit more severe deficits in auditory cognition.
|
|---|
