Objective: Auditory processing disorder (APD) is diagnosed on the basis of listening difficulties despite normal audiogram, although the cause is unknown. This study examined the hypothesis that the underlying cause of APD is a modality-specific deficit in auditory temporal processing and also considered how far the auditory impairments in APD differ from those in children with dyslexia.
Design: Performance of children diagnosed with APD (N = 22) was compared with that of a normative group (N = 98) as well as with children with dyslexia (N = 19) on a battery of temporal auditory tasks; 2-Hz frequency modulation (FM), 40-Hz FM, and iterated rippled noise detection as well as a control task (240-Hz FM), which is thought to draw on peripheral spectral mechanisms. Visual tasks were coherent form and coherent motion detection.
Results: On average, the APD group performed more poorly than the normative group on the 40-Hz FM, 240-Hz FM, and iterated rippled noise tasks. There were no significant differences between the APD and dyslexia group's performance and no evidence for a specific temporal auditory impairment. A higher proportion of children in the APD group performed poorly (<-1 SD) on the visual tasks than those in the normative group. Auditory psychophysical performance correlated positively with the performance on the SCAN-C, a standardized test of auditory processing, but not with reading ability.
Conclusions: The research did not support a modality-specific impairment of temporal auditory processing as being the underlying cause of APD. In both the APD and dyslexia groups, a similar proportion displayed poor auditory performance, and this does not seem entirely accounted for by attention or performance I.Q. However, the significance of these auditory difficulties is uncertain. Serious difficulties with auditory assessment were also identified. Currently, auditory perceptual deficits may be better seen as a part of a multifactorial description of learning problems rather than as part of a diagnostic category in their own right.