Auditory processing disorder (APD): Definition, diagnosis, neural basis, and intervention

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Abstract
Auditory processing disorder (APD) is a label that has become increasingly popular in recent years to describe a variable set of symptoms that have in common a difficulty listening to sounds in the absence of an audiometric deficit. The label has been applied to a variety of populations, notably children who may have learning problems, older people who may have sensitivity problems, and patients of all ages with frank brain lesions. This paper focuses on children without known lesions and attempts to develop a diagnostic framework, within the recent definitions of APD proposed by British and US audiological societies. Key to this approach is the notion that APD is primarily a difficulty in processing non-speech sounds. Existing diagnostic practice is too variable to underpin meaningful research, so a population-based approach to identifying outlying performers is advocated. An outstanding diagnostic challenge is the level of perceptual complexity, in terms of stimulus and task/test, at which the difficulty resides. While APD is commonly called ‘C(entral)APD’, it does not map simply onto the function of the traditional central auditory system. This is itself undergoing a transformation as we understand more about dynamic processing in the cochlea, the role of descending (efferent) pathways in cochlear and brain processing, and the role of forebrain structures outside the posterior temporal lobe in hearing and listening. The management of childhood APD has been mainly achieved through modifications to the acoustic environment and sound delivery to the ears, and through auditory and speech training. Recent advances in sensory learning research have led to recommendations that include the use of specific training stimuli (e.g. phonemes), adaptive training algorithms that keep the listener alert, on-task and challenged, and the deployment of motivating computer games that a child is happy to play over multiple training sessions.