Dear Colleagues,

Auditory processing disorder (APD) is a complicated concept. APDs are a collection of conditions in which the ability to detect sounds, localize their sources, or determine their identity and meaningfulness is impaired. This is because of a functional defect in the central auditory nervous system due to disease, damage, or maldevelopment. In the mid 1950's, Ettore Bocca and his colleagues (1954) reported that patients with temporal lobe tumors complained of hearing difficulties, despite the presence of normal hearing thresholds and normal speech recognition in quiet. Meanwhile, other researchers demonstrated that central auditory function should be considered and assessed in children with communication disorders. Over the past few decades, different studies have shown that impaired structure and/or function of the brain may have little or no effect on hearing thresholds. However, they may cause deficits in other aspects of the hearing process in what are collectively referred to as APD. APDs can be either genetic or acquired, and occur in both children and adults. The incidence of APDs has been increasing, but the reasons are not fully understood. Although initial studies of APDs focused on adults with vivid structural lesions of the auditory system, over the past decades interest has also grown in APD in children. APD is defined as defective performance in localization and lateralization, discrimination, pattern recognition, temporal integration, gap detection, temporal ordering, masking perception, dichotic listening, or in the identification of degraded signals.

Recent advances in the auditory processing system have shed light on the role of the central auditory nervous system in hearing. In this regard, neural representations of the acoustic signal at rostral levels are shaped by convergent inputs and show some degree of plasticity, even in adults. So-called higher-level disorders (e.g., phonologic ones) are become increasingly understood, largely through work in cognitive neuroscience which has begun to describe the functional architecture of the processes that mediate sound recognition and comprehension.

This thematic issue aims to discuss auditory processing deficits and related disabilities in neurological disorders such as cerebrovascular accidents and demyelinating disease. Studies of patients with defined anatomical lesions may be complementary to functional imaging studies in normal populations in that they may help to define brain regions that are necessary to support specific auditory functions. We will review recent breakthroughs in auditory cognitive neuroscience and the presence and impact of auditory processing deficits in patients with developmental disorders such as dyslexia and attention deficit disorder, as well as specific language impairments such as tinnitus, stuttering, and hearing loss. Also covered are advances in mechanism-based auditory processing, impairments in disorders such as tinnitus, speech recognition and recent findings on pitch perception and extraction, mismatch negativity, pre-attentive processing, predictive coding mechanisms, and auditory memory.

Ali Yadollahpour
Guest Editor