Physiological and Behavioral Evidence of Auditory Processing Deficit in Children Suspected of Auditory Processing Disorder

A series of studies were carried out to examine the neural and behavioral processing of acoustic stimuli in children with suspected auditory processing disorder (sAPD). The click-evoked auditory brainstem responses recorded from children with sAPD and adults were analyzed using traditional clinical measures and detailed analysis seeking to explore the separate contributions of axonal conduction and synaptic transmission. Clinical measures revealed significant prolongation of absolute latencies and interwave intervals in children with sAPD compared to adults. Examination of responses delineating axonal vs. synaptic transmission showed frequent delays in synaptic factors and fewer instances of delays related to axonal conduction in children with sAPD compared to adults. Inefficient neural transmission in the auditory brainstem may lead to difficulty in coding of dynamic acoustic cues (envelope, fine structure or spectral shape) that are necessary for recognizing speech in quiet and in noise. The ability to use envelope and fine structure cues to recognize speech in noise was therefore examined in children with sAPD, typically developing children and adults. Typically developing children showed developmental trend in use of envelope cues. Whereas children with sAPD were less efficient in using envelope and fine structure cues to recognize speech in noise compared to age-matched children and adults. Perception of speech based on fine structure alone was difficult for both TD children and children with sAPD compared to adults. This could be due to developmental difficulty in integrating frequency information from different bands. Difficulty in integrating auditory filter outputs may lead to the inadequate representation of spectral shape, which is necessary for recognizing speech sounds. Spectral shape perception was assessed using a spectral ripple discrimination task in typically developing children, children with sAPD, and adults. Young children could resolve fewer of ripples per octave when compared older children and adults. The performance of children with sAPD was poor compared to age-matched controls and young adults. Spectral-ripple discrimination showed a strong trend for improvement in thresholds as a function of age in both typically developing children and children with sAPD. This suggests that spectral shape is a learned cue and may take a longer time to mature