Measures of Acoustic Reflexes in Typically Developing Children and Children with Suspected Auditory Processing Disorder

A series of studies were conducted to examine the acoustic reflex in normal hearing adults, typically developing children and children with suspected auditory processing disorder (APD). Elevated acoustic reflex thresholds (ART) and shallower acoustic reflex growth functions (ARGF) were found in children with suspected APD in comparison to typically developing children and normal hearing adults. These effects were strongest in the crossed condition. There were no group differences for acoustic reflex latency (ARL) or acoustic reflex decay (ARD). In all studies the children with suspected APD were divided into two groups based on the diagnosis made on the basis of a behavioral APD battery; (1) APD which included children who received APD diagnosis and (2) Clinical non-APD who did not receive APD diagnosis. Children in the clinical non-APD and APD groups had similar ART and ARGF abnormalities highlighting a potential weakness in relying strictly on behavioral tests in the assessment of children suspected of APD. The effect of acoustic reflex activation on middle ear absorbance (MEA) and middle ear resonant frequency (MERF) was also investigated. It was found that the activation of the acoustic reflex resulted in a decrease of MEA between 226 and 1000 Hz, an increase MEA between 1000 and 2000 Hz and shift of MERF to a higher frequency. These changes in middle ear function may be critical to speech in noise perception. The effect of reflex activation was diminished in children with suspected APD. Across studies, acoustic reflex measures including ART, ARGF and the effect of the reflex on MEA and MERF showed a trend suggesting age-related changes but the trends did not reach statistical significance. However, a significant developmental trend in ARTs was found when corrected for ear canal volume differences. These results suggest that acoustic reflex measures in clinical children should be compared with those of typically developing children rather adults