| Description |
Hearing sensitivity in infants and adults is often assessed by measuring brain waves in response to sound. Common neural measurements of hearing sensitivity are the compound action potential (CAP) and auditory brainstem response (ABR), which emphasize activity from neurons in the auditory nerve (AN) and brainstem, respectively. The sounds that produce the largest CAP and ABR amplitudes are those that evoke a synchronous response from AN fibers tuned to frequencies across the range of human hearing. Traditionally, the sound used to evoke this synchronous response is a short acoustic click; however, research has shown that the cochlear traveling wave temporally smears the inner ear's response to clicks, resulting in slightly asynchronous neural activity from the AN. To compensate for this temporal smearing, sounds that quickly sweep from low to high frequencies (i.e., an acoustic "chirp") have been developed and these chirps result in larger CAP and ABR amplitudes for low-intensity sounds; however, little is known about whether this chirp benefit exists for high-intensity sounds. In this paper, we report on the use of chirps for CAPs elicited by high-intensity sounds. We presented a click and three forms of chirp stimuli at five different intensities to twelve human subjects with normal hearing in order to determine which stimulus elicits the largest CAP and ABR amplitudes. The results show that CAP amplitudes for clicks are greater than those for chirps for high intensities and that this lack of a chirp benefit is rectified by using the modified chirps. Applications of this research could inform the clinical use of chirps in the assessment of human hearing using CAP and ABR measures. |
