Interaural differences in the bottlenose dolphin (Tursiops truncatus) auditory nerve response to jawphone click stimuli.

Suction cup transducers, also known as "jawphones," are now commonly used to deliver acoustic stimuli to odontocete cetaceans during hearing studies. It is often assumed that stimulation is primarily limited to the ear ipsilateral to a jawphone; however, the actual differences in auditory stimulation at the two ears are not well understood. To examine these differences, auditory evoked potentials (AEPs) were simultaneously recorded from both ears during jawphone stimulation in two bottlenose dolphins. The amplitudes and latencies of auditory nerve responses (ANRs) elicited by broadband clicks were measured as functions of stimulus level and used to estimate the difference in received level and interaural time difference (ITD) between the two ears. Results indicated that clicks received at the ear contralateral to the jawphone were attenuated by approximately 20 dB relative to the level at the ipsilateral ear. The ITD between the contralateral and ipsilateral ears was 70 μs for the first dolphin and 118 μs for the second dolphin. While these results provide support for a notable degree of acoustic isolation of the ears for jawphone-delivered stimuli, there are implications for studies involving processes such as sound localization and unilateral hearing loss.