Sound transmission through the avian interaural pathways

Abstract

1. The magnitude and phase of sound transmitted through the avian interaural pathways were measured acoustically and with cochlear microphonic recordings. 2. The acoustic measures indicated that a sound stimulus on one side of the head could be conducted through the tympanic membrane and across the interaural pathway to the opposite middle ear with an attenuation of about 25–35 dB. 3. The acoustic loss was primarily due to sound transmission across the tympanic membrane, with no further attenuation attributed to sound conduction through the interaural pathways. 4. A comparison of cochlear microphonic recordings during ipsilateral or contralateral stimulation indicated a loss of 15–20 dB due to sound conduction across the contralateral tympanic membrane and interaural pathways. 5. Sound conducted through the interaural pathway exhibited a frequency dependent phase delay. 6. The consequences of binaural stimulation on the cochlear microphonic response could be predicted by a vector addition of the response to monaural ipsilateral or contralateral stimulation. 7. The maintenance of a constant SPL at the contralateral ear varied the cochlear response to ipsilateral stimuli, in a frequency dependent manner, by as much as ±2 dB. 8. It is hypothesized that the chick interaural pathways act like the air filled trachae of insects, which connect the bilateral ears and are thought to be important in auditory localization.