Acoustic properties of the interaural pathway in the chicken

Abstract

The acoustic transmission properties of the avian interaural pathway were measured in the chicken with a sound probe placed within the middle ear. Ten chickens, 3–9 days old, were anesthetized, both external meati were surgically excised, the animal was placed in a head holder, and sound tubes with associated probe microphones were sealed over the right and left tympanic rings. The left middle ear was opened, and a 1-mm-diam sound probe was placed in the middle ear. The ear was then resealed. Continuous pure tone stimuli of approximately 110 dB SPL and of various frequencies was presented first to one ear and then to the other. With each stimulus presentation SPL was measured at three places: the stimulated external ear, the opposite external ear, and in the middle ear. A reduction in SPL of 25–30 dB was noted in the left middle ear regardless of whether the left or right external ear was stimulated. These observations suggest that the interaural pathway imposes no attenuation on transmitted sound at frequencies within the audible range of the chicken. The importance of the interaural pathway in avian hearing has yet to be determined. [Work supported by NSF.]