Interaural attenuation as measured with differential electrodes in guinea pig and chinchilla

Abstract

Acoustic energy delivered to one ear can, through cross conduction, stimulate the contralateral cochlea. The effects of cross conduction can complicate studies attempting to define binaural mechanisms. For instance, acoustic energy delivered directly to one ear can interact with the cross-conducted acoustic energy delivered to the other ear, thus confounding the independence of the two auditory channels. This constraint upon the independence of the acoustic channels might be more severe for small animals such as the guinea pig and chinchilla that for larger animals such as the cat, monkey, and man. We have determined isopotential curves (Turn I, differential electrodes) for the guinea pig and chinchilla from which interaural attenuation has been estimated. Below 10 kHz, interaural attenuation decreases from about 50–60 dB below 1 kHz to about 40–50 dB around 10 kHz. Differences in curves due to open and closed bullae appear for some animals. For ipsilateral stimulus levels greater than 90 dB SPL, frequencies above 10 kHz produced direct electrical pickup in differential electrodes whether they were into the cochlea or suspended in a saline-filled bulla. Contralateral stimulus levels above 100 dB produced similar phenomena.