Effect of efferent-induced changes on acoustical reflex.

The efferent auditory pathway is known to alter the cochlear electrical properties, at low stimulus levels. This study aims to identify the effect of activation of the efferent auditory pathway through contralateral wide- and narrow-band noise at high sound levels. Acoustical reflex threshold and acoustical reflex amplitude (at ART + 10 dB) were obtained at three frequencies (500 Hz, 1 kHz, 2 kHz) in 60 normally hearing subjects, in the presence and absence of contralateral wide-and narrow-band noise (centred around reflex activating stimuli) at 30 dB SL. Results showed a consistent reduction in amplitude, and an increase in threshold, for 1- and 2-kHz tones in the presence of contralateral wideband but not narrow-band noise. Results are discussed with reference to the electrical properties of the cochlea, and the response properties of the efferent auditory pathway and cochlear nucleus.