Effects of efferent acoustic reflex activation on psychoacoustical tuning curves in humans

The results show that, in humans, activation of the contralateral EAR makes the PTC narrower at 1 kHz but wider at 4 kHz. These data are consistent with those reported previously in animals and demonstrate that, during medial efferent stimulation in humans, frequency resolution is improved at low frequencies but impaired at high frequencies.

To evaluate, in humans, the effect of activation of the contralateral efferent acoustic reflex (EAR) on the psychoacoustical tuning curves (PTCs) recorded for 1- and 4-kHz probe tones. MATERIAL AND METHODS. Ten young (20-30 years) volunteers served as subjects. They had normal hearing (thresholds <20 dB HL in the frequency range 0.25-8 kHz) and a functioning EAR (contralateral suppression of transient-evoked otoacoustic emissions > or = 0.8 dB). Frequency resolution was evaluated using PTCs. PTCs were recorded at 1 and 4 kHz using a simultaneous masking method. Q10 and Q20 were calculated as the ratio between the test frequency and the bandwidth of the PTC at 10 and 20 dB above the tip of the curve, respectively. The EAR was activated with a 40-dB SL contralateral narrow-band noise centered on the characteristic frequency of the PTC (1 or 4 kHz). Q10 and Q20 were measured in the presence and absence of the contralateral noise.

Activation of the EAR led to a significant increase (p < 0.001) in Q10 at 1 kHz and a significant decrease (p <0.001) at 4 kHz. Changes in the value of Q20 were not significant.