| Abstract #814, Date 2/17/99, Session Y3, Poster (B79) |
| Suppression of the click-rate induced facilitation of acoustic reflex thresholds due to contralateral stimuli |
| *V.W. Rawool (Bloomsburg University) |
Ipsilateral acoustic reflex thresholds are known to improve with an increase in the click-repetition rate (Rawool, Scand Audiol 1995; 24:199-205; J Gerontol Biol Sci 1996; 51A:B124-131). Contralateral acoustic stimuli are known to cause suppression of otoacoustic emissions and auditory nerve response due to the activation of the efferent pathways. Since the acoustic reflex pathway includes both the cochlea and the auditory nerve, a similar suppressive effect may occur for the click-rate induced improvement of the acoustic reflex thresholds. The effect of contralateral stimulation on the click-rate induced improvement of the acoustic reflex thresholds was investigated in the current study. Twenty-one normal female subjects in the age-range of 19-32 years participated in the study. The reflex activating stimuli were clicks presented at the rate of 50 and 100/sec. The probe tone frequency was 226 Hz and the intensity was 85 dB SPL. Acoustic reflex thresholds were established for each subject by placing the probe in the left ear and presenting the clicks to the right ear, in two conditions. In the first condition (pulsed), the presentation of the probe tone was alternated with the presentation of the clicks. Thus, the reflex was measured after the clicks were turned off for a brief period by presenting the probe tone. This is possible since the reflex has a relatively long `off' latency. In the second condition (simultaneous), the probe tone and the clicks were presented simultaneously which allowed measurement of the click rate induced improvement of the acoustic reflex thresholds while activating the efferent pathways. For each subject the click-rate induced facilitation (RIF) was calculated by subtracting the threshold obtained at the click-rate of 100/sec from that obtained at the rate of 50/sec. The repeated measures Multivariate Analyses of Variance revealed that the simultaneous presence of the probe tone during acoustic reflex measures can suppress the click-rate induced facilitation of the acoustic reflex thresholds. |