Objective: Contralateral suppression of the transient-evoked otoacoustic em
issions (TEOAEs) provides a means of studying auditory efferent function, b
ut the temporal dynamics of the reflex are not fully understood. The most f
undamental parameter is the time-course of activation of contralateral supp
ression. The stimulus parameters are likely to be important; this may inclu
de temporal dynamics of the suppressor itself. This investigation thus was
devoted to the further study of 1) delay of contralateral suppression of TE
OAEs-effect of delay of the ipsilateral probe-and 2) temporal variation of
the suppressor-effect of amplitude modulation of the contralateral noise st
imulus.
Design: Measurements were made in three samples of normal-hearing subjects
(N-total = 71), employing well-established methods of TEOAE assessment.
Results: Statistically significant contralateral suppression occurred some
60 msec after onset of the contralateral noise; thereafter, the effect was
essentially constant (i.e., to >180 msec). The results for click delays les
s than 60 msec, nevertheless, were systematic and readily fitted by a slopi
ng straight line (dB suppression versus time) reminiscent of the concept of
threshold power integration. The onset of suppression may thus be characte
rized by a time constant. The delay of suppression also was found to be red
uced by contralateral amplitude-modulated noise.
Conclusions: These findings reinforce a growing consensus in the literature
that, despite initiation perhaps some milliseconds after onset of the cont
ralateral stimulus, there is a substantial delay, i.e., in the tens of mill
iseconds, before maximal suppression is achieved. The exact time constant o
f this effect appears to depend upon the combination of probe and suppresso
r levels, including the temporality of the suppressor. These factors are li
kely to delimit the role/influence of this reflex in real-world function, f
avoring perhaps more-or-less sustained suppression that is activated in a t
ime-varying sound environment.