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Temporal non-linearities of the cochlear amplifier revealed by maximum length sequence stimulation
A R Thornton1, K Shin, E Gottesman
1MRC Institute of Hearing Research, Royal South Hants Hospital, Brinton's Terrace, SO14 0YG, Southampton, UK. ardt@soton.ac.uk
Objectives:
The objective of this study was to examine whether temporal non-linearities of the cochlear amplifier, as reflected by otoacoustic emissions (OAEs), exist and are distinct from any recording system non-linearities.
Methods:
Maximum length sequence stimulation, at various stimulus rates, was used to evoke OAEs from normally hearing subjects. Recordings from a 2cc cavity were also made. The data were analyzed to obtain the linear response and estimates of the slices of the 2nd and 3rd order Volterra kernels. This provided a measure of two and 3 click non-linear temporal interactions, respectively.
Results:
The results showed that temporal non-linearities of OAEs do exist, are stable and repeatable within individuals and have properties that differ from those shown by the conventional linear response. Whilst some of the non-linear response properties conformed to the expected pattern, of increasing amplitude with increase in stimulus rate, there are some areas in which they show an unpredicted complexity.
Conclusions:
Whilst system non-linearities could be found, there was no difficulty in distinguishing between the physiological and system non-linear components. New areas of research and application may result from the use of these new OAE responses.