Some effects of tonal fatiguing on spontaneous and distortion-product otoacoustic emissions

Auditory fatiguing can be considered a suitable test to assess some cochlear mechanisms and diseases otherwise not easily detectable. Since spontaneous otoacoustic emissions (SOAEs) originate from active sources within the cochlea they show sensitive and early vulnerability to noise, displaying informative time-courses after overstimulation in the short (0-6 s) and in the long term (1-10 min) depending on the frequency of the fatiguing stimulus. Distortion product otoacoustic emissions too, in subjects with SOAEs, show interesting modifications after pure-tone exposure, detectable either on distortion product audiograms or in the growth functions. The modifications take place within a period of 5-7 minutes and strongly depend on the frequency of the fatiguing stimulus and on the closeness between SOAE and distortion product place. The data suggest that not only the interaction place between f1 and f2 has to be considered from a biomechanical and clinical point of view, but also the specific distortion product place on the cochlear partition.