Threshold of octave masking as a tool to explain cochlear nonlinearity

Abstract

Background and Aim: The threshold of octave masking test has been used to assess the growth rate of aural harmonics, the intercept point helped differentiate between normal-hearing individuals and sensorineural hearing loss due to noise exposure. With fewer literatures that have been documented, there is a need to explore this test procedure, and hence the purpose of this research is to evaluate the utility of the threshold of octave masking (TOM) procedure in understanding the frequency selectivity and non-linear function of cochlea.
 Methods: A total of 10 adults (20 ears) were considered for the test. The TOM test procedure was performed on the subjects where the subjects had to identify the presence of a maskee tone (1 kHz) in the presence of a masker tone (500 Hz) across 5 dB increment of masker tone until the subjects uncomfortable level. A line graph was drawn, extrapolated to identify the point of intercept, which is the threshold of octave masking.
 Results: Results reveal that 17 ears did not have a linear growth but had a 10 to 20 dB gap after a particular maskee level. The intercept point of the initial two extreme points was relatively more than the intercept point of the extreme points at higher intensities.
 Conclusion: Results from the present study have thrown light on the fact that TOM can be used as a test to measure the frequency selectivity along with the tests of psychophysical tuning curves, notched noise method, non-simultaneous masking, and other non-peripheral masking phenomena.
 Keywords: Threshold of octave masking; active mechanism; passive mechanism; nonlinearity;frequency selectivity; psychophysical tuning curves