Schroeder phase harmonic tone complex (SCHR) is composed of a fundamental tone with its harmonics, and the phases of the tones is defined as θn = Cπn(n + 1)/N; -1≦C≦1, where θn is the phase of the n th harmonic. SCHR has been known for its unique characteristics, in that it has a large difference of masking effect and middle ear muscle reflex (MEMR) with the C value. Since SCHR has a characteristic that it repeats with the fundamental period, it can also be used as probe tone for detecting MEMR. Thus, time series change of intra-ear canal sound level of SCHR can be utilized for MEMR detection. Seven normal hearing subjects were measured, and showed that sound level changed from the onset and reached plateau after around 200 ms. The plateau levels differed with C value as well as stimulus levels. Detection thresholds were much smaller than those with current clinical methods. The level difference with C values showed quite similar patterns to that of masking effect. These results lead that this method can replace the current measuring method of MEMR and be utilized as a novel technique for detecting retro-cochlear function.
Tatsuhiko Harada (2025) studied this question.