Previous studies have shown that slowly-varying amplitude modulations (AM) are crucial for speech comprehension. Moreover, recent neurophysiological studies showed low-frequency neural oscillations (< 10 Hz) are taking roles in tracking such critical AM cues which facilitate speech comprehension. However, many of such studies neglected the detailed spectral information (frequency modulations (FM)). The current paper conducted a behavioral experiment to study the relative importance of AM and FM cues for sentence intelligibility based on the hypothesis that such importance is modulated by speaking rate. By measuring the intelligibility of Mandarin sentences with selective removal of AM cues at particular AM rates or replacing FM cues with Gaussian noise, the current study found: (1) at a low speaking rate (4-Hz syllable rate), FM cues and high-rate AM cues made only marginal contributions to speech intelligibility, which is consistent with previous findings; (2) at high speaking rates (6- and 8-Hz syllable rates), however, FM cues made significant contributions even greater than AM cues at the rates suggested to be essential by previous neurophysiological studies. This result thus illustrates the relative importance of AM and FM cues at different speaking rates in Mandarin and implications for the neurophysiological speech processing were further discussed.
Bibliographic reference. Mai, Guangting (2014): "Relative importance of AM and FM cues for speech comprehension: effects of speaking rate and their implications for neurophysiological processing of speech", In INTERSPEECH-2014, 2585-2589.