The synergy between speech production and perception
Shihab A. Shamma · The Journal of the Acoustical Society of America · 2001
Speech intelligibility is relatively unaffected by certain spectro-temporal deformations of the signal spectrogram. These include spectral and dynamic translations, stretching or contracting dilations, and shearing of the spectrogram along its temporal or logarithmic frequency axis. We shall argue that this stability results from a synergy between the dynamics and characteristics of the auditory cortex (the receiver) and of the vocal tract (the source). Specifically, on the perception side, neurophysiological evidence suggests that the acoustic spectrogram is represented in the primary auditory cortex along multiple spectro-temporal scales, and that the above deformations correspond to simple translations of the representation of the dynamic acoustic spectrum along these axes. On the production side, these spectro-temporal distortions can be caused by common variations among talkers in speaking rates, slurred articulatory dynamics, vocal tract length, cross-sectional profile, and losses. Using a simplified sinusoid model of the vocal tract, it is possible to relate ‘‘articulatory’’ parameters (e.g., the extent and location of a vocal tract constriction) directly to the formants, and hence to the cortical representation of the spectrum. A similar remarkable synergy exists between the dynamics of perception (e.g., via the perceived spectro-temporal modulation transfer functions) and the speed of articulation and hence the syllabic rates of speech. These results suggest an intimate link between perception and production, a view which offers new insights into the organization of speech phonemes (such as vowels) in terms of different vocal tract configurations.