Spectro-temporal modulation transfer functions and speech intelligibility

Detection thresholds for spectral and temporal modulations are measured usi ng broadband spectra with sinusoidally rippled profiles that drift up or do wn the log-frequency axis at constant velocities. Spectre-temporal modulati on transfer functions (MTFs) are derived as a function of ripple peak densi ty (Omega cycles/octave) and drifting velocity to (omega Hz). The MTFs exhi bit a low-pass function with respect: to both dimensions, with 50% bandwidt hs of about 16 Hz and 2 cycles/octave. The data replicate las special cases ) previously measured purely temporal MTFs (Omega=0) [Viemeister, J. Acoust . Sec. Am. 66, 1364-1380 (1979)] and purely spectral MTFs (omega=0) [Green, in Auditory Frequency Selectivity (Plenum, Cambridge, 1986), pp. 351-359]. A computational auditory model is presented that exhibits spectre-temporal MTFs consistent with the salient trends in the data. The model is used to demonstrate the potential relevance of these MTFs to the assessment of spee ch intelligibility in noise and reverberant conditions. (C) 1999 Acoustical Society of America. [S0001-4966(99)02210-9].