Abstract
In this paper, several speech sounds are examined by masking methods to show typical examples of speech spectrum representation in the auditory pathway represented by a spatio-temporal masking pattern and to clarify differences between internal and physical representation of speech spectrum. Three types of Japanese speech, monosyllables, a sentence utterance and a time-reversed monosyllable, are chosen for masker sounds. Using 1/3 octave band noise bursts of 25ms duration as probe signals, simultaneous and temporal masking values are measured for the whole period of each masker. The spatio-temporal masking pattern thus obtained is an internal speech spectrum. Com-pared with the physical spectral pattern, speech onsets and the formant structure, parti-cularly the formant transition, are enhanced and prominently represented in the masking patterns. These spectral enhancements in the auditory pathway are assumed to be the result of three auditory peripheral functions, AM/FM masking, forward/backwardmasking and adaptation. Further, taking into account the considerable differences between the internal and the physical representation of speech spectrum, the importance of the internal speech spectrum representation in the field of speech science is discussed.
