抄録
Spectral envelopes are important for vowel recognition. Psychophysical studies have previously showed that the sharpness of formants can contribute to the vowel quality. However, it is unclear how cortical neurons process this parameter. In this study we investigated this issue in primary auditory cortex (A1) neurons of awake cats. Stimuli were the multi-frequency tones with a spectral prominence. The spectral peak frequency was always located at the cell’s best frequency, while the prominence-amplitude was shifted systematically. Pure and two tone stimuli were used to delineate excitatory and inhibitory subfields of the frequency response field (FRF). The cell’s responses to different prominence-amplitudes were investigated with reference to the spectral location of the prominence relative to cell’s FRF. We found that A1 cells showed preference of higher prominence-amplitude when the sound energy was on a portion of FRF including moderate inhibitory subfield, while the same A1 cell could show preference of lower prominence-amplitude when the sound energy was on a portion of FRF including negligible inhibitory subfield. The results suggest that A1 can discriminate the sharp-prominence from the dull-prominence when the prominences have the same spectral peak frequency; and the prominence preference is originated from the shift of balance of the spectral excitation and inhibition. The present study has provided physiological data supporting the interpretation that the vowel perception is processed in A1 by analysis of the spectral shape cues. [Jpn J Physiol 55 Suppl:S170 (2005)]
