Psychophysical pitch biases related to vowel quality, intensity difference, and sequential order.

This study investigates two types of psychophysical pitch bias, one related to vowel acoustical characteristics and the other to sequential order. Based on the analysis of the variation of the subjective equality of pitch in subjects' responses, a multivariate interaction model is used to explain the experimental results and also to demonstrate the existence of the two types of psychophysical pitch bias. The first pitch bias related to a vowel acoustical characteristic is due to the vowel quality difference as a pitch difference at equal fundamental frequency. By using /a/ as a common reference, this bias for three test vowels /e, i, u/ is found to be lower than /a/ by values of 0.54 1.25, and 2,80 Hz, respectively. The other pitch bias related to acoustical characteristic is due to the vowel intensity difference. With intensity difference ranges from 0 to 30 dB, the pitch shift (bias) does not exceed 0.2 Hz at a test F0 of 100 Hz. Apparently, an intensity difference produces insignificant pitch shift in vowel sounds. The pitch bias related to the sequential order of stimuli presentation is a --0.33-Hz bias, i.e., a trend of overestimating the pitch of the second sound in temporal pitch comparison. The pitch discriminability, i.e., the just noticeable difference (JND) at 75% threshold, in an environment with three acoustical parameters varing simultaneously is found to be 1.5%, about three times greater than the previously reported 0.5% DL when F0 varies alone. Finally, the psychophysical bias of vowel is also found to depend upon the power spectrum and negatively correlated to the magnitude of the F0 production discrepancies of the average vowel sounds.