The effect of formant trajectory and spectral shape on the tense/Lax distinction in American vowels

Perceptual tests in which subjects were asked to identify tense and lax vowels were used to examine the interaction among properties which have been observed to accompany the tense/lax distinction in General American English. The results yield information on the perception of vowels in general. Four vowel parameters were manipulated in synthetic nonsense words of the form /dVs/: target formant frequency, duration, formant trajectory, and F1-prominence (a measure of spectral shape, defined as the ratio of the amplitude of the first-formant peak to the amplitude of the fundamental harmonic). The perceptual tests involved acoustic continua between adjacent pairs of stimuli in the series /i I ε æ/ and in the series /u U Λ a/. F1- prominence could not be shown to affect the identification of any vowel. The results for the duration and trajectory manipulations for non-high vowels can be predicted by hypothesizing a perceptual averaging of formant frequency over the duration of the vowel. These findings seem to be in conflict with findings of other investigators which suggest perceptual overshoot in vowel perception.