Traversing upper vowel space: A smooth or a bumpy ride?

It has been found in vowel imitation studies that subjects' responses to steadystate isolated vowels from an acoustic continuum exhibit categorical tendencies: Some adjacent vowels are responded to more similarly than others, and the distribution of formant frequencies in the total set of responses is decidedly nonuniform. The present study investigated whether these tendencies originate in perception or in articulation. Subjects were asked to produce continuous glides from iiI to lrel and from lrel to IiI at three different speeds, as well as discrete vowels along the same continuum, without any auditory models. The results show that categorical tendencies of the kind observed previously in imitation tasks emerge as soon as vowel glides are produced at a rate that requires conscious control over the articulatory trajectory. The categorical tendencies thus seem to originate in the speech production system, although on-line perceptual guidance through auditory feedback cannot be ruled out at this stage.