Cricothyroid activity in high and low vowels: exploring the automaticity of intrinsic F0

Abstract

Although vowels can be produced with any F0 in a speaker's range, the high vowels tend to be produced with a higher F0 than low vowels. This “intrinsic F0” (IF0) has been found for every language that has been examined for it (Whalen & Levitt, 1995) and has also been found in the babbling of prelinguistic infants (Whalen, Levitt, Hsiao & Smorodinsky, 1995), suggesting that it is an automatic consequence of articulation. Nonetheless, some researchers have suggested that IF0 is a deliberate enhancement of the perception of vowel height (Diehl & Kluender, 1989; Kingston, 1992; Fahey & Diehl, 1996). The only positive evidence in favor of this view is that EMG activity for the cricothyroid (CT) muscle has been reported to be higher for high vowels than for low, suggesting active control of F0. The present experiment examines CT activity in four English-speaking subjects saying isolated vowels. In one condition, target tones that differed by the same amount as the IF0 magnitude itself were presented for the subjects to match; in the other condition, there were no targets. CT activity for the condition with targets was higher for the high vowels for only one of the four subjects; the patterns for the other three were negative, neutral or mixed. Since only two subjects from the previous literature are comparable to the present work, the basic assumption of higher CT activity for high vowels must be called into question. Further, when F0 was shifted by an amount equivalent to that seen in IF0, it was found that the high vowels needed more CT activity to effect a change than the low vowels did. This indicates that it is impossible to compare absolute values of CT activity as indications of direct F0 control. In the condition without targets, CT activity for three subjects followed the pattern of the target condition, being neutral, negative or mixed. Thus, the EMG evidence cited in favor of IF0 being deliberate is contradicted, leaving a preponderance of evidence that IF0 is an automatic consequence of successful vowel articulation.