Speaking rate, VOT, and quantity: The search for higher-order invariants for two Icelandic speech cues

Abstract

The temporal structure of speech is highly variable. Speaking rate, stress among other factors influence the duration of speech sounds. A number of speech cues are by their nature temporal. This holds, e.g., for voice onset time as well as for duration as a cue to phonemic quantity. The highly ‘‘elastic’’ nature of speech would seem to pose a problem for the listener: How does he or she achieve an invariant percept in the face of this great temporal variability? Data for two Icelandic speech cues under different speaking rates are reported. Results show that manipulations of rate have the effect of slightly blurring the distinction between unaspirated and aspirated stops. In spite of great changes in the absolute durations of long and short vowels and consonants the two categories of syllables, V:C and VC:, are in fact kept totally distinct. In perceptual experiments it is shown that the ratio of vowel to consonant duration is the primary cue to quantity and remains invariant at different rates. Perceptual experiments show a small effect of rate on the boundaries for VOT. The two temporal speech cues of VOT and quantity are thus shown to behave quite differently under transformations of rate.