Voice onset time and fundamental frequency as cues to the /zi/-/si/ distinction

The present series of experiments used factorial designs to evaluate which acoustic features are primarily responsible for the voicing distinction in the syllables Izil and Isi/. Increases in frication duration tend to make the syllable more voiceless only if vocal cord vibration is absent or at a very low level during the frication period. Increasing the period between the onset of frication and the onset of vocal cord vibration changes the syllable from a predominantly voiced to a predominantly voiceless sound. This period, called voice onset time, can account for the change in perception regardless of simultaneous changes in the total frication duration or the relative duration of the frication period that contains vocal cord vibration. Changes in fundamental frequency had a large influence on the voicing judgments. With low fundamental frequencies, the judgments were predominantly voiced, whereas with high fundamental frequencies, voiceless judgments were predominant. The quantitative judgments of individual observers were described by a ratio-rule model that assumes a multiplicative combination of the independent cues, voice onset time and fundamental frequency. The, model also provided a good description of previous studies of the acoustic cues used in the perception of voicing of fricatives.