Acoustical correlates of the perception of speech rate: an experimental investigation.

The purpose of the study was to investigate the influence of vocal frequency and vocal intensity upon the perception of speech rate at three levels of actual speech rate. A single sample of spontaneous speech was electronically varied to produce nine stimulus segments that factorially combined three levels each of vocal frequency and intensity. The nine stimuli were recorded such that preceding each was the original segment that served as the standard with which each of the nine stimuli was to be compared. The speech rate of the set of nine stimulus pairs was then electronically altered to obtain a slow set, a moderate set, and a fast set, although the duration of every segment in the three sets was 20 seconds. The sets were rated by different groups of judges in terms of four 7-point scales that measured perceived speech rate, pitch, loudness, and perceived duration. The results indicate that the perception of speech rate is positively related to vocal frequency and intensity at each of the three actual speech rates, and suggest that these relationships are a function of the repeated experience of almost always hearing such covariation in spontaneously occurring speech.