The perception of speech rate for time manipulated and vocoded sentences

Abstract

Naturally produced fast speech reduces certain acoustic-phonetic features that may limit intelligibility relative to linear time compression. However, how reduction affects judgments of speaking rate has not been systematically investigated. The purpose of this study was to examine the effects of linear time compression and spectral reduction on judgments of speaking rate. Listeners provided speech rate judgments of sentences. Conditions compared rate perceptions for naturally spoken sentences at slow and fast rates with linearly time-compressed/expanded versions of the same sentence, matched for duration. Conditions also examined rate judgments for noise vocoded sentences that varied in intelligibility and signal-correlated noise that examined rate judgments based only on temporal acoustic features. Our preliminary results demonstrate that linear time-compressed/expanded sentences were judged as faster than naturally produced sentences. This difference was also found for noise-vocoded versions of the sentences, as well as for signal-correlated noise. Additionally, vocoded stimuli were perceived as faster than naturally produced stimuli. These preliminary results suggest that acoustic-phonetic reductions in naturally produced speech do not appear to increase the perceived speaking rate relative to linear time manipulations. Significantly, temporal properties of speech rhythm appear responsible for coding perceptual aspects of speaking rate independently from factors related to linguistic processing.