On the just noticeable difference for tempo in speech

Speakers vary their speech tempo (speaking rate), and such variations in tempo are quite noticeable. But what is the just noticeable difference (JND) for tempo in speech? The present study aims at providing a realistic and robust estimate, by using multiple speech tokens from multiple speakers. The JND is assessed in two (2IAX and 2IFC) comparison experiments, yielding an estimated JND for speech tempo of about 5%. A control experiment suggests that this finding is not due to acoustic artefacts of the tempo-transformation method used. Tempo variations within speakers typically exceed this JND, which makes such variations relevant in speech communication.