The effect of filled pauses and speaking rate on speech comprehension in natural, vocoded and synthetic speech

It has been shown that in natural speech filled pauses can be beneficial to a listener. In this paper, we attempt to discover whether listeners react in a similar way to filled pauses in synthetic and vocoded speech compared to natural speech. We present two experiments focusing on reaction time to a target word. In the first, we replicate earlier work in natural speech, namely that listeners respond faster to a target word following a filled pause than following a silent pause. This is replicated in vocoded but not in synthetic speech. Our second experiment investigates the effect of speaking rate on reaction times as this was potentially a confounding factor in the first experiment. Evidence suggests that slower speech rates lead to slower reaction times in synthetic and in natural speech. Moreover, in synthetic speech the response to a target word after a filled pause is slower than after a silent pause. This finding, combined with an overall slower reaction time, demonstrates a shortfall in current synthesis techniques. Remedying this could help make synthesis less demanding and more pleasant for the listener, and reaction time experiments could thus provide a measure of improvement in synthesis techniques.