Within speaker rate variability limits habitual speech rate tracking

Listeners track the habitual speech rate of talkers and use this information to resolve temporal ambiguities in vowels by normalizing vowel length for the surrounding speech rate. Previous studies supporting this effect have also shown that the habitual rate of one talker is perceived relative to the habitual rate of another talker. These studies mainly involved speakers with constant habitual rates. However, given the large within-speaker variability in speech rate, it remains unclear whether this mechanism is applicable in natural conversation. This study, therefore, assessed the influence of within-speaker rate variability of one talker on the perception of the Dutch vowel contrast /ɑ/–/a:/ in a second talker. 38 Dutch speakers heard two talkers speaking at different rates. Half of the participants heard Talker A speak at a normal rate and Talker B at a fast rate intermixed with normal rate trials. The other half heard the same Talker A but Talker B at a slow rate and normal rate. Contrary to previous studies, we did not find that Talker B's rate affected perception of Talker A's ambiguous vowels. Therefore, habitual rate tracking seems to be hindered by within-speaker variability in speech rate.