The role of probability and duration in perception of speech sounds

When listeners are hearing sounds in the speech signal and have not yet heard enough acoustic cues to know what a sound is, they might predict the upcoming sound based on likelihood in the language or likelihood of occurrence after the preceding sound (overall and conditional probability of sounds). A related factor may be how long the sound goes on: listeners might be more able to identify sounds that go on longer because they have more time to hear the acoustic cues. However, additional duration may only be useful to listeners if it contains new acoustic cues (acoustic change). This paper investigates whether these factors have a role in how listeners perceive or predict sounds. This study presents further analysis of the perception data collected by the English Diphones project (Warner et al., 2014). The results show that listeners predict upcoming phonemes based on a guessing strategy, not based on lexical probability, with a small influence of syllable structure. Longer duration in itself does not produce better identification, but rather plays a role when important acoustic changes occur within the additional duration. The present study suggests that listeners use acoustic information rather than probability, and that they are sensitive to dynamic changes in spectral structure.