The Effects of Quantized Re-timing of Speech Rhythm on Spoken Language

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OverviewWhat's going to happen next? is a question the brain constantly seeks to answer. Inneuroscience, prediction is increasingly seen as the key to language comprehension, but lessis known about how listeners predict when linguistic events (sounds, syllables) will occur,than about what is coming. Current theories of neural speech processing suggest a key rolefor rhythm, yet neuroscience and the speech sciences lack a shared understanding of thebasics of rhythm. This project seeks to address this gap by asking: Can speech be re-timed soas to maximise its comprehensibility? The research will use phonetic and musicalapproaches to inform the re-timing of speech and the effects on comprehension will betested using innovative eye-tracking and EEG paradigms.ContextA crucial aspect of speech comprehension is the ability to anticipate lexical or grammaticalunits. This has been demonstrated by extensive research showing characteristic neuralresponses to violations of expectation in speech (e.g. Hagoort et al., 2004). According torecent theories in cognitive neuroscience, listeners achieve such anticipation in part bytracking regularities in speech rhythm, at timescales roughly corresponding to individualvowels and consonants, and to syllables (e.g. Giraud and Poeppel, 2012; Gross et al., 2013).However, this picture does not match well with phonetic or behavioural reality. First, thereis little evidence of rhythmic regularity in the production of syllables in naturally occurringspeech (Cummins, 2012). Second, the rhythm-tracking approach suggests that makingspeech more regular would help comprehension. But, while presenting isolated syllables atregular time intervals can yield processing benefits (Otterbein et al., 2012), regularising theintervals between syllables in connected speech instead has a processing cost (Aubanel etal., 2016). In sum, regularity can be beneficial, but is not always: the relationships have to beright for the speech being presented, in ways that are poorly understood.A speech signal does not necessarily need to be regular to be rhythmic. In response tomusical rhythms, neural correlates of the pulse (or beat) can be found when listeners arepresented with complex polyrhythms where the pulse is not physically present in the signal(Tal et al., 2017). Similar principles might apply in speech, but the relevant empirical workhas not been done, and speech research has a much reduced lexicon of terminology forrhythm compared to music (Smith et al, 2014). In order to understand how the temporalcharacteristics of speech facilitate comprehension, it may be necessary to consider a morenuanced approach to rhythm, informed by music.This project seeks to improve understanding of the role of rhythm in speech comprehensionby answering two Research questions:1. Does re-timing speech to increase its rhythmicity help speech comprehension, when amore sophisticated approach than equalising syllable durations is used?2. If so, on which properties of the speech signal should re-timing ideally be based?