Final Report Summary - PREDICTSPEECH (Predictable Rhythm in Speech - Benefits for Perception and Production) What comes next? We are constantly asking this question – whether in times of economical crisis, when crossing a street or when having an argument with someone. Making predictions about future events is essential for adapting our communicative and social actions. Predictions rely on regularities that we have encountered before. In the auditory domain, we extract regularities most efficiently on the basis of rhythmic patterns. Generally speaking, a rhythmic sound pattern is a recurring pattern of prominence contrasts. Some events in the sound are more prominent because they are louder, more high-pitched or longer than others. Previous research showed that temporal regularity of such rhythmic patterns is particularly efficient in building expectations in the listener. This facilitates processing of information and coordination of actions: changes in the auditory signal are better detected, we can sing, make music, dance and move together in time. While most of this research was done on simple tone sequences or music, much less is known on the benefits and effects of predictable rhythmic patterns in speech. The project PREDICTSPEECH aimed at clarifying under which conditions predictable rhythmic patterns (i.e. regularly recurring accent patterns) in speech help to improve speech perception and production in healthy adults and individuals with speech disorders. Furthermore, the project investigated how speakers/listeners coordinate their actions in relation to predictable rhythmic patterns in French and German speech, two major rhythmic types in the languages of Europe, and how this serves communicative functions, like language processing and fluency in speech production in healthy and stuttering individuals. In the past years, speech rhythm and its correlates have been a focus of interest in the phonetic/linguistic community. The communicative function of rhythm in speech and its relation to other human rhythmic behaviour, for example in the music or motor domain, however, was so far rarely addressed. The project was carried out in collaboration with researchers at the Laboratoire Parole et Langage and in collaboration with external partners in the movement sciences (Prof. Simone Dalla Bella, EuroMov, University of Montpellier) and the neurosciences (Dr. Daniele Schön, Brain Dynamics Institute, Inserm, Aix-Marseille University).In a series of experiments combining verbal and motor tasks, we studied how motor action couples with predictable rhythmic patterns in speech to foster speech processing. We found major differences between German and French listeners. German listeners showed an enhancement of semantic processing when they synchronized a motor rhythm (i.e. finger tapping) with the perceived prominent syllables in a regular speech rhythm. Their processing capacities decreased significantly when a mismatch occurred between speech accents and motor actions. In contrast, French listeners performed equally well in the task independently of the fact that motor performance was synchronized or not to the speech accents. This result indicates that accents and their language-specific phonetic implementation are crucial for auditory-motor coupling with speech. Moreover, German and French listeners showed language-specific synchronization patterns, related to the specific accentual structures of the languages. The results provide first evidence of differences in accentual perception in both languages which are revealed through motor patterns.On the background of these promising results, we continued investigating further aspects of rhythm in order to explore how strongly the motor and verbal domains are intertwined. While research has shown close links between upper body motion and speech (head, arm, hand movements), very few studies so far have addressed the relation between speech and gross motor functions such as walking. Therefore, we designed an experiment in order to test the relation between verbal tempo perception and walking. We hypothesized that the tempo of rhythmic verbal stimuli will entrain walking cadence in the listener. Participants listened to rhythmically regular word lists at three different tempi while walking. Our results showed that walking pace was indeed influenced by stimulus tempo, confirming that even gross motor functions are related to rhythmic speech processes.In addition, we wanted to further clarify how rhythmic speech structure is processed in the brain and if sensitivity to the rhythmic structure of speech could be enhanced by non-verbal auditory rhythmic stimulation. In an EEG-study, we presented rhythmic French sentences to French listeners. The stimuli were preceded by an auditory non-verbal cue (i.e. a sequence of tones) that either matched the rhythmic structure of the French sentences or that had no rhythmic relation to the sentence. Neural oscillations were phase-locking to relevant frequencies of recurring events (e.g. syllables, accents) in speech. Our results show that neural oscillations were enhanced at the frequencies of both the syllabic and the accentual level when the rhythmic cue matched the rhythmic structure of the sentence. These findings provide first evidence for the underlying mechanisms of rhythmic facilitation of speech processing induced by non-verbal / musical cues, a highly timely topic. The potential societal impact of this research consists in the advancement of a better understanding of the origins of cultural achievements linked to verbal rhythms (like poetry, rhythmic games, theatre, song) and our cognitive and motor capacities that are related to these achievements. The results are also relevant for language acquisition: a scientific background is provided to develop auditory-motor trainings for children, but also adults with rhythmic material during first and second language acquisition. The second major objective of PREDICTSPEECH was to clarify the role of rhythmic processes in speech disorders such as stuttering. In a series of experiments, we sought evidence that stuttering is linked to a rhythmic deficit encompassing the verbal and non-verbal domain. Adults who stutter, but also children and adolescents, were tested in a series of experiments on their rhythmic skills (i.e. sensorimotor synchronization, verbal synchronization, verbal and musical perception of synchronicity between two rhythmic auditory stimuli and other tasks taken from a battery for the assessment of sensorimotor and timing abilities, Benoît et al., 2014). The findings of this part of the project support the idea that stuttering is related to a timing deficit. First, participants who stutter show non-verbal deficits in the consistency and the accuracy of sensorimotor synchronization compared to fluently speaking control groups. With respect to accuracy, participants who stutter over-anticipate the beat in the pacing stimuli. Consistency deficits are most evident in participants with severe stuttering. Individual characteristics in terms of consistency and accuracy were found that could point to different underlying subtypes of stuttering – a promising avenue for future research. Second, participants who stutter were less skilled in perceiving synchronous alignment of two verbal stimuli. Moreover, perceptual rhythmic capacities were linked to sensorimotor synchronization. These results and further analyses on this extensive data set linking perception and production capacities underscores the important role of rhythm and timing in stuttering. Moreover, they show that stuttering is also entailing rhythmic deficits in the non-verbal domain. The results provide fresh insights to understand the origins and individual variations in stuttering and to identify challenges for future progress in therapy. Non-verbal and verbal rhythmic capacities may serve as a point of departure for developing interventions and diagnostics of stuttering. On the basis of these findings, we will continue the dialogue with key partners in stuttering therapy (e.g. L’assocation Parole-Bégaiement, France) and transfer between fundamental research and therapeutic intervention as well as parental care. Moreover, the findings will be of interest to therapists and patients concerned with other speech disorders that show a relation to timing processes (e.g. dyslexia, Parkinson's disease, apraxia).The highly interdisciplinary nature of our findings will be of interest to researchers of several disciplines and communities such as prosody research, language typology, (neuro)phonetics, movement sciences, neurosciences, stuttering therapy, music and language research, and psycholinguistics. On the methodological side, our newly developed methods of combining verbal and sensorimotor tasks to study speech processing opens up exciting new perspectives for use in future projects.
