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Prosody is a rich source of information that heavily supports spoken language comprehension. In particular, prosodic phrase boundaries divide the continuous speech stream into chunks reflecting the semantic and syntactic structure of an utterance. This chunking or prosodic phrasing plays a critical role in both spoken language processing and language acquisition. Aiming at a better understanding of the underlying processing mechanisms and their acquisition, the present work investigates factors that influence prosodic phrase boundary perception in adults and infants. Using the event-related potential (ERP) technique, three experimental studies examined the role of prosodic context (i.e., phrase length) in German phrase boundary perception and of the main prosodic boundary cues, namely pitch change, final lengthening, and pause. With regard to the boundary cues, the dissertation focused on the questions which cues or cue combination are essential for the perception of a prosodic boundary and on whether and how this cue weighting develops during infancy.
Using ERPs is advantageous because the technique captures the immediate impact of (linguistic) information during on-line processing. Moreover, as it can be applied independently of specific task demands or an overt response performance, it can be used with both infants and adults. ERPs are particularly suitable to study the time course and underlying mechanisms of boundary perception, because a specific ERP component, the Closure Positive Shift (CPS) is well established as neuro-physiological indicator of prosodic boundary perception in adults.
The results of the three experimental studies first underpin that the prosodic context plays an immediate role in the processing of prosodic boundary information. Moreover, the second study reveals that adult listeners perceive a prosodic boundary also on the basis of a sub-set of the boundary cues available in the speech signal. Both ERP and simultaneously collected behavioral data (i.e., prosodic judgements) suggest that the combination of pitch change and final lengthening triggers boundary perception; however, when presented as single cues, neither pitch change nor final lengthening were sufficient. Finally, testing six- and eight-month-old infants shows that the early sensitivity for prosodic information is reflected in a brain response resembling the adult CPS. For both age groups, brain responses to prosodic boundaries cued by pitch change and final lengthening revealed a positivity that can be interpreted as a CPS-like infant ERP component. In contrast, but comparable to the adults’ response pattern, pitch change as a single cue does not provoke an infant CPS. These results show that infant phrase boundary perception is not exclusively based on pause detection and hint at an early ability to exploit subtle, relational prosodic cues in speech perception.
Speech and action sequences are continuous streams of information that can be segmented into sub-units. In both domains, this segmentation can be facilitated by perceptual cues contained within the information stream. In speech, prosodic cues (e.g., a pause, pre-boundary lengthening, and pitch rise) mark boundaries between words and phrases, while boundaries between actions of an action sequence can be marked by kinematic cues (e.g., a pause, pre-boundary deceleration). The processing of prosodic boundary cues evokes an Event-related Potentials (ERP) component known as the Closure Positive Shift (CPS), and it is possible that the CPS reflects domaingeneral cognitive processes involved in segmentation, given that the CPS is also evoked by boundaries between subunits of non-speech auditory stimuli. This study further probed the domain-generality of the CPS and its underlying processes by investigating electrophysiological correlates of the processing of boundary cues in sequences of spoken verbs (auditory stimuli; Experiment 1; N = 23 adults) and actions (visual stimuli; Experiment 2; N = 23 adults). The EEG data from both experiments revealed a CPS-like broadly distributed positivity during the 250 ms prior to the onset of the post-boundary word or action, indicating similar electrophysiological correlates of boundary processing across domains, suggesting that the cognitive processes underlying speech and action segmentation might also be shared.
Early sensitivity to prosodic phrase boundary cues: Behavioral evidence from German-learning infants
(2023)
This dissertation seeks to shed light on the relation of phrasal prosody and developmental speech perception in German-learning infants. Three independent empirical studies explore the role of acoustic correlates of major prosodic boundaries, specifically pitch change, final lengthening, and pause, in infant boundary perception. Moreover, it was examined whether the sensitivity to prosodic phrase boundary markings changes during the first year of life as a result of perceptual attunement to the ambient language (Aslin & Pisoni, 1980).
Using the headturn preference procedure six- and eight-month-old monolingual German-learning infants were tested on their discrimination of two different prosodic groupings of the same list of coordinated names either with or without an internal IPB after the second name, that is, [Moni und Lilli] [und Manu] or [Moni und Lilli und Manu]. The boundary marking was systematically varied with respect to single prosodic cues or specific cue combinations.
Results revealed that six- and eight-month-old German-learning infants successfully detect the internal prosodic boundary when it is signaled by all the three main boundary cues pitch change, final lengthening, and pause. For eight-, but not for six-month-olds, the combination of pitch change and final lengthening, without the occurrence of a pause, is sufficient. This mirrors an adult-like perception by eight-months (Holzgrefe-Lang et al., 2016). Six-month-olds detect a prosodic phrase boundary signaled by final lengthening and pause. The findings suggest a developmental change in German prosodic boundary cue perception from a strong reliance on the pause cue at six months to a differentiated sensitivity to the more subtle cues pitch change and final lengthening at eight months. Neither for six- nor for eight-month-olds the occurrence of pitch change or final lengthening as single cues is sufficient, similar to what has been observed for adult speakers of German (Holzgrefe-Lang et al., 2016).
The present dissertation provides new scientific knowledge on infants’ sensitivity to individual prosodic phrase boundary cues in the first year of life. Methodologically, the studies are pathbreaking since they used exactly the same stimulus materials – phonologically thoroughly controlled lists of names – that have also been used with adults (Holzgrefe-Lang et al., 2016) and with infants in a neurophysiological paradigm (Holzgrefe-Lang, Wellmann, Höhle, & Wartenburger, 2018), allowing for comparisons across age (six/ eight months and adults) and method (behavioral vs. neurophysiological methods). Moreover, materials are suited to be transferred to other languages allowing for a crosslinguistic comparison. Taken together with a study with similar French materials (van Ommen et al., 2020) the observed change in sensitivity in German-learning infants can be interpreted as a language-specific one, from an initial language-general processing mechanism that primarily focuses on the presence of pauses to a language-specific processing that takes into account prosodic properties available in the ambient language. The developmental pattern is discussed as an interplay of acoustic salience, prosodic typology (prosodic regularity) and cue reliability.