Refine
Has Fulltext
- no (4) (remove)
Document Type
- Article (4)
Language
- English (4)
Is part of the Bibliography
- yes (4)
Keywords
- speech perception (4) (remove)
Institute
Infants as young as six months are sensitive to prosodic phrase boundaries marked by three acoustic cues: pitch change, final lengthening, and pause. Behavioral studies suggest that a language-specific weighting of these cues develops during the first year of life; recent work on German revealed that eight-month-olds, unlike six-month-olds, are capable of perceiving a prosodic boundary on the basis of pitch change and final lengthening only. The present study uses Event-Related Potentials (ERPs) to investigate the neuro-cognitive development of prosodic cue perception in German-learning infants. In adults’ ERPs, prosodic boundary perception is clearly reflected by the so-called Closure Positive Shift (CPS). To date, there is mixed evidence on whether an infant CPS exists that signals early prosodic cue perception, or whether the CPS emerges only later—the latter implying that infantile brain responses to prosodic boundaries reflect acoustic, low-level pause detection.
We presented six- and eight-month-olds with stimuli containing either no boundary cues, only a pitch cue, or a combination of both pitch change and final lengthening. For both age groups, responses to the former two conditions did not differ, while brain responses to prosodic boundaries cued by pitch change and final lengthening showed a positivity that we interpret as a CPS-like infant ERP component. This hints at an early sensitivity to prosodic boundaries that cannot exclusively be based on pause detection. Instead, infants’ brain responses indicate an early ability to exploit subtle, relational prosodic cues in speech perception—presumably even earlier than could be concluded from previous behavioral results.
Prosodic information is crucial for spoken language comprehension and especially for syntactic parsing, because prosodic cues guide the hearer's syntactic analysis. The time course and mechanisms of this interplay of prosody and syntax are not yet well-understood. In particular, there is an ongoing debate whether local prosodic cues are taken into account automatically or whether they are processed in relation to the global prosodic context in which they appear. The present study explores whether the perception of a prosodic boundary is affected by its position within an utterance. In an event-related potential (PRP) study we tested if the brain response evoked by the prosodic boundary differs when the boundary occurs early in a list of three names connected by conjunctions (i.e., after the first name) as compared to later in the utterance (i.e., after the second name). A closure positive shift (CPS)-marking the processing of a prosodic phrase boundary-was elicited for stimuli with a late boundary, but not for stimuli with an early boundary. This result is further evidence for an immediate integration of prosodic information into the parsing of an utterance. In addition, it shows that the processing of prosodic boundary cues depends on the previously processed information from the preceding prosodic context.
Previous studies have revealed that infants aged 6-10 months are able to use the acoustic correlates of major prosodic boundaries, that is, pitch change, preboundary lengthening, and pause, for the segmentation of the continuous speech signal. Moreover, investigations with American-English- and Dutch-learning infants suggest that processing prosodic boundary markings involves a weighting of these cues. This weighting seems to develop with increasing exposure to the native language and to underlie crosslinguistic variation. In the following, we report the results of four experiments using the headturn preference procedure to explore the perception of prosodic boundary cues in German infants. We presented 8-month-old infants with a sequence of names in two different prosodic groupings, with or without boundary markers. Infants discriminated both sequences when the boundary was marked by all three cues (Experiment 1) and when it was marked by a pitch change and preboundary lengthening in combination (Experiment 2). The presence of a pitch change (Experiment 3) or preboundary lengthening (Experiment 4) as single cues did not lead to a successful discrimination. Our results indicate that pause is not a necessary cue for German infants. Pitch change and preboundary lengthening in combination, but not as single cues, are sufficient. Hence, by 8 months infants only rely on a convergence of boundary markers. Comparisons with adults' performance on the same stimulus materials suggest that the pattern observed with the 8-month-olds is already consistent with that of adults. We discuss our findings with respect to crosslinguistic variation and the development of a language-specific prosodic cue weighting.
Speech perception requires rapid extraction of the linguistic content from the acoustic signal. The ability to efficiently process rapid changes in auditory information is important for decoding speech and thereby crucial during language acquisition. Investigating functional networks of speech perception in infancy might elucidate neuronal ensembles supporting perceptual abilities that gate language acquisition. Interhemispheric specializations for language have been demonstrated in infants. How these asymmetries are shaped by basic temporal acoustic properties is under debate. We recently provided evidence that newborns process non-linguistic sounds sharing temporal features with language in a differential and lateralized fashion. The present study used the same material while measuring brain responses of 6 and 3 month old infants using simultaneous recordings of electroencephalography (EEG) and near-infrared spectroscopy (NIRS). NIRS reveals that the lateralization observed in newborns remains constant over the first months of life. While fast acoustic modulations elicit bilateral neuronal activations, slow modulations lead to right-lateralized responses. Additionally, auditory-evoked potentials and oscillatory EEG responses show differential responses for fast and slow modulations indicating a sensitivity for temporal acoustic variations. Oscillatory responses reveal an effect of development, that is, 6 but not 3 month old infants show stronger theta-band desynchronization for slowly modulated sounds. Whether this developmental effect is due to increasing fine-grained perception for spectrotemporal sounds in general remains speculative. Our findings support the notion that a more general specialization for acoustic properties can be considered the basis for lateralization of speech perception. The results show that concurrent assessment of vascular based imaging and electrophysiological responses have great potential in the research on language acquisition.