Mothers Reveal More of Their Vocal Identity When Talking to Infants

Voice timbre – the unique acoustic information in a voice by which its speaker can be recognized – is particularly critical in mother-infant interaction. Correct identification of vocal timbre is necessary in order for infants to recognize their mothers as familiar both before and after birth, providing a basis for social bonding between infant and mother. The exact mechanisms underlying infant voice recognition remain ambiguous and have predominantly been studied in terms of cognitive voice recognition abilities of the infant. Here, we show – for the first time – that caregivers actively maximize their chances of being correctly recognized by presenting more details of their vocal timbre through adjustments to their voices known as infant-directed speech (IDS) or baby talk, a vocal register which is wide-spread through most of the world’s cultures. Using acoustic modelling (k-means clustering of Mel Frequency Cepstral Coefficients) of IDS in comparison with adult-directed speech (ADS), we found in two cohorts of speakers - US English and Swiss German mothers - that voice timbre clusters of in IDS are significantly larger to comparable clusters in ADS. This effect leads to a more detailed representation of timbre in IDS with subsequent benefits for recognition. Critically, an automatic speaker identification using a Gaussian-mixture model based on Mel Frequency Cepstral Coefficients showed significantly better performance in two experiments when trained with IDS as opposed to ADS. We argue that IDS has evolved as part of an adaptive set of evolutionary strategies that serve to promote indexical signalling by caregivers to their offspring which thereby promote social bonding via voice and acquiring linguistic systems

Infant prosodic expressions in mother-infant communication

Prosody, generally defined as any perceivable modulation of duration, pitch or loudness in the voice that conveys meaning, has been identified as part of the linguistic system, or compared with the sound system of Western classical music. This thesis proposes a different conception, namely that prosody is a phenomenon of human expression that precedes, and to a certain extent determines the form and function of utterances in any particular language or music system. Findings from studies of phylogenesis and ontogenesis are presented in favour of this definition. Consequently, prosody of infant vocal expressions, which are made by individuals who have not yet developed either language or musical skills, is investigated as a phenomenon in itself, with its own rules. Recognising theoretical and methodological deficiencies in the linguistic and the Piagetian approaches to the development of infant prosodic expressions, this thesis supports the view that the origins of language are to be sought in the expressive dialogues between the mother and her prelinguistic child that are generated by intuitive motives for communication. Furthermore, infant vocalisations are considered as part of a system of communication constituted by all expressive modalities. Thus, the aim is to investigate the role of infant prosodic expressions in conveying emotions and communicative functions in relation to the accompanying non vocal-behaviours. A crossectional Pilot Study involving 16 infants aged 26 to 56 weeks and their mothers was undertaken to help in the design of the Main Study. The Main Study became a case description of two first born infants and their mothers; a boy (Robin) and a girl (Julie) both aged 30 weeks at the beginning of the study. The infants were filmed in their home every fortnight for five months in a structured naturalistic setting which included the following conditions: mother-infant free-play with their own toys, mother-infant play without using objects, the infant playing alone, motherinfant play with objects provided by the researcher, a 'car task' for eliciting cooperative play, and the mother staying unresponsive. Each filming session lasted approximately thirty minutes. In order to get an insight into the infants' 'meaning potential' expressed in their vocalisations, the mothers were asked to visit the department sometime in the interval between two filming sessions and, while watching the most recent video, to report what they felt their infant was conveyingif anything- in each vocalisation. Three types of analysis were carried out: a) An Analysis of Prosody - An attempt was made to obtain an objective, and not linguistically based account of infant prosodic features. First measurements were obtained of the duration and the fundamental frequency curve of each vocalisation by means of a computer programme for sound analysis. The values of fundamental frequency were then logarithmically transformed into a semitone scale in order to obtain measurements more sensitive to the mother's perception. b) A Functional Micro-Analysis of Non-Vocal Behaviours from Videos - The non vocal behaviours of mother and infant related with each vocalisation were codified without sound to examine to what extent the mothers relied for their interpretations on non-vocal behaviours accompanying vocalisations. c) An Analysis of the Mothers' Interpretations - The infants' messages were defined as perceived by their mother. The corpus comprised 713 vocalisations (322 for the boy and 391 for the girl) selected from a corpus of 864, and 143 minutes of video recording (64 for the boy and 79 for the girl). Correlations between the above three assessments were specified through statistical analysis. The findings from both infants indicate that between seven and eleven months prosodic patterns are not related one to one with particular messages. Rather, prosody distinguishes between groups of messages conveying features of psychological motivation, such as 'emotional', 'interpersonal', 'referential', 'assertive' or 'receptive'. Individual messages belonging to the same message group according to the analysis of prosody, are distinguished on the basis of the accompanying nonvocal behaviours. Before nine months, 'interpersonal' vocalisations display more 'alerting' prosodic patterns than 'referential' vocalisations. After nine months prosodic patterns in Robin's vocalisations differentiate between 'assertive' and 'receptive' messages, the former being expressed by more 'alerting' prosodic patterns than the latter. This distinction reflects a better Self-Other awareness. On the other hand, Julie's vocalisations occurring in situations of 'Joint Interest' display different prosodic patterns from her vocalisations uttered in situations of 'Converging Interest'. These changes in the role infant prosody reflect developments in the infants' motivational organisation which will lead to a more efficient control of intersubjective orientation and shared attention to the environment. Moreover, it was demonstrated that new forms of prosodic expression occur in psychologically mature situations, while the psychologically novel situations are expressed by mature prosodic forms. The above results suggest that at the threshold to language, prosody does not primarily serve identifiable linguistic functions. Rather, in spite of individual differences in form of their vocalisations, both infants use prosody in combination with other modalities as part of an expressive system, that conveys information about their motives. In this way prosody facilitates intersubjective and later cooperative communication, on which language development is built. To what extent such prelinguistic prosodic patterns are similar in form to those of the target language is a crucial issue for further investigation

Symbolic play provides a fertile context for language development

In this study we test the hypothesis that symbolic play represents a fertile context for language acquisition because its inherent ambiguity elicits communicative behaviours that positively influence development. Infant-caregiver dyads (N = 54) participated in two 20-minute play sessions six months apart (Time 1 = 18 months, Time 2 = 24 months). During each session the dyads played with two sets of toys that elicited either symbolic or functional play. The sessions were transcribed and coded for several features of dyadic interaction and speech; infants’ linguistic proficiency was measured via parental report. The two play contexts resulted in different communicative and linguistic behaviour. Notably, the symbolic play condition resulted in significantly greater conversational turn-taking than functional play, and also resulted in the greater use of questions and mimetics in infant-directed speech (IDS). In contrast, caregivers used more imperative clauses in functional play. Regression analyses showed that unique properties of symbolic play (i.e., turn-taking, yes-no questions, mimetics) positively predicted children’s language proficiency, whereas unique features of functional play (i.e., imperatives in IDS) negatively predicted proficiency. The results provide evidence in support of the hypothesis that symbolic play is a fertile context for language development, driven by the need to negotiate meaning

Defining the cognitive phenotype of autism

Although much progress has been made in determining the cognitive profile of strengths and weaknesses that characterise individuals with autism spectrum disorders (ASDs), there remain a number of outstanding questions. These include how universal strengths and deficits are; whether cognitive subgroups exist; and how cognition is associated with core autistic behaviours, as well as associated psychopathology. Several methodological factors have contributed to these limitations in our knowledge, including: small sample sizes, a focus on single domains of cognition, and an absence of comprehensive behavioural phenotypic information. To attempt to overcome some of these limitations, we assessed a wide range of cognitive domains in a large sample (N = 100) of 14- to 16-year-old adolescents with ASDs who had been rigorously behaviourally characterised. In this review, we will use examples of some initial findings in the domains of perceptual processing, emotion processing and memory, both to outline different approaches we have taken to data analysis and to highlight the considerable challenges to better defining the cognitive phenotype(s) of ASDs. Enhanced knowledge of the cognitive phenotype may contribute to our understanding of the complex links between genes, brain and behaviour, as well as inform approaches to remediation

A forensic phonetic study of the vocal responses of individuals in distress

The production and perception of emotional speech is of growing importance to forensic speech scientists. They are often asked by instructing parties to provide an opinion as to whether recordings representing a violent attack are genuine, and whether speech material reflects real distress. However, they are prohibited from making statements regarding the psychological states of speakers by the International Association of Forensic Phonetics and Acoustics Code of Practice (IAFPA 2004). This study investigates two principal questions. First, it investigates how distress speech can be manifested acoustically. In so doing it proposes a taxonomy for comparing distress speech across speakers, assists in delimiting the boundaries of the vocal repertoire, and considers the extent to which acoustic measures of distress speech can distinguish between the vocalisations of real victims and actors. Second, it investigates whether listeners can discriminate between genuine and acted distress portrayals, and to what extent familiarity with forensic material increases listeners’ ability. Recordings from authentic criminal cases involving violent attack are compared with re-enactments by trained actors. Acoustic analyses examine F0, intensity, vowel formant frequencies and articulation rate. The recordings are also used as stimuli in a perceptual listening test, comparing the performance of lay listeners, police call takers and forensic practitioners. The findings lend support to the view that assessments of distress should be exercised with extreme caution. On the one hand, acoustic parameters can distinguish between non-distress and distress conditions, but cannot discriminate between acted and authentic distress, and so IAFPA’s refrain from such an assessment is justified. On the other, listeners who are familiar with authentic distress data, such as police call takers and forensic practitioners, are better able to differentiate between acted and authentic distress than lay listeners. Thus, if an assessment were to be made, the forensic practitioners may be the best group to do so

Factors that influence the language and communication of hearing-impaired children

Studies have shown that permanent childhood hearing impairment can have detrimental consequences for spoken-language development. It is widely accepted that early detection and intervention may improve outcomes for profoundly hearing-impaired children. However, few studies evaluate the influence on the families or give particular attention to children with mild-to-severe hearing impairments. This research used spoken language and communication to focus on a range of factors that may influence outcomes for children with permanent sensorineural hearing impairments. In two studies, children with a range of hearing impairments, aged 32 to 85 months (mean = 63, s = 14) were audio- and video-recorded at home interacting with a major care-giver. Measures of spoken language for the children and their interlocutors were derived from transcripts. Controlling for the age of the child, spoken-language outcomes were evaluated in relation to factors such as the severity of the child's hearing impairment, age of intervention and the language addressed to the child during the interaction. The first study indicated that hearing severity, excluding profound hearing impairments, may not be the most important influence on spoken language. However, earlier intervention corresponded to better language performance. The second study failed to replicate these findings but suggested that a complex interaction of factors - including earlier referral for hearing assessment - may influence spoken language production for hearing-impaired children. Questionnaires revealed the families' attitudes and feelings towards the diagnosis of their child's hearing-impairment, showing that parents often experienced negative emotions at the time and that intervention provisions often fail to take parental attitude into consideration at this time. Results also suggested that earlier and prompt intervention for childhood hearing-impairment is viewed as beneficial and essential. This may have important implications for habilitation and intervention programmes for hearing-impaired children and their families. The conclusions suggest that further studies - which evaluate and detail the potential long-term benefits of very early intervention for hearing-impaired children - need to be conducted

Artificial grammar learning in primates :behaviour and neuroimaging

PhD ThesisNeuroimaging studies have shown that natural language processes engage left hemisphere perisylvian brain regions. Artificial Grammars (AG), which are designed to emulate aspects of language syntactic structure, recruit comparable brain areas. Nonhuman animals have been shown to learn a range of different AGs. However, no data is currently available regarding the brain areas that support these processes. In this thesis, I combined behavioural artificial grammar learning (AGL) and fMRI experiments to generate insights regarding language evolution, and as a first step to developing animal model systems for aspects of language processing. These experiments provide novel evidence that nonhuman primates are able to learn a non-deterministic AG, designed to emulate some of the variability of the structure of sentences in natural language, and demonstrated notable correspondences between the brain regions involved in macaque and human AGL. I developed a quantitative method to compare AGL abilities across species and studies, and a novel eye-tracking technique with which to collect objective behavioural data. Using this technique, and a refined version of a traditional video-coding paradigm, I demonstrated that Rhesus macaques notice violations of the AG structure and that these results could not be explained by reliance on simple cues. Common marmosets also showed evidence of AGL however, these results may have been driven by simple learning strategies. Comparative fMRI experiments showed that, in humans, violations of the AG activated a number of perisylvian brain regions associated with language processing, including the ventral frontal cortex (vFC), temporal and temporo-parietal regions, although not Broca’s area (BA44/45). In Rhesus macaques, comparable patterns of activation were seen in the ventral frontal cortex and temporo-parietal regions. Additional activation in BA44/45 in macaques provides interesting insights into the evolution of this region. These experiments provide novel evidence regarding the AGL capabilities of nonhuman primates, and the brain areas that support them, suggesting that some language related functions may represent generic, rather than language specific processes. Therefore, some of the brain regions involved in AGL in both species might share a common evolutionary heritage, and therefore Rhesus macaques might represent a valuable animal model system for aspects of language processing

Behavioural and neural insights into the recognition and motivational salience of familiar voice identities

The majority of voices encountered in everyday life belong to people we know, such as close friends, relatives, or romantic partners. However, research to date has overlooked this type of familiarity when investigating voice identity perception. This thesis aimed to address this gap in the literature, through a detailed investigation of voice perception across different types of familiarity: personally familiar voices, famous voices, and lab-trained voices. The experimental chapters of the thesis cover two broad research topics: 1) Measuring the recognition and representation of personally familiar voice identities in comparison with labtrained identities, and 2) Investigating motivation and reward in relation to hearing personally valued voices compared with unfamiliar voice identities. In the first of these, an exploration of the extent of human voice recognition capabilities was undertaken using personally familiar voices of romantic partners. The perceptual benefits of personal familiarity for voice and speech perception were examined, as well as an investigation into how voice identity representations are formed through exposure to new voice identities. Evidence for highly robust voice representations for personally familiar voices was found in the face of perceptual challenges, which greatly exceeded those found for lab-trained voices of varying levels of familiarity. Conclusions are drawn about the relevance of the amount and type of exposure on speaker recognition, the expertise we have with certain voices, and the framing of familiarity as a continuum rather than a binary categorisation. The second topic utilised voices of famous singers and their “super-fans” as listeners to probe reward and motivational responses to hearing these valued voices, using behavioural and neuroimaging experiments. Listeners were found to work harder, as evidenced by faster reaction times, to hear their musical idol compared to less valued voices in an effort-based decision-making task, and the neural correlates of these effects are reported and examined