This paper presents the Word Complexity Measure for Swedish (WCM-SE), an adaptation of the original WCM developed for English by Stoel-Gammon. These measures are used to calculate the phonological complexity of words or vocalizations, based on a number of phonological complexity parameters. Each production receives a complexity score based on how many of the parameters are present in the production.Using phonological complexity scores to measure expressive phonology is suitable for assessing very young children, children with early phonology and children with phonological deficits. It is useful forboth relational and independent analyses and enables comparisons between children and across development.The original WCM uses eight phonological complexity parameters in three domains: word patterns, syllable structures and sound classes. The parameters selected are phonological characteristics that are acquired late in development among English-speaking children.In the WCM-SE, complexity parameters in the domain sound classes were modified or added according to Swedish or universal patterns of phonology development. The parameters' complexity is accounted for in terms of language-general phonetic characteristics.

Infants prefer to listen to infant-directed speech (IDS) over adult-directed speech (ADS). IDS contains a greater amount of affect than ADS (Singh, Morgan & Best, 2002). Affect in infant-directed speech has been said to foster social bonds, maintain attention and teach language. In order to identify phonetic correlates of affect, prosodic features such as fundamental frequency, pitch range, pitch contour, vowel duration and rhythm have been tried (Katz, Cohn & Moore, 1996; Trainor, Austin & Desjardins, 2000). However, affect ratings are typically carried out on low-pass filtered speech in order to obscure semantic cues to affect. It is possible that more than semantic meaning is distorted by the filtering process. In the present study, acoustic-phonetic correlates to affect were studied in un-filtered short speech segments. One-syllable speech segments were rated on a scale ranging from highly negative via neutral to highly positive affect. Formant (F1, F2, F3), pitch (mean, maximum, minimum, range, contour), and vowel duration measures were obtained from the speech samples, and relations between acoustic measures and rated affect were analyzed. The speech samples were the syllables /mo/, /na/, and /li/ produced by Swedish mothers (n = 29) and fathers (n = 21) when talking to their 12-month-old children. Recordings of IDS took place during free play in a laboratory setting, and the syllables were the names of soft toys that the parents were asked to use when interacting with their child. Parents and children participated in a longitudinal interaction study, and this was their fourth visit at the laboratory, so they were familiar with task, setting and toys. ADS exemplars of the syllables were also selected from a sub-sample of the mothers (n = 14), recorded at their first visit to the laboratory. Participants in the perceptual rating experiment (n = 35; 21 female; mean age = 28.6 years; age range = 19-45 years) were presented with one syllable at a time and asked to rate the affect conveyed on a scale from -4 (high negative affect) to +4 (high positive affect), with 0 as midpoint (neutral affect). The experiment was self-paced, and participants could listen to each syllable as many times as they liked. Each experiment session lasted between 30 and 50 minutes. A mixed-effects model was designed with AffectRating as dependent variable, Rater as random effects variable, and RaterGender, RaterHasChildren, F1, F2, F3, MeanPitch, PitchRange as well as VowelDuration as fixed effects variables. Minimum pitch, maximum pitch and pitch contour were excluded from the analysis since they were correlated with pitch range. Significant results were found for F1, F3, MeanPitch, PitchRange and VowelDuration. Higher F1 and/or F3 resulted in more negative perceived affect whereas higher mean pitch, greater pitch range, and/or longer vowel duration resulted in more positive perceived affect. The relation between perceived affect and formant values could be related to differences in perceived affect for different vowels, rather than variations in the formant values per se. It would be interesting to look at variation within separate vowel categories. The relation between positive affect and prosodic exaggerations suggests that some acoustic characteristics of IDS could be a result of parents conveying positive affect to their children.

Affect is an important feature of infant-directed speech (IDS). IDS towards infants during the first year of life varies in degree of affect. In Australian English (AuE), positive affect in mothers’ IDS increases over age from birth to twelve months, with a dip at nine months (Kitamura & Burnham, 2003).

This study investigates whether affect in Swedish (Swe) mothers’ IDS towards their infants develops in a similar pattern compared to the Australian English data. It also introduces a cross-linguistic perspective of affect perception in IDS as Swedish native speakers rate both the Swe and AuE IDS samples.

The adult raters (N=16; 8 female, mean age 36.4 years; SD = 10.1) assessed affect polarity and affect degree in low-pass filtered IDS samples on a scale from -4 to +4 (highly negative to highly positive). The 25 s long samples were cut from interactions between mothers and their infants at three, six, nine and twelve months and low-pass filtered. The Australian material was sampled from the same dataset as used in Kitamura and Burnham (2003); the Swedish material was recorded at Stockholm Babylab (Gerholm et al., 2015).

Separate repeated measures ANOVAs were conducted on the mean affect ratings of AuE and Swe IDS, with infant age as within-subject factor, followed up with polynomial contrasts. For AuE IDS, a significant main effect was found for age (F(45,3)=10.356; p<.001), with a linear (F(15,1)=20.542; p<.001) and a cubic trend (F(15,1)=7.780; p=.014). For Swe IDS, a significant main effect was found for age (F(45,3)=4.186; p=.011), with a linear (F(15,1)=10.993; p=.005) and a quadratic trend (F(15,1)=6.124; p=.026). In both languages, positive affect decreases over age.

While cross-linguistic affect perception of AuE IDS is still similar to the original, Kitamura and Burnham’s data show a more pronounced cubic trend and a general increase of affect in IDS over the first year. In this study, affect development in AuE IDS shows a steep increase from three to six months, followed by a decrease from six to nine months and a slight recovery from nine to twelve months. Affect in Swe IDS follows a different developmental trajectory, as it decreases from three to nine months to recover with an increase from nine to twelve months. This is a first indication for language-specific differences in IDS affect over the first year. Future ratings of the same material with AuE native speakers will show if the difference in the AuE results is an effect of rater language.

This paper describes the development of a vocabulary for Profiles of Early Expressive Phonological Skills for Swedish (PEEPS-SE), a tool for assessment of expressive phonology in Swedish-learning children in the age range of 18-36months. PEEPS-SE is the Swedish version of the original PEEPS, Profiles of Early Expressive Phonological Skills, which uses two age-adequate word listsa basic word list (BWL) for the assessment of 18-24-month-old children, to which an expanded word list (EWL) is added for assessment of 24-36-month-old children, or children with more than 250 words in their expressive vocabulary.The selection of words in PEEPS-SE is based on two types of criteria: age of acquisition and phonological complexity. The words also need to be easy to elicit in a natural way in test situations. Vocabulary data previously collected with the Swedish Early Communicative Development Inventory are used for selection of age-adequate words, where the BWL contains words acquired earlier compared to the additional words in the EWL. The latter also contains words that are more phonologically complex compared to those in the BWL. Word complexity was determined by the Swedish version of word complexity measure. PEEPS-SE has made an attempt to match the original version of PEEPS in terms of both assessment method and word selection.

This thesis focuses on contingency in parent-child interaction, investigating it in the light of the linguistic capacity of the child and the status of the caregiver. Further, the thesis covers the development of two tools to assess the developmental maturity level of expressive phonology. A functional emergentist perspective on language acquisition is taken, which includes a phonetic perspective on phonological development. Both infant language development and factors that influence parent responsiveness are explored. 

The thesis contains four studies. In the first study, durations of parents’ utterances and pauses in interaction with their 18-month-old infants were related to the infant’s vocabulary size. Recordings of interactions of fifteen children and their parents were made at home in daily life situations. The children were divided into three groups according to their vocabulary size: large, typical or small. The main finding is that parents in the large vocabulary size group responded faster to their children compared to the parents in the typical size vocabulary group, who in turn responded faster than the parents in the small vocabulary size group. 

In study two, duration in vocal turn-taking between 6-month old infants and their caregivers was investigated, in terms of the status of the caregiver and the sex of the infant. Caregivers’ pauses were measured in 10-minute caregiver-infant interactions recorded at home. It was found that primary caregivers responded faster to their infants compared to secondary caregivers, and that in turn, infants responded faster to the primary caregiver than to the secondary caregiver. 

Study three introduces the Word Complexity Measure for Swedish (WCM-SE), a tool for calculating phonological complexity in words or utterances. Calculations are based on ten parameters describing speech structures that are considered phonetically complex to produce. In the development of  the WCM-SE, both language-specific and language-general descriptions of speech development were considered, as well as universal acoustic and aerodynamic principles. 

Study four documents the selection of Swedish words for the word lists in the test Profiles of Early Expressive Phonological Skills for Swedish (PEEPS-SE). The selection was based on criteria of age of acquisition and word complexity, as measured by the WCM-SE. 

The findings presented in this thesis contribute to our knowledge of early interaction and parents’ potential impact on the child’s early language and communication development. Further, the tools developed for the assessment of Swedish are valuable contributions both to the research field of early phonology and to clinical work in Sweden. 

Contingent turn-taking between parents and infants is positively correlated with child language outcome (Tamis-LeMonda, Bornstein & Baumwell, 2001; Marklund, Marklund, Lacerda & Schwarz, 2015). Many studies focus exclusively on mothers (e.g., Sung, Fausto-Sterling, Garcia Coll & Seifer, 2013). However, infants in Western countries acquire language with input both from mothers and fathers in varying degree, depending on how the family chooses to organize their parental leave. Sweden is an ideal country to study both mothers and fathers as caregivers for infants.

Parental contingency is often reported as response frequency within a time window after infant vocalizations (e.g., Johnson, Caskey, Rand, Tucker & Vohr, 2014). In this study, turn-taking contingency is measured by the duration of parent-child and child-parent switching pauses around infant vocalization with potential communicative intent. Fourteen (7 girls) infants and their primary and secondary caregivers were recorded in the family home when the infant was six months (M = 5 months 29 days, range: 5 months 3 days – 6 months 16 days). The audio recordings were collected two different days and lasted approximately ten minutes each. One of the days was a typical weekday on which the primary caregiver – in all cases the mother – was at home with the infant. The other day was a typical weekend day on which also the secondary caregiver – in all cases the father – was at home and spent time with the infant. On each of these days, a daylong LENA recording was also made to estimate the amount of exposure to female and male speech input on a typical day. Using Wavesurfer 1.8.5 (Sjölander & Beskow, 2010), on- and offset of all infant vocalizations were tagged as well as on- and offset for the surrounding switching pauses. If parent utterance and infant vocalization overlapped, switching pause duration received a negative value.

Two repeated measures ANOVAs were used to determine the effects of caregiver type (primary/secondary) and infant sex (girl/boy) on pause duration in infant-parent and parent-infant switching pauses. A main effect was found for caregiver type in infant-parent switching pauses (F(12,1) = 5.214; p = .041), as primary caregivers responded on average about 500 ms faster to infant vocalizations than secondary caregivers, with no effect of or interaction with infant sex. In parent-infant switching pauses, the main effect for caregiver type was almost significant (F(12,1) = 4.574; p = .054), with no effect of or interaction with infant sex. It is therefore fair to say that turn-taking between primary caregivers and 6-month-olds is more contingent than turn-taking between secondary caregivers and 6-month-olds.

Four linear regressions were then used to predict parent-infant and infant-parent switching pause duration from the average duration of female speech exposure and the average duration of male speech exposure across the two days, with the assumption that female speech duration equals speech input from the primary caregiver and male speech duration the secondary caregiver. None of the regression analyses turned out to be significant. However, it is likely that the greater contingency between primary caregivers and the infant is a function of greater turn-taking experience, that is, conversational turns rather than mere exposure to speech. Therefore, we will look next at the number of conversational turns for each caregiver separately and investigate whether they predict parental response contingency.

The present study shows that vocal turn-taking is more contingent between infants and primary caregivers than with secondary caregivers. Primary caregivers respond significantly faster to infant vocalizations than secondary caregivers and in turn, infants have a tendency to respond faster to primary caregivers. It is likely that this relationship is mediated by turn-taking experience, although this could not be shown with regression analyses using LENA estimates of total duration of speech exposure to primary and secondary caregiver.

This study compares parental pause and utterance duration in conversations with Swedish speaking children at age 1;6 who have either a large, typical, or small expressive vocabulary, as measured by the Swedish version of the McArthur-Bates CDI. The adjustments that parents do when they speak to children are similar across all three vocabulary groups; they use longer utterances than when speaking to adults, and respond faster to children than they do to other adults. However, overall pause duration varies with the vocabulary size of the children, and as a result durational aspects of the language environment to which the children are exposed differ between groups. Parents of children in the large vocabulary size group respond faster to child utterances than do parents of children in the typical vocabulary size group, who in turn respond faster to child utterances than do parents of children in the small vocabulary size group.

WILD 2015 is the second Workshop on Infant Language Development, held June 10-12 2015 in Stockholm, Sweden. WILD 2015 was organized by Stockholm Babylab and the Department of Linguistics, Stockholm University. About 150 delegates met over three conference days, convening on infant speech perception, social factors of language acquisition, bilingual language development in infancy, early language comprehension and lexical development, neurodevelopmental aspects of language acquisition, methodological issues in infant language research, modeling infant language development, early speech production, and infant-directed speech. Keynote speakers were Alejandrina Cristia, Linda Polka, Ghislaine Dehaene-Lambertz, Angela D. Friederici and Paula Fikkert.

Organizing this conference would of course not have been possible without our funding agencies Vetenskapsrådet and Riksbankens Jubiléumsfond. We would like to thank Francisco Lacerda, Head of the Department of Linguistics, and the Departmental Board for agreeing to host WILD this year. We would also like to thank the administrative staff for their help and support in this undertaking, especially Ann Lorentz-Baarman and Linda Habermann.

The WILD 2015 Organizing Committee: Ellen Marklund, Iris-Corinna Schwarz, Elísabet Eir Cortes, Johan Sjons, Ulrika Marklund, Tove Gerholm, Kristina Nilsson Björkenstam and Monika Molnar.