Are Words Easier to Learn From Infant‐ Than Adult‐Directed Speech? A Quantitative Corpus‐Based Investigation

We investigate whether infant‐directed speech (IDS) could facilitate word form learning when compared to adult‐directed speech (ADS). To study this, we examine the distribution of word forms at two levels, acoustic and phonological, using a large database of spontaneous speech in Japanese. At the acoustic level we show that, as has been documented before for phonemes, the realizations of words are more variable and less discriminable in IDS than in ADS. At the phonological level, we find an effect in the opposite direction: The IDS lexicon contains more distinctive words (such as onomatopoeias) than the ADS counterpart. Combining the acoustic and phonological metrics together in a global discriminability score reveals that the bigger separation of lexical categories in the phonological space does not compensate for the opposite effect observed at the acoustic level. As a result, IDS word forms are still globally less discriminable than ADS word forms, even though the effect is numerically small. We discuss the implication of these findings for the view that the functional role of IDS is to improve language learnability.     

Neural correlates of infant accent discrimination: an fNIRS study

The present study investigated the neural correlates of infant discrimination of very similar linguistic varieties (Quebecois and Parisian French) using functional Near InfraRed Spectroscopy. In line with previous behavioral and electrophysiological data, there was no evidence that 3‐month‐olds discriminated the two regional accents, whereas 5‐month‐olds did, with the locus of discrimination in left anterior perisylvian regions. These neuroimaging results suggest that a developing language network relying crucially on left perisylvian cortices sustains infants’ discrimination of similar linguistic varieties within this early period of infancy.     

Why the body comes first: effects of experimenter touch on infants' word finding

The lexicon of 6‐month‐olds is comprised of names and body part words. Unlike names, body part words do not often occur in isolation in the input. This presents a puzzle: How have infants been able to pull out these words from the continuous stream of speech at such a young age? We hypothesize that caregivers' interactions directed at and on the infant's body may be at the root of their early acquisition of body part words. An artificial language segmentation study shows that experimenter‐provided synchronous tactile cues help 4‐month‐olds to find words in continuous speech. A follow‐up study suggests that this facilitation cannot be reduced to the highly social situation in which the directed interaction occurs. Taken together, these studies suggest that direct caregiver–infant interaction, exemplified in this study by touch cues, may play a key role in infants' ability to find word boundaries, and suggests that early vocabulary items may consist of words often linked with caregiver touches. A video abstract of this article can be viewed at http://youtu.be/NfCj5ipatyE     

Development of infants' segmentation of words from native speech: a meta‐analytic approach

Infants start learning words, the building blocks of language, at least by 6 months. To do so, they must be able to extract the phonological form of words from running speech. A rich literature has investigated this process, termed word segmentation. We addressed the fundamental question of how infants of different ages segment words from their native language using a meta‐analytic approach. Based on previous popular theoretical and experimental work, we expected infants to display familiarity preferences early on, with a switch to novelty preferences as infants become more proficient at processing and segmenting native speech. We also considered the possibility that this switch may occur at different points in time as a function of infants' native language and took into account the impact of various task‐ and stimulus‐related factors that might affect difficulty. The combined results from 168 experiments reporting on data gathered from 3774 infants revealed a persistent familiarity preference across all ages. There was no significant effect of additional factors, including native language and experiment design. Further analyses revealed no sign of selective data collection or reporting. We conclude that models of infant information processing that are frequently cited in this domain may not, in fact, apply in the case of segmenting words from native speech.     

Developmental changes in the weighting of prosodic cues

Previous research has shown that the weighting of, or attention to, acoustic cues at the level of the segment changes over the course of development (Nittrouer & Miller, 1997; Nittrouer, Manning & Meyer, 1993). In this paper we examined changes over the course of development in weighting of acoustic cues at the suprasegmental level. Specifically, we tested English-learning 4-month-olds' performance on a clause segmentation task when each of three acoustic cues to clausal units was neutralized and contrasted it with performance on a Baseline condition where no cues were manipulated. Comparison with the reported performance of 6-month-olds on the same task (Seidl, 2007) reveals that 4-month-olds weight prosodic cues to clausal boundaries differently than 6-month-olds, relying more heavily on all three correlates of clausal boundaries (pause, pitch and vowel duration) than 6-month-olds do, who rely primarily on pitch. We interpret this as evidence that 4-month-olds use a holistic processing strategy, while 6-month-olds may already be able to attend separately to isolated cues in the input stream and may, furthermore, be able to exploit a language-specific cue weighting. Thus, in a way similar to that in other cognitive domains, infants begin as holistic auditory scene processors and are only later able to process individual auditory cues.     

Mechanisms underlying accent accommodation in early word learning: evidence for general expansion

Previous work reveals that toddlers can accommodate a novel accent after hearing it for only a brief period of time. A common assumption is that children, like adults, cope with nonstandard pronunciations by relying on words they know (e.g. ‘this person pronounces sock as sack, therefore by black she meant block’). In this paper, we assess whether toddlers might additionally use a general expansion strategy, whereby they simply accept non‐standard pronunciations when variability is expected. We exposed a group of 24‐month‐old English‐learning toddlers to variability in indexical cues (very diverse voices from native English talkers), and another to variability in social cues (very diverse‐looking silent actors); neither group was familiarized with the target novel accent. At test, both groups succeeded in recognizing a novel word when spoken in the novel accent. Thus, even when no lexical cues are available, variability can prepare young children for non‐standard pronunciations.     

A systematic review suggests marked differences in the prevalence of infant-directed vocalization across groups of populations

Anthropological reports have long suggested that speaking to young children is very infrequent in certain populations (notably farming ones), which is in line with scattered quantitative studies. A systematic review was undertaken to use available literature in order to estimate the extent of population variation. Database searches, expert lists, and citation searches led to the discovery of 29 reports on the frequency of vocalizations directed to infants aged 24 months or younger, based on systematic observations of spontaneous activity in the infant's natural environment lasting at least 30 min in length. Together, these studies provide evidence on 1314 infants growing up in a range of communities (urban, foraging, farming). For populations located outside of North America, the frequency with which vocalization was directed to urban infants was much higher than that for rural infants (including both foraging and farming, medians = 12.6 vs. 3.6% of observations contained infant-directed vocalization behaviors). We benchmarked this effect against socio-economic status (SES) variation in the United States, which was much smaller. Infants in high SES American homes were spoken to only slightly more frequently than those in low SES homes (medians = 16.4 vs. 15.1% of observations contained infant-directed vocalization behaviors). Although published research represents a biased sample of the world's populations, these results invite further cross-population research to understand the causes and effects of such considerable population group differences.