Development of rapid word-object associations in relation to expressive vocabulary: Shared commonalities in infants and toddlers with and without Williams syndrome.

Associative word learning, i.e., associating a word with an object, is an important building block of early word learning for TD infants. This study investigated the development of word-object associations by TD infants and infants and toddlers with Williams syndrome (WS), a rare genetic disorder associated with delayed language and cognitive development. The specific reasons for the language delays remain unknown. We investigated whether their early language delay could be related to differences in how word-object associations are formed. Fifty-nine 11- to 14-month-old TD infants and thirty-one 12- to 35-month-olds with WS were tested on a modified version of the "switch" task (Werker, Cohen, Lloyd, Casasola, & Stager, 1998) using phonetically dissimilar words and novel objects. Infants were classified as word learners or novice word learners based on their expressive vocabularies (greater than 10 words vs. 10 words or fewer). We found similar developmental patterns across both populations: Expressive vocabulary size classification was an important index of the development of word-object associations. Moreover, the development of word-object associations evidenced a domain-general progression from independent (processing objects separately from words) to integrated (processing associations between words and objects). As a group, word learners formed word-object associations, but novice word learners did not; instead, they focused primarily on the objects. Findings build on previous research suggesting that although early language acquisition is delayed in infants with WS, infants and toddlers with and without WS share a common developmental pattern and set of mechanisms in early word learning.

Infants with Williams syndrome detect statistical regularities in continuous speech.

Williams syndrome (WS) is a rare genetic disorder associated with delays in language and cognitive development. The reasons for the language delay are unknown. Statistical learning is a domain-general mechanism recruited for early language acquisition. In the present study, we investigated whether infants with WS were able to detect the statistical structure in continuous speech. Eighteen 8- to 20-month-olds with WS were familiarized with 2min of a continuous stream of synthesized nonsense words; the statistical structure of the speech was the only cue to word boundaries. They were tested on their ability to discriminate statistically-defined "words" and "part-words" (which crossed word boundaries) in the artificial language. Despite significant cognitive and language delays, infants with WS were able to detect the statistical regularities in the speech stream. These findings suggest that an inability to track the statistical properties of speech is unlikely to be the primary basis for the delays in the onset of language observed in infants with WS. These results provide the first evidence of statistical learning by infants with developmental delays.

Developmental origins of the face inversion effect.

A hallmark of adults' expertise for faces is that they are better at recognizing, discriminating, and processing upright faces compared to inverted faces. We investigate the developmental origins of "the face inversion effect" by reviewing research on infants' perception of upright and inverted faces during the first year of life. We review the effects of inversion on infants' face preference, recognition, processing (holistic and second-order configural), and scanning as well as face-related neural responses. Particular attention is paid to the developmental patterns that emerge within and across these areas of face perception. We conclude that the developmental origins of the inversion effect begin in the first few months of life and grow stronger over the first year, culminating in effects that are commonly thought to indicate adult-like expertise. We posit that by the end of the first year, infants' face-processing system has become specialized to upright faces and a foundation for adults' upright-face expertise has been established. Developmental mechanisms that may facilitate the emergence of this upright-face specialization are discussed, including the roles that physical and social development may play in upright faces' becoming more meaningful to infants during the first year.

Toddlers with Williams syndrome process upright but not inverted faces holistically.

Holistic processing of upright, but not inverted, faces is a marker of perceptual expertise for faces. This pattern is shown by typically developing individuals beginning at age 7 months. Williams syndrome (WS) is a rare neurogenetic developmental disorder characterized by extreme interest in faces from a very young age. Research on the effects of inversion on holistic processing of faces by older children and adults with WS has produced mixed results. Younger children with WS were not included in these previous studies. Using the habituation switch paradigm, we demonstrated that 15-35-month-olds with WS process upright, but not inverted, faces holistically. This study provides evidence of perceptual expertise for faces in individuals with WS early in life.

A U-shaped relation between sitting ability and upright face processing in infants.

A growing body of research indicates connections exist between action, perception, and cognition in infants. In this study, associated changes between sitting ability and upright face processing were tested in 111 infants. Using the visual habituation "switch" task (C. H. Cashon & L. B. Cohen, 2004; L. B. Cohen & C. H. Cashon, 2001), holistic processing of faces was assessed in same-aged non- and near sitters (22-25 weeks) and same-aged new and expert sitters (27-32 weeks). U-shaped relation was found between sitting stage and holistic face processing such that only nonsitters and expert sitters processed faces holistically. It is posited that the results are due to a reorganization of the upright face-processing system resulting from infants' learning to sit independently and trying to incorporate the meaning of upright faces.

The Development of Specialized Processing of Own-Race Faces in Infancy.

In this study, we examined developmental changes in infants' processing of own- versus other-race faces. Caucasian American 8-month-olds (Experiment 1) and 4-month-olds (Experiment 2) were tested in a habituation-switch procedure designed to assess holistic (attending to the relationship between internal and external features of the face) versus featural (attending to individual features of the face) processing of faces. Eight-month-olds demonstrated holistic processing of upright own-race (Caucasian) faces, but featural processing of upright other-race (African) faces. Inverted faces were processed featurally, regardless of ethnicity. Four-month-olds, however, demonstrated holistic processing of both Caucasian and African upright faces. These results demonstrate that infants' processing of own- versus other-race faces becomes specialized between 4 and 8 months.

Eight-Month-Old Infants' Perception of Possible and Impossible Events.

This study investigated 8-month-old infants' perception of object permanence in an extension of the rotating screen studies by Baillargeon (1987) and Baillargeon, Spelke, and Wasserman (1985). Using computer-animated stimuli similar to the "live" stimuli used by Baillargeon and her colleagues (Baillargeon, 1987; Baillargeon et al., 1985), 48 8-month-old infants were habituated to 1 of 4 computer-animated events and then tested on all 4 events. The events involved a screen that rotated in either a 180° or 120° arc*** and a block that either was sitting in the path of the rotating screen or absent from the event. The results provided no evidence that infants responded on the basis of the possibility or impossibility of the events as claimed by Baillargeon and her colleagues, but instead indicated that the infants responded on the basis of perceptual novelty. These results are consistent with the findings of Schilling (this issue) and Bogartz, Shinskey, and Schilling (this issue). Taken together, along with the findings of Rivera, Wakeley, and Langer (1999), these more recent findings suggest that Baillargeon's (1987; Baillargeon et al., 1985) results should not be interpreted as definitive evidence of object permanence in very young infants.