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The mark test is a popular test for self-recognition. Although the extent to which self-recognition can be assessed remains controversial, the test elicits visually guided, self-oriented, and spontaneous reaching movements. In this study, we demonstrated that this self-oriented reaching is suitable for estimating sensorimotor body representation in toddlers. We developed a non-verbal task (Bodytoypo) to assess the localization of body parts by gamifying the mark test and conducted it with thirty 2- and 3-year old children. Specifically, we detected the children9s skeletal data in real-time, displayed virtual marks on various parts of their body, and estimated their reaction time and accuracy of body part localization. Subsequently, a statistical-based automated analysis using 2-D image processing and conventional frame-by-frame coding were performed. The results revealed developmental changes in the children9s reaching strategies. A few errors were observed around the face. A reduction in the error rate for joint and movable areas was observed in children between the ages of 2 and 3 years. An analysis of movement trajectories using a combination of image processing and machine learning algorithms showed that 2-year-olds acquired visually guided reaching (feedback control) from ballistic exploratory reaching and 3-year-olds acquired rapid and predictive reaching (feedforward control) from visually guided cautious reaching. It was also found that the accuracy of localization could be predicted by examining the coordination of body parts. Evaluation of the developmental changes in self-oriented reaching reveals new possibilities for the mark test and development of body representation.

Infants increasingly gaze at the mouth of talking faces during the latter half of the first postnatal year. This study investigated mouth-looking behavior of 120 full-term infants and toddlers (6 months-3 years) and 12 young adults (21-24 years) from Japanese monolingual families. The purpose of the study included: (1) Is such an attentional shift to the mouth in infancy similarly observed in Japanese environment where contribution of visual speech is known to be relatively weak? (2) Can noisy conditions increase mouth-looking behavior of Japanese young children? (3) Is the mouth-looking behavior related to language acquisition? To this end, movies of a talker speaking short phrases were presented while manipulating signal-to-noise ratio (SNR: Clear, SN+4, and SN-4). Expressive vocabulary of toddlers was obtained through their parents. The results indicated that Japanese infants initially have a strong preference for the eyes to mouth which is weakened toward 10 months, but the shift was later and in a milder fashion compared to known results for English-learning infants. Even after 10 months, no clear-cut preference for the mouth was observed even in linguistically challenging situations with strong noise until 3 years of age. In the Clear condition, there was a return of the gaze to the eyes as early as 3 years of age, where they showed increasing attention to the mouth with increasing noise level. In addition, multiple regression analyses revealed a tendency that 2- and 3-year-olds with larger vocabulary increasingly look at the eyes. Overall, the gaze of Japanese-learning infants and toddlers was more biased to the eyes in various aspects compared to known results of English-learning infants. The present findings shed new light on our understanding of the development of selective attention to the mouth in non-western populations.

Infants communicate their emotions to caregivers mainly through vocalizations. Research has shown that maternal oxytocin levels relate to adaptive parenting; however, little empirical research exists regarding the effects of endogenous oxytocin levels on maternal responses to infant vocalizations. Thus, in this study, we examined the relationship between mothers’ salivary oxytocin levels, subjective feelings, and behavioral response to infants’ emotional vocalizations. Additionally, we examined the relationship between psychological traits and maternal behavioral responses to infant vocalizations. In this study, 39 mothers were asked to stand on a balance board while listening to infant vocalization stimuli, to measure movements of their center of pressure, an index of approach-avoidance behavior. Sixty infant vocalizations (laughter, crying, and neutral) were presented for 6 ​s each. Afterwards, participants were asked to rate their subjective responses to each stimulus (not aroused – aroused, displeased – pleased, not urgent – urgent, and healthy – sick). Maternal oxytocin levels were negatively correlated with anterior movement of the center of pressure in response to infants’ crying and babbling vocalizations, though no relationship was found between maternal approach-avoidance behavior toward infant laughter and oxytocin levels. This study indicated that maternal approach behavior toward infant vocalizations varies as a function of maternal endogenous oxytocin and the type of infant vocalization.

This study investigated the lexical use of Japanese pitch accent in Japanese-learning infants. A word-object association task revealed that 18-month-old infants succeeded in learning the associations between two nonsense objects paired with two nonsense words minimally distinguished by pitch pattern (Experiment 1). In contrast, 14-month-old infants failed (Experiment 2). Eighteen-month-old infants succeeded even for sounds that contained only the prosodic information (Experiment 3). However, a subsequent experiment revealed that 14-month-old infants succeeded in an easier single word-object task using pitch contrast (Experiment 4). These findings indicate that pitch pattern information is robustly available to 18-month-old Japanese monolingual infants in a minimal pair word-learning situation, but only partially accessible in the same context for 14-month-old infants.

Infant vocalization plays a pivotal role in communicating infant mood to parents and thereby motivating parenting responses. Although many psychological and neural responses to infant vocalization have been reported, few studies have examined maternal approach-avoidance behavior in response to infant vocalization. Thus, this research sought to determine how infant emotional vocalization affects maternal behavior. Twenty mothers participated in this behavioral study, all of whom had infants of 24 months old or less. In the experiment, they stood on a Balance Board that collected real-time data regarding center of pressure (COP), while listening to a series of infant vocalizations including cry, laugh, and babbling. They then listened to the same vocalizations for a second time and rated their felt emotions in response to each vocalization. The participants demonstrated significant postural movements of approaching in response to cry stimuli or to stimuli regarded as highly urgent. In contrast, they demonstrated postural movement of avoidance in response to laugh vocalization. These findings suggest that parenting behavior in response to infant emotional vocalization is regulated not by the pleasant-unpleasant axis but by the urgency of the stimulus.

Japanese 8-month-olds were tested to investigate the matching of particular lip movements to corresponding non-canonical sounds, namely a bilabial trill (BT) and a whistle (WL). The results showed that the infants succeeded in lip-voice matching for the bilabial trill, whereas they failed to do so for the whistle.

Japanese infants at the ages of 6, 12, and 18 months were tested on their ability to discriminate three nonsense words with different phonotactic status: canonical keetsu, noncanonical but possible keets, and noncanonical and impossible keet. The results showed that 12 and 18 months olds discriminate the keets/keetsu pair, but infants in all age groups fail to discriminate the keets/keet pair. Taken together with the findings in our previous study [Kajikawa et al., J. Acoust. Soc. Am. 120(4), 2278-2284 (2006)], these results suggest that Japanese infants develop the perceptual sensitivity for native phonotactics after 6 months of age, and that this sensitivity is limited to canonical patterns at this early developmental stage.

This study explored sensitivity to word-level phonotactic patterns in English and Japanese monolingual infants. Infants at the ages of 6, 12, and 18 months were tested on their ability to discriminate between test words using a habituation-switch experimental paradigm. All of the test words, neek, neeks, and neekusu, are phonotactically legitimate for English, whereas the first two words are critically noncanonical in Japanese. The language-specific phonotactical congruence influenced infants' performance in discrimination. English-learning infants could discriminate between neek and neeks at the age of 18 months, but Japanese infants could not. There was a similar developmental pattern for infants of both language groups for discrimination of neek and neeks, but Japanese infants showed a different trajectory from English infants for neekusu/neeks. These differences reflect the different status of these word patterns with respect to the phonotactics of both languages, and reveal early sensitivity to subtle phonotactic and language input patterns in each language.

This study investigated vowel length discrimination in infants from 2 language backgrounds, Japanese and English, in which vowel length is either phonemic or nonphonemic. Experiment 1 revealed that English 18-month-olds discriminate short and long vowels although vowel length is not phonemically contrastive in English. Experiments 2 and 3 revealed that Japanese 18-month-olds also discriminate the pairs but in an asymmetric manner: They detected only the change from long to short vowel, but not the change in the opposite direction, although English infants in Experiment 1 detected the change in both directions. Experiment 4 tested Japanese 10-month-olds and revealed a symmetric pattern of discrimination similar to that of English 18-month-olds. Experiment 5 revealed that native adult Japanese speakers, unlike Japanese 18-month-old infants who are presumably still developing phonological perception, ultimately acquire a symmetrical discrimination pattern for the vowel contrasts. Taken together, our findings suggest that English 18-month-olds and Japanese 10-month-olds perceive vowel length using simple acoustic?phonetic cues, whereas Japanese 18-month-olds perceive it under the influence of the emerging native phonology, which leads to a transient asymmetric pattern in perception.

Recent studies using a violation-of-expectation task suggest that preverbal infants are capable of recognizing basic arithmetical operations involving visual objects. There is still debate, however, over whether their performance is based on any expectation of the arithmetical operations, or on a general perceptual tendency to prefer visually familiar and complex displays. Here we provide new evidence that 5-month-old infants recognize basic arithmetic operations across sensory modalities. Using a violation-of-expectation task that eliminated the possibility of the familiarity and complexity preference, 5-month-old infants were presented alternatively with two types of arithmetical events: the expected, correct outcomes of operations (1 object+1 tone=2 objects and 1 object+2 tones=3 objects) and the unexpected, incorrect ones (1 object+2 tones=2 objects and 1 object+1 tone=3 objects). Results showed that subjects looked significantly longer at the unexpected events than at the expected events, suggesting that infants are able to recognize basic arithmetic operations across sensory modalities.

Acceptable phonotactics differ among languages. Japanese does not allow consonant clusters except in special contexts and this phonotactic constraint has a strong effect on adults speech perception system. When two consonants follow one another in nonsense words, adult Japanese listeners hear illusory epenthetic vowels between the consonants. The current study is aimed at investigating the influence of language‐specific phonotactic rules on infants’ speech perception development. Six‐, 12‐, and 18‐month‐old infants were tested on their sensitivity to phonotactic changes in words using a habituation‐switch paradigm. The stimuli were three nonsense words: ‘‘keet (/ki:t/),’’ ‘‘keets (/ki:ts/),’’ and ‘‘keetsu (/ki:tsu/).’’ ‘‘Keetsu’’ perfectly follows Japanese phonotactic rules. ‘‘Keets’’ is also possible in devoicing contexts in fluent speech, but the acceptability of ‘‘keets’’ for adult native Japanese speakers is much less than ‘‘keetsu.’’ ‘‘Keet’’ is phonotactically impossible as a Japanese word. The resu...

Previous research with an identification task suggests that native Japanese speakers perceive a moraic obstruent categorically (Amano et al., 2005). However, it is still unclear whether the suggestion would be confirmed by other tasks. This study used an AX discrimination task to investigate whether the performance is highly sensitive around the perceptual boundaries that were obtained from the identification task. Native Japanese speakers (N=40) were presented with a pair of two‐mora nonsense syllables (/bipa/, /guku/, /kuku/, /kuto/) and then required to judge whether the stimulus pair was acoustically identical. The stimulus set was produced by reducing or increasing the closure duration between the successive moras in 5‐ms steps (−95 to 240 ms). Results showed that the participants discriminated more precisely around closures duration ranging from approximately 150 to 180 ms (/bipa/: 180 ms, /guku/: 160 ms, /kuku/: 155 ms, /kuto/: 175 ms). Although the results indicate, to some degree, the possibility...

Native Japanese speakers perceive a moraic obstruent when the closure duration between successive moras is longer than a normal obstruent. However, it has not been well clarified how the perception of the moraic obstruent relates to the closure and neighboring moras’ duration. To investigate this point, a perceptual experiment was conducted with stimuli consisting of two‐mora nonsense syllables with a closure between the moras (/bipa/, /guku/, /kuku/, /kuto/, and /tapi/). The closure duration was shortened or lengthened in 10‐ms steps. The duration of the first mora was modified by changing its vowel duration to 50%, 100%, and 150% by the STRAIGHT method. Forty native Japanese speakers identified whether the nonsense syllable contained a moraic obstruent with the 2AFC method. Results showed that the perceptual boundaries of the moraic obstruent were 182 ms (SD=13.2 ms), 204 ms (SD=14.7 ms), and 222 ms (SD=16.6 ms), respectively, with 50%, 100%, and 150% vowel durations in the first mora, and that a logist...