Publications by authors named "Sachiyo Kajikawa"

Efficient data collection in developmental studies is facing challenges due to the decreased birth rates in many regions, reproducibility problems in psychology research, and the COVID-19 pandemic. Here, we propose a novel platform for online developmental science research, the Baby's Online Live Database (BOLD), which extends the scope of the accessible participant pool, simplifies its management, and enables participant recruitment for longitudinal studies. Through BOLD, researchers can conduct online recruitment of participants preregistered to BOLD simply by specifying their attributes, such as gender and age, and direct the participants to dedicated webpages for each study.

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Previous research has shown that not only adults but also two-and-a-half-year-old children associate higher-frequency sounds with smaller objects and with objects of brighter colors, suggesting that these intersensory correspondences are based on neural connections present very early in life. The present research examined whether 10-month olds are sensitive to these intersensory correspondences using a violation-of-expectation procedure. The results of Experiment 1 indicated that 10-month-olds associate a higher-frequency tone with an object of a brighter color and a lower-frequency tone with an object of a darker color.

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Six-, 12-, and 18-month-old English-hearing infants were tested on their ability to discriminate nonword forms ending in the final stop consonants /k/ and /t/ from their counterparts with final /s/ added, resulting in final clusters /ks/ and /ts/, in a habituation-dishabituation, looking time paradigm. Infants at all 3 ages demonstrated an ability to discriminate this type of contrast, a contrast that constitutes one phonetic cue for the English morphological concepts of plural, possession, and person. These results suggest that across a significant portion of the development of infants' speech perception, this type of final contrast is discriminable.

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In this work, we examine a context in which a conflict arises between two roles that infant-directed speech (IDS) plays: making language structure salient and modeling the adult form of a language. Vowel devoicing in fluent adult Japanese creates violations of the canonical Japanese consonant-vowel word structure pattern by systematically devoicing particular vowels, yielding surface consonant clusters. We measured vowel devoicing rates in a corpus of infant- and adult-directed Japanese speech, for both read and spontaneous speech, and found that the mothers in our study preserve the fluent adult form of the language and mask underlying phonological structure by devoicing vowels in infant-directed speech at virtually the same rates as those for adult-directed speech.

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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.

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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.

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Across the first year of life, infants show decreased sensitivity to phonetic differences not used in the native language [Werker, J. F., & Tees, R.

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The canonical form for Japanese words is (Consonant)Vowel(Consonant) Vowel-. However, a regular process of high vowel devoicing between voiceless consonants and word-finally after voiceless consonants results in consonant clusters and word-final consonants, apparent violations of that phonotactic pattern. We investigated Japanese adults' perceptions of these violations, asking them to rate both canonical and noncanonical nonsense forms on a scale of goodness.

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This study aimed to clarify the development of conversational style in Japanese mother-child interactions. We focused on the frequency of speech overlap as an index of Japanese conversational style, with particular attention to ne, a particle produced by the speaker, and to backchannels, such as 'uh-huh', produced by the listener that support sympathetic conversation. The results of longitudinal observations of two Japanese mother-child dyads from approximately 0;11 to 3;3 suggest that an adultlike conversational style with frequent overlaps emerges in Japanese child-directed speech around the two-word utterance period, and a child's development of ne use is closely related to this shift.

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The present experiment investigated the ability of recognition and long-term retention of sound pattern of words extracted from spoken sentences in preverbal infants. When preferences of 8-month-old Japanese infants for target words and for novel words were tested by head-turn preference procedure, immediately after being auditory exposed to spoken sentences that included the target words, they showed preference for target words significantly over novel words. They were able to recognize words that were presented within sentences previously.

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