Ryoko Mugitani

Baby arithmetic: one object plus one tone

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.

Longitudinal developmental changes in spectral peaks of vowels produced by Japanese infants.

This paper describes a longitudinal analysis of the vowel development of two Japanese infants in terms of spectral resonant peaks. This study aims to investigate when and how the two infants become able to produce categorically separated vowels, and covers the ages of 4 to 60 months in order to provide detailed findings on the developmental process of speech production. The two lower spectral peaks were estimated from vowels extracted from natural spontaneous speech produced by the infants. Phoneme labeled and transcription-independent unlabeled data analyses were conducted. The labeled data analysis revealed longitudinal trends in the developmental change, which correspond to the articulation positions of the tongue and the rapid enlargement of the articulatory organs. In addition, the distribution of the two spectral peaks demonstrates the vowel space expansion that occurs with age. An unlabeled data analysis technique derived from the linear discriminant analysis method was introduced to measure the vowel space expansion quantitatively. It revealed that the infants vowel space becomes similar to that of an adult in the early stages. In terms of both labeled and unlabeled properties, these results suggested that infants become capable of producing categorically separated vowels by 24 months.

Audiovisual matching of lips and non-canonical sounds in 8-month-old infants

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.

Perception of a Japanese moraic obstruent in a discrimination task

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...

Perception of a Japanese moraic obstruent in an identification task

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...