Development of single/geminate obstruent discrimination by Japanese infants: early integration of durational and nondurational cues

The Japanese language has single/geminate obstruents characterized by durational difference in closure/frication as part of the phonemic repertoire used to distinguish word meanings. We first evaluated infants' abilities to discriminate naturally uttered single/geminate obstruents (/pata/ and /patta/) using the visual habituation-dishabituation method. The results revealed that 9.5-month-old Japanese infants were able to make this discrimination, t(21) = 2.119, p = .046, paired t test, whereas 4-month-olds were not, t(25) = 0.395, p = .696, paired t test. To examine how acoustic correlates (covarying cues) are associated with the contrast discrimination, we tested Japanese infants at 9.5 and 11.5 months of age with 3 combinations of natural and manipulated stimuli. The 11.5-month-olds were able to discriminate the naturally uttered pair (/pata/ vs. /patta/), t(20) = 4.680, p < .000, paired t test. Neither group discriminated the natural /patta/ from the manipulated /pata/ created from natural /patta/ tokens: For 9.5-month-olds, t(23) = 0.754, p = .458; for 11.5-month-olds, t(27) = 0.789, p = .437, paired t tests. Only the 11.5-month-olds discriminated the natural /pata/ and the manipulated /patta/ created from /pata/ tokens: For 9.5-month-olds, t(24) = 0.114, p = .910; for 11.5-month-olds, t(23) = 2.244, p = .035, paired t tests. These results suggest that Japanese infants acquire a sensitivity to contrasts of single/geminate obstruents by 9.5 months of age and that certain cues that covary with closure length either facilitate or interfere with contrast discrimination under particular conditions.