Six- and ten-month-old infants' perception of non-contrastive variation

Recent evidence suggests that infants do not perceive all existing speech sounds from birth. For example, the velar and alveolar nasal place contrasts are so subtle that infants require experience to perceive it (e.g., Narayan et al., 2012). Here, we examine English-learning infants' perception of another subtle contrast: pre-voicing on stop consonants. Six- and ten- month-olds' ability to discriminate between voiced and voiceless stops (phonemically contrastive in English) as well as voiced and pre-voiced stops (allophonic in English, but contrastive in other languages such as Dutch) was tested using a variant of the Stimulus Alternation Paradigm (SAPP). Six-month-olds (N=34) distinguished between voiced and voiceless stops (p < .05), but not between voiced and pre-voiced stops. Ten-month-olds (N=32) failed to discriminate either contrast. We conclude that 1) English pre-voicing may be a subtle contrast requiring experience to perceive, and 2) this version of the SAPP might not be an ideal methodology to examine discrimination abilities in 10-month-olds. Overall, our findings thus far fit well with the notion that some contrasts require experience to perceive, as well as with past studies reporting mixed results regarding English-learning infants' ability to perceive pre-voicing contrasts (e.g. Aslin et al., 1981; Lasky et al., 1975).