Finding the signal by adding noise: The role of noncontrastive phonetic variability in early word learning.

It is well attested that 14-month olds have difficulty learning similar sounding words (e.g. bih/dih), despite their excellent phonetic discrimination abilities. In contrast, Rost and McMurray (2009) recently demonstrated that 14-month olds' minimal pair learning can be improved by the presentation of words by multiple talkers. This study investigates which components of the variability found in multi-talker input improved infants' processing, assessing both the phonologically contrastive aspects of the speech stream and phonologically irrelevant indexical and suprasegmental aspects. In the first two experiments, speaker was held constant while cues to word-initial voicing were systematically manipulated. Infants failed in both cases. The third experiment introduced variability in speaker, but voicing cues were invariant within each category. Infants in this condition learned the words. We conclude that aspects of the speech signal that have been typically thought of as noise are in fact valuable information - signal - for the young word learner.