e., Allen & Miller, 1999) as both were lower for /puk/ than /buk/. F0 was the only cue near significance INCB018424 supplier for distinguishing between /buk/ and /puk/. Phonetic data suggest that F0 should be lower for /b/ than /p/, and at voicing onset, /buk/’s F0 was indeed 27 msec lower than /puk/’s; this was not even marginally significant, t(106) = 1.59, p = .11. However, it seems unlikely that F0 could serve even to augment the noncontrastive variability in Experiment 3 as 28 /buk/s had F0 values less than the median, compared with 26 /puk/s. Although there was an almost marginal effect in the right direction, there were not

enough tokens showing this relationship to make F0 a worthwhile cue. Moreover, Experiment 2 ruled out that F0 in the absence of noncontrastive variability drives this effect. As a result, the cue that came closest to distinguishing the words does not appear to have much utility as a constrastive cue in this particular set of

stimuli. These experiments investigated the role of contrastive and noncontrastive phonetic variability in infants’ word learning in the switch-task procedure. Experiments 1 and 2 examined whether variability in a contrastive cue was necessary for LY2157299 chemical structure minimal-pair learning in the switch task. Our initial hypothesis was that the switch task requires children to determine that a given exemplar is not a member of the /buk/ (or /puk/) category, and as a result, some estimate of the extent of a category along the contrastive dimension may be needed to make this determination. However, this was not the case: across both experiments there was no evidence for learning, even when three cues to voicing varied simultaneously. Indirectly, this provides evidence that the kind of statistical learning first reported by Maye et al. (2002, 2008) (see also Kuhl et al., 2007; McMurray et al., 2009; Vallabha et al., 2007) can not account why for learning in Rost and McMurray (2009) as variability along the contrastive dimension of voicing alone is not sufficient to support learning. We do not

argue that infants ignore variability along dimensions, such as VOT. Indeed, it is likely to be important in establishing the location of categories within a dimension. However, it seems that this is not the information that they must glean to succeed here by this more advanced age. This suggests that the perceptual development that supports learning on this task is not simply locating categories within a dimension. Rather, some other component of perceptual development must be occurring. By contrast, Experiment 3 suggests that variability along noncontrastive acoustic dimensions supports minimal-pair learning in the switch task, even when contrastive variability is minimized. Before reaching this conclusion, however, it is important to assess several alternatives. One possible explanation for this is that the stimuli presented in Experiment 3 are more natural than those in Experiments 1 and 2.