Search for: All records

At birth, infants discriminate most of the sounds of the world’s languages, but by age 1, infants become language-specific listeners. This has generally been taken as evidence that infants have learned which acoustic dimensions are contrastive, or useful for distinguishing among the sounds of their language(s), and have begun focusing primarily on those dimensions when perceiving speech. However, speech is highly variable, with different sounds overlapping substantially in their acoustics, and after decades of research, we still do not know what aspects of the speech signal allow infants to differentiate contrastive from noncontrastive dimensions. Here we show that infants could learn which acoustic dimensions of their language are contrastive, despite the high acoustic variability. Our account is based on the cross-linguistic fact that even sounds that overlap in their acoustics differ in the contexts they occur in. We predict that this should leave a signal that infants can pick up on and show that acoustic distributions indeed vary more by context along contrastive dimensions compared with noncontrastive dimensions. By establishing this difference, we provide a potential answer to how infants learn about sound contrasts, a question whose answer in natural learning environments has remained elusive. 

Infants learn the sound categories of their language and adults successfully process the sounds they hear, even though sound categories often overlap in their acoustics. Most researchers agree that listeners use context to disambiguate overlapping categories. However, they differ in their ideas about how context is used. One idea is that listeners normalize out the systematic effects of context from the acoustics of a sound. Another idea is that contextual information may itself be an informative cue to category membership, due to patterns in the types of contexts that particular sounds occur in. We directly contrast these two ways of using context by applying each one to the test case of Japanese vowel length. We find that normalizing out contextual variability from the acoustics does not improve categorization, but using context in a top-down fashion does so substantially. This reveals a limitation of normalization in phonetic acquisition and processing and suggests that approaches that make use of top-down contextual information are promising to pursue. 

Listeners quickly adapt to novel accents. There are three main hypotheses for how they do so. Some suggest that listeners expand their phonetic categories, allowing more variability in how a sound is pronounced. Others argue that listeners shift their categories instead, only accepting deviations consistent with the accent. A third hypothesis is that listeners both shift and expand their categories. Most work has supported the category expansion hypotheses, with the key exception of Maye et al. (2008) who argued for a shifting strategy. Here, we apply the ideal adaptor model from Kleinschmidt & Jaeger (2015) to reexamine what conclusions can be drawn from their data. We compare adaptation models in which categories are shifted, expanded, or both shifted and expanded. We show that models involving expansion can explain the data as well as, if not better than, the shift model, in contrast to what has been previously concluded from these data.