While much of our work in the MAClab concerns auditory and perceptual aspects of words, the process of mapping sounds to meaning offers some conceptually similar problems.

Between birth and adulthood children must learn about 60,000 words. That translates to 8-10 words per day! Words rarely occur in isolation, many of them do not have observable meanings (what does the word “the” mean?") and even when they do it's not always clear what the speaker is referring to. Thus, similar to speech perception we see a problem of coping with massive ambiguity.

Because of this challenge, a lot of researchers have posited specialized mechanisms that help children analyze the auditory and visual inputs and learn what words mean. However, it is unclear what those mechanisms are and even if they are necessary. Our work in the MAClab is investigating this. In particular, we are investigating two broad perspectives, and their ability to solve basic problems of word learning.

First, development happens over two timescales. Children must simultaneously learn word/object mappings slowly over weeks and years, and they must be able to use words in the moment when a person is talking about them. Prior work on ideas like “fast-mapping” often conflates these ideas, assuming that what children do in the moment is the same as learning.

Second, simple associative mechanisms (while clearly not the whole story) may have a lot of power to solve word learning problems when they are embedded in more realistic systems (e.g., systems with two-timescales or processing).

Putting these two simple ideas together has led to a number of interesting investigations. In collaboration with Larissa Samuelson and Jessica Horst to understand a phenomena known as fast-mapping, in which children use words they know to help learn new words. While this has often been seen as a specialized word learning mechanism our work suggests that children do not always retain the meanings of fast-mapped words, and we are investigating how it relates to learning.

We've also investigated the so-called vocabulary spurt or the naming explosion. Typically after learning the first 50 words or so many children's word learning literally takes off as they start learning 8-10 words per week. Researchers have long assumed that mechanisms like fast-mapping are required to explain this word spurt, but working with Mathematician Colleen Mitchell we've found that mathematically acceleration is almost always guaranteed when children are learning multiple things at the same time.

Finally, a number of ongoing studies are examining how learning words impacts speech perception. Our work on infants is showing how it may help them sort out what cues are relevant, and ongoing work is examining how the timing of learning words can influence how sounds are processed, and examining what it takes for words to be embedded in the lexical processing system.

Relevant Papers

Rost, G., and McMurray, B. (2009) Speaker variability augments phonological processing in early word learning. Developmental Science, 12(2), 339-349.

Rost, G.C., and McMurray, B. (2010) Finding the signal by adding noise: The role of non-contrastive phonetic variability in early word learning. Infancy, 15(6), 608-635.

McMurray, B. (2007) Defusing the childhood vocabulary explosion. Science, 317(5838), 631.

Mitchell, C., and McMurray, B. (2009) On leveraged learning in lexical acquisition and its relationship to acceleration. Cognitive Science, 33(8), 1503-1523.

Horst, J.S., Samuelson, L.K., Kucker, S. & McMurray, B. (2011) What's new? Children prefer novelty in referent selection. Cognition, 118(2), 234-244.