Fast mapping means when a child hears a word, they’ll pick it up quickly, even if they are not familiar with its meaning.[1]
It’s a fairly complex process; toddlers hear a word, process its meaning quickly, use it in context, and remember it. Carey and Bartlett suggested that children could remember words for up to a week, or possibly a month, if they weren't presented with them again in that time.
Your toddler's brain stores words and makes a map of when and how to use them. So, you might have said a word in front of toddler while talking. Although they might not have responded to that word, a couple of days later you hear them say that word in context. An example would be that you give your toddler a drink, saying, “Take a sip.” They haven’t heard the word sip before, yet when you both have a drink on different day, your toddler says, “Sip.”
Toddlers find it more challenging to learn and remember new words when they are introduced to lots at one time.
Toddlers can only keep so much information in one go, and if they hear too many unfamiliar words, it becomes difficult for them to remember them all.[2]
Studies suggest that toddlers have a greater ability to fast map words because of the amount of sleep they have.[3]
According to research, toddlers deepen their understanding of words and their meanings when they are sleeping.[3,4,5] The words become strengthened and more deeply ingrained in their memory.
And we couldn’t leave it without mentioning that if attention is drawn to a new or novel word, your toddler is more likely to remember it!
There may be times when your toddler hears a word you prefer them not to use – perhaps someone swears in front of them. It might catch you off guard and your toddler will probably instantly gather from your reaction that the word is ‘interesting’ so fast map it for future use; this can be why toddlers can end up using their new-found words at the worst moments!
References:
[1] Carey, S, Bartlett, E. (1978). Acquiring a Single New Word. Proceedings of the Stanford Child Language Conference.
[2] Spiegel, C., Halberda, J (2011) Rapid fast-mapping abilities in 2-year-olds. Journal of Experimental Child Psychology. Volume 109, Issue 1.
[3] Xiaoxue He, A., Huang, S., Waxman, S., Arunachalam, S. (2020) Two-year-olds consolidate verb meanings during a nap. Cognition. Volume 198.
[4] Axelsson, E. L., Swinton, J., Winiger, A. I., & Horst, J. S. (2018). Napping and toddlers’ memory for fast-mapped words. First Language, 38(6), 582–595.
[5] Friedrich M, Wilhelm I, Born J, Friederici AD. (2015) Generalization of word meanings during infant sleep. Nat Commun.