Sometime around 18 months, most children experience a “word spurt” (or “naming explosion”) that leads to large increases in their spoken vocabulary. Although 18 months is a common age for this increase, it can occur in children between the ages of 15 and 24 months. Some children never seem to “spurt” at all, but they still show normal language development. During this time, children come to understand that all things have names and gain the ability to “fast map,” meaning that they can hear a new word and “map” its meaning after hearing it only a few times (or even once). In one study, researchers put five objects in front of children, and one of these objects was completely new to them (a garlic press or some other strange kitchen tool). Then the researchers asked the children to “pass the lep,” using a made-up word to make sure the children hadn’t heard it before. At 18 to 24 months, children knew that the new word “lep” must refer to the new object (the garlic press), and they learned this new word after hearing it only a few times. Fast mapping, along with new skills in being able to put objects in categories, leads to this astonishing vocabulary growth.
Huttenlocher, P., Haight, W., Bryle, A., Seltzer, M., & Lyons, T. (1991). Early vocabulary growth: Relation to language input and gender. Developmental Psychology, 27, 238
Reznick, J. S., & Goldfield, B. A. (1992). Rapid change in lexical development in comprehension and production. Developmental Psychology, 28, 406