Listen to part of a lecture in a psychology class.

(professor) One aspect of how children begin talking, how they acquire language. That\'s had a lot of research, has to do with how fast children acquire vocabulary, how fast they learn new words.

One widely accepted view says that somewhere near the end of their second year, most children undergo a vocabulary spurt.

(female student) Oh, so they suddenly learn a whole bunch of words in a very short time?

(professor) Well, that\'s the standard meaning of the word spurt. Sometime between about 14 and 24 months of age, toddlers go from, like, say, learning 1 to 3 words a month to 10 or 20 a week.

So, it is a significant gain. But to study this gain scientifically, we have to define what we really mean by vocabulary spurt.

Well, two researchers Ganger and Brent decided to try to define the characteristics of a true vocabulary spurt, they decided that a meaningful spurt would have to have an inflection point.

An inflection point is a point on a graph. That\'s an indicator of a fast, dramatic change rather than a gradual one. Um, the term is used a lot in business, like when say a company sale suddenly skyrocket, like, you know, some internet companies recently. And that change can be clearly seen on a chart or a graph, like on a sales chart.

You have a line showing low sales, and then boom, it\\\'s up and it stays up. The inflection point is the location on the chart, that\'s right between the two distinct stages.

One before the change happened, and one after. So, why do you think Ganger and Brent decided to use that to look for a vocabulary spurt?

(male student) Um… It must have to do with the two different stages. If a child\'s rate of word acquisition is just a steady climb, that\\\'s not the same as a spur. A spurt means something’s changed quickly.

(professor) Something\'s changed?

(male student) Um, a developmental change like, a cognitive breakthrough.

(professor) Right. Ganger and Brent were looking for evidence of a sudden and fundamental change in the way children process Information. That\'s why they\'re interested in an inflection point.

Um. The literature is filled with theories about what kind of cognitive breakthrough would cause a vocabulary spurt. One is called the naming insight.

According to the naming insight, the reason for the spurt is that the child suddenly understands that words refer to things, and that all things have names.

Before that words are used mainly as a way to communicate a need or desire, like saying milk when thirsty. After children reach the naming insight, they\'d start learning words at a faster rate.

Another theory about why the spurt exists is… uh, that it\'s linked to the ability to sort objects into groups. But Ganger and Brent wanted to check whether it exists at all.

So rather than collecting all new data, they took a look at the results of some existing research. They looked at three separate studies, okay? 3 sets of data. And they found that only about one in five children actually had an identifiable spurt.

(female student) According to their definition, you mean?

(professor) Right. see, they looked at the data in a couple of different ways, and they plotted it all on a graph. And they found that in most cases, there was no evidence of an inflection point.

(female student) So, they\'re saying everybody was wrong?

(professor) Well, some earlier studies didn\'t look for two discrete stages, a slow rate before the spurt and a faster one after the spurt. In some studies, um, the researchers were only looking for evidence of crossing a threshold, say, 50 words.

Other researchers studied children\'s vocabulary charts for a jump. Well, a sudden jump that comes right back down doesn\'t mean it\'s a true spurt.

Ganger and Brent conclude that some children do have a vocabulary spurt, but that it\'s by no means universal. The non-universal nature of the vocabulary spurt leads the authors to conclude that the spurt doesn\'t necessarily reflect a cognitive breakthrough.

Obviously, children get better and better at learning new words. It\'s just that for most children, it\'s more of a steady climb than a sudden jump.

Quite convincing. I have to say, though, when I first read this study, I couldn\'t believe it. I\'d always assume that the spurt was a part of most children\'s development.