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Unfortunately for me, Jim's language development didn't cooperate with my class schedule. He didn't produce any new words between 13 and 16 months -- he had found that pretty much all his requirements could be taken care of with three: "na-na" (no, bad), "da-da" (yes, good), and "bah-pul" (give me food -- now -- preferably in liquid form!).
Nora, on the other hand, was producing many words by 13 months, and many more at 16 months. But she was born about 19 months too late to be of use in my developmental psychology class. So why is it that some kids talk early and others talk late? Part of the answer comes from a study by a team led by Feng-Ming Tsao. Tsao and his colleagues tested the language ability of 26 six-month-old infants, then re-evaluated them at 13, 16, and 24 months of age.
The test they gave at 6 months was very similar to the study we discussed a few weeks ago (in fact, it was conducted in the same lab). The babies sat on a parent's lap and listened to one of two prototypical sounds (/u/ or /y/), which was repeated every two seconds. Every so often a different sound was played, and if the babies looked in the direction of the different sound, they got to see a toy bear bang on a drum. Once they reliably responded, they moved on to a second phase where they were tested until they got 7 out of 8 correct responses. During this phase researchers wanted to know how many trials it would take until the task was learned. Finally they were randomly tested on 30 trials to get an overall accuracy score.
As it turned out, the second phase -- number of trials until the task was learned -- was most reliably correlated with future language ability. Take a look at this graph charting the results for the 13 toddlers the researchers were able to locate at age 24 months:
The fewer trials babies took to perform the task at age 6 months, the more words they were able to produce at age 24 months. Just this simple task of distinguishing between two different vowel sounds was significantly correlated with speaking ability 18 months later! A number of other measures of language ability also correlated with performance at 6 months. Consider this graph:
Once again, the toddlers who produced more grammatically complex language at 24 months were the babies who could more readily distinguish between vowel sounds at age 6 months. The researchers examined other factors as well, such as the socioeconomic status of the parents, and the only other factor in language development of the 24-month-olds was whether the mother had a job, which was weakly (and non-signficantly) correlated with production of irregular words at 24 months. None of these external factors had made a difference in the performance of the task at 6 months.
Unfortunately, this study can't show us why ability at 6 months correlates with ability at 24 months. Perhaps different kids have different language abilities that are manifested as early as 6 months old. Perhaps some unknown environmental factor plays a part. Perhaps the better-performing children are simply more intelligent than the others. The team is working on a follow-up study of a larger group, which controls for some of these factors while following the kids for a longer period.
Tsao, F., Liu, H., & Kuhl, P.K. (2004). Speech perception in infancy predicts language development in the second year of life: A longitudinal study. Child Development, 75(4), 1067-1084.
Humanities & Social Science
Comments
It seems straightforward that being able to distinguish speech sounds is important for learning language. Anything that interferes with the ability to do that is going to make it harder to develop the building blocks for language such as learning new words. So it's not surprising at all that differences in ability to distinguish sounds at 6 months predict language ability 18 months later. In my mind, the real question is what factors influence the ability to discriminate between speech sounds, and how does one tell early on which are just innocuous differences in rate of developmental vs. those due to problems with hearing, delays in auditory processing ability, etc.
Posted by: Meredith Warshaw | October 23, 2007 4:26 PM
Looks like the paper is gated so I will admit I didn't read it. However, just looking at the graphs you included in the post, the results don't seem to be statistically significant. The variance/error is way too large and the sample is way too small for those trend lines to be meaningful. I'd be very cautious about drawing conclusions from such a small amount of date.
Posted by: Sally LeRoy | October 23, 2007 7:54 PM
Sally,
I agree, the sample size is quite small. The results I've reported are significant. The effect size is quite large, and that makes up for the small sample.
What's more, they also gathered data at 13 months and 16 months, with a higher retention rate, and found the same results.
In addition, they report on their ongoing research with a larger sample of 40 children, and again they say these results are replicated.
I'll be interested to see those results when they are finally published in peer-reviewed form.
Posted by: Dave Munger | October 23, 2007 9:32 PM
One possible aspect which is related and may be more difficult to analyze quantitatively is how much is the baby 'talked to';
Exposure to regular well-formed speech from a parent may be a factor here. It may seem obvious, but some parents continue to talk with their babies as if in a conversation. I feel that one of those social factors is exposure to the nuances of the language Early on.
Posted by: Gibran | October 24, 2007 8:31 AM
A preprint of the paper is available at http://ilabs.washington.edu/kuhl/publications.html , my fellow academiphiles.
Included are some test statistics, suggesting that the findings are at least somewhat significant.
Posted by: FhnuZoag | October 24, 2007 11:05 AM
It's interesting that for kindergarteners, phonemic awareness ability, the ability to discriminate, sequence, and manipulate sounds in words, is one of te strongest predictors for success in learning to read and write. This effect is very well eatablished by research.
Posted by: m dreyer | October 24, 2007 8:58 PM
I don't think there is strong evidence that early language aquisition is associated with higher intelligence. Often, later speakers catch up with early speakers, just as later readers often catch up with early readers. It is possible that some of us are gifted with a "ear" for speech.
Posted by: Ann | October 24, 2007 11:31 PM
Hah. I started talking about 36 months, and grew up to be quite verbal. My hearing's not the best though, and my father's was worse, so maybe there's something there.
Posted by: Damien | October 25, 2007 2:40 PM
Without even having read the paper, I would like to add one other point of view. There may be a difference in learning ability that underlies the observations. But there may also be a difference in (the level of) desire to interact with the outside world. Which might influence both the initial test and the child's progress in speaking ability.
Posted by: Frans van Otten | October 28, 2007 6:03 PM
Haven't had a chance to read the paper, but it's worth noting that the test at six months may have nothing to do with language ability. The test may be vowel discrimination, but variance in 6mos babies may be entirely due to some other measure of intelligence (processing speed, rule-learning, etc)- it shouldn't be surprising that smarter babies learn language earlier. It would be interesting to see if a similar preferential looking procedure on a non-linguistic task (say, discriminating pure tones) also correlated with later ability, or if their 6mos test also was associated with better performance on non-linguistic measures of the older babies. Without these sorts of controls, it's hard to know exactly what's being tested. Older work has shown that trials to habituation (another design used in infant studies) for all kinds of stimuli correlates with later intelligence..
Posted by: Bruce Poisson | November 5, 2007 9:17 PM
So the conclusion is there really isn't a definitive answer as to what made them pick up a language or talk at an earlier stage. I didn't see nurturing involved whereby the parents are just so active in talking to the infant. I do understand the significance and factors that affect language learning at an early age or as an adult while enrolling a study abroad program.
Posted by: Frank Rollins | November 7, 2007 10:15 AM