When children learn to talk, they pass through a stage when they make certain kinds of errors. These errors are not exactly grammatical errors, but they are due to the fact that language has certain conventions and irregularities. They make mistakes such as "Yesterday I holded the bunny".
Until recently, it was assumed that children make these "errors" because they learn the structure of grammar and apply it to irregular words as well as to regular words - because they don't know which are the irregular words. However, two neuroscientists from Georgetown University Medical Center have discovered that this idea only applies to boys.
The researchers concluded that boys and girls use different parts of the brain while using language, suggesting that sex is an important factor in the acquisition and use of language. Girls mainly use a system that is for memorizing words and for making associations between them (such as rhymes), whereas boys rely primarily on a system that governs the rules of language. In other words, the use of language is more like a puzzle game for girls while for boys it is more like a lego game.
"Sex has been virtually ignored in studies of the learning, representation, processing and neural bases of language," said the lead author, Michael Ullman, PhD, professor of neuroscience, psychology, neurology and linguistics. "This study shows that differences between males and females may be an important factor in these cognitive processes."
He added that since the brain systems they tested are responsible for more than just language use, the study might have more far reaching consequences. "Men and women may tend to process various skills differently from one another," Ullman said.
Ullman and his colleague Joshua Hartshorne knew that previous studies with adults, including studies conducted by Hartshorne, had shown that women are better at remembering lists of words (verbal memory tasks), which involves declarative memory. On the other hand, men and women seem equally adept to combine words into sentences, a process called procedural memory and which involves a different part of the brain.
Based on this knowledge, Ullman and Hartshorne expected that girls would make fewer mistakes like "holded" than boys because "over-regularization" is caused by the children's inability to remember the actual words used by the adults and then just recreate the past tense by analogy with regular words like "walked". However, the experiments showed just the opposite.
They studied how a group of 10 boys and 15 girls, age 2 to 5, used regular and irregular past-tense forms in their normal speech. To their surprise, the girls over-regularized far more than boys.
Intrigued, researchers investigated to which verbs the girls are more prone to errors. They found that a word was over-regularized if it rhymed with other verbs. The words that didn't have many available rhymes were left intact. For example, girls tended to say "holded" or "blowed" because many other rhyming verbs use the regular past-tense form (such as folded, molded, and flowed, rowed, stowed, respectively).
This discovery reveals that girls aren't really relying on procedural memory to generate past tenses, but more on declarative memory. "This memory is not just a rote list of words, but underlies common patterns between words, and can be used to generalize these patterns," Ullman said. "In this case, the girls had memorized the regular past tenses of rhyming words, and were generalizing these patterns to new words, resulting in over-regularization errors."
In case of boys on the other hand, there was no association between the number of similar sounding regular past-tense verbs and the particular verbs that were over-regularized. Verbs like "holded" or "blowed" didn't feature more prominently among their "errors". According to Ullman, this suggests that the boys are probably using the rule-governed system to combine verbs with -ed endings.
"Although the two sexes seem to be doing the same thing, and doing it equally well, they are using two different neurocognitive brain processes to do it," Ullman said. "This is a novel and exciting finding."