Young tortoises and old hares?
Given Hartshorne et al’s study finding that the ability to learn grammar decreases from late adolescence, the question is: what kind of changes in the brain are causing this?
There are specific parts of the brain associated with processing grammar and there also more general essential processes such as memory and attention. Developmental changes might involve these specific pathways, more general functions, or both.
To investigate this, Menks and colleagues recruited 165 monolingual Dutch speakers aged eight to 25 years. The participants were taught a sample of Icelandic words and tested online until they had a perfect score. The words chosen were Dutch-Icelandic cognates with the aim of focussing brain activity on differences in grammar rather than vocabulary.
Each participant was then given a task that required some grammatical judgement while having their brain scanned by functional magnetic resonance (fMRI). This scanning technique records levels of brain activity by monitoring increases in blood flow.
After the first fMRI scan they played a grammar training game every day for five days. The game asked players to match pictures to Icelandic sentences and then presented the correct answer. No rules of Icelandic grammar were given, but these were implicit in the matching task. Then each participant had another fMRI during which they performed another grammatical judgement task.
The grammatical judgement task consisted of 192 trials presenting Icelandic sentences. Players had to indicate whether the sentences followed or violated the rules that they had encountered in the grammar training game. This enabled the researchers to analyse how the age of the participants influenced how well they picked up the implicit grammar rules while simultaneously recording areas of the brain activated during the task.
Overall, the 15 to 25-year olds outperformed the eight to 15-year-olds in their ability to learn new grammar. This may seem surprising, but there is evidence that adults may learn a second language faster than children in the very early stages. After a slower start, however, younger learners are more likely to reach the proficiency level of native-speakers.
The ability to learn grammar in this setting was found to increase from age eight to 15.4 then remain steady. Dividing the participants into those under or over 15.4 years showed that more areas of the brain were activated in participants over 15.4 years, especially relating to working memory (such as short-term memory) and syntax-associated pathways.
This suggests that both younger and older language learners are using the same pathways in the brain and that age-related differences in ability arise when these pathways reach their peak development. This particular study showed a peak but no decline in ability; but then the oldest ‘adults’ were only 25.
REFERENCE
Menks, W. M., Ekerdt, C., Lemhöfer, K., Kidd, E., Fernández, G., McQueen, J. M. and Janzen, G. (2024) Developmental changes in brain activation during novel grammar learning in 8-25-year olds. Developmental Cognitive Neuroscience. 66: 101347
