Trees and Forest in Language: Canʼt See the Rule for the Words?

Babies also exhibit differences in their learning patterns. They first recognise individual words and are later able to understand the subtle changes implied by different rule transformations. Why is there a developmental distinction? One way to approach this question is by emulating a personʼs first contact with an unknown language. In our laboratory we observed how electrical brain activity developed while adults were trying to learn a simplified artificial language in which new words with embedded rules were introduced repeatedly.

 

Participants were fitted with an elastic cap similar to a swimming cap, with sensors at different locations on the scalp, to record event-related potentials that measured changes in the electroencephalogram induced by the successive words of the artificial language. As learning progressed, brain responses associated with word-learning indicated a progressive process of memorization that appeared early in the course of learning. In contrast, the responses related to rule-learning appeared later and were completely different to those observed for word memorization. In this case, the brain responses were similar to those detected when control of attention is required to filter out irrelevant information. Refocusing attention to the commonalities embedded in this sea of words appeared to be necessary to extract the rules of the language. This specific response was only present in those subjects that were able to learn: the greater the acquisition, the greater the specific electrophysiological response. Although language has classically been studied independently of other intellectual functions, our results indicate that core aspects of human language require the coordination of other functions such as memory and attention in the course of language acquisition.

 

One structure particularly suited to this coordination task, given its deep and central location in the brain, is the nucleus striatum. It is extensively connected to multiple areas of the brain associated with language, attention and memory and is an essential structure in the acquisition of motor sequences. Despite this, there have been few studies of its role in language development. We tested patients with degenerative lesions in the nucleus striatum caused by a rare inherited condition called Huntingtonʼs disease. These patients displayed considerable difficulties when learning the simplified artificial language, particularly in extracting the linguistic rules.   We also observed that those patients who found attention control more difficult also had greater difficulties in acquiring the rules of the language.

 

In children, research on attention deficit hyperactivity disorder (ADHD) has also revealed abnormalities in the striatum and problems with language acquisition. In the light of the results reported above, we hypothesize that a close relationship may exist between these characteristics. Understanding the influence of attention on language development could have a major impact on our ability to prevent the development of language acquisition disorders. This is important because early detection and treatment of at-risk individuals is crucial to increasing the chances of recovery. Deeper knowledge of these issues could facilitate the design of more appropriate rehabilitation programmes for adults and children. In other words, if we know that rule-learning is dependent on adequate development of attention skills, early intervention with treatment targeted specifically at this function could indirectly improve language acquisition. In addition, more detailed understanding of the brain circuits involved in the acquisition of these two components of language is important when dealing with brain damage where neural regeneration is possible or removable brain tumours. Enhanced knowledge will increase the chances of obtaining satisfactory post-treatment results for improved preservation of the linguistic function.