Understanding speech in context: an opportunistic, proactive brain at work
Recent research has shown how the human brain makes efficient use of even the tiniest cue to interpret speech, anticipating what might be said, about whom, sometimes ignoring the rules of language and performing rapid experiments to arrive at the earliest possible interpretation. Professor Jos Van Berkum from the Max Planck Institute for Psycholinguistics in the Netherlands discussed recent studies of brain waves and linguistic interpretation in the journal Current Directions in Psychological Science. 'Language comprehension looks pretty easy,' says Professor Van Berkum. 'You strike a conversation and listen to whatever the other person has to say. Although what you're taking in is a bunch of letters and sounds, what you really perceive - if all goes well - is meaning. But how do you get from one to the other so easily?' Professor Van Berkum and his team carried out a number of experiments over the past few years, studying event-related potentials (ERPs) obtained from data recorded from people listening to or reading a series of critical sentences in various contexts. ERPs indicate changes in brain activity in different situations, in response to a stimulus such as a word or tone. The results from all studies made it clear that interpretation involves many areas of the brain, each reacting to different situations and working in concert to put things in context and anticipate meaning. The so-called 'N400' is strongest over the back of the head; it is associated with the analysis of meaning but is not directly sensitive to how a sentence is put together. The N400 effect, which is seen for example when someone with a posh accent says, 'I have a large tattoo on my back,' showed how listeners immediately take the speaker into account and apply stereotypes to speed up their anticipation of what will be said. The effect of hearing or reading sentences in which the reference is ambiguous is different from the N400 effect, and is seen largely over the front of the head. Another ERP effect, called P600, was always elicited by hearing or reading a word that defies the listener's anticipated analysis. Taken together, Professor Van Berkum believes the results suggest an opportunistic, proactive brain at work, and that the importance of context cannot be underestimated. Also, he says, different aspects of interpretation are handled by at least partly different networks in the brain, and this inference has recently been confirmed with fMRI. 'When interpreting language, people don't just slavishly follow the syntax,' says Professor Van Berkum. Data from his team's studies show how listeners can determine whether a word is out of place before the speaker has finished saying it. The studies also show how the brain makes great use of social stereotypes in order to more quickly interpret the meaning of what is being said. According to the Professor, this is only one of many 'quick-and-dirty shortcuts' we use to anticipate speech. Professor Van Berkum does not believe that simply conducting more experiments will advance our understanding of interpretation. The big challenge, he says, 'is to construct precise models of interpretation that not only fit the behavioural facts and linguistic analyses, but whose machinery can also be mapped onto the neuroimaging data.' But also, he believes, neuroimaging studies should shift into the arena of real language use. 'Many interesting questions await us there,' he says. 'One set of issues revolves around the speaker, the type of discourse, and 'layers' in communication: For example, how does your brain respond to "the clouds are whispering" if you know that the speaker is a poet, a patient suffering from word-finding problems, or a protagonist in a story you are reading? [...] And what about the intentions of the speaker? [...] Intentional acts are at the heart of everyday communication, but right now, we haven't got a clue as to how the brain works out all of this as words come in. It is time to find out.'
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