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Scientists from Freie Universität Berlin and the MRC Cognition and Brain Sciences Unit in Cambridge launch study about the speed of word recognition
27 March 2012
Freie Universitaet Berlin
Scientists from Freie Universität and the MRC Cognition and Brain Sciences Unit in Cambridge have discovered that word recognition works much faster than previously assumed. Within a tenth of a second after the sound waves of the relevant part of a word hit the eardrum, there are, according to the study, the first indications of comprehension in the brain. The results were published in the latest online-version of the journal Nature.
The group of scientists led by the neurobiologist and linguist Prof. Dr. Dr.. Friedemann Pulvermüller from Freie Universität Berlin and Prof. Yury Shtyrov from the MRC Cognition and Brain Sciences Unit in Cambridge presented their participants with spoken words like "note" and pseudowords like "noke." At the beginning of each syllable, when only "no" has been heard, the brain cannot decide with certainty if the word is real or fake. To identify the word with certainty, the brain requires the additional information at the end of the syllable. The researchers discovered that already within 50-80 milliseconds after the incoming sound signals first allowed the participants to recognize the words with certainty, a brain indicator differentiated between the meaningful and the meaningless items. This is much earlier than a previously established brain indicator of comprehension, the so-called N400-component, which peaks only at a latency of about half a second. In their present study, the scientists were also able to re-confirm another early brain indicator of speech understanding. This indicator, which occurs after 150-200 milliseconds, was discovered by Prof. Pulvermüller's group in Cambridge a few years ago. The other early component, sometimes called the "semantic mismatch negativity," was found to indicate rather fine-grained features of meaning comprehension, for example whether an incoming word relates to mouth or leg movements (examples: "talk" or "walk").
"Behavioral experiments had already indicated that human speech processing works very quickly," said Prof. Friedemann Pulvermüller. "However, here for the first time we see physiological evidence backing that assumption with brain measurements and defining the exact time course and unbelievable speed with which our brain decides between what makes sense and what doesn't." The scientists used a new technique for their study, called magnetoencephalography, and distributed source analysis. With magnetoencephalography it is possible to localize even the miniscule magnetic fields that the brain produces while working. Using distributed source analysis, the activation patterns in the brain can be located even if they involve several brain areas at the same time. The temporal precision of this method is unexcelled.
In the future Friedemann Pulvermüller, who just moved to Berlin after 12 years of work at Cambridge, and his new team would like to use the new knowledge about rapid language comprehension on patients with language problems following a stroke. "The early brain responses of word recognition might help us in measuring the progress made by stroke patients with a loss of normal language ability who undergo intensive speech therapy."