THE brain works harder when gearing up to understand sentences that present
information out of chronological order, say scientists in Germany and
California. They have measured the effect at work just milliseconds after people
start reading a sentence.
Thomas M眉nte of the Medical College of Hannover and his colleagues from
the University of California at San Diego took 24 volunteers and asked them to
read 120 sentences. Using electrodes attached to the volunteers鈥� scalps, they
tracked the electrical activity in their brains.
The researchers were particularly interested in how readers responded to
sentences beginning with the words 鈥渂efore鈥� and 鈥渁fter鈥�. When they read the
sentence, 鈥淏efore the psychologist submitted the paper, the journal changed its
policy,鈥� for instance, there was a sharp increase in activity in the left
frontal cortex, a region associated with working memory. This response occurred
within a mere 300 milliseconds.
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When the word 鈥渁fter鈥� was substituted for 鈥渂efore鈥� in the same sentence,
activity also increased, but by a smaller amount. This indicates that less
working memory is required for 鈥渁fter鈥� sentences, the researchers say.
M眉nte reckons that because people naturally think in terms of sequential
events, more mental processing is required to make sense of sentences in which
this order is disrupted (Nature, vol 395, p 71). 鈥淎fter鈥� sentences fit
our chronological view, whereas 鈥渂efore鈥� sentences do not, so need extra
computation. 鈥淵ou have to keep the first chunk in working memory,鈥� says
惭眉苍迟别.
The size of the difference between the responses to the two word cues gives
an indication of a person鈥檚 level of understanding, the team says. The
differences were more pronounced in people who understand sentences easily than
in those with poor comprehension.