Washington, December 20: University of Chicago researchers say that
they have identified brain regions where speech sounds are perceived as
having abstract meaning, rather than as just a stream of sensory input.

Lead researcher Steven Small says that the new findings suggest that
the understanding of speech does not just emerge from lower-level
processing of speech sounds, but involves a specialized perceptual
region.

During the study appearing in the journal Neuron, published by Cell
Press, the researchers asked volunteer subjects to listen to a series
of simple speech sounds while watching video of people pronouncing the
sounds. The speech sounds might either match the video representations
or not.

The subjects’ brains were scanned using functional magnetic resonance
imaging, in which harmless magnetic fields and radio waves image blood
flow in brain regions and reflect brain activity in such regions.

The researchers manipulated the sequences of the various combinations
of speech sounds and video of the sounds, which enabled them to
distinguish brain regions that were active in abstract processing of
the speech sounds versus only their sensory properties.

Upon analysis of the results of their experiments, the researchers came
to the conclusion that two areas of known left-hemisphere
speech-processing regions, namely, pars opercularis and planum polare
coded speech at an abstract level.

The researchers said: “We have shown that there are neurophysiological
substrates that code properties of an audiovisual utterance at a level
of abstraction that corresponds to the speech category that is ‘heard,
’ which can be independent of its sensory properties. ”

They added: “We set out from the observation that there is no need to
posit the existence of abstract coding to explain emergent features of
audiovisual speech, because these features may just be the result of
joint activity in lower-level unisensory regions. Yet, our results
indicate that neural activity in left-hemisphere regions does indeed
track the experienced speech percept, independent of its sensory
properties. ” (ANI)