In Brief

Both halves of the brain are involved in understanding emotional speech, with the left side focusing on "what" and the right sight focusing on "how," according to a recent study in Neuropsychology (Vol. 17, No. 1).

Psychologist Guy Vingerhoets, PhD, and his collaborators at Ghent University in Belgium used a technique called functional transcranial Doppler ultrasonography (fTCD), a form of ultrasound, to measure brain activity. Compared with other brain-imaging methods, fTCD is noninvasive (no radioactive tracers or X-rays are used), inexpensive and easy to administer. Its main limitation is its very low spatial resolution.

Thirty-six right-handed, Dutch-speaking students and hospital staff participated in the study. They listened to recordings of actors pronouncing sentences with happy, sad, angry, fearful and neutral meanings using tones of voice that were either neutral or emotional. When the actors' meaning and tone of voice signaled different emotions--for example, when the sentence, "The little girl lost both her parents," was spoken in a happy tone--participants were asked to pay attention to either the meaning or the tone.

Vingerhoets and his collaborators found that the left side of the brain was equally active whether participants paid attention to meaning or tone, but the right side was more active when they paid attention to tone. Activity on both sides of the brain increased most when the meaning and tone were in conflict.

The results suggest the right side of the brain is important for processing emotional tone, or prosody, while the left side is important for processing emotional meaning, or semantics. Previous studies have come to similar conclusions, but this one adds to those findings by showing that the left-right difference is robust enough to be detected even by fTCD, a relatively insensitive measure of brain activity.

The left half may be equally active in both conditions because the semantics of an utterance are processed automatically, notes Vingerhoets. "Even if you pay attention to the 'how' information," he says, "you can't help hearing the semantic content, the 'what' of the message. We do this all the time; we're trained in it."

--E. BENSON