Like gestures, analog acoustic expression expands people's capacity to communicate and typically happens with little intention on the part of the speaker, although it is possible to use this expression explicitly to dramatize an utterance.

Although researchers have been aware that people modulate their speech, they assumed that some of this modulation was intentional and was merely meant to emphasize points or communicate emotion. The new discovery is the first experimental evidence showing that people unconsciously modulate their voices in ways that provide an additional channel of expression understood by listeners, the researchers said.

"I think we've all noticed this form of communication, but have not paid too much attention to it," said co-author Howard Nusbaum, Chairman of the Department of Psychology at the University of Chicago "Someone will raise his voice slightly at the end of the sentence when saying, 'the stock market is going up' or lower it when saying 'the stock market is going down'." The modulations also make telephone conversations and words spoken on the radio more comprehensible, he added.

The study on this verbal gesturing was reported in the paper "Analog Acoustic Expression Speech Communication" and published in the current issue of the Journal of Memory and Language. Its authors are Nusbaum, Hadas Shintel, a research associate in the Center for Cognitive and Social Neuroscience in the Department of Psychology at the University and Arika Okrent, a 2002 Ph.D. graduate in Psychology at the University.

People also use analog acoustic expression when they unconsciously compress words to indicate meaning, Shintel said. "For example, in describing the Cuban Missile Crisis, Robert McNamara said it brought the superpowers "thisclose" to a nuclear war." By running together "this close" in speaking, McNamara conveyed the proximity to war. This message depends on continuous variation of acoustic properties of speech that go beyond specific choice of words and linguistic structure."

To determine if these vocal modulations were produced even when not explicitly needed, the research team conducted experiments in which they had subjects describe action they saw on a screen and also read sentences.

In the first experiment, research subjects looked at video screens with animated dots and described whether they saw them going up or going down. They also read the sentences, "It is going up" or "It is going down" without seeing any action.

When they watched the dots go up on the screen, their pitch rose as they followed the action. When they watched the dots go down, their pitch lowered.

"Interestingly, speakers analogically varied fundamental frequency both when they described actual visual motion as well as when they read a sentence describing motion," the scholars wrote.

"The results demonstrate that speakers naturally use analog acoustic expression when talking, even when there is no intent to dramatize a description."

To determine if people use analog acoustic expression to communicate information not communicated in their words, the researchers constructed a pair of experiments in which the subjects described the movement of a dot from left to right. The researchers speeded the motion of the dot and discovered that people spoke faster when they saw the dot moving faster.

When the scholars played recordings of the speech, listeners were able to determine which speaker was describing a fast-moving dot and which was describint a slow- moving dot.

The new work suggests that the field of analog acoustic expression could be an emerging horizon for the study of speech, Nusbaum said. Research on gesture has shown how people use their hands to help manage the burden of thinking and communicating. Likewise, studying analog acoustic expression could open new pathways in understanding how the mind works, Nusbaum said.

"We have only looked so far at the simplest, most obvious forms of this communication. We will doubtless find more when we look at more complicated, less obvious forms of analog acoustic expression," he said.

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