Sometimes it's not what you say, but how you say it. That's a truism most people can relate to-but computers can't. While speech recognition software has gotten quite good at understanding words, it still can't discern punctuation like periods and commas, or choose between ambiguous sentences whose meanings depend on the speaker's emotion. That's because such software still can't make sense of the intonations, emphases and pauses-collectively known as prosody-that people intuitively use to make such distinctions.

But with more than a hundred corporate and academic research groups working on the problem, attempts at incorporating prosody into speech software are enjoying growing success. Prosody-based tools are already used for speech synthesis-to improve the naturalness of computer voices like those that recite your bank balance over the telephone. As prosody research advances, these automated systems will sound more and more natural even when speaking complex sentences.