Binaural hearing for the hearing-impaired

Listening to someone in a noisy restaurant is easier with two ears (binaural) than with just one, for three reasons. When speech and noise come from spatially separate sources, differences in both their volume and arrival time at the two ears help the listener to separate them. (For more on interaural differences, see the article by Bill Hartmann, Physics Today, November 1999, page 24.) But even when speech and noise are coincident in space, the third reason, an effect called binaural summation, centrally integrates the signals from both ears, and the signal—the speech—is enhanced over the surrounding noise. Many profoundly deaf people have regained some hearing through using cochlear implants either in both ears (bilateral) or in just one with a hearing aid in the other (bimodal). But which of the three speech-recognition advantages accrue most with which device configuration has been indeterminate. Now Kostas Kokkinakis and Natalie...