It's because sound plays an important role in consolidating memory, says Delphine Oudiette, a postdoctoral fellow in Northwestern's psychology department. The more you think about something, the greater chance you'll remember it later. "Sound can act as a cue," she explains.
It's widely believed among neuroscientists that a lot of memory consolidation happens during sleep. But you can't control which memories you think about—or, as Oudiette calls it, "rehearse"—while you're asleep.
Or can you?
Oudiette thinks the key lies in sound cues, and in a paper just published in the Journal of Neuroscience on which she's the lead author, she's starting to prove it.
The paper describes an experiment in which Oudiette and her colleagues showed the subjects a series of everyday objects (a tea kettle, a dog, a lipstick) on a computer screen. The screen had a grid so the subjects could remember where each object was located, and each object was assigned a monetary value which (theoretically) would be awarded to the subjects if they remembered the correct location later.
In the second run-through, Oudiette attached sound cues as well as monetary values to the objects. A whistling sound accompanied the picture of the tea kettle, for instance, and barking the picture of the dog. During the rest period, a signal box played the noises to the sleeping group. Afterward, they were better able to remember the locations of the objects with sound cues, regardless of how much money they were allegedly worth.
"Whatever makes you rehearse during sleep is going to determine what you remember later, and, conversely, what you're going to forget," says Ken Paller, a professor of psychology at Northwestern and one of Oudiette's co-authors on the study.
In the next phase of her research, Oudiette plans to have her research subjects study information in a notebook while listening to music and then play that music back (at a low volume) while they sleep.
"You regulate memory during sleep," she says, "and the more you regulate your memory, the better it will be. You want to rescue things from forgetting."