At a retirement community in San Francisco, a 71-year-old woman is having her brain trained. She sits at a computer, poised to react to a sequence of sounds, like “baa, tack, tab, cat.” As she hears them, she clicks on the written equiva­lents on the computer screen. As her speed and accuracy improve, the sounds come faster, the sequences grow longer. The process, researchers say, could give her more years of auditory acuity.

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