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I’m pretty sure my wife asked me to do something this morning. I think it’s important and I know if I don’t do it I will miss a deadline or an appointment or a mortgage payment. Or maybe not. I honestly don’t know, and the reason is simple: it was my wife who was doing the talking—and it’s not her fault that I wasn’t listening.

Spouses have always had a funny way of both hearing and not hearing each other. On the one hand, the person you married is the person with whom you conduct the most intimate business of your life, and on a day to day, moment to moment basis, you must always be in communication. On the other hand, that constant stream of talk can become something of a hum—the conversational equivalent of the buzz of a fan or the thrum of an air conditioner that you hear so much you stop hearing at all. At least that’s the faintly scientific excuse I, and I suspect a lot of other husbands and wives, inwardly make when we’re caught not listening. Now, that excuse has gone from faintly to very scientific, thanks to a study just published in the journal Psychological Science.

To test how people both hear and don’t hear the very familiar spousal voice, investigators at Queen’s University in Ontario recruited a sample group of married couples, aged 44 to 79—all of whom had been married long enough to become well and truly familiar with every tonal blip of their spouse’s speech. All of the volunteers were first given a scripted page from an instruction manual to read aloud into a tape recorder. All of them then listened to the playback of their spouse, along with the playback of an unfamiliar voice speaking at the same time. In a simple way, that two-voice sound stream simulated the auditory clutter in which we all live our lives, with familiar and important sounds and voices commingling with unfamiliar, unimportant ones.

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Finally, the subjects were asked to concentrate on one voice or the other and to report what they heard. Across the age spectrum, the husbands and wives were significantly better at hearing and understanding their spouse than they were the unfamiliar voice, even though both were playing at the same volume. “Familiar voices appear to influence the way an auditory scene is perceptually organized,” said lead researcher Ingride Johnsrude, in a statement that accompanied the release of the study. “The benefit of familiarity is very large.”

But that’s not all there was to it. Yes, we hear a husband or wife well when we want to, but what about when we don’t? Here there were differences, and they depended on age. On the portion of the test in which the subjects were asked to shut out their spouse and listen to the stranger, the middle-agers performed a lot better than the seniors. Indeed, so good were they at it, that when they listened to another tape—this one of two strangers talking—they did a worse job of mentally silencing one of them than they’d done of hushing a spouse. “The middle-aged adults were able to use what they knew about the familiar voice to perceptually separate and ignore it, so as to hear the unfamiliar voice better,” Johnsrude said.

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Maddening as an oblivious husband can be to a wife—or vice versa—there is something adaptive about such selective hearing. The brain can take in only so much input at any one time, and it must constantly make decisions about what is urgent and what can slide. When a person you see only fleetingly is giving you information you need, it’s a lot more important to get it right than than it is when it’s coming from someone you see every day and can always ask for a reminder. This is part of what brain expert and biologist Nina Kraus of Northwestern University calls “sculpting the nervous system” and it’s critical to making us perceptually efficient. “You learn to pick out relevant sounds from a noisy soundscape,” she says, “a restaurant, the outdoors, a classroom.” How you define what’s relevant is dependent upon a lot of things—not least, how possible it is to take a mulligan on what someone’s saying and have it repeated later. With a spouse that’s always an option.

Still, the new study does show that we lose a lot of our ability to ignore a spouse as we get older, and that’s probably adaptive too—sweetly so. As our faculties fade with age, we become increasingly dependent on the person who knows us best, and the ability to pick out that person’s voice above all others can play a real role in our health, safety and even survival. Your ability to hear may not be what it was when you were young, but your ability to listen gets a whole lot better.

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