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Couples who have been together for decades can still pick out their partner's voice perfectly at a crowded party - and it even helps them hear others, researchers have found.

The quirk, which is evident in partners who have spent more than 18 years together, found that having a partner present actually boosts hearing.

The researchers say the discovery is a 'glass half full' aspect of aging.

The study found that people, particularly those who are middle-aged, are able to separate and ignore a familiar voice to hear an unfamiliar voice better

'We're all familiar with the glass half empty view of aging – that, as you get older, everything gets worse' said lead researcher Ingrid Johnsrude of Queen's University, Canada.

'You need glasses, your memory goes, and it's harder to hear when you're conversing in a busy place like a restaurant or a party, where many people are talking at once.

'We wanted to investigate the glass-half full side of aging. One thing that older people have more of than younger people is experience.

'I study how the experience of older people, like their familiarity with the voice of their significant other, helps them compensate for age-related declines in other abilities.'

The studies have revealed that the brain does not simply rely on the incoming sounds that reach the ear to understand and retain speech, but rather also relies on information from other senses and prior knowledge to facilitate comprehension.

These results were presented at the 8th Annual Meeting of the Canadian Association for Neuroscience held in Montreal, Canada May 25 to 28th 2014.

Dr. Johnrude's studies exposed test subjects to degraded or clear speech in the presence or absence of distraction.

By looking at activation of different brain regions while test subjects were exposed to different listening conditions, Dr. Johnsrude's research has revealed that the early processing of sound, which occurs in a brain region called the primary auditory cortex, depends on higher-level linguistic knowledge encoded in other regions of the brain.

Following a conversation in a noisy environment also requires one to disregard surrounding noises and distractions and specifically focus on a conversational partner.

While clear speech was understood and remembered whether subjects were distracted or not by other tasks, attention was shown to be critically important to understand degraded speech.

What you hear and understand of a conversation is influenced by what you are used to hearing, so it will be easier to understand a familiar voice than that of a stranger.

This was shown to be especially true for older adults, who were shown to have more difficulty understanding new voices in a cocktail party situation as they age, but did not show a decline in the ability to understand familiar voices in the same situation.

In a noisy room, the familiar voice of a spouse stands out against other voices, helping to sharpen auditory perception and making it easier to focus on one voice at a time

'Familiar voices appear to influence the way an auditory "scene" is perceptually organised,' said Johnsrude.

Ms Johnsrude and her colleagues asked married couples, aged 44-79, to record themselves reading scripted instructions out loud. 

Later, each participant put on a pair of headphones and listened to the recording of his or her spouse as it played simultaneously with a recording of an unfamiliar voice.

On some trials, participants were told to report what their spouse said. On others they were reported what they thought the unfamiliar voice said.

The researchers wanted to see whether familiarity would make a difference in how well the participants understood what the target voice was saying.

The results, published in Psychological Science, a journal of the Association for Psychological Science, reveal a clear benefit of listening to the familiar voice.

Participants were more accurate on the task when they had to listen to their spouse's voice compared to an unfamiliar voice matched on both age and sex. During this test they perceived their spouse's voice more clearly.

The researchers found that accuracy didn't change as participants got older when they were listening to their spouse's voice.

'The benefit of familiarity is very large,' Ms Johnsrude said.

'It's on the order of the benefit you see when trying to perceptually distinguish two sounds that come from different locations compared to sounds that come from the same location.'

The research found that the older the participant, the less able he or she was to report correctly what the unfamiliar voice was saying

But when participants were asked to report the unfamiliar voice, age-related differences emerged.

Middle-aged adults seemed to be relatively adept at following the unfamiliar voice, especially when it was masked by their spouse's voice - that is, they were better at understanding the unfamiliar voice when it was masked by their spouse's voice compared to when it was masked by another unfamiliar voice.

Middle-aged adults were better at understanding the unfamiliar voice when it was masked by their spouse's voice

'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,' Ms Johnsrude said.

Performance on these trials declined as the participants went up in age.

The older the participant, the less able he or she was to report correctly what the unfamiliar voice was saying.

'Middle-age people can ignore their spouse - older people aren't able to as much,' Ms Johnsrude concluded.

The researchers suggest that as people age, their ability to use what they know about voices to perceptually organise an auditory 'scene' may become compromised.

While this may make it more difficult for older adults to pick out an unfamiliar voice, it has an interesting consequence; the benefit of having a familiar voice as the target actually increases with age.

'These findings speak to a problem that is very common amongst older individuals - difficulty hearing speech when there is background sound,' Ms Johnsrude said.

'Our study identifies a cognitive factor - voice familiarity - that could help older listeners to hear better in these situations.'