Bradley Cooper and Lady Gaga in a scene from "A Star is Born." Picture: AP

London - Even if it hasn’t been played on the radio for decades, a favourite song – maybe the soundtrack to a first kiss, or the first dance at a wedding – can be recognised in the blink of an eye.

People’s pupils generally grow bigger when they hear music. Now a study has found they become significantly more dilated when a well-loved song is played, compared to a similar one they didn’t know – and this was seen from a tenth of a second in.

Researchers asked ten people to name songs which held important memories for them and gave them the "chills". The songs they chose included 'The Way We Were' by Barbra Streisand, 'You Never Can Tell' by Chuck Berry, and Paolo Nutini’s 'Candy'.

The study showed that a favourite track triggers the part of the brain which retrieves emotional memories within half a second.

Even hearing bursts of music lasting three-quarters of a second, people recognised a favourite song with 92 percent accuracy. The results, published in the journal Scientific Reports, may explain why memory function for people with dementia can improve when they hear a song from their childhood or a favourite tune.

Professor Maria Chait, from University College London, said: "Understanding how the brain recognises tunes is useful for music-based therapeutic interventions."

In a separate study in 2015, researchers discovered that the amount of dilation could reveal how much a song really touches us. 

It could even help us retain more information - is we listen to our "happy songs" when we are learning.  

Research teams from the University of Vienna and the University of Innsbruck, led by Bruno Gingras, used a laser pupil tracking device to measure the response of participants to short music excerpts from different piano melodies. 

The results showed that both the emotional content of the music and the listener’s personal attachment to the music were found to be the dominant factors influencing the participant’s pupil dilation.

Daily Mail