Page last updated at 16:54 GMT, Monday, 13 July 2009 17:54 UK

Cats 'exploit' humans by purring

By Victoria Gill
Science reporter, BBC News

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See Pepo the cat employing his 'soliciting purr'

Cat owners may have suspected as much, but it seems our feline friends have found a way to manipulate us humans.

Researchers at the University of Sussex have discovered that cats use a "soliciting purr" to overpower their owners and garner attention and food.

Unlike regular purring, this sound incorporates a "cry", with a similar frequency to a human baby's.

The team said cats have "tapped into" a human bias - producing a sound that humans find very difficult to ignore.

Dr Karen McComb, the lead author of the study that was published in the journal Current Biology, said the research was inspired by her own cat, Pepo.

"He would wake me up in the morning with this insistent purr that was really rather annoying," Dr McComb told BBC News.

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"After a little bit of investigation, I discovered that there are other cat owners who are similarly bombarded early in the morning."

While miaowing might get a cat expelled from the bedroom, Dr McComb said that this pestering purr often convinced beleaguered pet lovers to get up and fill their cat's bowl.

To find out why, her team had to train cat owners to make recordings of their own cats' vocal tactics - recording both their "soliciting purrs" and regular, "non-soliciting" purrs.

"When we played the recordings to human volunteers, even those people with no experience of cats found the soliciting purrs more urgent and less pleasant," said Dr McComb.

How annoying?

She and her team also asked the volunteers to rate the different purrs - giving them a score based on how urgent and pleasant they perceived them to be.

"We could then relate the scores back to the specific purrs," explained Dr McComb. "The key thing (that made the purrs more unpleasant and difficult to ignore) was the relative level of this embedded high-frequency sound."

"When an animal vocalises, the vocal folds (or cords) held across the stream of air snap shut at a particular frequency," explained Dr McComb. The perceived pitch of that sound depends on the size, length and tension of the vocal folds.

Cat (BBC)
Impossible to resist: Cats use sounds that humans are "highly sensitive" to

"But cats are able to produce a low frequency purr by activating the muscles of their vocal folds - stimulating them to vibrate," explained Dr McComb.

Since each of these sounds is produced by a different mechanism, cats are able to embed a high-pitched cry in an otherwise relaxing purr.

"How urgent and unpleasant the purr is seems to depend on how much energy the cat puts into producing that cry," said Dr McComb.

Previous studies have found similarities between a domestic cat's cry and the cry of a human baby - a sound that humans are highly sensitive to.

Dr McComb said that the cry occurs at a low level in cats' normal purring. "But we think that (they) learn to dramatically exaggerate it when it proves effective in generating a response from humans."

She added that the trait seemed to most often develop in cats that have a one-on-one relationship with their owners.

"Obviously we don't know what's going on inside their minds," said Dr McComb. "But they learn how to do this, and then they do it quite deliberately."

So how does Dr McComb feel about Pepo now she knows he has been manipulating her all these years?

"He's been the inspiration for this whole study, so I'll forgive him - credit where credit's due."



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