July 13, 2009
Cats Employ Unique Purr To Receive Human Attention
Researchers recently reported that felines have found a way to manipulate humans through vocalizations.
A team at the University of Sussex discovered that cats use a "soliciting purr" to overpower their owners and garner attention and food by producing a sound that incorporates a "cry" with a similar frequency to a human baby's.
Cats have tapped into a human bias by producing a sound that humans find very difficult to ignore, the researchers wrote in the journal Current Biology.
Lead author Dr. Karen McComb said the research was inspired by her own cat, who would wake her up in the morning with this insistent purr that was really rather annoying.
"After a little bit of investigation, I discovered that there are other cat owners who are similarly bombarded early in the morning," she said.
Dr. McComb said the pestering purr often convinced beleaguered pet lovers to get up and fill their cat's bowl, as opposed to meowing"”which might get a cat expelled from the bedroom.
Her team recruited cat owners to make recordings of their own cats' vocal tactics -- recording both their "soliciting purrs" and regular "non-soliciting" purrs.
McComb noted that when they played the recordings to human volunteers, even those people with no experience of cats found the soliciting purrs more urgent and less pleasant. Volunteers were also asked to rate the different purrs -- giving them a score based on how urgent and pleasant they perceived them to be.
She said that they could then relate the scores back to the specific purrs.
"The key thing that made the purrs more unpleasant and difficult to ignore was the relative level of this embedded high-frequency sound," she said.
McComb explained that when an animal vocalizes, the vocal folds (or cords) held across the stream of air snap shut at a particular frequency, and the perceived pitch of that sound depends on the size, length and tension of the vocal folds.
"But cats are able to produce a low frequency purr by activating the muscles of their vocal folds - stimulating them to vibrate," she added.
Cats are essentially able to embed a high-pitched cry in an otherwise relaxing purr since each of these sounds is produced by a different mechanism.
The urgency and unpleasantness of the purr seems to depend on how much energy the cat puts into producing that cry, according to McComb.
Similarities have been noted in previous studies between the cry of domestic cats and those of human babies.
While the cat's cry occurs at a low level in its normal purring, the researchers think that they learn to dramatically exaggerate it when it proves effective in generating a response from humans.
McComb noted 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. But they learn how to do this, and then they do it quite deliberately."
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