It is well accepted that dogs, like humans, use specific vocal sounds to convey information. Barks, growls, whimpers and other vocal signals, give nearby individuals information about what the dog is thinking, feeling, and intends to do.
Sometimes vocal information used by dogs can carry quite specific information, as demonstrated by Péter Pongrácz, an ethologist at Eötvös Loránd University in Hungary, and his colleagues. They demonstrated that there is a specific growl that canines use when they are guarding a desired object. Thus when hovering over a bone it might mean "This bone is mine!" When other approaching dogs hear that particular sound they inevitably stop moving toward the growling dog, as if anticipating that if they draw any nearer they will be met by hostility.
More recent work by this research team suggests that dogs also make estimates about the physical characteristics of other individuals based upon the sounds coming from their mouth. Specifically, they seem to correlate the pitch of the sound with the size of the animal that is making it. This is possible because of a basic physical principle. The larynx, or voice box, of a larger animal is bigger. Sound resonating in a large chamber tends to be lower in pitch, as can be observed by noting that the pitch of the sounds from a cello are lower made by its smaller cousin the violin. This means that the growl of the larger animal will be deeper and lower than the corresponding growl in a smaller animal. From the viewpoint of evolution, it is certainly helpful and adaptive to recognize the size of the animal that is producing a particular growl, even before it is visible, since obviously larger animals are likely to be more dangerous.
Although this relationship between size and sound exists in nature, the question is whether or not dogs recognize it and use this information. To answer the question this Hungarian research team used a procedure which is becoming more common in our studies of the canine mind, which involves modifying tests which are used to see how much young human infants understand (even if they are too young to have useful speech) so that they can be used to test dogs.
This time the test involved something called "selective viewing." Owners brought their pet dogs to the laboratory for testing. The dog was seated in front of a screen, with his owner seated quietly behind. The dogs were shown images of two dogs, one on each side of the screen. One of the dogs was large, and the other was considerably smaller. The researchers then used food guarding growls taken from either a large or a small dog, which were played back from a speaker in the middle of the screen. The notion is quite simple, namely, if the dog believes that the sound is coming from the larger animal on the screen, then he will look in that direction, and if he believes that the sound is coming from the smaller one he will look at it. Cameras were set up to monitor where the dog was looking at any time and the video was later scored by individuals who did not know which images or growls were involved in each instance.
To be sure that the dogs were actually responding to information about other dogs, the large and small dog could be replaced by a large and small triangle or cat. As expected, when presented with the food guarding growl of a large dog, the dogs being tested looked first at the image of the large dog and stared at it for a longer time. The flipside of the coin is that when presented with a growl from the smaller dog, it was the small dog's image which attracted the viewing dog's attention. When presented with images of cats or triangles, dogs first flick their eyes to the left (the most common response of dogs to unexpected events) but then did not selectively stare at one or the other images based on the sound that had been played. The simple conclusion is that dogs recognize the size of another dog based upon his vocal communication. Furthermore dogs recognize that these sounds are coming from dogs not from cats or inanimate objects.
Pongrácz summarized his research by noting that the findings mean that "when growling, dogs don't lie about their size, so a listening dog can find out exactly the other dog's size"-and then decide whether to fight or step away."
This is useful and helpful information for any dog, but it also opens the question as to what other characteristics dogs may be inferring from the vocal sounds made by other dogs or perhaps even people. For example, although it is not unusual for dog owners to report that their dog seems to be afraid of men, I have yet to hear someone say that their dog is selectively afraid of women. One notable characteristic difference between men and women is that males have a deeper voice. Perhaps this same mechanism that causes a dog to recognize that the deep sound and lower pitch of a vocal utterance means a bigger and perhaps more dangerous animal is near can also account for the difference observed in the responses of dogs to men and women.
Stanley Coren is the author of many books including: Born to Bark, The Modern Dog, Why Do Dogs Have Wet Noses? The Pawprints of History, How Dogs Think, How To Speak Dog, Why We Love the Dogs We Do, What Do Dogs Know? The Intelligence of Dogs, Why Does My Dog Act That Way? Understanding Dogs for Dummies, Sleep Thieves, The Left-hander Syndrome
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission
