I had just finished giving a talk about dog behavior in Victoria (the capital of British Columbia, Canada). Some people who had attended the talk, and who I had met previously, approached me with an invitation to join them at a local pub for a drink and some conversation. A short time later the five of us were gathered at a table sharing a pitcher of dark beer and chatting about how dogs know and interpret their world. It was then that one of them mused, "I wonder what it would be like if we could identify our dogs by their smell alone, the same way that they can identify us by our scent."
While it is certainly the case that dogs have a remarkable ability to detect and identify odors (click here for an example), it is also the case that human beings do not completely lack this ability. The dog's sense of smell is 1000 times stronger than that of humans, and the dog uses scent information in many common identification tasks. Humans have considerably less nasal sensitivity, and generally speaking for us odors tend to be unconsciously registered, although they often produce an emotional response. Under certain circumstances, especially if our attention is directed toward the odors and if we are forced to choose among them, humans do have a reasonable degree of accuracy in recognizing the scents of living things. The studies which demonstrated this all tended to use a similar technique. Specifically the target individuals were asked to wear a T-shirt for a day or two, and then that T-shirt was sealed in a plastic bag. Later on other individuals were asked to sniff the contents of the bag and attempt to make a recognition. In this way it was found that postpartum human mothers can accurately identify their own newborns by scent alone, and both mothers and fathers can correctly discriminate the odors associated with their own children. Furthermore, women (who seem to be a bit better at this task than men) are able to roughly categorize the age of strangers by their scent, dividing them into infants, young children, sexually mature adults, and elderly groups using only their scent as a guide.
Perhaps it was not surprising to find that this technique was eventually modified and used to determine whether humans could identify their own dogs by scent alone. This study was conducted by psychologists Deborah Wells and Peter Hepper of Queens University in Belfast Northern Ireland, and published in the journal Perception*.
Instead of T-shirts, the target dog odor came from a flannel blanket. The blanket was placed in the dog's bed for three consecutive nights. No other bedding was available to the dog, and the dogs in the study did not sleep in the same room as their owner. Twenty-six dog owners were then asked to sniff the blanket that was impregnated with the odor of their own dog and another one which had the scent of an unfamiliar dog. That unfamiliar dog was chosen to be as similar as possible to the participant's dog in terms of breed and sex, and the dog's ages did not differ by more than 18 months. During testing the dog owners were blindfolded while they sniffed the blankets (you don't want the color of dog hairs clinging to the blanket to serve as a cue). The owners were allowed to continue sniffing for as long as they needed in order to answer three questions: "Which of the odors smells the strongest?", "Which of the odors is the most pleasant?" and "Which of these blankets smells like it belongs to your dog?"
The results were quite remarkable in that most of the participants (88.5%) were able to recognize the odor of their own dog. Although the experimenters had expected that the dog owners would have considered their own dog's odor to be somewhat weaker and more pleasant than the unfamiliar dog's odor that was not the case.
The researchers were concerned that perhaps it was not the scent of the dog that the participants were recognizing, but rather the scent of their home. To control for this they conducted a second experiment in which a blanket was hung in the room where the dog normally slept, but out of reach of their pet. When tested in the same way, comparing the blanket impregnated with their home's odor to a blanket which carried the odor of a house unfamiliar to the participant, they were unable to accurately identify which of the scents belonged to their own home.
The researchers summarize their results saying, "Daily exposure to the dog may result in owners unconsciously learning the smell of the animal. Interestingly, many of the subjects were somewhat skeptical regarding their ability to accurately identify their own dog's odor prior to the study. Findings indicate, however, that owners are more aware of their pet's individual scents than they believe."
When I described this research to my acquaintance she laughed and said, "When I get home I am going to give my dog a great big sniff!"
Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? 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
* Deborah L. Wells and Peter G. Hepper (2000). The discrimination of dog odours by humans. Perception, 29, 111 – 115.