The accuracy of drug- and explosives-sniffing dogs is affected by human handlers’ beliefs, possibly in response to subtle, unintentional cues, UC Davis researchers have found.

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The study, published in the January issue of the journal Animal Cognition, found that detection-dog teams erroneously “alerted,” or identified a scent, when there was no scent present more than 200 times — particularly when the handler believed that there was scent present.

“It isn’t just about how sensitive a dog’s nose is or how well-trained a dog is,” says Lisa Lit, a postdoctoral fellow in the Department of Neurology and the study’s lead author. “There are cognitive factors affecting the interaction between a dog and a handler that can impact the dog’s performance.”

And it turns out, these factors can be even more important than the sensitivity of a dog’s sniffer.

“Dogs are exceptionally keen at interpreting subtle cues, so handlers need to be cognizant of that to optimize the overall team performance,” adds Anita M. Oberbauer, UC Davis chair of the Department of Animal Science and the study’s senior author.

To evaluate the effects of handler beliefs and expectations on detection-dog performance, the researchers recruited 18 handler-detection dog teams from law-enforcement agencies. All of the teams were certified by an agency for either drug detection, explosives detection or both drug.

The dogs all were trained to either alert passively at the location of a scent by sitting or laying down, alert actively by barking or by doing both. The teams included 14 male dogs and four female dogs, including Labrador retrievers, Belgian Malinois, German Shepherd dogs and Dutch Shepherd dogs. The dogs’ level of experience ranged from two to seven years and their human partners had as many as 18 years of dog-handling experience.

A church was selected as the location for the study, since it was unlikely to have contained either explosives or drugs in the past. It was also a place where neither the dogs nor the handlers had been before. The researchers created four separate rooms for the dogs to examine or “clear.”

The handlers were told that there might be up to three of their target scents in each room, and that there would be a piece of red construction paper in two of the rooms that identified the location of the target scent. However, there were no target scents — explosives or drugs — placed in any of the rooms.

Each room represented a different experimental condition or scenario:

In room #1 the experimenter did nothing.

In room #2 she taped a piece of red construction paper to a cabinet.

In room #3 she placed decoy scents, two sausages and two tennis balls hidden together out of view.

In room #4 she placed a piece of red construction paper at the location of hidden decoy scents, two sausages and two tennis balls.

The dog-handler teams conducted two separate, five-minute searches of each room. When handlers believed their dogs had indicated a target scent, an observer recorded the location indicated by handlers. All of the teams searched the rooms in a different order.

Although there should have been no alerts in any of the rooms, there were alerts in all of them. And more alerts occurred at the target locations indicated by human suggestion (red construction paper) than at locations of increased dog interest (sausages and tennis balls).

In the early 20th century in Germany, a horse named Clever Hans was believed to be capable of counting and other tasks. It was later determined that Clever Hans was actually responding to the minute, postural and facial cues of his trainer and other observers. Similarly, detection dogs may be alerted to subtle and unintentional human cues that direct dog responses, including pointing, nodding head-turning and gazing.

Although Lit is careful to note that her findings do not mitigate the abilities of handlers and their dog teams to perform successfully, she believes they are significant. It is her hope that the study can be replicated and expanded to further assess hidden cues handlers may be giving their dogs. “It might be the case that everyone is doing the same types of things so that [they could be addressed] directly,” she says.