Search dogs - Clever Hans effects?

Search dogs trained to detect drugs and explosives could be susceptible to the 'Clever Hans' effect, a new study suggests. Hans was the German horse whose counting abilities were exposed as being dependent on his detection of cues from his trainer. Now a team led by Lisa Lit at the University of California at Davis has shown that search dogs are especially prone to barking false alerts in locations where their handlers have been tricked into thinking drugs or explosives are located (Animal Cognition: tinyurl.com/5ugjpgl).

Eighteen handler - dog pairs twice searched four rooms in a church. The handlers were told that each room contained up to three target scents, but this was a lie as no target scents were present. The sight of an experimenter entering the rooms with drugs and explosives heightened the deception.

One of the rooms had red paper markers to indicate the (false) target locations to the handlers; another had decoy sausage scents to trick the dogs; one room had both types of decoy; the final room was decoy free.

Rates of false alarm were high, with 85 per cent of runs leading to one or more false alerts from the dogs. Although the frequency of false alerts didn't vary according to room type, they were more likely to occur where the handlers thought the scents were located, thus indicating the influence of human expectations on the dogs' behaviour.
'[The] findings confirm that handler beliefs affect working dog outcomes, and human indication of scent location affects distribution of alerts more than dog interest in a particular location,' the researchers said. 'These findings emphasise the importance of understanding both human and human - dog social cognitive factors in applied situations.'

--Christian Jarrett