The illusion that a horse could do maths may be behind sniffer dogs falsely ‘detecting’ illicit substances according to an intriguing study covered by The Economist.
The horse in question was called Clever Hans and he was rumoured to be able to do complicated maths, work out the date, spell German words – all from questions called out by the audience.
The trainer would run his hand across possible responses on, for example, a piece of paper, and Hans would tap with his hoof to signal when the correct answer was being pointed to.
Psychologist Oskar Pfungst became suspicious and eventually worked out than the horse was doing no more than waiting until his trainer changed his body posture when he hit on the right answer.
His trainer was completely unaware that his expectancies were shaping the horse’s behaviour but this form of unintentional behavioural influence over animal behaviour has become known as the ‘Clever Hans effect‘.
The Economist reports on a new study of sniffer dogs that seems to show a similar effect in action.
Sniffer dogs and their handlers were told to search an area that that might have up to three target scents and that on two occasions the scents would be clearly marked with bits of red paper.
In reality, there were no target scents, so anything the dogs detected was a false alert.
When handlers could see a red piece of paper, allegedly marking a location of interest, they were much more likely to say that their dogs signalled an alert. Indeed, in the two rooms where red paper was present and sausages were not, 32 of a possible 36 alerts were raised. In the two where both red paper and sausages were present that figure was 30–not significantly different. In contrast, in search areas where a sausage was hidden but no red piece of paper was there for handlers to see, it was only 17.
The dogs, in other words, were distracted only about half the time by the stimulus aimed at them. The human handlers were not only distracted on almost every occasion by the stimulus aimed at them, but also transmitted that distraction to their animals–who responded accordingly. To mix metaphors, the dogs were crying “wolf” at the unconscious behest of their handlers.
In other words, when the human handlers become suspicious the dogs are more likely to seem to detect suspicious scents, making the process a lot more subjective than the search teams like to believe.
Link to The Economist article ‘Clever hounds’.