The Blank Search – where your dog is required to search an environment that doesn’t contain his target scent – continues to be a common feature of many Scent Detecting Courses. If you’ve already spent many hours encouraging your dog to search for, and locate, his target scent, why might you want (or need) to train your dog to search an area when it isn’t there?
Two common responses to this question, include;
- Blank searches will increase your dog’s motivation to search.
- Future search areas may not contain your dog’s target scent. He needs to be ‘trained’ in preparation for this.
So, let’s examine each of these claims in turn and see just how much water they hold.
Do these claims hold any water?
Blank searches will increase your dog’s motivation to search.
In a study by Gazit, et al (2005), seven highly trained explosives detection dogs took part in a series of 4 experiments.
In the first experiment the dogs were trained alternately on two very similar paths. Path A always contained 5 hidden explosives whilst Path B contained no explosives. In just a few sessions the dogs demonstrated a significant decrease in search behaviour on Path B but not on Path A. This seems to offer the first, albeit small, piece of evidence that blank searches may actually reduce, rather than increase, a dog’s motivation to search.
In the second experiment the dogs were trained exclusively on Path B. 1 explosive was hidden on the path every 4 days. The dogs detection rates during this second experiment were found to be significantly lower than in the first experiment.
The third experiment was conducted on Path C. As in the second experiment, only 1 explosive was hidden on this new path every 4 days. Interestingly, both the probability of detection and motivation to search were significantly higher than in second experiment despite the number of hidden explosives being the same in both experiments.
In the fourth experiment the dogs were returned to Path B. Despite being trained for another 12 days, with 1 explosive being hidden on the path on each of the daily sessions, the dogs failed to demonstrate the levels of motivation that they had previously shown when searching any of the other paths that had usually contained explosives.
According to Gazit, et al (2005), these findings suggest that even a highly trained Explosives Detection Dog will quickly learn that a specific area does not contain explosives and, as a result, the dog will be “less motivated to search and will miss newly placed targets”.
As the Gazit, et al (2005) study demonstrates, the loss in search and detection performance following exposure to only a small number of blank searches, is ‘context specific’. In other words, the decline in the dogs performance is limited to the area in which they have been exposed to the blank search condition. These findings are further supported by Porritt, et als (2015) study into performance decline in search dogs. They state that “without the opportunity to find rewarded targets in repetitive search environments, scent detecting dogs will become ineffective after a short period, and this performance decrement is hard to reverse”.
So, what are the implications of these study results for your own scent detecting training? Because of the speed at which this decline in motivation to search is evidenced, I no longer set up any blank searches for my own dogs and actively discourage my clients from doing so too. Although this reported decline in motivation is said to be context specific, this may actually cause you extra difficulties. For many of you, choice of training area can be very limited and if you practice blank searches in your regular venue it seems likely that this will be to the detriment of any future training in this same area. As Gazit, et al (2005) conclude, “if the [search] behavior is extinguished in a specific context, it will be very difficult to restore that [search] behavior in that context”.
Some anecdotal evidence, provided by my own two dogs, may lend further support to my ‘Just say NO to Blank Searches‘ training stance. ‘L’ has experienced a number of blank searches in her scent detecting training career. ‘BB’, has no experience of blank searches. Although it has been many years since ‘L’s’ last blank search, her motivation to search is, in my opinion, markedly reduced. She has a tendency to slow down and eventually stop searching if she doesn’t locate her target scent within just a few minutes. In contrast, ‘BB’s’ motivation to locate the target scent increases (faster and more thorough) the longer the search continues. ‘L’ has been ‘fooled’ in the past – asked to search when the area was blank. ‘BB’ has never experienced this ‘deception’ – if asked to search all his experiences tell him that his target scent will be present, he just needs to continue searching (perhaps more thoroughly) until he can locate it … and he does!
It seems worth asking ourselves here whether it’s reasonable to cue our dogs to perform a behaviour that we know, because of the set-up, they won’t be able to complete? One example that comes immediately to mind is the practice of pretending to throw a toy. The dog rushes off to find it, searches around for a while, looks back, ‘puzzled’, at the ‘thrower’ and, eventually, gives up. Personally, I dislike this practice and I’m pretty sure the dog isn’t too keen on it either!
Pretending to throw a toy …
Similarly, with the blank search, the dog is cued to perform a very specific behaviour chain – search an area, locate the target scent and indicate its location. Except … it can’t. It’s been set-up to fail. There is no target scent to find. Not only does this practice run the very real risk of diminishing the dog’s motivation to search but I wonder what it does for the relationship between dog and handler? Worth thinking about?
Future search areas may not contain your dog’s target scent. He needs to be ‘trained’ in preparation for this.
For the pet, hobby or sports dog I can think of no convincing reason that they should ever have to search an area devoid of target scent. Unfortunately, because blank searches continue to appear in the competition scent-work arena, handlers may feel that they have little option but to train for this possibility. I would simply urge caution.
In contrast, blank searches are a very real, everyday, experience for the working dog team; those that earn their living by scent detecting. But does this have to be the case?
According to Porritt, et al (2015) “a co-trained, non-contraband odour, secreted in a dog’s working environment and contingently reinforced upon being found, acts to maintain performance in finding contraband target odours that would be rarely encountered during a dog’s working life”.
In Porritt, et als (2015) study, 21 labrador retrievers were trained to detect 3 ‘contraband’ odours (explosives) and 1 ‘non-contraband’ odour. They were then exposed to a number of different experimental search conditions. The group of dogs who had worked extensively with the non-contraband odour showed “little difference in their detection on non-explosive and explosive targets in the test phase. … maintenance of expectation to find any target was sufficient to maintain attention to all odour targets”.
So, what does this all mean? Put simply, it suggests a highly practical method by which the blank search problem can be managed. Working dogs can be trained to detect multiple scents (Williams and Johnston (2002) suggest that dogs can be trained to detect up to ten different scents) including one that can be placed in the working environment prior to a search to ensure that there is always a find for the dog. A highly practical solution to the blank search problem!
Blank searches. Yes or No? I think you know my answer.
© Scent : Detect : Find Ltd 2018
References / Further Reading
- Gazit I, Goldblatt A and Terkel J (2005) The role of context specificity in learning: The effects of training context on explosives detection in dogs. Animal Cognition. August. 143-150.
- Porritt F, Shapiro M, Waggoner P, Mitchell E, Thomson T, Nicklin S and Kacelnik A (2015) Performance decline by search dogs in repetitive tasks, and mitigation strategies. Applied Animal Behaviour Science. 166. 112-122.
- Williams M and Johnston J M (2002) Training and maintaining the performance of dogs (canis familiaris) on an increasing number of odor discriminations in a controlled setting. Applied Animal Behaviour Science. 78(1). 55-65.
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