a b s t r a c tDifferences between training and working contexts have the potential to be a major cause of deficits in performance of searching animals. Detection responses of individuals trained with high rates of target stimulus presentation tend to extinguish when moved to a new context where their rate of target encountering is low. This problem is acute with some contraband and people detection dogs where the rate of target encountering in the work context is significantly lower than during training. While the rate of extinction can be mitigated by planting known targets in the working contexts, this is often logistically difficult, dangerous, or impractical; an alternative solution would therefore be beneficial. Here, we explore the novel approach of adding non-contraband target stimuli to the training set and then presenting these innocuous targets periodically in the work context, thereby avoiding the logistic difficulties attached to the use of real contraband targets. Our rationale is that the search persistence caused by the innocuous targets could generalise to the real targets, thus increasing resistance to extinction in the latter. The potential problem with this approach is that dogs may learn to focus on the innocuous targets in the work context to the detriment of the real targets. In our experiments, 21 dogs were trained with three contraband (explosive) and one innocuous (non-explosive) odours. When they were transferred to a "work" context, they were separated into three groups, as follows: Group "0T" (zero target) were not exposed to any targets in the work environment; Group 1T (one target) were exposed to and rewarded on one innocuous target in the work environment; and Group 3T (three target) were exposed to and rewarded on three contraband targets in the work location. These regimens continued for six weeks during which time all dogs received two refresher training days away from their work location, where they were rewarded on all four target odours. Following this work phase, search and detection performance was tested in the work location for all stimuli. In the work phase, search vigilance in the 0T group dropped considerably compared with the 1T and 3T groups. Critically, when dogs were reexposed to all four targets in the work location at the end of the work phase, detection rates were significantly reduced for the 0T group, but were maintained on all targets for the 1T Abbreviations: SDD, scent detecting dogs; NE, non-explosive; DR, detection rate. 113 and 3T group. Our results show that rewarding search persistence with innocuous stimuli is potentially a successful strategy to maintain detection-dog performance across a range of trained contraband odours.Crown
Dogs trained to search for contraband perform a chain of behavior in which they first search for a target and then make a separate response that indicates to the trainer that they have found one. The dogs often conduct multiple searches without encountering a target and receiving the reinforcer (i.e., no contraband is present). Understanding extinction (i.e., the decline in work rate when reinforcers are no longer encountered) may assist in training dogs to work in conditions where targets are rare. We therefore trained rats on a search-target behavior chain modeled on the search behavior of working dogs. A discriminative stimulus signaled that a search response (e.g., chain pull) led to a second stimulus that set the occasion for a target response (e.g., lever press) that was reinforced by a food pellet. In Experiment 1 training with longer search durations and intermittent (partial) reinforcement of searching (i.e. some trials had no target present) both led to more persistent search responding in extinction. The loss of search behavior in extinction was primarily dependent on the number of non-reinforced searches rather than time searching without reinforcement. In Experiments 2 and 3, delivery of non-contingent reinforcers during extinction increased search persistence provided they had also been presented during training. Thus, results with rats suggest that the persistence of working dog performance (or chained behavior generally) may be improved by training with partial reinforcement of searching and non-contingent reinforcement during both training and work (extinction).
12A short odour discrimination test has been designed to allow rapid quality assurance of odour 13 recognition by detection dogs. The test comprises five repeats per target and a minimum of 20 14 associated non-target odours. The mean time taken to conduct the test is 5.6 min per target type. A 15 pass criterion of "a detection rate at least 70% greater than false alarm (FA) rate, with a 15% cap on 16 total allowable false alarms " is used which equates to 4/5 correct indications and 2 FAs, or 5/5 17 correct indications and 3 FAs; the probability of passing this test by chance is <1%. A Microsoft Excel 18 ™ programme has been written to rapidly generate balanced running orders that allow search runs 19 to be truncated following correct indications; this speeds up testing whilst maintaining 20 standardisation; the programme is available free-to-use. The test's internal validity has been 21 measured by conducting test re-test analysis on a range of target types on 19 operational search 22 dogs, and external validity has been measured by completing the test and an equivalent 23 operationally relevant building search on 26 operational search dogs. In both cases there is good 24 overall reliability (Kappa ≥0.80). The test is thus deemed suitable for complementary assessment of 25 detection dog ability during detailed accreditation procedures or as a standalone quality assurance 26 test in between accreditation or licensing. 27
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