Effects of learning an increasing number of odors on olfactory learning, memory and generalization in detection dogs

Detection dogs continue to represent the most effective technology for the detection of explosives and other contraband. As the number of target odors and their variants that detection dogs are required to learn continues to increase, understanding the capacity for odor learning and the effects on performance of training on an increasing number of target odors on performance is critical. In the present study, we examined dogs' ability to learn an increasing number of odor discriminations and the effects of learning new odors on the recall of pre-viously trained odors. We trained dogs to respond to up to 40 odors in an odor discrimination task over the span of 16 months. Odors were trained in sets of 10 every three months. Recall of previously trained subsets was assessed at intervals of < 1, 4, and 12 months since last exposure, and after learning 10, 20, 30, and 40 cu-mulative odors. We assessed the effects of training on these large numbers of target odors on generalization to untrained, but related, target odors. In addition to assessing performance in an odor discrimination task, we also evaluated the effects of learning many odor discriminations and the passage of time on performance in an operationally relevant search task. Dogs rapidly learned new odor discriminations across the 40 odors, with little to no decrease in the recall of previously trained odors or generalization to related odors. Further, dogs recalled odors not experienced within 12 months with 100% accuracy and no increase in false alarm rate. The results indicate that the limits of odor identification recall capabilities of dogs were not challenged by training on a cumulative total of 40 odor discriminations nor by up to a 12-month gap in exposure to those odors, therefore establishing the robust capabilities of dogs for learning and remembering many odor identifications.