Training with Multiple Structurally Related Odorants Fails to Improve Generalization of Ammonium Nitrate Detection in Domesticated Dogs (Canis familiaris)

A critical aspect of canine scent detection involves the animal’s ability to respond to odors based on prior odor training. In the current study, dogs (n = 12) were initially trained on an olfactory simple discrimination task using vanillin as the target odorant. Based on their performance on this task, dogs were assigned to experimental groups. Dogs in group 1 and 2 (n = 5 dogs/group; 1 dog/group were removed due to low motivation or high error rates) were trained with either two or six forms of ammonium nitrate (AN), respectively. Dogs were then assessed with a mock explosive with AN and powdered aluminum. Dogs in both groups failed to respond to the novel AN-aluminum odor. Mean success rates were 56 ± 5 and 54 ± 4% for groups 1 and 2, respectively. Overall, and individual dog performance was not statistically higher than chance indicating that dogs did not generalize from AN to a similar AN-based odorant at reliable levels desired for explosive detection dogs. These results suggest the use of authentic explosive materials, without the added complication of including category-learning methods, likely remains a cost-effective and efficient way to train explosive scent detection dogs.

Narrow Versus Wide Tuning Curves: What's Best for a Population Code?

Neurophysiologists are often faced with the problem of evaluating the quality of a code for a sensory or motor variable, either to relate it to the performance of the animal in a simple discrimination task or to compare the codes at various stages along the neuronal pathway. One common belief that has emerged from such studies is that sharpening of tuning curves improves the quality of the code, although only to a certain point; sharpening beyond that is believed to be harmful. We show that this belief relies on either problematic technical analysis or improper assumptions about the noise. We conclude that one cannot tell, in the general case, whether narrow tuning curves are better than wide ones; the answer depends critically on the covariance of the noise. The same conclusion applies to other manipulations of the tuning curve profiles such as gain increase.

The Perky Effect Revisited: Blocking of Visual Signals by Imagery

Perky's 1910 observation that mental images were indistinguishable from external stimuli is considered as two issues: (1) description of images which apparently resemble the unidentified stimulus, has been given, but not satisfactorily measured; (2) poorer detection of ambiguous signals while experiencing images, has been consistently demonstrated. While distraction may play some role, the critical finding was with sensitivity ( d′), which was highest in a simple discrimination task, intermediate when Ss were told both to describe imagery and detect the signals, and poorest when they lacked information that signals might be present during imaging and relied on retrospective judgments (Perky replication). In the intermediate task, alerting Ss to the signals by having them project the slides themselves, did not alter sensitivity or bias (Lx).