Abstract
Similarity between odours is notoriously difficult to measure. Widely used behavioural approaches in insect olfaction research are cross-adaptation, masking, as well as associative tasks based on olfactory learning and the subsequent testing for how specific the established memory is. A concern with such memory-based approaches is that the learning process required to establish an odour memory may alter the way the odour is processed, such that measures of perception taken at the test are distorted. The present study was therefore designed to see whether behavioural judgements of perceptual distance are different for two different memory-based tasks, namely generalization and discrimination. We used odour–reward learning in larval Drosophila as a study case. In order to challenge the larvae's olfactory system, we chose to work with binary mixtures and their elements (1-octanol, n-amyl acetate, 3-octanol, benzaldehyde and hexyl acetate). We determined the perceptual distance between each mixture and its elements, first in a generalization task, and then in a discrimination task. It turns out that scores of perceptual distance are correlated between both tasks. A re-analysis of published studies looking at element-to-element perceptual distances in larval reward learning and in adult punishment learning confirms this result. We therefore suggest that across a given set of olfactory stimuli, associative training does not grossly alter the pattern of perceptual distances.
Highlights
Understanding perception is one of the more challenging tasks in science
Afterwards, they were tested for their preference for the trained element plus a previously non-trained odour
Task i-b In a corresponding mixture-to-element generalization task, larvae were trained with a binary mixture (XY) against the no-odour, ‘empty’ condition
Summary
Understanding perception is one of the more challenging tasks in science. Among many other difficulties, developing experimental handles on perception in non-verbal animals is a major practical concern. In cross-adaptation, an odour A is presented at high concentration and for an extended period of time, such that responses are adapted out If, in such an adapted state, animals still respond to a probe odour B, one can conclude that the two odours use at least partially nonoverlapping input channels, and that they are discriminable. If you return your car to the garage after a faculty club dinner, you may be adapted to the smell of the heavy Havana cigars your dean likes to smoke. This adaptation may partially carry over to the smell of cigarettes but not to the smell of cat urine. You would hardly recognize that your rascal twin sons had been secretly smoking in the garage, while you would immediately realize that your neighbours’ cat has paid another visit
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