Contrasting patterns of specificity and transfer in human odor discrimination learning

Abstract

Practice enhances olfactory performance. However, laboratory studies to date suggest that olfactory learning is largely restricted to the trained odors, posing a significant challenge for training-based rehabilitation therapies for olfactory loss. In this study, we introduce various types of odors to olfactory discrimination training, conducted unilaterally. We demonstrate contrasting patterns of specificity and transfer of learning, independent of adaptation and task difficulty. Individuals trained with odor mixtures of different ratios show long-term perceptual gains that completely transfer to the untrained nostril and effectively generalize to untrained mixtures dissimilar in structure and odor quality from the trained ones. Conversely, those trained with odor enantiomers show no transfer of learning across nostrils or to unrelated enantiomers, replicating our earlier findings (Feng & Zhou, 2019). Our observations indicate that concentration ratio and chirality represent distinct olfactory attributes. Furthermore, discrimination learning occurs at different stages of olfactory processing, depending on which attribute is task-relevant. These findings open up new avenues to enhance the effectiveness of olfactory training.