Separate signals for orthonasal vs. retronasal perception of food but not nonfood odors.

There is a controversy concerning whether smelling via the nose (ortho-nasally) or the mouth (retro-nasally) represent two routes to the same modality or two distinct submodalities. Since olfactory coding is dependent upon experience, and since food odors are experienced retro-nasally, the authors tested the hypothesis that whether an odor represents a food may influence whether sensation via the two routes leads to separable responses. The authors demonstrate that salivary response to food odors decrease with repeated presentation and show that this response rebounds upon presentation of a novel food odor via the same route and upon presentation of the same food odor via a novel route. This finding indicates that the novel odor and the novel route represent distinct sensory signals. This effect is specific, in that it does not depend on differences in odor intensity or pleasantness and is selective, in that it occurs for food odors but not for equally pleasant and intense nonfood odors. These results demonstrate that separable signals are generated for the same food odor depending upon route and support the existence of category-specific processing.