Olfactory notes in the mind space: a registered report

Olfaction is an archaic sense but its central mechanisms are lesser known than those of other senses. Here we address a possible link between olfactory stimuli and mental spatial representations. Although olfactory percepts are not commonly related to space, perfumiers tend to describe scents in terms of top/head or base notes and arrange them vertically on olfactory pyramids, with the most volatile on top. We tested whether odors evoke in naïve participants a mental vertical representation dependent on odor quality, in the absence of explicit references to elevation. In a speeded choice classification task, 110 participants pressed one of two vertically aligned buttons in response to fruity or gourmand odors. A spatial stimulus-response compatibility (SRC) effect was expected to emerge from compatible versus incompatible mappings of stimuli to responses, due to the hypothesised dimensional overlap. However, the preregistered contrast on means of median correct responses neither confirmed the presence of a vertical SRC effect at the group level, nor provided conclusive evidence for its absence. An analogous exploratory test on means of restricted means supported the presence of the predicted effect but its Bayesian counterpart found the outcome inconclusive. Exploratory analyses revealed three distinct clusters of participants with regards to the vertical SRC effect for odors, with two (N = 61 and N = 19) showing a significant effect in the expected direction and one (N = 30) showing a significant effect in the opposite direction. These results call for replications that factor in potential sources of individual differences.