Predicting Odor Pleasantness from Odorant Structure: Pleasantness as a Reflection of the Physical World

Abstract

Although it is agreed that physicochemical features of molecules determine their perceived odor, the rules governing this relationship remain unknown. A significant obstacle to such understanding is the high dimensionality of features describing both percepts and molecules. We applied a statistical method to reduce dimensionality in both odor percepts and physicochemical descriptors for a large set of molecules. We found that the primary axis of perception was odor pleasantness, and critically, that the primary axis of physicochemical properties reflected the primary axis of olfactory perception. This allowed us to predict the pleasantness of novel molecules by their physicochemical properties alone. Olfactory perception is strongly shaped by experience and learning. However, our findings suggest that olfactory pleasantness is also partially innate, corresponding to a natural axis of maximal discriminability among biologically relevant molecules.

Where is the chocolate? Rapid spatial orienting toward stimuli associated with primary rewards

“…Participants evaluated, on a visual analogue scale presented on the screen, the pleasantness (from ''extremely unpleasant'' to ''extremely pleasant''), familiarity (from ''not familiar at all'' to ''extremely familiar''), edibility (from ''not edible'' to ''extremely edible''), and intensity (from ''not perceived'' to ''extremely strong'') of the chocolate odor and of the odorless air (e.g., Delplanque et al, 2008;Khan et al, 2007). Subsequently, they answered questions about chocolate (back translated to French from Rolls & McCabe, 2007) that allowed investigation of whether participants associated chocolate with the two components of reward (Berridge & Robinson, 2003): motivation (i.e., ''On a scale from 1 to 10, how much would you say that you sometimes crave chocolate?'')…”

Perceptual convergence of multi-component mixtures in olfaction implies an olfactory white

“…We obtained 86 monomolecular odorants that were well distributed in both perceptual (Fig. 1A) (1,(11)(12)(13) and physicochemical ( Fig. 1B) (1, 14, 15) stimulus space.…”

“…Each target mixture (1,4,10,15,20,30,40, or 43 components) was compared with all other mixtures (1,4,10,15,20,30,40, or 43 components) and, as a control, with itself. Other than comparisons of a mixture with itself, all comparisons were nonoverlapping; in other words, each pair of mixtures being compared had no components in common.…”

“…To provide a better notion of what olfactory white does smell like, we summarized the applicability of 146 verbal descriptors provided by the 85 participants who smelled white repeatedly (SI Appendix, Table S3). Moreover, we asked 20 participants to rate 20 different odorants along VAS scales representing two principal axes of human olfactory perception, one axis ranging from very pleasant to very unpleasant and the other ranging from highly edible to highly poisonous (1,13,18). Of the 20 odorants participants rated, 12 were previously well-characterized monomolecular odorants that span the first principal component of perception, four were previously used versions of 40-component olfactory white, and four were 10-component mixtures which provided a maximal span of olfactory space.…”

“…odor | sensory perception | smell S everal studies have linked human perception of monomolecular odorants to their physical structure (1,2) and specific receptors (3,4). The real olfactory world, however, is made not of monomolecular stimuli but rather of complex olfactory mixtures, and the rules underlying the perception of such mixtures remain largely unknown.…”