A study on the relationship between odor hedonic ratings and individual odor detection threshold

Abstract

Odor hedonic perception (pleasant/unpleasant character) is considered as the first and one of the most prominent dimensions in olfaction and is known to depend on several parameters. Among them, the relation between the odorant concentration and the hedonic estimation has been widely studied. However, few studies have considered odor hedonic ratings (OHR) in relation to individual detection thresholds (IDT). Thus, the aim of this study was to determine olfactory detection thresholds and to describe hedonic rating variations from individual thresholds to higher concentrations. IDT were performed for two pleasant (apple and jasmine) and two unpleasant (durian and trimethylamine) odorant stimuli. The experimenter presented one by one in a randomized order, the different odorant concentrations above IDT. Participants rated odor hedonic valence of these stimuli on a visual analog scale. Results showed, except for trimethylamine, the same relationship between hedonic ratings and stimulus concentration, i.e., an increase of pleasantness (apple and jasmine)/unpleasantness (durian) ratings at low and middle concentrations followed by a plateau at high concentrations. Correlations between OHR and concentrations as well as between OHR and threshold steps were always significant. Moreover, comparisons between both conditions showed that the correlation coefficient was significantly higher for trimethylamine (and a trend for apple) when IDTs were considered, while no difference was found for jasmine and durian. Overall, results suggested that the relationship between OHR and IDT is odor specific. These findings contribute to explain the large variability of the hedonic tone (i.e., weakly vs. very pleasant, weakly vs. very unpleasant) at specific concentration in the general population and could serve future research in this field (e.g., olfactory preferences in nutrition studies, anhedonia in psychiatric disorders…).

Figure 1

Boxplots of the IDT for apple, jasmine, durian, and trimethylamine odorants. In each boxplot, the middle line of the box corresponds the mean of odor detection threshold, the inferior line of the box corresponds to the first quartile, and the upper line of the box corresponds to the third quartile.

Figure 2

Hedonic scores at IDT for pleasant odors: number of subjects for each score range (e.g., [− 2 to − 1] means that odor hedonic rating is comprised between − 2 and − 1). OHR were assessed on a visual analog scale ranging from 0 to + 9 for the pleasant polarity and from 0 to − 9 for the unpleasant polarity.

Figure 3

Hedonic scores at IDT for unpleasant odors: number of subjects for each score range (e.g., [− 2 to − 1] means that OHR is comprised between − 2 and − 1). OHR were assessed on a visual analog scale ranging from 0 to + 9 for the pleasant polarity and from 0 to − 9 for the unpleasant polarity.

Figure 4

Odor hedonic ratings above odor detection thresholds: mean hedonic ratings in relation to concentrations. (A) apple, (B) jasmine, (C) durian, (D) trimethylamine. The line grey color responds to the polynomial regression. Equations of polynomial regressions is given on each graph.

Figure 5

Odor hedonic ratings above odor detection thresholds: mean hedonic ratings in relation to individual detection threshold in step of 3 concentrations. (A) apple, (B) jasmine, (C) durian, (D) trimethylamine. The line grey color responds to the polynomial regression. Equations of polynomial regressions is given on each graph.