Hedonic appreciation and verbal description of pleasant and unpleasant odors in untrained, trainee cooks, flavorists and perfumers

Olfaction is characterized by a salient hedonic dimension. Previous studies have shown that these affective responses to odors are modulated by physicochemical, physiological, and cognitive factors. The present study examined expertise influenced processing of pleasant and unpleasant odors on both perceptual and verbal levels. For this, performance on two olfactory tasks was compared between novices, trainee cooks, and experts (perfumers and flavorists): Members of all groups rated the intensity and pleasantness of pleasant and unpleasant odors (perceptual tasks). They were also asked to describe each of the 20 odorants as precisely as possible (verbal description task). On a perceptual level, results revealed that there were no group-related differences in hedonic ratings for unpleasant and pleasant odors. On a verbal level, descriptions of smells were richer (e.g., chemical, olfactory qualities, and olfactory sources terms) and did not refer to pleasantness in experts compared to untrained subjects who used terms referring to odor sources (e.g., candy) accompanied by terms referring to odor hedonics. In conclusion, the present study suggests that as novices, experts are able to perceptually discriminate odors on the basis of their pleasantness. However, on a semantic level, they conceptualize odors differently, being inclined to avoid any reference to odor hedonics

Universality and diversity of the human olfactory perception : psychophysical, molecular and neurobiological approaches

Dans une société allant de l'avant et voulant couper avec son côté animal, la perception olfactive a été jugée inutile et limitée à sa plus simple expression. Il n'est donc pas étonnant que la perception olfactive soit une des dimensions de notre univers sensoriel les plus difficiles à appréhender. Cette thèse de doctorat étudie la perception des odeurs chez l'Homme. La recherche s'est centrée sur deux aspects importants de l'odorat : la valence hédonique de l'odeur (son caractère agréable ou désagréable) et la qualité de l'odeur (par exemple, son caractère floral ou fruité). L'olfaction a également pour caractéristique d'être très variable d'un individu à l'autre. En effet, bien que certaines odeurs soient perçues de la même manière par la majorité de la population, de nombreuses autres sont perçues de manière très différente entre individus. Ainsi, le principal objectif de la thèse a été d'apporter des éléments d'explication des facteurs déterminant la variabilité interindividuelle dans la perception qualitative et hédonique des odeurs. Sans aller jusqu'à une explication totalement déterministe selon laquelle la perception olfactive serait « inscrite dans la molécule », les résultats de cette thèse renforcent ainsi l'idée que la perception hédonique et qualitative de l'odeur est construite à travers une hiérarchie de traitements débutant par l'association d'une structure moléculaire bien précise (ou d'un attribut particulier) et d'un ensemble de récepteurs olfactifs. L'expression différentielle de ces récepteurs olfactifs selon les individus et les populations, ainsi que l'apprentissage par simple exposition ou par acquisition d'une expertise, coloreront alors de manière personnelle la valence et la qualité perçue des odeurs, conduisant ainsi à une hétérogénéité interindividuelle en matière de perception olfactiveIn a society moving forward and wanting to cut with his animal side, olfactory perception has been judged unnecessary and limited to its simplest expression. Unsurprisingly, olfactory perception was found to be one of the most difficult dimensions to understand in our sensory universe. This dissertation examines the perception of odors in humans. The research effort has been focused on two important aspects of smell: the hedonic valence of odor (ie the pleasantness or unpleasantness of the sample) and odor quality (eg, its floral or fruity note). Olfaction is also known to be highly variable from one individual to another. Indeed, although some odors are perceived in the same way by the majority of the population, many others are perceived very differently between individuals. Thus, the main objective of the research was to provide some explanation on important factors of inter-individual variability in the qualitative and hedonic perception of odors. Without making the complete deterministic claim that olfactory perception is "written in the molecule", the results in this dissertation reinforce the idea that the hedonic and qualitative perceptions of smell are built through a hierarchy of treatments starting with the combination of molecular structure (or of a particular structural attribute) and a very specific set of olfactory receptors. The difference in expression of these olfactory receptors as individuals and populations, as well as learning by mere exposure or acquisition of expertise will then color in a personal way the valence and perceived quality of odors, leading to inter-individual heterogeneity in olfactory perceptio

Learning to name smells increases activity in heteromodal semantic areas

International audienceSemantic description of odors is a cognitively demanding task. Learning to name smells is, however, possible with training. This study set out to examine how improvement in olfactory semantic knowledge following training reorganizes the neural representation of smells. First, 19 nonexpert volunteers were trained for 3 days; they were exposed (i) to odorants presented without verbal labels (perceptual learning) and (ii) to other odorants paired with lexicosemantic labels (associative learning). Second, the same participants were tested in a brain imaging study (fMRI) measuring hemodynamic responses to learned odors presented in both the perceptual and associative learning conditions. The lexicosemantic training enhanced the ability to describe smells semantically. Neurally, this change was associated with enhanced activity in a set of heteromodal areas—including superior frontal gyrus—and parietal areas. These findings demonstrate that odor‐name associative learning induces recruitment of brain areas involved in the integration and representation of semantic attributes of sensory events. They also offer new insights into the brain plasticity underlying the acquisition of olfactory expertise in lay people