Using response consistency to probe olfactory knowledge

Wearable Sensors to Characterize the Autonomic Nervous System Correlates of Food-Like Odors Perception: A Pilot Study

Background: The sense of smell has been recently recognized as one of the most important sensory features in the human being, representing a reliable biomarker for a number of clinical conditions. The relationship between olfactory function and the person’s attitude towards food has frequently been investigated, often using questionnaires. The administration of minimally invasive methods for characterizing autonomic nervous system (ANS) functionality could help in objectivizing such measurements. Methods: The present study assessed ANS activation through the analysis of the electrocardiogram (ECG) and galvanic skin response (GSR) signals, in response to olfactory stimuli using non-invasive wearable devices. The ANS activation was also studied with respect to the odor familiarity, as well as with other olfactory and food dimensions (e.g., odor identification, odor pleasantness, food neophobia). Results: We demonstrated a significant activation of the ANS, in particular of its sympathetic branch, during the olfactory stimulation, with the ECG signal seen as more sensitive to detect ANS response to moderate olfactory stimuli rather than the GSR. Conclusions: When applied to a greater number of subjects, or to specific groups of patients, this methodology could represent a promising, reliable addition to diagnostic methods currently used in clinical settings.

Pleasantness, familiarity, and identification of spice odors are interrelated and enhanced by consumption of herbs and food neophilia

The primary dimension of odor is pleasantness, which is associated with a multitude of factors. We investigated how the pleasantness, familiarity, and identification of spice odors were associated with each other and with the use of the respective spice, overall use of herbs, and level of food neophobia. A total of 126 adults (93 women, 33 men; age 25-61 years, mean 39 years) rated the odors from 12 spices (oregano, anise, rosemary, mint, caraway, sage, thyme, cinnamon, fennel, marjoram, garlic, and clove) for pleasantness and familiarity, and completed a multiple-choice odor identification. Data on the use of specific spices, overall use of herbs, and Food Neophobia Scale score were collected using an online questionnaire. Familiar odors were mostly rated as pleasant (except garlic), whereas unfamiliar odors were rated as neutral (r = 0.63). We observed consistent and often significant trends that suggested the odor pleasantness and familiarity were positively associated with the correct odor identification, consumption of the respective spice, overall use of herbs, and food neophilia. Our results suggest that knowledge acquisition through repetitive exposure to spice odor with active attention may gradually increase the odor pleasantness within the framework set by the chemical characteristics of the aroma compound.

Chocolate smells pink and stripy: Exploring olfactory-visual synesthesia

Odors are often difficult to identify, and can be perceived either via the nose or mouth (“flavor”; not usually perceived as a “smell”). These features provide a unique opportunity to contrast conceptual and perceptual accounts of synesthesia. We presented six olfactory-visual synesthetes with a range of odorants. They tried to identify each smell, evaluate its attributes and illustrate their elicited visual experience. Judges rated the similarity of each synesthetes’ illustrations over time (test-retest reliability). Synesthetic images were most similar from the same odor named consistently, but even inconsistently named same odors generated more similar images than different odors. This was driven by hedonic similarity. Odors presented as flavors only resulted in similar images when consistently named. Thus, the primary factor in generating a reliable synesthetic image is the name, with some influence of odor hedonics. Hedonics are a basic form of semantic knowledge, making this consistent with a conceptual basis for synaesthetic links.

Why does the sense of smell vanish in the mouth? Testing predictions from two accounts

When participants perceive flavor they do not recognise the role of smell. We examined two possible accounts of why: (1) a common attentional channel activated by taste; and (2) prior learning between taste and smell. Participants were asked to sniff food-related odors with a fluid in their mouth and profile each odor after expectorating. This process was later repeated for each odor, with some odors experienced with water on both occasions, and others with water on one occasion and sucrose (weak or strong) on the other. We investigated how reliable these odor profiles were and whether they were influenced by prior odor-taste learning (indexed by odor sweetness). For non-sweet smells, the presence of a tastant significantly improved profile reliability relative to water in the mouth. For sweet smells, tastant had no effect, which we suggest represents a cancelling out of the beneficial effects of the common attentional channel by the detrimental effects of prior learning. Thus, both mechanisms may contribute to masking the modal identity of smell thereby contributing to flavor binding.

Object concepts in the chemical senses

This paper examines the applicability of the object concept to the chemical senses, by evaluating them against a set of criteria for object-hood. Taste and chemesthesis do not generate objects. Their parts, perceptible from birth, never combine. Orthonasal olfaction (sniffing) presents a strong case for generating objects. Odorants have many parts yet they are perceived as wholes, this process is based on learning, and there is figure-ground segregation. While flavors are multimodal representations bound together by learning, there is no functional need for flavor objects in the mouth. Rather, food identification occurs prior to ingestion using the eye and nose, with the latter retrieving multimodal flavor objects via sniffing (e.g., sweet smelling caramel). While there are differences in object perception between vision, audition, and orthonasal olfaction, the commonalities suggest that the brain has adopted the same basic solution when faced with extracting meaning from complex stimulus arrays.