Odor Objects Research Articles

Behavioral separation of liking and wanting in response to olfactory and visual food cues

In real-world settings, food rewards are processed in parallel across several sensory modalities, but paradigms that compare contributions of different modalities are lacking. While odor perception in particular is frequently implicated in appetite regulation, the mechanisms by which food odors differentially evoke experiences of wanting and liking remain poorly understood. This study addressed this gap by dissociating liking from wanting responses for olfactory stimuli, and establishing commonalities and differences relative to the visual modality. In two separate experiments, participants (n1=37, n2=43) rated content-matched batteries of odors and pictures, respectively, for their ability to elicit pleasure (liking) and the desire to eat (wanting). A third experiment (n3=39) utilized a combined olfactory-visual paradigm to test the separation of these dimensions in a multisensory context. Our results show that participants differentiated clearly and reliably between liking and wanting for both odors and pictures, as demonstrated by a high difference score between the two in non-food (high liking, low wanting), but not in food (both high) or disgusting stimuli (both low), and high within-session retest reliability. Higher variability for olfactory relative to visual assessments was observed and likely reflects well-established difficulties with odor object identification. Taken together, our study demonstrates that olfactory stimuli can be used in experimental settings to evoke separable experiences of liking and wanting for food and non-food stimuli. Manipulating these components independently across sensory modalities in experimental studies could generate novel insights into how olfactory and visual cues differentially contribute to anticipatory and consummatory food reward processing, in healthy and disordered eating.

An olfactory figure-ground segregation: The resistance fluctuation analysis of acetone gas for acetone/random gas mixtures recognition

Recognizing the disease-specific odor in human breath is a feasible non-invasive disease detection strategy. The most critical issue of olfactory diagnosis lies in recognizing the target gas among complex respiration compounds accurately. This paper demonstrated a novel approach to binary gas mixture recognition, exploring nature-related features of the target “odor object” (acetone gas) regardless of its “noisy background” (ethanol or methanol gases). Those features were extracted from time-series resistance fluctuations collected with one conventional SnO2 thin film gas sensor (TF) or our sensitivity-controllable lines gas sensor (TL). 6 features (variance, root mean square, band power, relative band power, entropy, and the number of values crossing mean value) were selected and analyzed with k-Nearest Neighbor regressor (KNN) and Support Vector Regressor (SVR). 18 types of acetone/ethanol mixtures and 3 acetone/methanol mixtures were tested with the proposed models and further explained with SHAP (SHapley Additive exPlanations). The model of TL and KNN achieved the optimal performance of regressing acetone concentrations with the coefficient of determination (R2) of 0.97 and 0.95 in individual gas and binary gas mixtures, respectively. Entropy was found to be the key feature that was linked to sensor properties. Finally, acetone gas data mixed with simulated gas and random noise data were experimented to evaluate our models’ potential for acetone/random gas mixture recognition and robustness.

Adaptive forgetting of place/object memory for dung in the domestic horse (Equus ferus caballus): Memory for a day

The domestic horse (Equus ferus caballus) makes dung deposits to form “stud-piles” and compulsively examines dung droppings, suggesting that dung contains species-relevant information. The present study investigates horses’ use of location (place), odor (object) and memory for dung sniff encounters. Horses were video recorded in 2 indoor and 4 outdoor riding arenas as they were taken at different time intervals to experimenter-determined objects or dung deposits that they could sniff. Frame-by-frame video analysis measured approaches, sniff duration, nostril use, ear position and blinking associated with dung investigation. Horses approached and sniffed dung-deposits for longer duration than non-dung objects in all test locations. They made head movements across the extent of dung-deposits when sniffing, showed no nostril or ear preference directed to the target, and blinked as they disengage from sniffing. Reduced approach probability and sniff duration showed that they displayed good place/object memory for dung previously visited at similar and different locations on the same day but poor memory for dung visited on a previous day. Adaptive forgetting of object/place memory for dung after a previous day’s dung visit may optimizes risk assessment, including the possibility of premature interruption of foraging by conspecifics.

Decomposition of an odorant in olfactory perception and neural representation.

Molecules-the elementary units of substances-are commonly considered the units of processing in olfactory perception, giving rise to undifferentiated odour objects invariant to environmental variations. By selectively perturbing the processing of chemical substructures with adaptation ('the psychologist's microelectrode') in a series of psychophysical and neuroimaging experiments (458 participants), we show that two perceptually distinct odorants sharing part of their structural features become significantly less discernible following adaptation to a third odorant containing their non-shared structural features, in manners independent of olfactory intensity, valence, quality or general olfactory adaptation. The effect is accompanied by reorganizations of ensemble activity patterns in the posterior piriform cortex that parallel subjective odour quality changes, in addition to substructure-based neural adaptations in the anterior piriform cortex and amygdala. Central representations of odour quality and the perceptual outcome thus embed submolecular structural information and are malleable by recent olfactory encounters.

Smelling things

Abstract In this paper, we outline and defend a view on which in olfactory experience we can, and often do, smell ordinary things of various kinds—for instance, cookies, coffee, and cake burnings—and the olfactory properties they have. A challenge to this view are cases of smelling in the absence of the source of a smell, such as when a fishy smell lingers after the fish is gone. Such cases, many philosophers argue, show that what we perceive in olfactory experience are odour objects, and not ordinary things. On behalf of our opponent, we articulate a screening-off argument based on cases of lingering smells for the thesis that we do not smell ordinary things. We then develop an alternative account of these cases that is consistent with our view. In doing so, we call into question two claims that are typically built into the notion of an odour object.

A Role of the Hippocampus in Perception and Memory of Odors. Hypothetical Neural Mechanism

Abstract—A mechanism for the interdependent functioning of the olfactory and hippocampal neural networks has been proposed. In this functioning, a significant role belongs to the long-term changes in the efficacy of connections between neurons from these networks, as well as from the ventral part of the basal ganglia, the frontal neocortical areas, the reuniens and mediodorsal thalamic nuclei. Odors are involved in spatial mapping and navigation since these two kinds of information are processed simultaneously and interdependently. The proposed mechanism for the formation of representations of “odor–object–place” associations in the activity of neurons from different hippocampal fields may underlie the participation of odors in the definition of “place fields”. The CA2 hippocampal field makes an important contribution to this process, facilitating the memorization and retrieval of information related to odors and their location. Due to hippocampal projections to olfactory structures, a spatial mapping of the environment is also formed in the activity of neurons in the piriform cortex. According to the proposed mechanism, damage to various parts of the analyzed chains, as well as weakening of neurogenesis in the dentate gyrus and olfactory bulb, should impair odor perception and memory for odors. This consequence is consistent with olfactory deficits in various neurodegenerative and viral diseases, as well as in aging.

OOPS, the Ontology for Odor Perceptual Space: From Molecular Composition to Sensory Attributes of Odor Objects.

When creating a flavor to elicit a specific odor object characterized by odor sensory attributes (OSA), expert perfumers or flavorists use mental combinations of odor qualities (OQ) such as Fruity, Green, and Smoky. However, OSA and OQ are not directly related to the molecular composition in terms of odorants that constitute the chemical stimuli supporting odor object perception because of the complex non-linear integration of odor mixtures within the olfactory system. Indeed, single odorants are described with odor descriptors (OD), which can be found in various databases. Although classifications and aroma wheels studied the relationships between OD and OQ, the results were highly dependent on the studied products. Nevertheless, ontologies have proven to be very useful in sharing concepts across applications in a generic way and to allow experts' knowledge integration, implying non-linear cognitive processes. In this paper, we constructed the Ontology for Odor Perceptual Space (OOPS) to merge OD into a set of OQ best characterizing the odor, further translated into a set of OSA thanks to expert knowledge integration. Results showed that OOPS can help bridge molecular composition to odor perception and description, as demonstrated in the case of wines.

Do you remember if you have olfactory dreams? A content analysis of LOFTER and a questionnaire survey conducted in China

ObjectivesDreams often involve visual and auditory sensations, but olfactory experiences have not received the same amount of attention. This study explores the prevalence and content of olfactory dreams in China and investigates the relationship between olfactory imagery, olfactory significance, and olfactory dreamers. MethodsIn the first part of the study, 4302 dream records from LOFTER were screened and classified to preliminarily identify the prevalence and content of olfactory dreams. In the second part, 718 participants completed an online questionnaire about olfactory dreams, imagery, and significance. ResultsThe prevalence of olfactory dreams in the diary dream entries and questionnaire survey participants were 3.95% and 18.70%, respectively. Instances in which odors appeared in dreams were more positive than negative and were mainly related to food, burning and smoke, body odor, nature, and certain environments and objects. Moreover, individuals with olfactory dreams showed better olfactory imagery, and stronger olfactory significance. ConclusionsOlfactory sensations occurred in the dreams of Chinese individuals, but their prevalence was very low. Most of the odors that emerged in these dreams were ones that the dreamers were familiar with in their daily lives.

Biological constraints on configural odour mixture perception.

Animals, including humans, detect odours and use this information to behave efficiently in the environment. Frequently, odours consist of complex mixtures of odorants rather than single odorants, and mixtures are often perceived as configural wholes, i.e. as odour objects (e.g. food, partners). The biological rules governing this 'configural perception' (as opposed to the elemental perception of mixtures through their components) remain weakly understood. Here, we first review examples of configural mixture processing in diverse species involving species-specific biological signals. Then, we present the original hypothesis that at least certain mixtures can be processed configurally across species. Indeed, experiments conducted in human adults, newborn rabbits and, more recently, in rodents and honeybees show that these species process some mixtures in a remarkably similar fashion. Strikingly, a mixture AB (A, ethyl isobutyrate; B, ethyl maltol) induces configural processing in humans, who perceive a mixture odour quality (pineapple) distinct from the component qualities (A, strawberry; B, caramel). The same mixture is weakly configurally processed in rabbit neonates, which perceive a particular odour for the mixture in addition to the component odours. Mice and honeybees also perceive the AB mixture configurally, as they respond differently to the mixture compared with its components. Based on these results and others, including neurophysiological approaches, we propose that certain mixtures are convergently perceived across various species of vertebrates/invertebrates, possibly as a result of a similar anatomical organization of their olfactory systems and the common necessity to simplify the environment's chemical complexity in order to display adaptive behaviours.

The female sex pheromone (Z)-4-undecenal mediates flight attraction and courtship in Drosophila melanogaster

Specific mate communication and recognition underlies reproduction and hence speciation. Our study provides new insights in Drosophila melanogaster premating olfactory communication. Mate communication evolves during adaptation to ecological niches and makes use of social signals and habitat cues. Female-produced, species-specific volatile pheromone (Z)-4-undecenal (Z4-11Al) and male pheromone (Z)-11-octadecenyl acetate (cVA) interact with food odour in a sex-specific manner. Furthermore, Z4-11Al, which mediates upwind flight attraction in both sexes, also elicits courtship in experienced males. Two isoforms of the olfactory receptor Or69a are co-expressed in the same olfactory sensory neurons. Z4-11Al is perceived via Or69aB, while the food odorant (R)-linalool is a main ligand for the other variant, Or69aA. However, only Z4-11Al mediates courtship in experienced males, not (R)-linalool. Behavioural discrimination is reflected by calcium imaging of the antennal lobe, showing distinct glomerular activation patterns by these two compounds. Male sex pheromone cVA is known to affect male and female courtship at close range, but does not elicit upwind flight attraction as a single compound, in contrast to Z4-11Al. A blend of the food odour vinegar and cVA attracted females, while a blend of vinegar and female pheromone Z4-11Al attracted males, instead. Sex-specific upwind flight attraction to blends of food volatiles and male and female pheromone, respectively, adds a new element to Drosophila olfactory premating communication and is an unambiguous paradigm for identifying the behaviourally active components, towards a more complete concept of food-pheromone odour objects.

An Evolutionary Microcircuit Approach to the Neural Basis of High Dimensional Sensory Processing in Olfaction.

Odor stimuli consist of thousands of possible molecules, each molecule with many different properties, each property a dimension of the stimulus. Processing these high dimensional stimuli would appear to require many stages in the brain to reach odor perception, yet, in mammals, after the sensory receptors this is accomplished through only two regions, the olfactory bulb and olfactory cortex. We take a first step toward a fundamental understanding by identifying the sequence of local operations carried out by microcircuits in the pathway. Parallel research provided strong evidence that processed odor information is spatial representations of odor molecules that constitute odor images in the olfactory bulb and odor objects in olfactory cortex. Paleontology provides a unique advantage with evolutionary insights providing evidence that the basic architecture of the olfactory pathway almost from the start ∼330 million years ago (mya) has included an overwhelming input from olfactory sensory neurons combined with a large olfactory bulb and olfactory cortex to process that input, driven by olfactory receptor gene duplications. We identify a sequence of over 20 microcircuits that are involved, and expand on results of research on several microcircuits that give the best insights thus far into the nature of the high dimensional processing.

Synthesis of Conserved Odor Object Representations in a Random, Divergent-Convergent Network

Animals are capable of recognizing mixtures and groups of odors as a unitary object. However, how odor object representations are generated in the brain remains elusive. Here, we investigate sensory transformation between the primary olfactory center and its downstream region, the mushroom body (MB), in Drosophila and show that clustered representations for mixtures and groups of odors emerge in the MB at the population and single-cell levels. Decoding analyses demonstrate that neurons selective for mixtures and groups enhance odor generalization. Responses of these neurons and those selective for individual odors all emerge in an experimentally well-constrained model implementing divergent-convergent, random connectivity between the primary center and the MB. Furthermore, we found that relative odor representations are conserved across animals despite this random connectivity. Our results show that the generation of distinct representations for individual odors and groups and mixtures of odors in the MB can be understood in a unified computational and mechanistic framework.

Encoding the Odor of Cigarette Smoke.

The encoding of odors is believed to begin as a combinatorial code consisting of distinct patterns of responses from odorant receptors (ORs), trace-amine associated receptors (TAARs), or both. To determine how specific response patterns arise requires detecting patterns in vivo and understanding how the components of an odor, which are nearly always mixtures of odorants, give rise to parts of the pattern. Cigarette smoke, a common and clinically relevant odor consisting of >400 odorants, evokes responses from 144 ORs and 3 TAARs in freely behaving male and female mice, the first example of in vivo responses of both ORs and TAARs to an odor. As expected, a simplified artificial mimic of cigarette smoke odor tested at low concentration to identify highly sensitive receptors evokes responses from four ORs, all also responsive to cigarette smoke. Human subjects of either sex identify 1-pentanethiol as the odorant most critical for perception of the artificial mimic; and in mice the OR response patterns to these two odors are significantly similar. Fifty-eight ORs respond to the headspace above 25% 1-pentanethiol, including 9 ORs responsive to cigarette smoke. The response patterns to both cigarette smoke and 1-pentanethiol have strongly responsive ORs spread widely across OR sequence diversity, consistent with most other combinatorial codes previously measured in vivo The encoding of cigarette smoke is accomplished by a broad receptor response pattern, and 1-pentanethiol is responsible for a small subset of the responsive ORs in this combinatorial code.SIGNIFICANCE STATEMENT Complex odors are usually perceived as distinct odor objects. Cigarette smoke is the first complex odor whose in vivo receptor response pattern has been measured. It is also the first pattern shown to include responses from both odorant receptors and trace-amine associated receptors, confirming that the encoding of complex odors can be enriched by signals coming through both families of receptors. Measures of human perception and mouse receptor physiology agree that 1-pentanethiol is a critical component of a simplified odorant mixture designed to mimic cigarette smoke odor. Its receptor response pattern helps to link those of the artificial mimic and real cigarette smoke, consistent with expectations about perceptual similarity arising from shared elements in receptor response patterns.

Superior Identification of Component Odors in a Mixture Is Linked to Autistic Traits in Children and Adults.

Most familiar odors are complex mixtures of volatile molecules, which the olfactory system automatically synthesizes into a perceptual whole. However, odors are rarely encountered in isolation; thus, the brain must also separate distinct odor objects from complex and variable backgrounds. In vision, autistic traits are associated with superior performance in tasks that require focus on the local features of a perceptual scene. The aim of the present study was to determine whether the same advantage was observed in the analysis of olfactory scenes. To do this, we compared the ability of 1) 40 young adults (aged 16-35) with high (n = 20) and low levels of autistic traits and 2) 20 children (aged 7-11), with (n = 10) and without an autism spectrum disorder diagnosis, to identify individual odor objects presented within odor mixtures. First, we used a 4-alternative forced choice task to confirm that both adults and children were able to reliably identify 8 blended fragrances, representing food-related odors, when presented individually. We then used the same forced choice format to test participants' ability to identify the odors when they were combined in either binary or ternary mixtures. Adults with high levels of autistic traits showed superior performance on binary but not ternary mixture trials, whereas children with an autism spectrum disorder diagnosis outperformed age-matched neurotypical peers, irrespective of mixture complexity. These findings indicate that the local processing advantages associated with high levels of autistic traits in visual tasks are also apparent in a task requiring analytical processing of odor mixtures.

Multisensory Enhancement of Odor Object Processing in Primary Olfactory Cortex

Identification of an object based on its odor alone is inherently difficult, but becomes easier when other senses provide supporting cues. This suggests that crossmodal sensory input facilitates neural processing of olfactory object information; however, direct evidence is still lacking. Here, we tested the effect of multisensory stimulation on information processing in the human posterior piriform cortex (PPC), a region linked to olfactory object encoding. Participants were exposed to familiar objects in the form of uni-, bi-, and trimodal combinations of odors, videos, and sounds. We hypothesized that the PPC would respond to non-olfactory object information, and that activity would increase linearly with the number of senses providing relevant object information. As predicted, visual object information activated the PPC and activity increased linearly with the number of relevant sensory channels. The crossmodal response pattern thus indicates that the PPC does not exclusively respond to olfactory information, but also to crossmodal object information important for olfactory processing. The continuous activity increase suggests that the PPC further acts as a multisensory binding site where pertinent input from multiple senses results in an increased neural response to the odor object. This potentially represents a neural mechanism for the well-known behavioral improvement present in odor object recognition during concurrent crossmodal sensory stimulation.

A Critique of Olfactory Objects.

Does the sense of smell involve the perception of odor objects? General discussion of perceptual objecthood centers on three criteria: stimulus representation, perceptual constancy, and figure-ground segregation. These criteria, derived from theories of vision, have been applied to olfaction in recent philosophical debates about psychology. An inherent problem with such framing of olfactory objecthood is that philosophers explicitly ignore the constitutive factors of the sensory systems that underpin the implementation of these criteria. The biological basis of odor coding is fundamentally different from the coding principles of the visual system. This article analyzes the three measures of perceptual objecthood against the biological background of the olfactory system. It contrasts the coding principles in olfaction with the visual system to show why these criteria of objecthood fail to be instantiated in odor perception. The argument demonstrates that olfaction affords perceptual categorization without the need to form odor objects.

Achieving Olfactory Expertise: Training for Transfer in Odor Identification.

Human olfactory function requires the identification of everyday odors. A characteristic feature of olfaction is that most people find it hard to identify and name common odors, and when odors are presented simultaneously in mixtures, performance is even further compromised. Few studies have systematically assessed how training might enhance identification of single odors and mixtures. This study compared how odor identification training with either single odors or binary mixtures affected identification performance, as well as transfer effects to untrained tasks and odors. Twenty-seven healthy participants (22 F; 28.0 ± 4.7 years old) completed identification training of 8 odors using a list of 16 veridical names. The study included 8 training sessions, as well as pretest and posttest evaluations. Results suggest notable effects of learning, as well as transfer to novel tasks and odors. Overall, training with single odors led to slightly better results than the binary mixture condition, suggesting that in novices, odor identification may be facilitated via consolidation of single odor objects, before learning to dissociate binary mixtures. Overall, odor identification may be trained to generate transfer of learning, although transfer effects were observed in both training methods. Our work suggests that odor identification abilities, while often limited, are highly trainable.

Nostril-specific and structure-based olfactory learning of chiral discrimination in human adults.

Practice makes perfect. In human olfaction, such plasticity is generally assumed to occur at the level of cortical synthetic processing that shares information from both nostrils. Here we present findings that challenge this view. In two experiments, we trained human adults unirhinally for the discrimination between odor enantiomers over a course of about 10 to 11 days. Results showed that training-induced perceptual gain was restricted to the trained nostril yet partially generalized to untrained odor enantiomers in a structure- rather than quality- based manner. In other words, learning enhanced the differentiation of chirality (molecular configuration) as opposed to overall odor quality (odor object) per se. These findings argue that, unlike earlier beliefs, one nostril does not readily know what the other learns. Moreover, the initial analytical processing of the structural features of uninarial olfactory input remains plastic in human adults.

Crossmodal Associations Between Olfaction and Vision: Color and Shape Visualizations of Odors

In the present study, we assessed crossmodal associations between odors and both color and shape, with particular interest in the principles beneath these mappings. We hypothesized that visual associations of odors would primarily reflect observable features of a smelling object and thus vary with different source assumptions of the very same smell. We asked 30 participants to visualize their odor associations on a drawing tablet, freely deciding on color and shape. Additionally, subjects provided ratings on perceptual and shape-related dimensions as well as a verbal label for each sample. With respect to color selection, the results confirmed a source-based mapping approach: odors rated as familiar were associated with very particular colors that typically resembled the appearance of their source. For less familiar odors, color selection was rather inconsistent but still then went along with assumed odor objects. Shape ratings changed with odor identifications as well, but considerably less than for color associations. Shape ratings and shape drawings produced very different results. While shape ratings were unlikely rooted in the mental imagery of a shape, drawings frequently displayed concrete objects that depended on odor label. Results confirm the existence of stable odor–vision correspondences and suggest that language plays a major part in mediating these mappings. The frequently assumed hedonic foundation of crossmodal matchings could not be confirmed for this stimuli set. Odor sensations may trigger odor naming spontaneously. Assumptions about an odor’s identity, as well as the multisensory knowledge we have acquired on it, affect the visual associations of an odor.

Visual-Olfactory Interactions: Bimodal Facilitation and Impact on the Subjective Experience.

Odors are inherently ambiguous and therefore susceptible to redundant sensory as well as context information. The identification of an odor object relies largely on visual input. Thus far, it is unclear whether visual and olfactory stimuli are indeed integrated at an early perceptual stage and which role the congruence between the visual and olfactory inputs plays. Previous studies on visual-olfactory interaction used either congruent or incongruent information, leaving it open whether nuances of visual-olfactory congruence shape perception differently. We aimed to answer 1) whether visual-olfactory information is integrated at early stages of processing, 2) whether visual-olfactory congruence is a gradual or dichotomous phenomenon, and 3) whether visual information influences bimodal stimulus evaluation and odor identity. We found a bimodal response time speedup that is consistent with parallel processing according to race models. Subjectively, pleasantness of bimodal stimuli increased with increasing congruence, and orange images biased odor composition toward orange. Visual-olfactory congruence was perceived in gradual and distinct categories, consistent with the notion that congruence is a gradual phenomenon. Together, the data provide evidence for bimodal facilitation consistent with parallel processing of the visual and olfactory stimuli, and that visual-olfactory interactions influence various levels of the subjective experience.