Auditory-olfactory integration: congruent or pleasant sounds amplify odor pleasantness

Even though we often perceive odors while hearing auditory stimuli, surprisingly little is known about auditory-olfactory integration. This study aimed to investigate the influence of auditory cues on ratings of odor intensity and/or pleasantness, with a focus on 2 factors: "congruency" (Experiment 1) and the "halo/horns effect" of auditory pleasantness (Experiment 2). First, in Experiment 1, participants were presented with congruent, incongruent, or neutral sounds before and during the presentation of odor. Participants rated the odors as being more pleasant while listening to a congruent sound than while listening to an incongruent sound. In Experiment 2, participants received pleasant or unpleasant sounds before and during the presentation of either a pleasant or unpleasant odor. The hedonic valence of the sounds transferred to the odors, irrespective of the hedonic tone of the odor itself. The more the participants liked the preceding sound, the more pleasant the subsequent odor became. In contrast, the ratings of odor intensity appeared to be little or not at all influenced by the congruency or hedonic valence of the auditory cue. In conclusion, the present study for the first time provides an empirical demonstration that auditory cues can modulate odor pleasantness.     

Microbial diversity associated with odor modification for production of fertilizers from chicken litter

Litter from the chicken industry can present several environmental challenges, including offensive odors and runoff into waterways leading to eutrophication. An economically viable solution to the disposal of waste from chicken houses is treatment to produce a natural, granulated fertilizer that can be commercially marketed for garden and commercial use. Odor of the final product is important in consumer acceptance, and an earthy odor is desirable. By understanding and manipulating the microbial processes occurring during this process, it may be possible to modify the odors produced. Geosmin and related volatiles produced by soil actinomycetes are responsible for earthy odors, and actinomycetes are likely to be present in the composting manure. Bacterial communities at each stage of the process were analyzed by culturing studies and denaturing gradient gel electrophoresis (DGGE). The processing steps changed the culturable bacterial community, but the total community was shown by DGGE to be stable throughout the process. A local agricultural soil was analyzed in parallel as a potential source of geosmin-producing actinomycetes. This agricultural soil had higher microbial diversity than the compost at both the culturable and the molecular levels. Actinomycete bacteria were isolated and analyzed by AromaTrax, a gas chromatography-olfactometry system. This system enables the odor production of individual isolates to be monitored, allowing for rational selection of strains for augmentation experiments to improve the odor of the final fertilizer product.     

Survey of wastewater indicators and human pathogen genomes in biosolids produced by class a and class B stabilization treatments

Accurate modeling of the infectious aerosol risk associated with the land application of biosolids requires an in-depth knowledge of the magnitudes and changes in pathogen concentrations for a variety of class A and class B stabilization methods. The following survey used quantitative PCR (qPCR) and culture assays to detect environmentally resistant bacterial and viral pathogens and biosolid indicator organisms for 36 biosolid grab samples. Biosolids were collected from 14 U.S. states and included 16 class B mesophilic anaerobic digestion (MAD) samples and 20 class A biosolid samples from temperature-phased anaerobic digestion (TPAD), MAD plus composting (COM), and MAD plus heat pelletization processes. The indicator concentrations of fecal coliforms and male-specific coliphages as well as pathogen genome concentrations for human adenovirus species, Legionella pneumophila, Staphylococcus aureus, and Clostridium difficile were significantly lower in the class A samples, and a multivariate analysis of variance ranked the stabilization processes from the lowest pathogen/indicator load to the highest as (i) class A COM, (ii) class A TPAD, and (iii) class B MAD. Human adenovirus genomes were found in 88% of the class B samples and 70 to 100% of the class A samples. L. pneumophila, S. aureus, and C. difficile genomes were detected at the qPCR assay detection limits in 19 to 50% of the class B and class A anaerobic digestion samples, while L. pneumophila was detected in 50% of the class A compost samples. When considering all the stabilization methods, both the fecal coliform and the male-specific coliphage concentrations show a significant linear correlation with the pathogen genome concentrations. This survey provides the necessary pathogen concentrations to add to biosolid aerosol risk and pathogen exposure analyses and clarifies the effectiveness of class A stabilization methods with the pathogen and indicator loads in biosolids.     

Effects of context on judgements of odor intensities in humans

This study evaluated whether the intensity of previously smelled odors could unintentionally influence the subsequent judgement of odor intensity. The predicted context effect was based on the adaptation- level theory. Before and 25 min after either WEAK or STRONG biasing odor concentrations, 51 subjects were required to rate the intensity of 10 different odor concentrations of California Orange Oil. After the WEAK bias, subjects judged the odor intensity as being stronger than they did after the STRONG bias. Thus the intensity of odors smelled 25 min earlier can unintentionally influence subsequent odor intensity judgement. The findings are discussed in the light of two alternative explanations, namely, a central implicit memory process and a stimulus- level-based change at the peripheral level.      

Ontogeny of odor liking during childhood and its relation to language development

One important aspect of odor hedonics is its plasticity during human development. The present study set out to probe the modulators of such olfactory change during that period by testing the hypothesis that language and semantic representations of objects are strong organizers of odor liking. To this end, 15 three-year-old children were tested in a longitudinal study. Participants were exposed to exactly the same 12 odorants once a year over a 3-year period. At each experimental session, they were asked to answer 2 questions: 1) "Do you like or dislike this odor?" and 2) "Can you tell me what it is?" The level of language production was assessed on a standardized test. The 3-year-old children were found to categorize the same number of odorants as liked and as disliked. The follow-up study, in contrast, showed that at 5 years of age they categorized more of these odors as liked and that the shift was significant only in the children with higher language production skills. Taken as a whole, these findings suggest that the 3- to 5-year age range, when children begin to master language, is a turning point in the construction of olfactory hedonic categories during childhood.     

Body odor similarity in noncohabiting twins

There is currently considerable interest in biometric approaches using human odor as a marker of disease or genetic individuality. Body odor is also thought to be used during mate choice to select genetically compatible mates. The idea that body odor reveals information about both genetic identity and genetic similarity is most readily tested by examining odor in twin pairs. However, although this idea can be traced back 130 years to Francis Galton in 1875, most studies using dogs fail to control for shared environmental effects associated with cohabitation. Here we show that odors of identical twins (but not dizygotic twins) can be matched by human sniffers at rates better than chance, even when the twins are living apart. In addition, matching frequencies for identical twin odors were not significantly different from those for duplicate odors from the same individual. These results indicate an important genetic influence on body odor and the potential for developing technologies for human odor printing in relation to underlying genotype.     

Central organization of a high-dimensional odor space

Animals recognize groups and mixtures of odors as a unitary object. This ability is crucial to generalize known odors to newly encountered ones despite variations. However, it remains largely unknown how multitudes of odors are represented and organized in the higher brain regions to support odor object recognition. Here we discuss recent advances uncovering the population odor responses in the rodent piriform cortex and the Drosophila mushroom body, and highlight the emerging principles on the organization, mechanism, stereotypy, and experience-dependence of central odor representations.     

An olfactory recognition model based on spatio-temporal encoding of odor quality in the olfactory bulb

In order to study the problem how the olfactory neural system processes the odorant molecular information for constructing the olfactory image of each object, we present a dynamic model of the olfactory bulb constructed on the basis of well-established experimental and theoretical results. The information relevant to a single odor, i.e. its constituent odorant molecules and their mixing ratios, are encoded into a spatio-temporal pattern of neural activity in the olfactory bulb, where the activity pattern corresponds to a limit cycle attractor in the mitral cell network. The spatio-temporal pattern consists of a temporal sequence of spatial firing patterns: each constituent molecule is encoded into a single spatial pattern, and the order of magnitude of the mixing ratio is encoded into the temporal sequence. The formation of a limit cycle attractor under the application of a novel odor is carried out based on the intensity-to-time-delay encoding scheme. The dynamic state of the olfactory bulb, which has learned many odors, becomes a randomly itinerant state in which the current firing state of the bulb itinerates randomly among limit cycle attractors corresponding to the learned odors. The recognition of an odor is generated by the dynamic transition in the network from the randomly itinerant state to a limit cycle attractor state relevant to the odor, where the transition is induced by the short-term synaptic changes made according to the Hebbian rule under the application of the odor stimulus. Received: 28 July 1997 / Accepted in revised form: 6 May 1998     

Context-dependent changes in the perception of odor quality

Ambiguous odor compounds, partly citrus-like and partly woodyin odor character, were seen to change in odor quality whenevaluated in the same session as more prototypical odors. Whentested with characteristically citrus odors, the ambiguous compoundsseemed more woody, and when tested with characteristically woodyodors, the ambiguous odorants were higher in citrus character,an example of perceptual contrast. Response frequency biaseswere ruled out as an explanation for this shift by an experimentin which responses other than citrus and woody ratings wereasked of the subjects during the contextual exposure. Simplesensory adaptation was found to be a potential contributor tothe effect, and a sufficient condition to produce similar shiftsin odor quality. However, adaptation was not a necessary conditionto produce the effect. This was seen in reversed pair experimentsin which the contextual odors were presented after the ambiguousstimuli. The contextual shift was robust—it was obtainedwith different ambiguous odors, contextual (conditioning) odors,numbers of contextual odors, orders of presentation of contextualodors relative to ambiguous odors, scale types, and rating tasksduring the presentation of contextual odors.     

Time course of androgenic modulation of odor preferences and odor cues in male meadow voles, Microtus pennsylvanicus.

During the breeding season, male meadow voles prefer female over male odors and females prefer male over female odors. Testosterone control of males' odor preferences and production of odors attractive to females differ. A male meadow vole's preference for female versus male odor was still evident 1 week after castration, but not 1 week later. This preference was reinstated in testosterone-treated male voles 2 weeks after the onset of hormone replacement. The attractiveness of male odors to females did not disappear until 3 weeks after castration. The attractiveness of male odors was reinstated 1 week after castrated males were treated with testosterone. The time course for the androgenic modulation of production of odors attractive to females may facilitate breeding. For example, at the end of the breeding season males may emit an odor that is still attractive to females. Similarly, at the beginning of the breeding season males may emit an odor that is attractive to females.     

Basic emotions evoked by eugenol odor differ according to the dental experience. A neurovegetative analysis.

Subjective individual experiences seem to indicate that odors may form strong connections with memories, especially those charged with emotional significance. In the dental field, this could be the case with the odorant eugenol, responsible for the typical clinging odor impregnating the dental office. The odor of eugenol could evoke memories of unpleasant dental experiences and, therefore, negative feelings such as anxiety and fear, since eugenates (cements containing eugenol) are used in potentially painful restorative dentistry. This hypothesis was tested by evaluating the emotional impact of the odor of eugenol through autonomic nervous system (ANS) analysis. The simultaneous variations of six ANS parameters (two electrodermal, two thermovascular and two cardiorespiratory), induced by the inhalation of this odorant, were recorded on volunteer subjects. Vanillin (a pleasant odorant) and propionic acid (an unpleasant one) served as controls. After the experiment, subjects were asked to rate the pleasantness versus unpleasantness of each odorant on an 11-point hedonic scale. The patterns of autonomic responses, obtained for each odorant and each subject, were transcribed into one of the six basic emotions defined by Ekman et al. (happiness, surprise, sadness, fear, anger and disgust). Results were compared between two groups of subjects divided according to their dental experience (fearful and non-fearful dental care subjects) and showed significant differences only for eugenol. This odorant was rated as pleasant by non-fearful dental subjects but unpleasant by fearful dental subjects. The evoked autonomic responses were mainly associated with positive basic emotions (happiness and surprise) in non-fearful dental subjects and with negative basic emotions (fear, anger, disgust) in fearful dental subjects. These results suggest that eugenol can be responsible for different emotional states depending on the subjects' dental experience, which seems to confirm the potential role of odors as elicitors of emotional memories. This study also supports the possible influence of the ambient odor impregnating the dental office, strengthening a negative conditioning toward dental care in some anxious patients.     

Dynamics of C, N and P in soil amended with biosolids from a pharmaceutical industry producing cephalosporines or third generation antibiotics: a laboratory study

Large parts of the central highlands of Mexico are heavily eroded and the success of a planned reforestation program will greatly improve when the organic matter and nutrient content of the soil increases prior to the planting of the trees. This study investigated how the application of biosolids from a pharmaceutical company producing cephalosporines or third generation antibiotics could be used as a soil amendment and affect dynamics of C, P and N in soil. A sandy clay loam soil was sampled, amended with 24 g of dry biosolids kg(-1) dry soil or approximately 32 x 10(3) kg ha(-1) for the 0-10 cm layer, and incubated aerobically while production of carbon dioxide (CO(2)), dynamics of ammonium (NH(4)(+)),nitrite (NO(2)(-)), nitrate (NO(3)(-)), sodium bicarbonate (NaHCO(3)) extractable phosphorus (PO(4)(3-)), and microbial biomass carbon (C) were monitored. Results showed that the biosolid with pH 12, organic C content 162 g kg(-1), total N 21 g kg(-1), was of excellent quality considering its heavy metal content (USEPA) and a class "B" (USEPA) biosolid considering the amount of pathogens. No cephalosporines could be detected in the biosolid. Addition of biosolid to soil increased production of CO(2) 1.4 times and added >60 mg NH(4)(+) kg(-1). The application of biosolids did not significantly increase the concentration of NO(2)(-) which remained <2 mg N kg(-1) soil, but the concentration of NO(3)(-) did increase with 175 mg N kg(-1) soil. The microbial biomass C did not change when sewage biosolids was added and concentrations of extractable PO(4)(3-) only increased temporarily. Washing the biosolids reduced concentrations of NH(4)(+) and NO(3)(-), but also reduced pathogens and concentrations of chloride (Cl(-)), which might pose a treat to humans and the environment, respectively. Although the biosolid added valuable nutrients to the soil and did not inhibit C and N mineralization, further investigation into possible long-term environmental effects on soil processes and plant growth is necessary before this biosolid can be used in the field.     

Verbal cues modulate hedonic perception of odors in 5-year-old children as well as in adults

The judgment of pleasantness/unpleasantness is the prominent reaction to the olfactory world. In human adults, the hedonic valence of odor perception is affected by various factors, among which is an individual's lexical knowledge about smells. The present study examined whether such top-down effects of lexical knowledge on hedonic judgment of olfactory input are similar in children (5-6 years) and adults (20-25 years). In both groups, the lexical knowledge was found to influence the perception of the least emotional (or most neutral) odors: the pleasantness of the smells of banana and mint was enhanced when participants were given the corresponding odor label before olfactory sensation. These results lend support to the notion that, during childhood, smells are not only encoded perceptually but that verbal encoding also steers contextual effects that may be prominent factors in the early memorization and categorization of odors.     

Effect of Aging on Hedonic Appreciation of Pleasant and Unpleasant Odors

Does hedonic appreciation evolve differently for pleasant odors and unpleasant odors during normal aging? To answer this question we combined psychophysics and electro-encephalographic recordings in young and old adults. A first study showed that pleasant odorants (but not unpleasant ones) were rated as less pleasant by old adults. A second study validated this decrease in hedonic appreciation for agreeable odors and further showed that smelling these odorants decreased beta event-related synchronization in aged participants. In conclusion, the study offers new insights into the evolution of odor hedonic perception during normal aging, highlighting for the first time a change in processing pleasant odors.     

An environmental nuisance: odor concentrated and transported by dust

Intensive swine production generates odorous emissions which flow from the buildings housing the animals. High ventilation rates bring in fresh air, remove heat and moisture and enhance pork productivity. Numerous compounds contribute to the uniquely offensive odors from swine facilities, including fatty acids, amines, aromatics and sulfur compounds. Dust particles, which originate predominantly from feces and feed, can adsorb and concentrate odorants in swine facilities. In addition, organic particles can decay and generate odorous compounds. Odorants can exist in much higher concentrations in the dust particles than in equivalent volumes of air. Thus, inhalation of odorous dust and deposition of the dust particles in the mucus overlying the olfactory mucosa are likely responsible for some odor-related complaints by swine farm neighbors. Accurate prediction of odor transport and dispersion downwind from swine farms may require models of dust dispersion and correlation between dust and odorant levels. Unfortunately, many approaches to estimating odor impact currently incorporate filtering of air to remove particulate matter before sensing by humans or electronic sensors. Accelerated progress in understanding this and other 'real world' odor control problems will require methodological innovations that allow quantification of odor in response to air streams containing vapor and particulate phases.     

Potential mechanisms of retronasal odor referral to the mouth

The current study took a first step toward elucidating the sensory input that drives retronasal odor referral to the mouth. In 2 experiments, subjects performed odor localization tasks under various oral-nasal stimulation conditions that allowed us to assess the effects of direction of airflow, taste, and tactile stimulation on retronasal odor referral. Subjects reported the locations of perceived odors when food odorants were inhaled through the mouth alone or in the presence of water or various tastants in the mouth. The results indicated that when perceived alone, vanilla and soy sauce odor were localized 54.7%: 26.4%: 18.9% and 60.0%: 21.7%: 18.3% in the nose, oral cavity, and on the tongue, respectively. The localization of odors alone was not significantly different from when water was presented simultaneously in the mouth, indicating that tactile stimulation itself is not sufficient to enhance odor referral. However, the presence of sucrose, but not other tastes, significantly increased localization of vanilla to the tongue. Likewise, only NaCl significantly augmented referral of soy sauce odor to the tongue. These data indicate that referral of retronasal odors to the mouth can occur in the absence of a either taste or touch but that referral to the tongue depends strongly on the presence of a congruent taste.     

Performance of mice in an automated olfactometer: odor detection, discrimination and odor memory

Mice were trained on a variety of odor detection and discrimination tasks in 100- or 200-trial sessions using a go, no-go discrete trials operant conditioning procedure. Odors, presented for 1 s on each trial, were generated by an air dilution olfactometer (for threshold tests) and an easily constructed eight-channel liquid dilution unit (for two- and multiple-odor discrimination tasks). Mice rapidly acquired the operant task and demonstrated excellent stimulus control by odor vapors. Their absolute detection threshold for ethyl acetate was similar to that obtained with rats using similar methods. They readily acquired four separate two-odor discrimination tasks and continued to perform well when all eight odors were presented in random order in the same session and when reinforcement probability for correct responding was decreased from 1 to 0.5. Memory for these eight odors, assessed under extinction after a 32 day rest period, was essentially perfect. Time spent sampling the odor on S+ and S- trials was highly correlated with response accuracy. When accuracy was at chance levels (e.g. initial trials on a novel task), stimulus sampling time on both S+ and S- trials was approximately 0.5-0.7 s. As response accuracy increased, sampling time on S+ trials tended to increase and remain higher than sampling time on S- trials.     

The Odor Awareness Scale: a new scale for measuring positive and negative odor awareness

The Odor Awareness Scale (OAS) is a questionnaire designed to assess individual differences in awareness of odors in the environment. The theory that odor awareness can be distinguished in awareness of negative (to be avoided) odors and positive (to be approached) odors was tested using confirmatory factor analysis (CFA) on the 34-item questionnaire after completion by 525 respondents. CFA (after deletion of 2 items) showed good fit of the 2-factor theory, resulting in a positive awareness subscale (11 items, Cronbach's alpha = .77) and a negative awareness subscale (21 items, Cronbach's alpha = .80). Furthermore, reports of sickness from environmental odors were correlated with the negative odor awareness factor, not the positive odor awareness factor. Respondents scoring high on the overall sum score of the OAS showed significantly better olfactory performance on an odor perception test battery than respondents with a low score. These results suggest a causal relation between awareness of potentially negative odors, olfactory performance and experiencing health effects from environmental odor exposure, that warrants further investigation.     

Attentional modulation of central odor processing

Two studies were conducted to investigate the influence of attention on the components of the chemosensory event-related potential (CSERP). In the first study the odors linalool and eugenol were delivered to six male subjects, in the second study three male and two female subjects were presented with their own body odor (axillary hair) and the body odor of a same sex donor. In both studies the odors were presented in an oddball paradigm under ignore and attend conditions via a constant- flow olfactometer. In the ignore condition attention was diverted from the odors with a distractor task, while in the attend condition the subjects were asked to respond to the infrequently occurring odor. In both studies the allocation of attention led to a decrease in the latency of the early components (N1, P2, N2) and to an increase in the amplitude of the late positivities. The modulation of the early components suggests that attentional gating in olfaction might already be effective at an early processing level.