Characteristic component odors emerge from mixtures after selective adaptation

Department of Psychology, Cornell University, Ithaca, NY, USA.
Brain Research Bulletin (Impact Factor: 2.72). 05/2007; 72(1):1-9. DOI: 10.1016/j.brainresbull.2006.12.010
Source: PubMed


Humans cannot reliably identify the distinctive characteristic odors of components in mixtures containing more than three compounds. In the present study, we demonstrate that selective adaptation can improve component identification. Characteristic component odors, lost in mixtures, were identifiable after presenting other mixture constituents for a few seconds. In mixtures of vanillin, isopropyl alcohol, l-menthol and phenethyl alcohol, this rapid selective adaptation unmasked each component. We suggest that these findings relate directly to how olfactory qualities are coded: olfactory receptors do not act as detectors of isolated molecular features, but likely recognize entire molecules closely associated with perceived olfactory qualities or "notes". Rapid and focused activation of a few distinct receptor types may dominate most odor percepts, emphasizing the importance of many dynamic and specific neural signals. An interaction between two fundamental coding strategies, mixture suppression and selective adaptation, with hundreds of potential olfactory notes, explains humans experiencing the appearance and disappearance of identifiable odors against ambient mixture backgrounds.

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Available from: Holly Franklin Goyert, Sep 15, 2014
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    • "Interactions occurring at the peripheral level of the olfactory system play a critical role in the processing of odorants' mixture (Berglund et al., 1976; Bell et al., 1987; Derby, 2000; Kay et al., 2003; Goyert et al., 2007). In both vertebrates and invertebrates, the periphery of the olfactory system triggers the first step of olfactory information coding. "
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    ABSTRACT: Smelling monomolecular odors hardly ever occurs in everyday life, and the daily functioning of the sense of smell relies primarily on the processing of complex mixtures of volatiles that are present in the environment (e.g., emanating from food or conspecifics). Such processing allows for the instantaneous recognition and categorization of smells and also for the discrimination of odors among others to extract relevant information and to adapt efficiently in different contexts. The neurophysiological mechanisms underpinning this highly efficient analysis of complex mixtures of odorants is beginning to be unraveled and support the idea that olfaction, as vision and audition, relies on odor-objects encoding. This configural processing of odor mixtures, which is empirically subject to important applications in our societies (e.g., the art of perfumers, flavorists, and wine makers), has been scientifically studied only during the last decades. This processing depends on many individual factors, among which are the developmental stage, lifestyle, physiological and mood state, and cognitive skills; this processing also presents striking similarities between species. The present review gathers the recent findings, as observed in animals, healthy subjects, and/or individuals with affective disorders, supporting the perception of complex odor stimuli as odor objects. It also discusses peripheral to central processing, and cognitive and behavioral significance. Finally, this review highlights that the study of odor mixtures is an original window allowing for the investigation of daily olfaction and emphasizes the need for knowledge about the underlying biological processes, which appear to be crucial for our representation and adaptation to the chemical environment.
    Full-text · Article · Jun 2014 · Frontiers in Psychology
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    • "Pink shading highlights the key selectively adapted mixture (NaCl + sucrose), which is preadapted either by 1 or the other of the 2 mixture components [X / XY, Y / XY]. The adapted component is ''ambient'' when tested and the additional unadapted component ''extra'' as in Goyert et al. (2007) and Frank et al. (2010). Tan shading identifies cases in which the mixture test stimulus is preceded by water or the mixture itself [0 / XY, XY / XY]. "
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    ABSTRACT: Little is known about coding of taste mixtures in complex dynamic stimulus environments. A protocol developed for odor stimuli was used to test whether rapid selective adaptation extracted sugar and salt component tastes from mixtures as it did component odors. Seventeen human subjects identified taste components of "salt + sugar" mixtures. In 4 sessions, 16 adapt-test stimulus pairs were presented as atomized, 150-μL "taste puffs" to the tongue tip to simulate odor sniffs. Stimuli were NaCl, sucrose, "NaCl + sucrose," and water. The sugar was 98% identified but the suppressed salt 65% identified in unadapted mixtures of 2 concentrations of NaCl, 0.1 or 0.05 M, and sucrose at 3 times those concentrations, 0.3 or 0.15 M. Rapid selective adaptation decreased identification of sugar and salt preadapted ambient components to 35%, well below the 74% self-adapted level, despite variation in stimulus concentration and adapting time (<5 or >10 s). The 96% identification of sugar and salt extra mixture components was as certain as identification of single compounds. The results revealed that salt-sugar mixture suppression, dependent on relative mixture-component concentration, was mutual. Furthermore, like odors, stronger and recent tastes are emphasized in dynamic experimental conditions replicating natural situations.
    Full-text · Article · May 2012 · Chemical Senses
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    • "Disadaptation , the restoration of sensitivity following adaptation , similarly varies from several seconds in the case of short-term adaptation to minutes for long-term adaptation (Zufall and Leinders-Zufall 2000). Psychophysical studies of odor adaptation in humans have likewise depended on procedures employing intermittent stimulation (Cain and Polak 1992; Hummel et al. 1996; Pierce et al. 1996; Dalton 2000; Sobel et al. 2000; Wang et al. 2002; Jacob et al. 2003; Goyert et al. 2007). Usually, these studies ask observers to inhale odor pulses, singly or in trains, before removing the conditioning or adapting odorant to permit observer estimation of odor intensity or of changes in odor threshold for a comparison odorant. "
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    ABSTRACT: In this presentation, we describe a novel method for estimating the onset time course of psychophysical odor adaptation in human observers. The method employs stimulus conditions derived from an analogous stimulus paradigm in audition. To test this procedure, we used liquid-dilution olfactometry to estimate 2-bottle discrimination thresholds for brief (600 ms) presentations of vanilla odor; 17 volunteers (14 females; ages 18-24) served as participants. The adapting odorant concentration for each participant was set relative to baseline threshold for the 600-ms target alone (i.e., the same level relative to each participant's threshold). To characterize the adaptation-onset time course, we compared thresholds for targets presented simultaneously with the adapting stimulus as a function of the relative delay between the onset of the adapting stimulus and onset of the target. As predicted from the analogous auditory studies, thresholds for the target stimulus increased in an orderly manner with increases in adaptation-to-target onset delay (i.e., as the adaptation process progressively decreased sensitivity). Initial increases in threshold were consistently observed for the briefest onset delays of 50-100 ms. An onset time constant was estimated at 319 ms by fitting a 2-component exponential to the mean group function. Adaptation magnitude was dependent on the level of adapting odorant, relative to threshold. When thresholds were measured in one participant with a different, unrelated target odorant, cineole, there was no effect of the vanilla-adapting stimulus on threshold. The results suggest that olfactory rapid adaptation is measurable psychophysically within 50-200 ms after odor onset, values consistent with physiological measures of adaptation in olfactory receptor neurons. This novel stimulus paradigm offers a powerful psychophysical tool to study both odor adaptation and stimulus interactions at the olfactory periphery.
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