Psychometrics of Odor Quality Discrimination: Method for Threshold Determination

Department of Psychology, Uppsala University, Box 1225, S-751 42 Uppsala, Sweden.
Chemical Senses (Impact Factor: 3.16). 11/2000; 25(5):493-9. DOI: 10.1093/chemse/25.5.493
Source: PubMed


There is no natural physical continuum for odor quality along which an odor quality discrimination (OQD) threshold can be measured. In an attempt to overcome this problem, the substitution-reciprocity (SURE) method defines a framework for the measurement of an OQD threshold. More specifically, it (i) defines a threshold concept for OQD, including the quantification of qualitative change of the stimulus, and (ii) suggests how to avoid perceived intensity as an unwanted cue for discrimination. In doing this, the psychometric properties of odor quality in the case of eugenol and citral are investigated using both discrimination (experiment 1) and scaling (experiment 2). Based on discriminatory responses, a change of approximately one-third in stimulus content was needed to reach the OQD threshold for eugenol and citral.

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Available from: William S. Cain, Mar 21, 2015
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    • "In the olfactory system, simultaneous presentation of two compounds in a 50:50 mixture generally evokes the same intensity as each single compound at 100% concentration. This is true even if both compounds are perceptually relatively different (Olsson and Cain, 2000, Boyle et al., 2009). In the gustatory system, however, a different picture emerges: binary taste mixtures consisting of two stimuli, which each evoke the same taste quality (e.g., sweet), may show effects of enhancement or suppression. "
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    ABSTRACT: The intranasal trigeminal system is a third chemical sense in addition to olfaction and gustation. As opposed to smell and taste, we still lack knowledge on the relationship between receptor binding and perception for the trigeminal system. We therefore investigated the sensitivity of the intranasal trigeminal system towards agonists of the trigeminal receptors TRPM8 and TRPA1 by assessing subjects' ability to identify which nostril has been stimulated in a monorhinal stimulation design. We summed the number of correct identifications resulting in a lateralization score. Stimuli were menthol (activating TRPM8 receptors), eucalyptol (TRPM8), mustard oil (TRPA1) and two mixtures thereof (menthol/eucalyptol and menthol/mustard oil). In addition, we examined the relationship between intensity and lateralization scores and investigated whether intensity evaluation and lateralization scores of the mixtures show additive effects. All stimuli were correctly lateralized significantly above chance. Across subjects the lateralization scores for single compounds activating the same receptor showed a stronger correlation than stimuli activating different receptors. Although single compounds were isointense, the mixture of menthol and eucalyptol (activating only TRPM8) was perceived as weaker and was lateralized less accurately than the mixture of menthol and mustard oil (activating both TRPM8 and TRPA1) suggesting suppression effects in the former mixture. In conclusion, sensitivity of different subpopulations of trigeminal sensory neurons seems to be related, but only to a certain degree. The large coherence in sensitivity between various intranasal trigeminal stimuli suggests that measuring sensitivity to one single trigeminal chemical stimulus may be sufficient to generally assess the trigeminal system's chemosensitivity. Further, for stimuli activating the same receptor a mixture suppression effect appears to occur similar to that observed in the other chemosensory systems.
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    • "In fact, the average rate of correct identification (i.e., naming) for a set of common odors (e.g., coffee, vanilla, tar) rarely exceeds 50%. Also, the most familiar item in a set does typically fall short of 100% correct identification (Engen 1991; de Wijk et al. 1995; Cain and Potts 1996; Herz and Engen 1996; Cain et al. 1998; Olsson and Cain 2000; Wise et al. 2000). Altogether, this olfactory " agnosia " mirrors the lack of importance of precise identification for the olfactory system and also suggests that verbal codes are not typically an aid to memory. "
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    ABSTRACT: Odor memory has been argued to exhibit unique characteristics in relation to memory for other types of stimuli such as visually presented words. Two experiments investigated episodic recognition performance as well as memory awareness for odors and words across manipulations of orienting task and retention interval. Orienting task mattered little to odor recognition. However, in contradiction with several previous studies, substantial forgetting of odors was found. After controlling for effects of odor identifiability, it was found that memory for identified odors exhibited greater similarities to memory for words than to memory for unidentified odors.
    Full-text · Article · Sep 2009 · Chemosensory Perception
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    • "For the mixtures of bourgeonal and undecanal, we employed one weaker and one stronger mixture series of 7 stimuli, each ranging from bourgeonal to an isointense undecanal over a 50/50 mixture (see Table 1). This mixing by substitution has previously been shown to produce roughly isointense series of mixtures (Olsson and Cain 2000; Boyle et al. 2009). The particular concentrations for the unmixed substances for the high and low series were chosen from the functions in Figure 1A–C. "
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    ABSTRACT: The perceived quality of a binary mixture will, as a rule of thumb, be dominated by the quality of the stronger unmixed component. On the other hand, there are mechanisms that, in theory, suggest that this will not always be true; one example being receptor antagonism. Undecanal has been indicated as an antagonist for bourgeonal-sensitive receptors in the human olfactory epithelium. Therefore, we investigated mixtures of isointense concentrations of bourgeonal and undecanal and, as a control, mixtures of isointense concentrations of bourgeonal and n-butanol. Both mixture types were investigated at 2 levels of concentration. The particular aim was to see if the bourgeonal-undecanal mixtures would exhibit asymmetric odor quality favoring the perception of the antagonist and the control mixture would not. For the control mixture, indeed odor quality tended to be dominated by the strongest component before mixing as would be suggested from previous studies. In line with the hypothesis, the bourgeonal-undecanal mixture was dominated by the antagonist's quality, but only when mixed at higher concentrations, altogether suggesting the effects of a low-affinity receptor antagonism. This is, to our knowledge, the first demonstration of how antagonistic interaction at the level of the receptor can affect the perception of odor mixtures in humans.
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