Remembered odors and mental mixtures: tapping reservoirs of olfactory knowledge.

Five experiments explored how (a) perceived and remembered odor intensities relate to concentration; (b) odor intensities integrate in perceptual, memorial, and mentally constructed mixtures; and (c) components vary in intensity in physical versus mental mixtures. Ss estimated the magnitude of unmixed stimuli presented physically (perceptual estimation) or represented symbolically (memorial estimation). Ss also judged mixtures and their components in combinations of perceptual and memorial presentation. Power functions with similar exponents described the relations between both perceived and remembered intensity and concentration. Perceptual, memorial, and mental mixtures all followed much the same interactive rule of integration. Correspondingly, the intensities of components varied similarly in mentally constructed and physical mixtures. The results imply intensive invariance across odor perception and odor memory.     

Physicochemical characteristics and supraliminal odor intensity: Reply to Mitchell

The rate of growth (exponent) of the psychophysical function for odor intensity depends upon the physicochemical properties of odorous substances. Although no single property is able to predict rate of growth, a model developed by Dravnieks and Laffort that combines three basic properties has been quite successful. The results of intra-O comparisons of the relative exponents for various odorants have withstood the test of replication, i.e., variation among Os has usually not been a serious problem. In the future, comparisons of the exponents obtained from one laboratory to another would be aided considerably by inclusion of a standard odorant in all scaling studies.     

Odor intensity and pleasantness for a diverse set of odorants

Data Analysis Office, U.S. Army Natick Laboratories, Natick, Massachusetts 01760 Observers compared the odor of butanol to the odors of various concentrations of 32 chemicals, and also rated the odor pleasantness and unpleasantness of these 32 odorants by a line matching procedure. All stimuli were presented to the observers by air dilution olfactometers. Odor intensity matches between each odorant and butanol were often describable by power functions. A derived magnitude estimate of odor intensity was obtained through a calibration of the butanol concentration scale. Most odorants grew less rapidly in intensity than butanol, and all odorants grew in intensity as decelerating functions of concentration. A more general function of the form P =: k₁ + k₂C^k3 was needed to account for the pleasantness-unpleasantness judgments. In this study, most odorants were rated either neutral or unpleasant. Observers showed far more variability in hedonic judgments than in intensity judgments.     

Some properties of the olfactory system of man

Preliminary investigations into the effects of a 12-h diurnal variation suggested there was a 10-fold decrease in odor sensitivity from morning to evening. For a selected group of odorants (methyl, t-butyl, and phenyl isonitrile), the difference between detection and recognition thresholds in general was found to be 10-fold; however, for some Ss the difference was less. When Ss were blindfolded, no changes in odor sensitivity were noted. Similarly, imposing an auditory stress on the test situation did not significantly alter odor sensitivity in either experienced or naive Ss,     

Toilet rooms, body massages, and smells: Two field studies on human evaluative odor conditioning

In two experimental field studies, the hypothesis was tested that Pavlovian conditioning may modify adults’ liking or disliking of an odor. In Experiment 1, an odor (CS) was first paired unobtrusively with toilet stimuli (US). Next, Ss rated the experimental and a control odor on Semantic Differential items. For Ss evaluating going-to-the-toilet negatively, an acquired dislike for the toilet-paired odor relative to a nonexposed control odor was observed, whereas in Ss evaluating going-to-the-toilet positively, the reverse was observed. In Experiment 2, a neutral odor (CS) was mixed into the massage oil with which a physiotherapist treated his patients. Half of the Ss were treated with Positive-relaxing massage, half of the Ss with Negative-painful massage. At the medical follow-up, Semantic Differential ratings were obtained both for the treatment-odor and for a control odor. In the Positive massage group, the treatment odor was rated as more positive and as less dynamic than the control odor. No similar effects were observed in the Negative massage group, a failure which was probably due to the intended Negative massage not really being experienced as a disliked event. In both experiments, an almost identical pattern of results was observed in the subgroup of Ss who didnot consciously recognize the experimental odor as the treatment odor, eliminating the possibility that the results should be due to demand. As mere exposure cannot account for the results, they most probably represent genuine instances of evaluative odor conditioning. The results are discussed in terms of the understanding of the origins of the affective meaning of odorants, and are related to human evaluative conditioning and implicit memory issues.     

Odor intensity: Differences in the exponent of the psychophysical function

A series of five experiments showed that there are reliable differences among the exponents of the psychophysical power functions for odorants. There was virtually a perfect rank-order correlation between the size of the exponent and the water-solubility of the odorants. The exponents for odorants that are completely soluble in water (n-propanol and acetone) were approximately 2.5 times the size of the exponents for odorants that are insoluble in water (n-octanol and geraniol). For n-aliphatic alcohols, the size of the exponent and solubility in water decrease as a function of carbon chain-length. Although the exponents were higher when the stimuli were delivered with an air-dilution olfactometer than when they were sniffed from cotton swabs, the relative values among odorants were independent of the method of stimulus presentation.     

On the consistency of intramodal intensity matching in olfaction

Magnitude matchings of odor intensity were obtained for three chemical compounds (hydrogen sulfide, pyridine, and dimethyl disulfide) in four experiments. An equal-sensation function in the form of a power function described the data well. This equation can be written neglecting the multiplicative constant, Ф_i = Ф_k ^b _ik, where i and k represent two different odorants. The exponent b_ik, where the first index stands for matching continuum and the second index for reference continuum, was fairly well predicted according to the formulae, (ie, 264, 2) where i, j, and k are three different odorants. The results validate the equal-sensation function and indicate implicitly that intensity matchings between different intramodal continua are approximately transitive and symmetric with respect to odor.     

Olfactory detection thresholds in man under conditions of rest and exercise

Detection thresholds for seilen odorants were measured under conditions of rest and exercise. The test panel comprised six males with previous experience in odor detection. Exercise was maintained constant by using a modified bicycle positioned within the context of an air-dilution olfactometer. The effects of exercise were idiosyncratic for Ss: odor sensitivity was increased in some Ss, decreased in some, and not changed in others. Results of these experiments are discussed in terms of intra-subject variance within sessions and from session to session. In addition, two test techniques—one a fixed series and the other a tracking procedure—were evaluated for rapid estimation of an odor threshold. The tracking procedure facilitated prompt detection of changes in sensitivity for individual Ss.     

Odor magnitude: Coarse vs. fine grain

Despite a dismal reputation, olfaction’s resolving power actually appears to be keen, especially when the contaminating influence of noise in the stimulus is discounted from psychophysical performance. In a previous investigation, subjects were able to resolve a change of 4% in the concentration of butyl alcohol. In the present experiment, these same subjects resolved a change of 9% in the concentration of amyl butyrate. The data imply that resolving power varies among odorants. The growth of odor intensity assessed by magnitude estimations of easily discriminable (i.e., grossly different) concentrations also varies among odorants. These observations prompt the question: Does an odorant for which resolution is relatively difficult lead to slower growth of perceived intensity with concentration than an odorant for which resolution is easy? In a scaling experiment, amyl butyrate indeed led to slower growth of intensity than butyl alcohol. Nevertheless, amyl alcohol, which permitted poorer resolution than butyl alcohol, led to approximately the same rate of growth as butyl alcohol. Accordingly, growth of odor intensity with concentration may correlate only weakly with resolving power.     

Odorous and pungent attributes of mixed and unmixed odorants

In order to explore functional properties of the olfactory and common chemical senses as well as their relation to the total nasal sensation experienced, various concentrations of two pungent odorants were presented alone and in the presence of different backgrounds of the other irritant. Stimuli comprised formaldehyde (at 1.0, 3.5, 6.9, and 16.7 ppm), ammonia (at 210, 776, 1,172, and 1,716 ppm), and their 16 possible binary mixtures. Subjects were asked to estimate the total nasal perceived intensity, and then to assess the olfactory (odor) and common chemical (pungency) attributes of the evoked sensations. The results showed that stimulus-response functions for pungency are steeper than those for odor. Furthermore, odor was always hypoadditive in mixtures (i.e., mixtures were perceived as less intense than the sum of their components), whereas pungency was, mainly, additive, and even suggested hyperadditivity. Total perceived intensity of the stimuli, alone and in mixtures, followed the stimulus-response patterns for pungency, which, therefore, emerged as the dominating attribute used by subjects in scaling the explored range of concentrations. The relationship between total nasal perceived intensity of the mixtures and that of their components reflected hypoaddition, resembling the outcome for the odor attribute.     

An examination of relationships between the pleasantness,intensity, and concentration of 10 odorous stimuli

Relationships between physical concentration, perceived pleasantness, and perceived intensity were established by the method of magnitude estimation for 10 diverse chemical stimuli. Estimates of pleasantness significantly correlated with those of intensity for seven of the compounds examined. In all cases, the relationships between perceived intensity and physical concentration were described relatively well by power functions. However, this was not true for the pleasantness/concentration relationships. Intensity exponents correlated moderately with a number of common physicochemical parameters. Large differences were present between individual observer’s ratings of the perceived pleasantness of the odorants. These data indicate that the perceived pleasantness of some odorants may be systematically related to their perceived intensity, but do not support the notion that these dimensions are equivalent.

     

The effect of color intensity and appropriateness on color-induced odor enhancement

Coloring solutions has been shown to increase perceived odor intensity. In Experiment 1, subjects rated the odor intensity of red strawberry and green mint solutions that had four levels of color intensity. Ratings of strawberry odor peaked at the medium color intensity and ratings of mint odor increased monotonically with color intensity. Thus, color-induced odor enhancement can increase with increasing color intensity but need not. Experiment 2 found that the color intensities producing maximum odor enhancement in Experiment 1 are not always the ones perceived as most appropriate for the odorants. Using different odors, Experiment 3 found that color intensity has some influence on the strength of the color-induced odor enhancement and color appropriateness has little. The presence or absence of color in the solution seems to be the most important variable.     

Old-age deficits in the sense of smell as gauged by thresholds, magnitude matching, and odor identification

Twenty elderly subjects (70-90 years old) and 20 young control subjects (18-24 years old) underwent three kinds of olfactory testing: absolute thresholds to three odorants (d-limonene, iso-amyl butyrate, benzaldehyde), magnitude matching of these odorants to salt tastes, and odor identification of 30 common substances. For all three odorants elderly subjects' mean threshold significantly exceeded that of the young by about ninefold for d-limonene, about threefold for benzaldehyde, and about twofold for iso-amyl butyrate. These threshold differences predict approximate concentration differences necessary to arouse the same estimated odor strength above the threshold for the elderly and the young. Young subjects also scored better than the elderly in odor identification, even when subjects were given four alternatives from which to select the correct label. Unimpaired olfactory functioning is uncommon in the elderly; correlational tests show that as a group the young have better olfactory ability and show more interindividual uniformity.     

Imagery and olfactory stimulation

The purpose of the present study was to investigate a possible odor-emotion interaction by determining whether humans could differentially detect other humans' odor collected under varying emotional conditions. Odorants were collected from the axillary apocrine glands of four female donors, each of whom underwent different imagery induction procedures of anxiety, relaxation, and sexual arousal. The odorants were chemically preserved and later evaluated by 16 naive white male judges as to the presence of discriminatory odor cues. Judges' imagery was differentially related to the anxiety imagery-produced odorants but only for those produced by the most imaginative donors. The relaxation odorants of all donors were correlated. The judges were unable to detect the sexual imagery arousal odorants.     

Multidimensional analysis of twenty-one odors

Berglund, B., Berglund, U., Engen, T., & Ekman, G.¹ Multidimensional analysis of twenty-one odors. Scand. J. Psychol., 1973, 14, 131–137.-The present paper reports an experiment on the application of multidimensional scaling to the sense of smell for the purpose of revealing basic psychophysical dimensions of odorants matched in perceived intensity and varying only in perceived quality. The results showed clear evidence for the existence of individual odor spaces, but in apparent contradiction to related studies in the literature individual differences were too large to establish a representative odor space for the whole group. For nearly all individual subjects one of the factors extracted seemed to represent a unique hedonic dimension apparently unrelated to the physical attributes of the odorants. It is suggested that such psychological factors may be as important a basis for the judgment of the similarity of odors as the physical attributes of the odorants. Both the interpretation of multidimensional analysis and the extent to which the sense of smell is analytic or synthetic depend on an understanding of this problem.     

Subject differences in cross-modality matching

Forty-eight Ss performed four tasks each: (1) magnitude estimation of area, (2) magnitude estimation of numerousness, (3) cross-modality matching of force of handgrip to area, and (4) cross-modality matching of force of handgrip to numerousness. An additional 48 Ss performed Tasks 2 and 4. Psychophysical power functions were fitted to the data of each S for each condition. Higher correlations between individual exponents were found for conditions employing a common response (i.e., estimating or squeezing) than were found for conditions with the same set of stimuli. Individual differences among exponents stem more from the idiosyncratic use of the dependent variable than from different sensory characteristics.     

Odor intensity of mixed and unmixed stimuli under environmentally realistic conditions

Subjects judged the odor intensity of single odorants and binary mixtures of fixed or varying proportions presented in the atmosphere of an environmental chamber. The subjects were exposed to the vapors either continuously (15 min) or periodically (once a minute for 15 min). As found previously, the mixtures smelled less intense than predicted from the simple sum of their unmixed components. The degree of hypoadditivity proved about the same for the four pairs of odorants studied, but varied from periodic to continuous exposure. Periodic exposure led to a greater departure from simple additivity and confirmed the presence of the phenomenon of compromise whereby the mixture can smell less intense than its stronger component alone. Continuous exposure led to a closer approximation to simple additivity and exhibited no compromise. Nevertheless, the behavior seen under continuous exposure apparently derived from a tendency for mixtures to exhibit less adaptation than their components. Whereas mixtures may seem to lack potency relative to their unmixed components, they may in fact compensate for any deficiency in momentary intensity through an increase in durability.     

The nature and duration of adaptation following long-term odor exposure

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.     

Invariance of odor strength with sniff vigor: an olfactory analogue to size constancy

Previous evidence has shown that detection threshold in humans and olfactory neural discharge rate in animal preparations both depend on flow rate of odorous vapor. But no data have been reported that show the effects of flow rate in humans on perceived odor strength at suprathreshold intensities. Subjects learned to inspire at two flow rates, one twice as great as the other, by adjusting (on a cathode ray tube) the transduced trace of a sniff-produced pressure change to match either of two target contours. They then made magnitude estimations of odor strength, while producing either weak or strong sniffs, for odorants presented over a wide range of concentrations via a specially designed sniff-bottle system. The odorant, diluted in diethyl phthalate, was n-butanol in two experiments and n-amyl acetate in two others. Subject-controlled flow rate had no effect on odor strength for either odorant. There was an apparent contradiction between these data and those on neural discharge rate that may, however, be resolved by adopting an odor constancy model: When sniff intensity varies during the olfactory exploration of an odor source, information about the rate at which odorant molecules are established at the receptor site is combined with information about sniff vigor so that the resulting percept is of invariant odor strength.     

Odor intensity after self-adaptation and cross-adaptation

Psychophysical functions for the odor intensity of n-propanol and n-pentanol were obtained after no adaptation and after self-adaptation and cross-adaptation. Adaptation caused the psychophysical function to become steeper and generally concave downward in log-log coordinates. Increase in the in tensity of a: self-adapting stimulus produced relatively greater increases in the steepness of the functions than did increases in adapting duration. A comparison between the odorants revealed that propanol and pentanol have equal self-adapting effects when their respective adapting concentrations are matched for subjective intensity. Cross-adaptation had approximately the same effect as self-adaptation on the form of the psychophysical function, but a cross-adapting stimulus of a specified subjective intensity was less effective than a self-adapting stimulus of the same intensity. Adaptation to pentanol caused a larger reduction in the perceived intensity of propanol than adaptation to propanol caused in the perceived intensity of pentanol.