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Personality and Olfactory Sensitivity
JOURNAL OF RESEARCH IN PERSONALITY ARTICLE NO.
32, 510–518 (1998)
RP982228
BRIEF REPORT Personality and Olfactory Sensitivity Bettina M. Pause, Roman Ferstl, and Gabriele Fehm-Wolfsdorf Institute of Psychology, Christian-Albrechts-Universita¨t, University of Kiel, Kiel, Germany Even though perceptional abilities have repeatedly been found to be associated with certain personality styles (e.g., extraversion), such connections were reported sparsely for the olfactory modality. Two studies were carried out to investigate the relationship between olfactory sensitivity and 12 personality dimensions (including extraversion and neuroticism). In the first study, single olfactory measurements were compared to repeated measurements. In the second study, twins were recruited as subjects to also examine the heredity of olfactory sensitivity. The results indicate that neuroticism is a stronger predictor for olfactory sensitivity than extraversion. Repeated measurements seem to be necessary to obtain valid data on olfactory performance. 1998 Academic Press
Eysencks’ theory of personality (Eysenck & Eysenck, 1985) postulates a higher level of arousal in introverts than in extraverts due to differences in the activity of the reticular formation. His theory predicts that the higher cortical excitability in introverts leads to a facilitation of learning and perception. Therefore, introverts should show a higher sensory sensitivity and lower sensory thresholds than extraverts. Both assumptions have repeatedly been confirmed. By means of EEG (electroencephalography) and OR (orienting response) measures, it has been shown that introverts have a higher chronic level of arousal than extraverts (review in Revelle & Loftus, 1990) and that introverts seem to have an enhanced sensitivity to sensory stimulation (e.g., Stelmack & Michaud-Achorn, 1985). The relationship between the second personality dimension (neuroticism/emotionality) and perception is less clear. According to Eysenck (Eysenck & Eysenck, 1985), a high level of emotionality is associated with a high activation of the visceral brain (amygParts of the study were supported by a grant from the DFG to GF-W. We thank S. Ehlert and K.-O. Schulz for their technical assistance. Address correspondence and reprint requests to Dr. Bettina M. Pause, Institute of Psychology, University of Kiel, Olshausenstr. 62, 24098 Kiel, Germany. Fax: ⫹⫹ 49/431/8801559. E-mail: [email protected]. 510 0092-6566/98 $25.00
Copyright 1998 by Academic Press All rights of reproduction in any form reserved.
BRIEF REPORT
511
dala, hippocampus, septum, cingulum, and hypothalamus) and a greater responsiveness of the sympathetic nervous system. However, as activity in the visceral brain can produce cortical arousal, the two personality dimensions can be correlated, e.g., for highly emotional people. The relationship between personality and olfactory perception is far less elaborated than for other modalities (vision, audition, gustation, pain). In 1970, Koelega carried out three different experiments to examine the relationship between extraversion, neuroticism, and olfactory threshold. He investigated different odors (amyl acetate, exaltolide, muscone, butanol, dupical, musk), tested males and females separately, and took into account the time of the day. However, he unexpectedly found some positive correlations between olfactory sensitivity and extraversion. The correlations between neuroticism and odor perception varied around zero. A later study by the same author (Koelega, 1994) revealed similar results. The olfactory thresholds to five odors (amyl acetate, butanol, iso-valeric acid, exaltolide, musk) were not related to extraversion/introversion. A relationship with emotionality varied with gender and odor quality: emotionally labile women showed a greater sensitivity for butanol and emotionally stable men a greater sensitivity for iso-valeric acid. Another study (Filsinger, Fabes, & Hughston, 1987) examined different dimensions of olfactory perception (strength, familiarity, pleasantness) but again could not find a relatedness to the degree of extraversion. The authors argued instead that odor perception (androstenone, androstenol, exaltolide, pyridine) and extraversion/introversion might describe independent psychological functions. However, two studies could report a relationship between emotional (personality) styles and olfactory sensitivity. Rovee, Harris, and Yopp (1973) examined olfactory thresholds (octanol) in high and low anxiety (Taylor Manifest Anxiety Scale) females. According to Eysencks’ theory, anxiety correlates highly with emotionality and introversion but might be associated with a lower performance as the attentional distractibility is increased (Eysenck & Eysenck, 1985). Indeed, it could be shown that high anxiety females had significantly higher thresholds than low anxiety females. Herbener, Kagan, and Cohen (1989) investigated male subjects differing in the degree of shyness. The authors discussed shyness as highly related to introversion. In a meta-analysis of two studies, they could show that shy men have indeed lower olfactory thresholds for butanol. Regarding the incoherent results concerning the relationship between personality and olfactory perception, the aim of the present study was to examine this relationship by use of 12 different dimensions of personality. In the first study, we also wanted to investigate whether the strength of this relationship depends on the reliability of olfactory testing. We therefore measured the olfactory thresholds 13 times in each subject and used the first threshold value as well as the mean of all measures as an index for olfactory
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sensitivity. In the second study, we used twins as subjects in order to also examine whether olfactory sensitivity has a genetic basis (review in Segal & Topolski, 1995). Olfactory sensitivity was assessed with four odors: androstenone (boar pheromone), citral (citrus), isoamylacetate (pear, banana), and linalool (lavender). METHOD Participants Twelve male subjects (age: 20–30) participated in study I. For study II, 30 twin pairs (30 MZ and 30 DZ subjects, 37 females) were recruited. However, due to technical reasons (see below), only the data from the first 26 twins (13 pairs) could be used for the personality analyses. The final subject group (age: 21–64) for study II included 18 females. All subjects were screened for an acute or chronic sickness of the respiratory system. All of them gave their written consent and were paid for participation.
Measures Olfactory thresholds. Olfactory thresholds were determined separately for linalool (⫹/⫺ linalool, 97%, Aldrich; Study I), androstenone (5-α-androst-16-en-3-one, 98%, Aldrich; Study II), citral (cis and trans, 97%, Fluka; Study II), and isoamylacetate (98%, Aldrich; Study II). For each odor, 14 concentration steps were prepared. Androstenone and linalool were diluted in 1,2-propanediol (99%, Merck) and citral and isoamylacetate were diluted in diethyl phthalate (98%, Fluka). The fluid odors (citral, linalool, and isoamylacetate) were diluted in half decimal log steps, beginning with an 1:2 dilution (v/v). The highest concentration of androstenone was 1.25 mg/ml and was diluted twofold for each consecutive concentration. Thresholds were measured according to a three-alternative forced-choice staircase detection threshold procedure. In each trial, subjects were presented with three bottles, one of which contained the odorant and the other two an identical volume (6.5 ml) of solvent (propanediol for androstenone and linalool, diethyl phthalate for citral and isoamylacetate). Subjects were forced to choose which bottle contained the odorant but were not given any feedback about their decision. First, an ascending series of concentration was presented with three dilution steps between two consecutive trials. When a correct trial occurred, the staircase was reversed (descending staircase) and every dilution step was presented. As soon as the subject did not correctly detect the odor, higher concentrations were again presented within an ascending series. The threshold was defined as the lower of two consecutive concentrations for which four successive correct detections were obtained (error probability for a false positive result ⫽ 1%). Due to the inherent difficulty in the recruitment of twins in study II, a 6-month break was necessary to call for further subjects. Before the break, 13 twin pairs were already tested. However, after the break, most of the subjects could detect the lowest concentration of all odor dilutions. It was therefore concluded that the quality and/or quantity of the odor dilutions changed in time and all data obtained after the break had to be rejected from the personality analyses. Personality inventory. All subjects completed a German personality questionnaire (Freiburger Personality Inventory, FPI-R; Fahrenberg, Hampel, & Selg, 1989). The FPI-R consists of 138 items, belonging to 10 subscales (satisfaction of life, social orientation, achievement orientation, shyness, excitement, aggressivity, strain, physical complaints, health concerns, honesty) and two additional scales (extraversion and emotionality). The items of the additional scales (14 items each) are partly overlapping the items of the 10 subscales (12 items each).
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TABLE 1 Relationship between Personality Traits a and Olfactory Sensitivity: Correlation Coefficients (r) b and Multiple Regression Analyses (R 2) Odors Study I
r(N scale)
r(E scale)
R 2(E/N scales)
R 2(scales 1–10)
0.000 F(2,9) ⫽ 0.00 0.375 F(2,9) ⫽ 2.70
0.999* F(10,1) ⫽ 1086 0.978 F(10,1) ⫽ 4.44
0.007 F(2,21) ⫽ 0.07 0.051 F(2,21) ⫽ 0.56 0.174 F(2,21) ⫽ 2.22
0.427 F(10,13) ⫽ 0.97 0.499 F(10,13) ⫽ 1.29 0.700* F(10,13) ⫽ 3.04
Linalool: measure 1
⫺.002
⫹.019
Linalool: measures 1–13
⫹.599*
⫺.308
Androstenone
⫺.082
⫺.005
Citral
⫺.024
Isoamylacetate
⫹.385
Study II
⫺.218 ⫹
⫺.220
Note. Study I: N ⫽ 12; Study II: N ⫽ 26. a Personality traits according to the ‘‘Freiburger Personality Inventory’’ with 10 subscales and the additional scales E (extraversion) and N (emotionality). b Correlation coefficients (r) were tested two-tailed. ⫹ p ⬍ .10, *p ⬍ .05.
Procedure In study I, the olfactory thresholds for linalool were determined 13 times for each subject. Thresholds were examined monorhinally every 30 min and two 1-hour breaks were included. In study II, five threshold values were determined: the thresholds for citral and isoamylacetate were tested for each nostril separately and the thresholds for androstenone birhinally. For the following calculations, the value of the most sensitive nostril was taken as a predictor for the general olfactory sensitivity (according to Hornung, Leopold, Mozell, Sheehe, & Youngentob, 1990). The order of the odor presentation in study II was always: citral, androstenone, isoamylacetate.
RESULTS To analyze the relationship between personality traits and olfactory sensitivity, correlations and regressions were carried out by SPSS (see Table 1). Two regression analyses were computed for each odor: in the first calculation, the subscales 1 to 10 were used as predictors for the olfactory sensitivity and, in the second calculation, the additional scales extraversion and emotionality served as predictors. Moreover, we used two different measures to assess the sensitivity to linalool. Once only the first threshold measurement was used as indicator for the olfactory sensitivity and once the mean threshold from the 13 measurements was used to describe the sensitivity. In addition to the regression analyses, correlations (Pearson correlations) were calculated between either extraversion or emotionality and the olfactory threshold. Based on repeated olfactory measures, emotionality (N scale) was significantly correlated with the sensitivity to linalool (p ⫽ .039). However, when
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FIG. 1. Raw data plot (Study I). Linalool dilution steps (a higher dilution step indicates a higher olfactory sensitivity) and neuroticsm scores. Top: single threshold measurements, r ⫽ ⫺.002. Bottom: mean thresholds of 13 measurements, r ⫽ ⫹.0599.
the olfactory threshold was measured only once, this correlation was absent (see Fig. 1). A similar tendency ( p ⫽ .063) could be found for isoamylacetate: a high value in emotionality was again correlated with a high olfactory sensitivity (see Fig. 2). However, emotionality (E scale) was not correlated with the sensitivity to androstenone or citral. Even though medium negative correlations between extraversion and olfactory sensitivity were obtained for citral, isoamylacetate, and linalool, they were not significant. Moreover, emotionality alone (r (N scale)) was a better predictor for the olfactory sensitivity (linalool and isoamylacetate) than a combination of emotionality and extraversion (R (E/N scale)). The 10 personality subscales served as a significant predictor for the single measurement of the sensitivity to linalool (R 2 ⫽ 0.999, p ⫽ .024). The best predictors (.01 ⬍ p(t) ⬍ .02) were ‘‘physical complaints’’ (β ⫽ ⫺1.52), ‘‘satisfaction of life’’ (β ⫽ ⫺1.42), and ‘‘shyness’’ (β ⫽ ⫺0.84). The negative values indicate that a higher score in these personality traits was correlated with a lower sensitivity. This interpretation is supported by the fact
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FIG. 2. Raw data plot (Study II). Isoamylacetate dilution steps (a higher dilution step indicates a higher olfactory sensitivity) and personality styles. Top: Extraversion, r ⫽ ⫺.220. Bottom: Neuroticsm, r ⫽ ⫹.385.
that these three scales also had negative single correlations with the criterion. However, when the mean threshold value was used as indicator of the sensitivity to linalool the predictive value (R 2) of the 10 subscales was not significant and neither were the single β-weights. While the sensitivity to androstenone and citral could not be predicted by the 10 personality scales, they could explain the sensitivity to isoamylacetate (R 2 ⫽ 0.700, p ⫽ .032). According to the β-weights the best predictors (.01 ⬍ p(t) ⬍ .03) were ‘‘honesty’’ (β ⫽ ⫺0.84), ‘‘excitement’’ (β ⫽ ⫺0.63), and ‘‘social orientation’’ (β ⫽ ⫹0.52). However, as ‘‘excitement’’ had a positive single correlation with the sensitivity to isoamylacetate, the negativity of the β-weight is difficult to interpret. To determine whether the olfactory sensitivity is genetically determined, correlations (intraclass) were carried out between monozygotic and dizygotic twins (Study II; these analyses were carried out on basis of all 60 subjects to receive a sufficient subject sample per twin group). While the ability to detect citral was not correlated between the twins (r(MZ) ⫽ ⫹.001, r(DZ) ⫽ ⫺.084), the correlations between monozygotic twins for androsten-
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one (r(MZ) ⫽ ⫹.248, r(DZ) ⫽ ⫹.094), and isoamylacetate (r(MZ) ⫽ ⫹.401, r(DZ) ⫽ ⫹.219) were slightly higher than for dizygotic twins. However, the correlations (Fisher-Z transformed) for monozygotic and dizygotic twins were not significantly different. DISCUSSION The results of the present study reveal a positive relationship between olfactory sensitivity and emotionality (neuroticsm) and a negative relationship between olfactory sensitivity and extraversion. However, significant results could only be found for the emotionality dimension. Concerning to Eysencks’ theory, it is somewhat surprising that the neuroticism dimension is closer related to olfactory thresholds than the extraversion dimension (see introduction). However, Eysenck proposed that people scoring high in emotionality show a higher activation of the limbic system. Different personality styles due to different reactivities in special brain systems have also been suggested by Gray (1994). Anxious people might, for example, show a higher reactivity of the BIS (Behavioral Inhibition System), which includes the hippocampal formation, the septal area, and the Papez circuit (Gray, 1990). As the primary olfactory information processing involves parts of the limbic system (e.g., the entorhinal cortex and the amygdala), it would not be surprising that emotionally highly reactive subjects also show a better olfactory performance. The strong connection between odor processing and the emotional stimulus significance within the amygdala has recently been shown by measures of the cerebral blood flow (Zald & Pardo, 1997). The results of our first study underline the importance of repeated measurement in olfaction. After the first threshold measurement, only zero order correlations between Eysencks’ personality dimensions and the olfactory sensitivity could be observed. Instead, the mean of 13 measurements (all obtained on the same day) showed that olfactory sensitivity is related to the degree of emotionality. Even though introversion and olfactory sensitivity correlated relatively high, the correlation was not significant due to the small sample size. Stevens, Cain, and Burke (1988) already pointed to the fact that intraindividual olfactory threshold measurements show an extreme variability which is similar to the interindividual variability. Regarding the present results, it seems that the validity of olfactory threshold testing can be substantially enlarged by repeated measurements. As repeated measurements might be very time consuming, the implementation of new olfactory methods could be an alternative approach. Pause, Sojka, Krauel, Fehm-Wolfsdorf, and Ferstl (1996) found that chemosensory event-related potentials reflect olfactory functions far more sensitive than the classical threshold tests. In our second study, the sensitivity to isoamylacetate showed the highest correlation with the degree of emotionality. Isoamylacetate was always the third odor tested; therefore, the subjects were able to practice their sniffing
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technique and adjust to the test requirements. Other olfactory threshold measurements (Doty, 1991) already take into account that subjects need a sufficient practice time and only those data are used for threshold calculations which are obtained after the subjects became acquainted with the testing procedure. The absence of a relationship between personality and androstenone perception confirms the results of Filsinger et al. (1987). As androstenone is discussed to be a human pheromone (Grammer, 1993), other biological markers such as gender or hormonal status might be more potent in explaining the sensitivity to androstenone than are personality styles. Moreover, the ability to perceive androstenone might be genetically determined (Wysocki & Beauchamp, 1984; Gross-Isseroff, Ophir, Bartana, Voet, & Lancet, 1992). The present twin study also showed a higher correlation for androstenone perception in monozygotic than dizygotic twins. However, the ceiling-effects in the second part of the olfactory measurements in study II might have been caused the lack of statistical significance. The 10 personality subscales of the ‘‘Freiburger Personality Inventory’’ could not reliably explain olfactory sensitivity. The predictors found for linalool (physical complaints, satisfaction of life, shyness) explained neither the sensitivity to other odors nor to linalool when repeated measurements were carried out. Also, the personality styles which could best explain the sensitivity to isoamylacetate (honesty, excitement, social orientation) did not explain olfactory sensitivity to other odors. Summarizing our results, it seems to be important not only to use repeated measurements but also to test different odors. Single threshold measurements of single odors might coincidentally produce accidental results. REFERENCES Doty, R. L. (1991). Olfactory system. In T. V. Getchell, R. L. Doty, L. M. Bartoshuk, & J. B. Snow (Eds.), Smell and taste in health and disease (pp. 175–203). New York: Raven Press. Eysenck, H. J., & Eysenck, M. W. (1985). Personality and individual differences. New York: Plenum Press. Fahrenberg, J., Hampel, R., & Selg, H. (1989). Das Freiburger Perso¨nlichkeitsinventar. Germany: Go¨ttingen, Hogrefe. Filsinger, E. E., Fabes, R. A., & Hughston, G. (1987). Introversion–extraversion and dimensions of olfactory perception. Perceptual and Motor Skills, 64, 695–699. Grammer, K. (1993). 5-α-androst-16-en-3-one: A male pheromone? A brief report. Ethology and Sociobiology, 14, 201–208. Gray, J. A. (1990). Brain systems that mediate both emotion and cognition. Cognition and Emotion, 4, 269–288. Gray, J. A. (1994). Personality dimensions and emotion systems. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion (pp. 329–331). New York: Oxford Univ. Press. Gross-Isseroff, R., Ophir, D., Bartana, A., Voet, H., & Lancet, D. (1992). Evidence for genetic
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determination in human twins of olfactory thresholds for a standard odorant. Neuroscience Letters, 141, 115–118. Herbener, E. S., Kagan, J., & Cohen, M. (1989). Shyness and olfactory threshold. Personality and Individual Differences, 10, 1159–1163. Hornung, D. E., Leopold, D. A., Mozell, M. M., Sheehe, P. R., & Youngentob, S. L. (1990). Impact of left and right nostril abilities on binasal olfactory performance. Chemical Senses, 15, 233–237. Koelega, H. S. (1970). Extraversion, sex, arousal and olfactory sensitivity. Acta Psychologica, 34, 51–66. Koelega, H. S. (1994). Sex differences in olfactory sensitivity and the problem of the generality of smell acuity. Perceptual and Motor Skills, 78, 203–213. Pause, B. M., Sojka, B., Krauel, K., Fehm-Wolfsdorf, G., & Ferstl, R. (1996). Olfactory information processing during the course of the menstrual cycle. Biological Psychology, 44, 31–54. Revelle, W., & Loftus, D. A. (1990). Individual differences and arousal: Implications for the study of mood and memory. Cognition and Emotion, 4, 209–237. Rovee, C. K., Harris, S. L., & Yopp, R. (1973). Olfactory thresholds and level of anxiety. Bulletin of the Psychonomic Society, 2, 76–78. Segal, N. L., & Topolski, T. D. (1995). The genetics of olfactory perception. In R. L. Doty (Ed.), Handbook of olfaction and gustation (pp. 323–343). New York: Marcel Dekker. Stelmack, R. M., & Michaud-Achorn, A. (1985). Extraversion, attention, and habituation of the auditory evoked response. Journal of Research in Personality, 19, 416–428. Stevens, J. C., Cain, W. S., & Burke, R. J. (1988). Variability of olfactory thresholds. Chemical Senses, 13, 643–653. Wysocki, C. J., & Beauchamp, G. K. (1984). Ability to smell androstenone is genetically determined. Proceedings of the National Academy of Science USA, 81, 4899–4902. Zald, D. H., & Pardo, J. V. (1997). Emotion, olfaction, and the human amygdala: Amygdala activation during aversive olfactory stimulation. Proceedings of the National Academy of Science USA, 94, 4119–4124.
32, 510–518 (1998)
RP982228
BRIEF REPORT Personality and Olfactory Sensitivity Bettina M. Pause, Roman Ferstl, and Gabriele Fehm-Wolfsdorf Institute of Psychology, Christian-Albrechts-Universita¨t, University of Kiel, Kiel, Germany Even though perceptional abilities have repeatedly been found to be associated with certain personality styles (e.g., extraversion), such connections were reported sparsely for the olfactory modality. Two studies were carried out to investigate the relationship between olfactory sensitivity and 12 personality dimensions (including extraversion and neuroticism). In the first study, single olfactory measurements were compared to repeated measurements. In the second study, twins were recruited as subjects to also examine the heredity of olfactory sensitivity. The results indicate that neuroticism is a stronger predictor for olfactory sensitivity than extraversion. Repeated measurements seem to be necessary to obtain valid data on olfactory performance. 1998 Academic Press
Eysencks’ theory of personality (Eysenck & Eysenck, 1985) postulates a higher level of arousal in introverts than in extraverts due to differences in the activity of the reticular formation. His theory predicts that the higher cortical excitability in introverts leads to a facilitation of learning and perception. Therefore, introverts should show a higher sensory sensitivity and lower sensory thresholds than extraverts. Both assumptions have repeatedly been confirmed. By means of EEG (electroencephalography) and OR (orienting response) measures, it has been shown that introverts have a higher chronic level of arousal than extraverts (review in Revelle & Loftus, 1990) and that introverts seem to have an enhanced sensitivity to sensory stimulation (e.g., Stelmack & Michaud-Achorn, 1985). The relationship between the second personality dimension (neuroticism/emotionality) and perception is less clear. According to Eysenck (Eysenck & Eysenck, 1985), a high level of emotionality is associated with a high activation of the visceral brain (amygParts of the study were supported by a grant from the DFG to GF-W. We thank S. Ehlert and K.-O. Schulz for their technical assistance. Address correspondence and reprint requests to Dr. Bettina M. Pause, Institute of Psychology, University of Kiel, Olshausenstr. 62, 24098 Kiel, Germany. Fax: ⫹⫹ 49/431/8801559. E-mail: [email protected]. 510 0092-6566/98 $25.00
Copyright 1998 by Academic Press All rights of reproduction in any form reserved.
BRIEF REPORT
511
dala, hippocampus, septum, cingulum, and hypothalamus) and a greater responsiveness of the sympathetic nervous system. However, as activity in the visceral brain can produce cortical arousal, the two personality dimensions can be correlated, e.g., for highly emotional people. The relationship between personality and olfactory perception is far less elaborated than for other modalities (vision, audition, gustation, pain). In 1970, Koelega carried out three different experiments to examine the relationship between extraversion, neuroticism, and olfactory threshold. He investigated different odors (amyl acetate, exaltolide, muscone, butanol, dupical, musk), tested males and females separately, and took into account the time of the day. However, he unexpectedly found some positive correlations between olfactory sensitivity and extraversion. The correlations between neuroticism and odor perception varied around zero. A later study by the same author (Koelega, 1994) revealed similar results. The olfactory thresholds to five odors (amyl acetate, butanol, iso-valeric acid, exaltolide, musk) were not related to extraversion/introversion. A relationship with emotionality varied with gender and odor quality: emotionally labile women showed a greater sensitivity for butanol and emotionally stable men a greater sensitivity for iso-valeric acid. Another study (Filsinger, Fabes, & Hughston, 1987) examined different dimensions of olfactory perception (strength, familiarity, pleasantness) but again could not find a relatedness to the degree of extraversion. The authors argued instead that odor perception (androstenone, androstenol, exaltolide, pyridine) and extraversion/introversion might describe independent psychological functions. However, two studies could report a relationship between emotional (personality) styles and olfactory sensitivity. Rovee, Harris, and Yopp (1973) examined olfactory thresholds (octanol) in high and low anxiety (Taylor Manifest Anxiety Scale) females. According to Eysencks’ theory, anxiety correlates highly with emotionality and introversion but might be associated with a lower performance as the attentional distractibility is increased (Eysenck & Eysenck, 1985). Indeed, it could be shown that high anxiety females had significantly higher thresholds than low anxiety females. Herbener, Kagan, and Cohen (1989) investigated male subjects differing in the degree of shyness. The authors discussed shyness as highly related to introversion. In a meta-analysis of two studies, they could show that shy men have indeed lower olfactory thresholds for butanol. Regarding the incoherent results concerning the relationship between personality and olfactory perception, the aim of the present study was to examine this relationship by use of 12 different dimensions of personality. In the first study, we also wanted to investigate whether the strength of this relationship depends on the reliability of olfactory testing. We therefore measured the olfactory thresholds 13 times in each subject and used the first threshold value as well as the mean of all measures as an index for olfactory
512
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sensitivity. In the second study, we used twins as subjects in order to also examine whether olfactory sensitivity has a genetic basis (review in Segal & Topolski, 1995). Olfactory sensitivity was assessed with four odors: androstenone (boar pheromone), citral (citrus), isoamylacetate (pear, banana), and linalool (lavender). METHOD Participants Twelve male subjects (age: 20–30) participated in study I. For study II, 30 twin pairs (30 MZ and 30 DZ subjects, 37 females) were recruited. However, due to technical reasons (see below), only the data from the first 26 twins (13 pairs) could be used for the personality analyses. The final subject group (age: 21–64) for study II included 18 females. All subjects were screened for an acute or chronic sickness of the respiratory system. All of them gave their written consent and were paid for participation.
Measures Olfactory thresholds. Olfactory thresholds were determined separately for linalool (⫹/⫺ linalool, 97%, Aldrich; Study I), androstenone (5-α-androst-16-en-3-one, 98%, Aldrich; Study II), citral (cis and trans, 97%, Fluka; Study II), and isoamylacetate (98%, Aldrich; Study II). For each odor, 14 concentration steps were prepared. Androstenone and linalool were diluted in 1,2-propanediol (99%, Merck) and citral and isoamylacetate were diluted in diethyl phthalate (98%, Fluka). The fluid odors (citral, linalool, and isoamylacetate) were diluted in half decimal log steps, beginning with an 1:2 dilution (v/v). The highest concentration of androstenone was 1.25 mg/ml and was diluted twofold for each consecutive concentration. Thresholds were measured according to a three-alternative forced-choice staircase detection threshold procedure. In each trial, subjects were presented with three bottles, one of which contained the odorant and the other two an identical volume (6.5 ml) of solvent (propanediol for androstenone and linalool, diethyl phthalate for citral and isoamylacetate). Subjects were forced to choose which bottle contained the odorant but were not given any feedback about their decision. First, an ascending series of concentration was presented with three dilution steps between two consecutive trials. When a correct trial occurred, the staircase was reversed (descending staircase) and every dilution step was presented. As soon as the subject did not correctly detect the odor, higher concentrations were again presented within an ascending series. The threshold was defined as the lower of two consecutive concentrations for which four successive correct detections were obtained (error probability for a false positive result ⫽ 1%). Due to the inherent difficulty in the recruitment of twins in study II, a 6-month break was necessary to call for further subjects. Before the break, 13 twin pairs were already tested. However, after the break, most of the subjects could detect the lowest concentration of all odor dilutions. It was therefore concluded that the quality and/or quantity of the odor dilutions changed in time and all data obtained after the break had to be rejected from the personality analyses. Personality inventory. All subjects completed a German personality questionnaire (Freiburger Personality Inventory, FPI-R; Fahrenberg, Hampel, & Selg, 1989). The FPI-R consists of 138 items, belonging to 10 subscales (satisfaction of life, social orientation, achievement orientation, shyness, excitement, aggressivity, strain, physical complaints, health concerns, honesty) and two additional scales (extraversion and emotionality). The items of the additional scales (14 items each) are partly overlapping the items of the 10 subscales (12 items each).
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TABLE 1 Relationship between Personality Traits a and Olfactory Sensitivity: Correlation Coefficients (r) b and Multiple Regression Analyses (R 2) Odors Study I
r(N scale)
r(E scale)
R 2(E/N scales)
R 2(scales 1–10)
0.000 F(2,9) ⫽ 0.00 0.375 F(2,9) ⫽ 2.70
0.999* F(10,1) ⫽ 1086 0.978 F(10,1) ⫽ 4.44
0.007 F(2,21) ⫽ 0.07 0.051 F(2,21) ⫽ 0.56 0.174 F(2,21) ⫽ 2.22
0.427 F(10,13) ⫽ 0.97 0.499 F(10,13) ⫽ 1.29 0.700* F(10,13) ⫽ 3.04
Linalool: measure 1
⫺.002
⫹.019
Linalool: measures 1–13
⫹.599*
⫺.308
Androstenone
⫺.082
⫺.005
Citral
⫺.024
Isoamylacetate
⫹.385
Study II
⫺.218 ⫹
⫺.220
Note. Study I: N ⫽ 12; Study II: N ⫽ 26. a Personality traits according to the ‘‘Freiburger Personality Inventory’’ with 10 subscales and the additional scales E (extraversion) and N (emotionality). b Correlation coefficients (r) were tested two-tailed. ⫹ p ⬍ .10, *p ⬍ .05.
Procedure In study I, the olfactory thresholds for linalool were determined 13 times for each subject. Thresholds were examined monorhinally every 30 min and two 1-hour breaks were included. In study II, five threshold values were determined: the thresholds for citral and isoamylacetate were tested for each nostril separately and the thresholds for androstenone birhinally. For the following calculations, the value of the most sensitive nostril was taken as a predictor for the general olfactory sensitivity (according to Hornung, Leopold, Mozell, Sheehe, & Youngentob, 1990). The order of the odor presentation in study II was always: citral, androstenone, isoamylacetate.
RESULTS To analyze the relationship between personality traits and olfactory sensitivity, correlations and regressions were carried out by SPSS (see Table 1). Two regression analyses were computed for each odor: in the first calculation, the subscales 1 to 10 were used as predictors for the olfactory sensitivity and, in the second calculation, the additional scales extraversion and emotionality served as predictors. Moreover, we used two different measures to assess the sensitivity to linalool. Once only the first threshold measurement was used as indicator for the olfactory sensitivity and once the mean threshold from the 13 measurements was used to describe the sensitivity. In addition to the regression analyses, correlations (Pearson correlations) were calculated between either extraversion or emotionality and the olfactory threshold. Based on repeated olfactory measures, emotionality (N scale) was significantly correlated with the sensitivity to linalool (p ⫽ .039). However, when
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FIG. 1. Raw data plot (Study I). Linalool dilution steps (a higher dilution step indicates a higher olfactory sensitivity) and neuroticsm scores. Top: single threshold measurements, r ⫽ ⫺.002. Bottom: mean thresholds of 13 measurements, r ⫽ ⫹.0599.
the olfactory threshold was measured only once, this correlation was absent (see Fig. 1). A similar tendency ( p ⫽ .063) could be found for isoamylacetate: a high value in emotionality was again correlated with a high olfactory sensitivity (see Fig. 2). However, emotionality (E scale) was not correlated with the sensitivity to androstenone or citral. Even though medium negative correlations between extraversion and olfactory sensitivity were obtained for citral, isoamylacetate, and linalool, they were not significant. Moreover, emotionality alone (r (N scale)) was a better predictor for the olfactory sensitivity (linalool and isoamylacetate) than a combination of emotionality and extraversion (R (E/N scale)). The 10 personality subscales served as a significant predictor for the single measurement of the sensitivity to linalool (R 2 ⫽ 0.999, p ⫽ .024). The best predictors (.01 ⬍ p(t) ⬍ .02) were ‘‘physical complaints’’ (β ⫽ ⫺1.52), ‘‘satisfaction of life’’ (β ⫽ ⫺1.42), and ‘‘shyness’’ (β ⫽ ⫺0.84). The negative values indicate that a higher score in these personality traits was correlated with a lower sensitivity. This interpretation is supported by the fact
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FIG. 2. Raw data plot (Study II). Isoamylacetate dilution steps (a higher dilution step indicates a higher olfactory sensitivity) and personality styles. Top: Extraversion, r ⫽ ⫺.220. Bottom: Neuroticsm, r ⫽ ⫹.385.
that these three scales also had negative single correlations with the criterion. However, when the mean threshold value was used as indicator of the sensitivity to linalool the predictive value (R 2) of the 10 subscales was not significant and neither were the single β-weights. While the sensitivity to androstenone and citral could not be predicted by the 10 personality scales, they could explain the sensitivity to isoamylacetate (R 2 ⫽ 0.700, p ⫽ .032). According to the β-weights the best predictors (.01 ⬍ p(t) ⬍ .03) were ‘‘honesty’’ (β ⫽ ⫺0.84), ‘‘excitement’’ (β ⫽ ⫺0.63), and ‘‘social orientation’’ (β ⫽ ⫹0.52). However, as ‘‘excitement’’ had a positive single correlation with the sensitivity to isoamylacetate, the negativity of the β-weight is difficult to interpret. To determine whether the olfactory sensitivity is genetically determined, correlations (intraclass) were carried out between monozygotic and dizygotic twins (Study II; these analyses were carried out on basis of all 60 subjects to receive a sufficient subject sample per twin group). While the ability to detect citral was not correlated between the twins (r(MZ) ⫽ ⫹.001, r(DZ) ⫽ ⫺.084), the correlations between monozygotic twins for androsten-
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one (r(MZ) ⫽ ⫹.248, r(DZ) ⫽ ⫹.094), and isoamylacetate (r(MZ) ⫽ ⫹.401, r(DZ) ⫽ ⫹.219) were slightly higher than for dizygotic twins. However, the correlations (Fisher-Z transformed) for monozygotic and dizygotic twins were not significantly different. DISCUSSION The results of the present study reveal a positive relationship between olfactory sensitivity and emotionality (neuroticsm) and a negative relationship between olfactory sensitivity and extraversion. However, significant results could only be found for the emotionality dimension. Concerning to Eysencks’ theory, it is somewhat surprising that the neuroticism dimension is closer related to olfactory thresholds than the extraversion dimension (see introduction). However, Eysenck proposed that people scoring high in emotionality show a higher activation of the limbic system. Different personality styles due to different reactivities in special brain systems have also been suggested by Gray (1994). Anxious people might, for example, show a higher reactivity of the BIS (Behavioral Inhibition System), which includes the hippocampal formation, the septal area, and the Papez circuit (Gray, 1990). As the primary olfactory information processing involves parts of the limbic system (e.g., the entorhinal cortex and the amygdala), it would not be surprising that emotionally highly reactive subjects also show a better olfactory performance. The strong connection between odor processing and the emotional stimulus significance within the amygdala has recently been shown by measures of the cerebral blood flow (Zald & Pardo, 1997). The results of our first study underline the importance of repeated measurement in olfaction. After the first threshold measurement, only zero order correlations between Eysencks’ personality dimensions and the olfactory sensitivity could be observed. Instead, the mean of 13 measurements (all obtained on the same day) showed that olfactory sensitivity is related to the degree of emotionality. Even though introversion and olfactory sensitivity correlated relatively high, the correlation was not significant due to the small sample size. Stevens, Cain, and Burke (1988) already pointed to the fact that intraindividual olfactory threshold measurements show an extreme variability which is similar to the interindividual variability. Regarding the present results, it seems that the validity of olfactory threshold testing can be substantially enlarged by repeated measurements. As repeated measurements might be very time consuming, the implementation of new olfactory methods could be an alternative approach. Pause, Sojka, Krauel, Fehm-Wolfsdorf, and Ferstl (1996) found that chemosensory event-related potentials reflect olfactory functions far more sensitive than the classical threshold tests. In our second study, the sensitivity to isoamylacetate showed the highest correlation with the degree of emotionality. Isoamylacetate was always the third odor tested; therefore, the subjects were able to practice their sniffing
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technique and adjust to the test requirements. Other olfactory threshold measurements (Doty, 1991) already take into account that subjects need a sufficient practice time and only those data are used for threshold calculations which are obtained after the subjects became acquainted with the testing procedure. The absence of a relationship between personality and androstenone perception confirms the results of Filsinger et al. (1987). As androstenone is discussed to be a human pheromone (Grammer, 1993), other biological markers such as gender or hormonal status might be more potent in explaining the sensitivity to androstenone than are personality styles. Moreover, the ability to perceive androstenone might be genetically determined (Wysocki & Beauchamp, 1984; Gross-Isseroff, Ophir, Bartana, Voet, & Lancet, 1992). The present twin study also showed a higher correlation for androstenone perception in monozygotic than dizygotic twins. However, the ceiling-effects in the second part of the olfactory measurements in study II might have been caused the lack of statistical significance. The 10 personality subscales of the ‘‘Freiburger Personality Inventory’’ could not reliably explain olfactory sensitivity. The predictors found for linalool (physical complaints, satisfaction of life, shyness) explained neither the sensitivity to other odors nor to linalool when repeated measurements were carried out. Also, the personality styles which could best explain the sensitivity to isoamylacetate (honesty, excitement, social orientation) did not explain olfactory sensitivity to other odors. Summarizing our results, it seems to be important not only to use repeated measurements but also to test different odors. Single threshold measurements of single odors might coincidentally produce accidental results. REFERENCES Doty, R. L. (1991). Olfactory system. In T. V. Getchell, R. L. Doty, L. M. Bartoshuk, & J. B. Snow (Eds.), Smell and taste in health and disease (pp. 175–203). New York: Raven Press. Eysenck, H. J., & Eysenck, M. W. (1985). Personality and individual differences. New York: Plenum Press. Fahrenberg, J., Hampel, R., & Selg, H. (1989). Das Freiburger Perso¨nlichkeitsinventar. Germany: Go¨ttingen, Hogrefe. Filsinger, E. E., Fabes, R. A., & Hughston, G. (1987). Introversion–extraversion and dimensions of olfactory perception. Perceptual and Motor Skills, 64, 695–699. Grammer, K. (1993). 5-α-androst-16-en-3-one: A male pheromone? A brief report. Ethology and Sociobiology, 14, 201–208. Gray, J. A. (1990). Brain systems that mediate both emotion and cognition. Cognition and Emotion, 4, 269–288. Gray, J. A. (1994). Personality dimensions and emotion systems. In P. Ekman & R. J. Davidson (Eds.), The nature of emotion (pp. 329–331). New York: Oxford Univ. Press. Gross-Isseroff, R., Ophir, D., Bartana, A., Voet, H., & Lancet, D. (1992). Evidence for genetic
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