Experimental Brain Research

, Volume 222, Issue 1–2, pp 89–97 | Cite as

Influence of background noise on the performance in the odor sensitivity task: effects of noise type and extraversion

  • Han-Seok Seo
  • Antje Hähner
  • Volker Gudziol
  • Mandy Scheibe
  • Thomas Hummel
Research Article

Abstract

Recent research demonstrated that background noise relative to silence impaired subjects’ performance in a cognitively driven odor discrimination test. The current study aimed to investigate whether the background noise can also modulate performance in an odor sensitivity task that is less cognitively loaded. Previous studies have shown that the effect of background noise on task performance can be different in relation to degree of extraversion and/or type of noise. Accordingly, we wanted to examine whether the influence of background noise on the odor sensitivity task can be altered as a function of the type of background noise (i.e., nonverbal vs. verbal noise) and the degree of extraversion (i.e., introvert vs. extrovert group). Subjects were asked to conduct an odor sensitivity task in the presence of either nonverbal noise (e.g., party sound) or verbal noise (e.g., audio book), or silence. Overall, the subjects’ mean performance in the odor sensitivity task was not significantly different across three auditory conditions. However, with regard to the odor sensitivity task, a significant interaction emerged between the type of background noise and the degree of extraversion. Specifically, verbal noise relative to silence significantly impaired or improved the performance of the odor sensitivity task in the introvert or extrovert group, respectively; the differential effect of introversion/extraversion was not observed in the nonverbal noise-induced task performance. In conclusion, our findings provide new empirical evidence that type of background noise and degree of extraversion play an important role in modulating the effect of background noise on subjects’ performance in an odor sensitivity task.

Keywords

Auditory–olfactory integration Background noise Eysenck Personality Questionnaire Introversion/extraversion Odor sensitivity task Verbal noise 

Introduction

There is growing interest in exploring cross-modal links between auditory and olfactory cues (Belkin et al. 1997; Spence and Shankar 2010; Wesson and Wilson 2010; Seo and Hummel 2011; Seo et al. 2011). A “congruency” between auditory and olfactory cues appears to modulate the auditory–olfactory integration. Specifically, compared with incongruent sounds, congruent sounds can increase pleasantness ratings of subsequently presented odors (Seo and Hummel 2011).

However, we frequently experience odors in the presence of background sound unrelated to the odors; for instance, at restaurant, people smell food odors while hearing background music or listening to patrons’ conversation. The current study attempted to focus on the influences of background sound on an odor perception. Only a few studies have reported the modulatory effect of background sound on an olfactory performance (Seo and Hummel 2011; Seo et al. 2011). Recently, Seo et al. (2011) examined whether background noise alters subjects’ performance in an odor discrimination task. Subjects were asked to select which of three pens were different (with two containing the same and one containing a different odorant) in either noisy or silent condition. Subjects’ performance in the odor discrimination task was impaired in the presence of background noise than in silence. Considering that the odor discrimination task is highly dependent on cognitive ability and education level (Boesveldt et al. 2008; Hedner et al. 2010), the noise-induced deteriorated performance seemed to be mediated by the interruption of cognitive processes required to perform the task (Seo et al. 2011). In fact, many studies have demonstrated that background noise significantly lessens the proficiency of cognitive process such as recall, memory, or reading comprehension in the tasks mainly associated with the visual and/or the motor system (LeCompte et al. 1997; Furnham and Bradley 1997; Furnham and Allass 1999; Furnham and Strbac 2002; Cassidy and MacDonald 2007).

Following the previous research (Seo et al. 2011), a present study was set out to determine whether the background noise can modulate subjects’ performance in the olfactory task, which is less dependent on the cognitive ability. The odor sensitivity task seems to put less demands on the cognitive ability than does the odor discrimination task (Hedner et al. 2010). Therefore, based on the two assumptions: (1) background sound interrupts with the performance of cognitive task (LeCompte et al. 1997; Furnham and Strbac 2002; Cassidy and MacDonald 2007) and (2) olfactory sensitivity task puts less demands on the cognitive ability (Hedner et al. 2010), we hypothesized that subjects’ performance in the odor sensitivity task is not influenced by the background noise.

Notably, the effect of background sound on subjects’ performance in the occupational or cognitive tasks has varied across earlier studies, that is, the background sound facilitated (Crawford and Strapp 1994; Furnham and Bradley 1997; Furnham and Strbac 2002; Cassidy and MacDonald 2007), impaired (Oldham et al. 1995; Furnham and Strbac 2002; Seo et al. 2011), or did not alter the task performance (Furnham and Allass 1999; Cassidy and MacDonald 2007; Seo et al. 2011). Many studies have demonstrated that the influence of background sound on task performance is altered by several factors such as type of background sound (Crawford and Strapp 1994; Cassidy and Macdonald 2007; Seo et al. 2011) and type of task (Oldham et al. 1995; Furnham and Bradley 1997; Furnham and Allass 1999; Belojevic et al. 2001; Cassidy and MacDonald 2007). For example, while background music improves subjects’ performance in the monotonous or routine tasks by reducing their boredom and tension and/or by increasing positive mood, the music deteriorates the performance in the complex tasks by distracting their attention from the target task (Oldham et al. 1995; Furnham and Allass 1999; Cassidy and MacDonald 2007).

Previous research has shown that personality trait affects the background sound effect on subjects’ task performance (Morgenstern et al. 1974; Crawford and Strapp 1994; Furnham and Bradley 1997; Furnham and Allass 1999; Furnham et al. 1999; Belojevic et al. 2001; Furnham and Strbac 2002; Cassidy and MacDonald 2007). To be specific, while extroverts outperformed a cognitive task in the noisy condition than in silence, introverts outdid in silence rather than in the presence of noise (Crawford and Strapp 1994; Furnham and Bradley 1997; Furnham and Allass 1999; Furnham and Strbac 2002; Cassidy and MacDonald 2007). In fact, compared with introverts, the extroverts are shown to be less sensitive to background noise (Smith 1968). Further, the extroverts are likely to prefer higher level of noise (Hockey 1972) and they more often work with the radio on than the introverts (Furnham and Bradley 1997). With this background, it can be thought that the introverts relative to the extroverts are more easily aroused and/or distracted by background noise.

Herein, it is worth noting that subjects’ selective attention has an impact on the odor perception (Krauel et al. 1998; Geisler and Murphy 2000; Masago et al. 2001; Anderson et al. 2009, 2011). Specifically, olfactory event-related potential studies have shown that attended olfactory stimuli produce shorter latencies and higher amplitudes of component peaks than ignored olfactory stimuli (Krauel et al. 1998; Geisler and Murphy 2000; Masago et al. 2001; Anderson et al. 2009, 2011). Further, the attention-induced odor perception has been also reported in the neuroanatomical studies (Small et al. 1997; Plailly et al. 2008; Veldhuizen and Small 2011). For example, in the cross-modal links of olfactory and gustatory cues, selective attention to odor (or taste) magnified neural activity in the primary olfactory (or gustatory) cortex but not in the primary gustatory (or olfactory) cortex, respectively. Accordingly, on the basis of two assumptions: (1) subjects’ selective attention to odors facilitates olfactory performance (Krauel et al. 1998; Masago et al. 2001; Plailly et al. 2008; Anderson et al. 2009, 2011) and (2) background noise can more easily distract subjects’ attention from the target task in the introverts than in the extroverts (Crawford and Strapp 1994; Belojevic et al. 2001; Furnham and Strbac 2002; Cassidy and MacDonald 2007), we hypothesized that background noise-induced performance in the odor sensitivity task is different between the introverts and extroverts. In fact, the most relevant study conducted by Koelega (1970) has showed that compared with male extroverts, male introverts were significantly less sensitive to olfactory stimuli in the distracting noisy place where about 50 other subjects were talking and laughing. However, the significant difference disappeared when each subject had the testing in a separate room (i.e., in silence).

It has been reported that as complexity of background sound increases, extroverts’ performance on the occupational and cognitive tasks is improved, whereas introverts’ performance is impaired (Furnham and Allass 1999; Cassidy and MacDonald 2007). With this background, to make a difference in the level of distraction, we used two types of background noise: nonverbal or verbal noise in the present study. In our earlier study (Seo et al. 2011), subjects appeared to be more distracted by verbal noise (i.e., audio book) than by nonverbal noise (i.e., party sound) during the odor discrimination testing. Therefore, using the identical auditory stimuli, we attempted to examine whether an interaction between (1) type of background noise (i.e., nonverbal or verbal noise) and (2) degree of extroversion (i.e., introverts or extroverts) can exhibit in the odor sensitivity task.

Materials and methods

Subjects

Thirty-nine healthy right-handed volunteers (27 females) with an age range between 19 and 41 years [mean age ± standard deviation (SD) = 25 ± 4 years] participated at this experiment. In order to minimize a modulating effect of handedness on olfactory performance and brain response (Bensafi et al. 2003; Royet et al. 2003), only right-handed volunteers took part in the experiment. For example, Bensafi et al. (2003) showed that right-handers judged the odor familiarity more quickly than left-handers. Handedness was determined using a German version of the Edinburgh inventory (Oldfield 1971). All subjects confirmed that they had no clinical history of major diseases (e.g., diabetes, cancer, hypertension, or renal diseases) and that they had normal senses of smell and hearing. All subjects had no impairment in auditory, olfactory, or cognitive function on the basis of the following test results: the tuning fork test (Doyle et al. 1984), the “Sniffin’ Sticks” screening test (Burghart Instruments, Wedel, Germany; for details, see Hummel et al. 2001), and the “Mini-Mental-State Examination” (Folstein et al. 1975), respectively. The experimental procedure was explained to all subjects in a great detail, and an informed written consent was obtained before the participation.

Personality questionnaire

To assess subjects’ personality trait, all subjects were asked to complete the German standard and short version (EPQ-RK; Ruch 1999) of the Eysenck Personality Questionnaire Revised (EPQ-R; Eysenck and Eysenck 1991). The EPQ-RK is a 50-item self-report questionnaire. It contains four major dimensions of personality trait: psychoticism (P: 14 items), extraversion (E: 12 items), neuroticism (N: 12 items), and lie-scale (L: 12 items).

Background noise and presentation

As a background noise (referred to “unwanted or irrelevant sound”) under this study, two auditory stimuli were used: the sound of crowded party (subsequently to be called “party sound”) obtained from a web provider of sound effects (http://free-loops.com) and the sound of audio book (Mario Barth: Langenscheidt “Frau-Deutsch Deutsch Frau 2,” Sony Music Entertainment Germany GmbH, Germany). The sound of the audio book (subsequently to be called “audio book”) presented a famous German comedian’s humorous speech. Both sounds were presented via a headphone at a loudness of 70 dB.

Odor sensitivity task

To assess subjects’ sensitivity to odor, we used an odor threshold task (subsequently to be called “odor sensitivity task”) of the “Sniffin’ Sticks” test (Hummel et al. 1997), which is well established as a clinical measure assessing olfactory function. In the “Sniffin’ Sticks” test, odorants were presented in felt-tip pens. The pen’s tampon is filled with 4 mL of a 4 % solution of 2-phenylethanol (PEA; Sigma-Aldrich) with propylene glycol. Further dilutions were established with a dilution ratio of 1:2. The 16 dilutions were prepared in a geometric series starting from a solution with a 4 % PEA. The length and the inner diameter of the pens are approximately 14 cm and 1.3 cm, respectively. For odor presentation, the cap of the pen was removed by the experimenter and the tip of the pen was placed 2 cm in front of both nostrils.

In the odor sensitivity task, triplets of pens with two containing no odorant and one containing an odorant (i.e., PEA) were presented in a randomized order. Using a 3-AFC task, subjects were asked to select which of three pens smelled. The interval between presentations of individual pens was approximately 3 s. The interval between presentations of odor triplets was 20–25 s. Reversal of the staircase toward lower concentrations was triggered either when the odor was correctly identified in two successive trials. Reversal of the staircase toward higher concentration was performed when the odor was incorrectly recognized in one trial. Among a total of seven reversals, odor sensitivity was defined as the mean of the last four staircase reversals.

Procedure

This study consisted of three sessions. In each session, subjects were instructed to perform an odor sensitivity task in the presence of one of three auditory stimuli: party sound, audio book, and silent condition. In the silent condition (subsequently to be called “silence”), no additional auditory stimulus was provided. To minimize a potential learning/training effect on task performance, the order of three sessions was randomly counterbalanced across subjects.

Subjects were seated on a chair 55 cm in front of a computer monitor. Subjects were asked to wear headphones (MDR-A44L, Sony Corporation, Tokyo, Japan) and watch the computer monitor. In the original version of the odor threshold task (Hummel et al. 1997), to prevent visual detection of the target odor pen, subjects are instructed to be blindfolded and an experimenter says the number (e.g., “one,” “two,” or “three”) of the pen while presenting each odorant pen. However, subjects had trouble listening to the experimenter’s saying in the presence of background noise. Accordingly, as in a previous study (Seo et al. 2011), subjects were required to watch the computer monitor where the number (e.g., “1,” “2,” or “3”) of the presented pen was shown. Instead, to minimize visual detection of the target pen with a cap colored in red, the cap (colored in green, red, or blue) of pens was concealed while the pen was presented to the subjects. When the experimenter held the pen, the colored cap was easily concealed. Although subjects could listen to the experimenter’s instructions in the silent condition, the identical procedure was employed in the silence. Subjects were asked to indicate the order number of the pen containing the PEA odorant in the presence of three auditory stimuli: silence, party sound, and audio book. The time interval between sessions was 10–15 min. During the break, no auditory or olfactory stimulus was presented.

Following the experimental session, subjects were asked to rate the arousal and pleasantness of two auditory stimuli (i.e., party sound and audio book) on two eleven-point scales ranging between −5 (extremely calm/extremely unpleasant) and +5 (extremely arousing/extremely pleasant), respectively.

Data analyses

Data analyses were performed using SPSS 12.0 for Windows™ (SPSS Inc, Chicago, IL, USA). Prior to data analyses, data of three subjects (one female) who showed a poor performance in the odor sensitivity task in silence (e.g., lower than 6.5-point) were excluded (Hummel et al. 2007), that is, subjects being considered as normosmic were used for data analyses.

To determine whether subjects’ performance in the odor sensitivity task can be different between in the silent and noisy conditions, the mean score of two noisy conditions was compared with the score of silent condition, using paired t test. In addition, to indicate the impact of background noise on the odor sensitivity task, the mean scores of task performance in the silent condition were distracted from those of the noisy condition (i.e., “party sound” − “silence” or “audio book” − “silence”). This difference of mean scores is subsequently to be called “background noise-induced difference.” Furthermore, to compare the background noise-induced difference in the odor sensitivity task between the introvert and extrovert groups, subjects were median split into either introvert or extrovert group according to their score on the extraversion scale of EPQ-RK.

To test the effects of two factors: (1) type of background noise (i.e., party sound or audio book) as within-subjects factor and (2) degree of extraversion (i.e., introvert or extrovert group) as between-subjects factor on the background noise-induced difference in the odor sensitivity task, two-way repeated measures analyses of variance (RM-ANOVAs) were used.

Finally, to examine whether the background noise-induced difference in the odor sensitivity task may be associated with the degree of extraversion, Pearson correlation analyses were used. Moreover, we explored whether the background noise-induced difference in the odor sensitivity task correlates with the degree of other dimensions (i.e., P, N, or L) in the EPQ-RK. To do this, partial correlation analyses with a covariance as the degree of extraversion were used. The alpha level was 0.05.

Results

In the odor sensitivity task, mean performance of the two noisy conditions (mean ± SD = 8.3 ± 1.6) did not significantly differ from that of the silent condition (8.5 ± 1.8) [t (35) = 0.83, P = 0.41].

Table 1 demonstrates that the introvert and extrovert groups were not significantly different in terms of personality trait except for the dimension of extraversion. Also, they were not significantly different in terms of gender ration and ratings of arousal or pleasantness on two types of background noise, respectively. The mean age of introvert group was slightly higher than that of extrovert (P = 0.046).
Table 1

Comparisons of mean scores (±standard deviation) between the introvert and extrovert groups in terms of demographic, personality trait, and ratings of arousal and pleasantness on the background noise

 

Groups

Group differences

Introvert

Extrovert

Gender (F/M)

12/6

14/4

n.s.

Age

26 (±5)

23 (±3)

P = 0.046

Personality trait

   

 Psychoticism

2.3 (±1.5)

2.9 (±1.6)

n.s.

 Extraversion

5.3 (±2.0)

9.9 (±1.3)

P < 0.001

 Neuroticism

4.2 (±3.2)

3.6 (±2.4)

n.s.

 Lie-scale

2.6 (±2.0)

2.2 (±1.9)

n.s.

Arousal rating

   

 Party sound

3.3 (±1.2)

3.1 (±1.7)

n.s.

 Audio book

2.6 (±2.2)

1.6 (±2.1)

n.s.

Pleasantness rating

   

 Party sound

−2.9 (±1.7)

−3.1 (±1.6)

n.s.

 Audio book

0.1 (±2.9)

−0.6 (±3.0)

n.s.

n.s. no significance

We determined whether an influence of background noise on the performance in an odor sensitivity task can be altered as a function of two factors: type of background noise and degree of extraversion. As mentioned above, to show the influence of background noise in the odor sensitivity task (i.e., “background noise-induced difference”), the mean scores of task performance in silence were distracted from those of the noisy condition (i.e., “party sound” − “silence” or “audio book” − “silence”). The background noise-induced difference in the odor sensitivity task was not significantly different as a function of either type of background noise [F (1, 34) = 0.40, P = 0.53] or degree of extraversion (i.e., introvert or extrovert group) [F (1, 34) = 2.12, P = 0.16] (Fig. 1).
Fig. 1

Comparison of the background noise-induced difference in the odor sensitivity task between the introvert and extrovert groups. The background noise-induced difference indicates the mean score difference of the noisy and silent conditions, that is, “party sound” − “silence” or “audio book” − “silence.” The extrovert group outperformed the odor sensitivity task in the presence of audio book than in silence, while the introvert group showed an opposite performance. The n.s. and asterisk indicate no significance and significance at P < 0.05, respectively. The error bars represent the standard errors of the means

However, there was a significant interaction between type of background noise (i.e., party sound or audio book) and degree of extraversion (i.e., introvert or extrovert group) in the background noise-induced difference in the odor sensitivity task [F (1, 34) = 4.61, P = 0.039]. Specifically, post hoc comparison using Bonferroni t tests demonstrated that the party sound-induced difference in the odor sensitivity task was not significantly different between the introvert and extrovert groups [t (34) = −0.01, P = 0.94]. However, the audio book-induced difference in the odor sensitivity task (i.e., “audio book” − “silence”) was significantly higher in the extrovert group than in the introvert one [t (34) = −2.34, P = 0.03]. In other words, while the extroverts outperformed the odor sensitivity task in the audio book condition than in silence, the introverts showed worsened task performance in the presence of audio book than in silence.

Figure 2 demonstrates that the degree of extraversion significantly correlated with the audio book-induced difference in the odor sensitivity task [r (36) = 0.35, P = 0.036]. Further, the significant correlation still exhibited in the partial correlation analysis controlling the degree of psychoticism, neuroticism, and lie-scale as covariance [r (31) = 0.38, P = 0.027]; namely, as subjects show higher scores in the scale of extraversion (i.e., more extroverted), they performed better in the odor sensitivity task in the presence of verbal noise than in silence. However, such a significant correlation was not obtained in the party sound-induced difference in the odor sensitivity task [r (36) = −0.03, P = 0.87].
Fig. 2

The relationships of individual scores between extraversion and background noise-induced difference in the odor sensitivity task as a function of type of background noise: nonverbal (party sound) or verbal (audio book) noise. The background noise-induced difference indicates the mean score difference of the noisy and silent conditions, that is, “party sound” − “silence” or “audio book” − “silence.” Correlation analyses revealed as subjects were more extraverted they significantly outperformed the odor sensitivity task in the presence of verbal noise (audio book) than in silence

We also investigated whether other dimensions (i.e., P, N, or L) of the Eysenck personality trait can be associated with the background noise-induced difference in the task performance. The partial correlation analyses with a covariance as the degree of extraversion revealed that the background noise-induced difference in the odor sensitivity task did not significantly correlate with the degree of psychoticism, neuroticism, or lie-scale (P > 0.05) as shown in Table 2.
Table 2

Partial correlation coefficients between the degree of psychoticism, neuroticism, or lie-scale and the background noise-induced difference in the performance of odor sensitivity task

Personality trait

Type of background noise

Party sound

Audio book

Psychoticism

0.06a

(P = 0.73)

−0.15

(P = 0.38)

Neuroticism

0.12

(P = 0.48)

0.11

(P = 0.53)

Lie-scale

0.13

(P = 0.46)

0.03

(P = 0.88)

aThe coefficient was obtained by the partial correlation analysis with a covariance as the degree of extraversion

Discussion

Numerous studies have elucidated that background noise significantly interferes with the subjects’ performance in the cognitive or occupational tasks mainly associated with the visual and/or motor system (LeCompte et al. 1997; Furnham and Bradley 1997; Furnham and Allass 1999; Furnham and Strbac 2002; Cassidy and MacDonald 2007). In a similar vein, recent research showed that background noise distorts subjects’ performance in the cognitively driven odor discrimination task (Seo et al. 2011). Therefore, the primary aim of the current study was to extend our previous research by examining whether the background noise can also affect subjects’ performance in the odor sensitivity task that is less cognitively loaded (Hedner et al. 2010).

Our findings demonstrate that on average, the background noise relative to the silence has no modulatory influence on subjects’ performance of odor sensitivity task. One plausible explanation for the lack of significance could be that the odor sensitivity task is a sensory-driven work (Hedner et al. 2010). Because the odor sensitivity task seems to rely more on peripheral function of the olfactory system than cognitive processes that are highly affected by background noise (Furnham and Strbac 2002; Cassidy and MacDonald 2007; Hedner et al. 2010), the background noise-induced change in the task performance might be less. In fact, using hierarchical regression analyses, Hedner et al. (2010) showed that proficiency in cognitive function (e.g., executive function and semantic memory) can account for subjects’ performance in the odor discrimination test but not in the odor threshold test.

It is interesting to note that a significant interaction between type of background noise and degree of extraversion was present in the background noise-induced performance in the odor sensitivity task (Fig. 1). Specifically, the introverts showed an impaired performance of odor sensitivity task when presented with the audio book sound compared with the situation when no additional sound was presented. In contrast, the extroverts performed better in the presence of audio book sound than in silence. The findings are in agreement with the previous study demonstrating that male extroverts relative to introverts showed significantly higher sensitivity to odors in the distracting noisy condition (Koelega 1970). One plausible explanation for the significant interaction between type of noise and degree of extraversion can be found in the Eysenck’s arousal theory of extraversion (1967). According to his theory, there is an optimal level of cortical arousal to improve a task performance. As people become more or less aroused than the optimal level, their task performances worsened (i.e., task performance shows an inverted U-shaped curve). The optimal level of cortical arousal is different between introverts and extroverts (Eysenck 1967). For example, the introverts have a lower optimum arousal threshold than the extroverts, that is, the introverts are more cortically aroused than the extroverts. Accordingly, while the introverts need less stimulation of external arousal, the extroverts seek more stimulation to reach the optimal level (Farley and Farley 1967). Therefore, it can be thought that the background noise-induced arousal leads the extroverts to be in the optimal arousal level to maximize their task performance, whereas the external arousal pushes the introverts to be over the optimum, resulting in a deteriorated performance. However, considering that the introvert and extrovert group were not significantly different in terms of ratings of arousal or pleasantness on two types of background noise (Table 1), the Eysenck’s arousal theory seems not to fully account for the significant interaction between type of background noise and degree of extraversion under the current design.

Another plausible explanation for the significant interaction between type of noise and degree of extraversion can be present in the allocation of subjects’ attention, that is, as addressed in the Introduction, it has been reported that olfactory stimuli are perceived more strongly and quickly when they are attended than when ignored (Small et al. 1997; Krauel et al. 1998; Geisler and Murphy 2000; Masago et al. 2001; Spence et al. 2001; Plailly et al. 2008; Anderson et al. 2009, 2011; Veldhuizen and Small 2011). For example, using olfactory event-related potentials (ERPs), Krauel et al. (1998) presented that the attended olfactory stimuli increased the amplitude of the late peak and decreased the latency of the early peaks compared with the olfactory stimuli presented during a distracting task. In addition, the cross-modal studies using a functional magnetic resonance imaging (fMRI) have demonstrated that the stimuli of attended modality enhanced neural activities in the brain regions associated with the modality, whereas the stimuli of unattended modality suppressed the neural responses (Small et al. 1997; Mozolic et al. 2008). A recent fMRI study by Plailly et al. (2008) suggested attention-dependent dual pathways in an olfactory processing. Specifically, when subjects attended to odors (vs. tones), the indirect transthalamic pathway (i.e., the projection from piriform cortex to orbitofrontal cortex via mediodorsal thalamus) was more enhanced than the direct pathway (i.e., the projection from piriform cortex to orbitofrontal cortex without thalamus relay). Therefore, it can be thought that during the odor sensitivity task with/without the background noise, the presented odor might be perceived via the indirect transthalamic pathway having additional intervening connections between anterior piriform cortex and orbitofrontal cortex. The indirect processing would be more influenced by cognitive factors (Plailly et al. 2008). Accordingly, under the idea that introverts are more distracted by background noise than are extroverts (Crawford and Strapp 1994; Belojevic et al. 2001; Furnham and Strbac 2002; Cassidy and MacDonald 2007), the odor presented together with the background noise could be perceived as being less intense in the introverts than in the extroverts. In particular, this explanation supports why the differential effect of introversion/extraversion on the noise-induced task performance exhibited in the audio book but not in the party sound, that is, given the assumption that the introverts are likely to be more easily distracted by the complex noise (Furnham and Allass 1999; Furnham et al. 1999; Furnham and Strbac 2002; Cassidy and MacDonald 2007), their performance in the odor sensitivity task would be more obviously impaired in the presence of audio book (i.e., verbal noise) than in the party sound (i.e., nonverbal noise) condition. The findings are also in line with previous studies showing that as background sound is more complex, the differential effect of introversion/extraversion on the background noise-induced performance becomes more pronounced (Furnham and Allass 1999; Furnham et al. 1999; Furnham and Strbac 2002; Cassidy and MacDonald 2007). For example, Furnham and Allass (1999) examined whether musical distraction on the cognitive performance of extroverts and introverts can be different in relation to the music complexity (in terms of tempo, repetition, rhythm, melody, and vocal meaningfulness). The extroverts or introverts were asked to conduct four different cognitive tasks in the presence of either complex or simple music, or in silence. In the immediate recall test, the introverts scored the highest in silence and the lowest in the presence of complex music, whereas the extroverts showed the opposite result: the highest in the complex music and the lowest in silence. In addition, Furnham et al. (1999) reported that the introverts judged background vocal music as more distracting than instrumental music, but the extroverts estimated both music stimuli as similar in terms of auditory distraction (Furnham et al. 1999).

The odor sensitivity task seems to require, to some extent, cognitive factors such as executive function and short-term memory, although it is assumed that the odor sensitivity task is a sensory-driven test (Hedner et al. 2010). Previous studies have also reported associations of cognitive factor and odor sensitivity (Djordjevic et al. 2008; Dulay et al. 2008; Seo et al. 2009). For example, Seo et al. (2009) showed that the odor sensitivity measured by T&T olfactometer correlated with cognitive performance or education level in the elderly. Additionally, using structural equation modeling techniques, Dulay et al. (2008) found that influences of working memory and cognitive processing speed on the performance of odor threshold tests were small but significant. Further, it should be noted that in the present study, subjects were asked to simultaneously perform three different activities: sniffing the odorant pen, listening to background noise, and watching the monitor, which might put more demands on cognitive factors such as executive function, as compared with the typical procedure of odor threshold test in the Sniffin’ Sticks test (Hummel et al. 1997). Brain imaging studies demonstrated different patterns of brain activation on cognitive demands between the extroverts and introverts (Stenberg et al. 1993; Kumari et al. 2004). For example, Kumari et al. (2004) found that the degree of extraversion correlates with the amount of neural activation in the dorsolateral prefrontal cortex and anterior cingulate cortex. Interestingly, these brain areas are considered as being associated with not only cognitive function such as memory or execution (MacDonald et al. 2000), but also cross-modal integration (Calvert 2001). The findings can indirectly reflect the idea that extroverts manage cognitive demands more efficiently than introverts.

To summarize, the current study provides empirical evidence that background noise has no influence on the subjects’ performance in an odor sensitivity task. However, the background noise-induced performance in the odor sensitivity task was different as a function of type of background noise and degree of extraversion. Compared with the silent condition, verbal noise, but not nonverbal noise, impaired, or improved the performance of odor sensitivity task in the introvert or extrovert group, respectively. Our findings suggest that type of background noise and degree of extraversion play an important role in modulating the influence of background noise on an odor sensitivity task.

Notes

Acknowledgments

This research was supported by a grant from the Centre National de la Recherche Scientifique to T.H. (European associated laboratory; EAL 549, CNRS-TUD) and was partly supported by a start-up fund from University of Arkansas to H.-S.S. In addition, all authors appreciate Dr. Willibald Ruch and Ms. Claudia Harzer (Department of Psychology, University of Zurich) for providing their EPQ-RK.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Han-Seok Seo
    • 1
    • 2
  • Antje Hähner
    • 2
  • Volker Gudziol
    • 2
  • Mandy Scheibe
    • 2
  • Thomas Hummel
    • 2
  1. 1.Department of Food ScienceUniversity of ArkansasFayettevilleUSA
  2. 2.Department of OtorhinolaryngologySmell and Taste Clinic, University of Dresden Medical SchoolDresdenGermany

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