Traffic noise is considered causing annoyance and severe health effects like cardiovascular disease (CVD). The present laboratory study examines the importance of individual factors, namely age, gender and personality traits on short term physiological and affective response to vehicle pass-by noises. Four groups of subjects (20-30 vs. 40-55 year-old male or female, n = 66 in total) were exposed to a series of vehicle pass-by noises. Physiological responses (finger-pulse amplitude [FPA], skin conductance level [SCL]) were registered during the exposure; affective responses and judgements regarding the sounds were assessed by questionnaires. Noise sensitivity and sensation seeking were measured by validated questionnaires. The results show different patterns of response depending on age, gender and personality. The strongest sympathetic stress reaction as measured by SCL was found for the older female group. In regression analysis, the SCL response was predicted by the female gender and low score of sensation seeking only (adjusted R2 = 0.139). The FPA response was strongest among the young men and age was the only significant predictor. For affective responses of pleasantness and activation, regression analysis proved noise sensitivity and sensation seeking to be significant predictors (adjusted R2 = 0.187 respectively 0.154). Age, gender and personality influence physiological and affective reactions to traffic noise, which might affect health conditions. Especially, a potential risk of older women for CVD owing to noise should be investigated further. Individual sensitiveness in terms of noise sensitivity or sensation seeking proves to be important for explaining differences in response to noise.
Keywords: Gender and age, noise sensitivity, physiological response, sensation seeking, traffic noise
|How to cite this article:|
Notbohm G, Schmook R, Schwarze S, Angerer P. Patterns of physiological and affective responses to vehicle pass-by noises. Noise Health 2013;15:355-66
| Introduction|| |
The health impacts of environmental noise in industrialized countries are a growing concern. A recent publication of the Regional Office for Europe of the World Health Organization estimated that applying the epidemiological measure of disability-adjusted life years (DALY) at least one million healthy life years are lost every year from traffic-related noise in the Western part of Europe.  Quantitatively, sleep disturbance and annoyance, mostly related to road traffic noise, comprise the main burden of environmental noise in this study, whereas cardiovascular diseases (CVD) represent the most severe health effects. Several epidemiological studies suggest a higher risk of hypertension or myocardial infarction in subjects exposed to high levels of traffic noise. , Annoyance itself might enhance cardiovascular health effects of noise, e.g. by increasing blood pressure.  However, whether these associations between noise and cardiovascular health are causal is still a matter of debate. In future studies on health effects of noise, a correct assessment of exposure is as important as identifying persons within the population who are at increased risk due to higher susceptibility, i.e. stronger reactions to noise especially on physiological (stress) or emotional (annoyance, arousal etc.) level.  As a first step, the present laboratory study aims at reassessing the influence of age, gender and personality factors on physiological and subjective responses to typical traffic noises.
It is well-established that at best one-third of the variance of annoyance reactions to environmental noise can be explained by acoustical factors, whereas the other two thirds are ascribed to personal and situational variables.  Less is known about physiological reactions. Therefore, the question, which noise affects whom in which way still needs further investigation. A better understanding of individual differences in response to noise could improve the epidemiological research on the health effects of environmental noise by identifying more specifically affected groups in the population. The same applies to the preventive measures for most noise effects. Several biological and personality factors influencing noise effects have been described in the literature:
The self-reported "noise sensitivity" as assessed by questionnaires such as the Weinstein scale  is considered a stable personal trait manifesting itself in subjective attitudes toward the noise in general and specific noise sources. ,, As shown in many environmental studies, self-reported noise sensitivity does not correlate with the intensity of noise exposure, but it covariates with reported annoyance or other effects of noise such as subjective sleep disturbance or impaired mental performance, thus moderating the noise effect. , Self-reported noise sensitivity is highly correlated with a general trait "negative affectivity," which describes a disposition of the individual to experience oneself and the environment negatively.  Empirical results on relations between noise sensitivity and self-reported health are controversial showing more frequently an association with self-reported mental health than physical health.  A literature review shows controversial results on the influence of noise sensitivity on physiological responses: Sometimes noise sensitivity is associated with stronger increases of heart rate and peripheral blood flow under mental stress, but some studies report no effects on heart rate.  Another study on mental tasks reports not only higher annoyance among noise sensitive subjects, but also higher levels of strain.  Annoyance, cardiovascular responses, work stress - all these results suggest an association between noise sensitivity and health, but a causal relationship has not yet been shown. Only in the follow-up of a Finnish case-control study on noise and hypertension, a significantly increased cardiovascular mortality was found among noise-sensitive women, but not among men. 
Thus, the findings on physiological components of noise sensitivity or of related psychological phenomena are still ambiguous and the underlying mechanisms of this construct not well-understood.  Nevertheless, this construct should be included in studies on noise effects as more understanding is needed on its role in the noise-health relationship. As indicated in a recent study, the lack of statistical significance concerning noise exposure and objective health outcomes might even mean that noise is not the causal agent, but "that individual vulnerability is reflected both in ill health and being sensitive to noise." 
A more general concept of sensory perception is put forward by the "sensation seeking" model, which emphasizes the role of individual preferences with regard to novel, complex or intense stimuli.  Laboratory research has proven that sensation seekers expose themselves to longer periods or higher intensities of auditory sensory stimulation  or are less prone to defensive reactions to novel or aversive stimulation.  These findings make sensation seeking a potential factor to be considered in human response to noise.
Age and gender are normally controlled for in field research. Meta-analyses show that at least age has a significant effect on annoyance due to traffic noise.  Basically, age and gender as possible modifiers of noise effects still need more research. 
The actual individual response to a given sound can be observed on several levels: Physiological arousal in terms of changes of finger-pulse amplitude (FPA) or skin conductance level (SCL) has proven to reflect the subjective evaluation of sound stimuli quite accurately.  The reduction of the FPA is part of the typical orienting reflex, which can be observed reliably with any loud or otherwise conspicuous sound, even during sleep and is considered part of the orientation reflex to any activating stimulus.  Electrodermal activity, however as measured by SCL reflects exclusively the sympathetic axis of the autonomic nervous system  and is considered a sensitive index of stressful emotional experience "indexing changes in sympathetic arousal associated with emotion, cognition and attention." 
The affective response to a sound can be described by the model of "arousal" and "valence" as developed in motivational and emotional psychology: The sensual perception leads to a more or less strong activation of physiological systems and at the same time, the arousal, i.e. the perceived activation and the valence, i.e. pleasantness or unpleasantness of the sensual experience, is evaluated consciously.  These two dimensions of affective response to external stimuli characterize a variety of affective responses to external stimuli as shown in [Figure 1]. (De) activation and (un) pleasantness due to the sound can be measured by appropriate questionnaires  and physiological measures can substantiate these tendencies in laboratory studies. 
|Figure 1: Dimensions of affective responses to external stimuli: Combination of the two axes activated - deactivated and pleasant - unpleasant (Västfjäll et al. 2002)|
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The personal judgment on a given environmental noise is related to situational aspects as well as actual or lasting subjective associations,  namely, the perception of the quality and the level of noise, individual expectancies concerning the situation or to disturbance in actual activities, such as relaxation, sleep, conversation, concentrated work or even to previous experiences with such a noise, which interact with the situation given. Of course, the subjective sensation of "annoyance" is of major importance in this context as it is assessed in most studies on noise.
In the present study, we sought to assess in a laboratory setting as near to reality as possible how age and gender - alone or combined with the personality factors "noise sensitivity" and "sensation seeking" - determine the individual physiological, affective and cognitive response to typical traffic noises and if so to which extent. Physiological response was assessed by FPA and SCL, affective and cognitive response was measured in terms of activation and pleasantness and by judgments on the sounds.
| Methods|| |
The sample consisted of 66 subjects who had to fulfil the inclusion criteria: Good state of health, especially no CVD, good hearing, no intake of medical drugs, alcohol or caffeine on the day of the experiment, no smoking in the last 3 h and no lack of sleep. Subjects were recruited through notice boards in the campus and information in local newspapers and radio stations and received a financial gratification for their participation. All subjects gave informed consent.
In order to assess effects of age and gender, female and male subjects from two contrasting age groups were recruited (younger group: 20-30 years; older group: 40-55 years). [Table 1] shows the distribution of the subjects to four subgroups according to gender and age.
[Table 2] gives detailed information on some socio- demographic and health-related data of the subjects, which were assessed to identify possible confounders: Exact age, educational background, smoking habits, pharmacological status and pulse and blood pressure at the onset of the experimental session.
Each subject was exposed to the same eight different single vehicle pass-by noises, which were presented varying in order:
- 1 and 2: A car driving at 50 km/h in the 2 nd gear with acceleration, original recording and digitally modified recording by changing the sound of the engine
- 3 and 4: A car driving at 70 km/h in the 3 rd gear with constant speed, original recording and digitally modified recording by changing the sound caused by the tyres
- 5 and 6: A brake - idle - acceleration sequence, petrol and diesel engine
- 7 and 8: A brake - idle - acceleration sequence, petrol engine with low and with higher capacity
Each recording consisted of repetitions of the respective sound for a total length of 2 min. The sound intensity of each recording was adjusted to the same L eq of 83 dBA, which had proven to be an effective stimulus in a former joint research project in which the affective and physiological responses of subjects to a number of vehicle pass-by noises of the same sound level were measured in a series of laboratory experiments.  Sound recordings from that project, which had proven to elicit distinct physiological responses had been chosen for the present study.
Measures of effect
Two physiological variables were recorded during the experiment:
- FPA as a measure of the peripheral blood circulation
- SCL as a measure of the electrodermal activity (EDA).
The physiological measurements were taken continuously during the experiment using the Varioport recorder system (Becker Meditec, Karlsruhe). For the statistical analysis, means for a specific time intervals (2-5 s) for each subject were calculated and transformed into changes by percentage in relation to the baseline value of 100% (for details see "Statistical Procedures").
In addition to the physiological measurements, the two dimensions of affective response according to [Figure 1] were assessed by questionnaires during repetition of the sounds in the last part of the experimental session: The following bipolar scales ranging from −4 to +4 were to be answered by the subjects while listening to the respective sound:
- "I feel as unpleasant as possible" (−4) to "I feel as pleasant as possible" (+4)
- "I feel as deactivated as possible" (−4) to "I feel as activated as possible" (+4).
These questionnaires had been developed in former laboratory experiments. 
Subjective judgement on the noises
During the last part of the experimental session, also individual judgements on each noise were assessed by a list of 21 items concerning connotations with the respective sounds - such as annoying, noisy, dangerous, disagreeable, which were to be marked on a scale from 1 to 9. For the present analysis, the individual means of these items which all refer to a negative assessment of the present sound were calculated constituting a new variable "negative judgement on the sounds."
Assessment of personality related variables
The two personality traits mentioned above as important moderating variables for the response to noise were assessed by the respective questionnaires before the start of the experimental session:
This questionnaire measures the psychological construct of a person's "noise sensitivity" by asking for the degree of approval to a list of relevant statements. Up to now, it is acknowledged and used frequently as the standard measure for this variable. It consists of 21 items on a scale from 0 to 5 resulting in a total score between 0 and 105.
- Noise sensitivity scale. 
This questionnaire assesses four different aspects of the sensation seeking construct: Thrill and adventure seeking - disinhibition - experience seeking - boredom susceptibility. The analysis can focus on the total score or on single aspects. Statistically, the raw values are converted to T-scores, i.e. individual results can be compared with a mean of 50 and a standard deviation of 10.
- Total score of sensation seeking questionnaire. 
For each subject, there was one experimental session. First, the participants were informed about the procedure. Second, they answered questions concerning their state of health, consumption of caffeine, alcohol and drugs and the quality of their sleep the night before. Third, they completed the personality questionnaires. Then, their hearing was tested by audiometry. If a participant fulfilled all criteria he or she was seated in an anechoic chamber, the sensing elements for the physiological measurements were fixed and ear-phones were attached. Then, the person was left alone, monitored by a video camera.
In the beginning, there was a 15-min period of silence for relaxation and habituation to the situation. After this period, two recordings of traffic noise were presented for familiarization as the reactions to the first sounds presented are extremely strong in many cases so that they cannot be compared with other sounds of the experimental session. Then, the eight experimental sounds mentioned above were presented to each subject varying in order systematically with the subjects sitting as relaxed and comfortable as possible. Each sound lasted for 2 min and was followed by a silent period of 4 min for relaxation. Thus, the complete session took 71 min including 20 min noise exposure for each subject. After presentation of the last sound, the electrodes were removed.
After a short break, the second part of the experiment started with handing out the questionnaires for the evaluation of the affective response and the subjective judgement on the eight sounds just heard. They had to be answered by the subjects while all sounds were repeated in the same order, but in a shortened version.
Physiological and subjective data
The analog recordings of the physiological responses were digitalized and transformed into a data format for further procession with statistical software (IBM SPSS Statistics version 19). The last 30 s before the onset of each sound exposure were averaged for each subject to establish his/her respective baseline value and the physiological responses during exposure are given in percentages of the individual baseline. The physiological responses of a person during all experimental pass-by noises were averaged. Therefore, the following analyses always include all responses of the subjects during all sounds omitting only the two introductory traffic sounds.
First, we analyzed the responses during the 2 min of sound exposure for all pass-by noises. By means of multivariate analysis of variance (MANOVA), the course of responses of the experimental groups was tested for differences. In addition, the total response during the 2 min of noise exposure was analyzed by calculating the integrals of the curves for each group and comparing them by analysis of variance (ANOVA).
The results differentiate within-subjects effects and between-subjects effects: The within-subjects effects give evidence whether there is a change during the time in the entire group, or differently between the four study groups. The between-subjects effects reflect differences between the four study groups with respect to the position of the curves.
Analog to the handling of the physiological data, also the subjective affective responses and judgment of each subject on all eight pass-by noises were included in the statistical analyses of the noise effects by ANOVAs.
The criterion of significance for all statistical analyses (MANOVAs, correlations, regression analyses) was set to P = 0.05.
For a further analysis of determinants influencing the physiological responses of FPA and SCL as well as the affective responses to and judgements on the sounds, appropriate regression analyses were carried out, using the enter method to estimate the simultaneous influence of all given parameters. For each regression analysis, the values of R2 and adjusted R2 reflect the explained variance of the criterion achieved by the predictors chosen - with the adjusted R2 taking the number of predictors into account.
| Results|| |
With regard to the change of the FPA during noise exposure, the MANOVA over time including the between-subjects factors age and gender shows statistically significant within-subjects effects for time (P < 0.001) and also significant interactions between age and time (P < 0.001), gender and time (P < 0.001) and between age, gender and time (P < 0.05). Also, the between-subjects effects of age (P < 0.001), gender (P < 0.001) and the interaction between age and gender (P < 0.001) are statistically significant.
[Figure 2]a shows the corresponding curves for the change of the FPA in percent of the baseline value during exposure for the four subgroups to the eight pass-by sounds. As the strongest changes can be seen in the initial phase of exposure, the response during the first 30 s is shown in means of 2-s-intervals and during the remaining time of exposure in means of 5-s-intervals. The four graphs show a rapid decline of the amplitude, reaching its minimum between 10 s (younger males) and 14 s (older females) after sound onset. During the remaining time of exposure, a partial recovery toward the baseline can be seen, which differs remarkably in strength between the four groups. The curve for the young men runs in a range between 65% and 45% of the baseline value all the time, whereas the other groups respond more weakly right from the beginning and start intersecting each other in the course of exposure.
|Figure 2: (a) Curve of the finger pulse amplitude in percent of baseline value for 2-s-intervals (during first 30 s) resp. 5-s-intervals (during 31st to 120th s) during experimental noise exposure for the four subgroups of the study (means of all eight pass-by noises). (b) Cumulated change of the finger pulse amplitude: Areas under the four curves [Figure 2a] - lines represent the standard deviations|
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The ANOVA of the integrals of the curves as seen in [Figure 2]a yields significant main effects of age (P < 0.001) and gender (P < 0.01) as well as a significant interaction between age and gender (P < 0.001). For clarification, the bars in [Figure 2]b represent the cumulated percentage of FPA reduction for each of the four subgroups as measured in integral calculus by the areas formed by the curves below the baseline in [Figure 2]a. The outstanding response of the young men and the relatively weak responses of the other three groups become evident.
Regarding the change of the SCL during noise exposure, the MANOVA over time with age and gender as between-subjects factors shows statistically significant within-subjects effects for time (P < 0.001) and a significant interaction between gender and time (P < 0.001). The between-subjects effect of gender (P < 0.001) is also significant.
Accordingly, [Figure 3]a shows the mean response of the SCL of the four subgroups during the 120 s of exposure to the eight pass-by noises. There is a steady increase in the initial phase after the onset of the sounds. The response is more pronounced for women during the entire exposure time, with the older women showing the strongest reaction.
|Figure 3: (a) Curve of the SCL in per cent of baseline value for 2-s-intervals (during first 30 s) resp. 5-s-intervals (during 31st to 120th s) during experimental noise exposure for the four subgroups of the study (means of all eight pass-by noises). (b) Cumulated change of the SCL: Areas under the four curves [Figure 3a] - lines represent the standard deviations|
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The ANOVA of the integrals of the curves shown in [Figure 3]a again results in main effects of gender (P < 0.001) and age (P < 0.05) as already seen with the FPA, but this time no significant interaction between the two factors is found. [Figure 3]b illustrates the mean response of the SCL for each subgroup during noise exposure based on the integrals for the four curves from [Figure 3]a above the baseline. As already seen in [Figure 3]a, the female groups react stronger than the male groups during which the older subjects show a slightly stronger response than the corresponding younger subjects.
Affective responses: Pleasantness and activation
During listening to the different pass-by sounds in the second part of the experimental session, the subjects were asked to evaluate their feelings in terms of "feeling unpleasant or pleasant" and "feeling deactivated or activated" on scales from −4 to +4. These judgements refer to the two dimensions of affective response to external stimuli as depicted in [Figure 1]. Accordingly, the means of the four subgroups for these judgements are shown in [Figure 4] using only the relevant part of the upper left quadrant of the same coordinate system. It becomes obvious that all the means are concentrated in the upper left quarter of the coordinates, i.e. the combination of feeling activated and unpleasant.
|Figure 4: Mean ratings of the four subgroups in the scales for "feeling unpleasant to pleasant" and "feeling deactivated to activated"|
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All noise evaluations of each subject were included in the analysis of affective responses. For the rating of unpleasantness, there is a statistically significant effect of age in the ANOVA (P < 0.05), but it cannot be interpreted adequately because of the significant interaction between age and gender (P < 0.001): In the female subgroups, the older subjects feel clearly more unpleasant, whereas in the male subgroups, the younger subjects feel slightly more unpleasant. Overall the older women feel the most unpleasant. For the judgement on activation, only the main effect for age is significant (P < 0.05): [Figure 4] shows the clear tendency that the older subgroups feel more activated than the younger ones.
Judgments on the sounds
In ANOVA, there is a main effect of gender (P < 0.05) as well as of age (P < 0.05), but no significant interaction. [Figure 5] displays the mean values for this scale among the subgroups of the sample. All means are close to each other with the older subjects judging a bit more negatively than the corresponding younger ones and the female subjects judging a bit more negatively than the respective male subjects.
|Figure 5: Mean ratings of the subgroups in their judgements on the sounds with the lines representing the standard deviations|
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In addition, the single item "annoyance" was analyzed separately because of its importance in environmental noise research. The mean rating for all 8 pass-by noises was 6.81 (s = 1.13); the lowest annoyance was reported by the older men (mean = 6.54, s = 1.59), the highest annoyance was reported by the older women (mean = 7.2, s = 0.79). No significant effects of age or gender were found.
Noise sensitivity and sensation seeking
As can be seen from [Figure 6], there are only slight differences between the four experimental groups with respect to their noise sensitivity: The older women are most sensitive and the younger women least. However, these small differences are not statistically significant (P > 0.1 for all).
With regard to the total score of sensation seeking, the mean for the group of young men is highest, followed by the young women. The means for the two older groups are clearly lower with the women showing the lowest value [cf. [Figure 6]]. However, the influence of age on sensation seeking misses significance (P < 0.1). There was no effect of gender and no interaction between both factors.
|Figure 6: Mean ratings of the four subgroups in the scales for noise sensitivity and sensation seeking with the lines representing the standard deviations|
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Patterns of individual response to pass-by noises
Correlations between the variables
As a first step in understanding the interconnections between the factors involved in the subjects' response to noise, [Table 3] shows the correlation coefficients between all the variables presented above. All correlations, which are significant on a level P < 0.05 are marked with bold figures.
As can be seen from [Table 3], the correlations between the two physiological measures as well as all the correlations between physiological measures and the affective responses of pleasantness and activation are very low. The FPA correlates significantly only with lower age whereas the SCL shows a significant correlation with (female) gender and with lower levels of sensation seeking. The two affective responses pleasantness and activity correlate negatively with each other (i.e. the more activated, the more unpleasant) and both correlate (with opposite signs) with noise sensitivity and sensation seeking: A more negative judgement on the sounds presented correlates with a stronger feeling of unpleasantness and of higher activation and with a higher degree of noise sensitivity.
In addition, the two personal factors "noise sensitivity" and "sensation seeking" correlate negatively with each other and "noise sensitivity" correlates also with a lower degree of negative judgement on the sounds. Thus, the correlation matrix reveals a complex pattern of interactions between the variables used.
Regression analyses for the physiological responses
[Table 4] shows the regression coefficients for the analyses of FPA and SCL. The regression of FPA with enter method misses significance (R2 = 0.101, F [4, 60] =1.682, P = 0.166, adjusted R2 = 0.041). Anyway it is interesting to note that the data show that the increment of FPA is predicted by younger age.
|Table 4: Regression analyses for the physiological criteria "finger-pulse amplitude" and "skin conductance level"|
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The regression of SCL reaches significance (R2 = 0.192, F [4, 61] =3.626, P < 0.015, adjusted R2 = 0.139). An increment of SCL is predicted by female sex and low values in sensation seeking.
Regression analyses for the affective responses "pleasantness" and "activation"
[Table 5] shows the regression analyses for the affective responses "feeling unpleasant to pleasant" and "feeling deactivated to activated." The regression of "feeling unpleasant to pleasant" reaches significance (R2 = 0.237, F [4, 61] = 4.746 P < 0.01, adjusted R2 = 0.187). Only noise sensitivity is included as a significant predictor, i.e. people feel less pleasant during noise exposure the more sensitive to the noise they are and all other predictors do not have a clear effect.
|Table 5: Regression analyses for the affective criteria "pleasantness" and "activation"|
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The regression for "feeling deactivated to activated," too, reaches significance (R2 = 0.206, F(4, 61) = 3.951, P < 0.01, adjusted R2 = 0.154). An increment of feeling activated is predicted by higher values for noise sensitivity and lower values for sensation seeking, whereas age and gender do not have any effect.
Regression analysis for the subjective judgement on the sounds
[Table 6] shows the regression analysis for the subjective judgements on the sounds as ascertained during the last part of the experimental session. The regression for "negative judgement on the sound" reaches significance (R2 = 0.245, F [4, 61] = 4.941, P < 0.01, adjusted R2 = 0.195). Only noise sensitivity has a significant influence on the judgement on noise: The higher the noise sensitivity, the more negative is the judgement of the subjects about the sounds presented. Statistically, this result equals strongly the prediction of "feeling unpleasant" by noise sensitivity as presented in [Table 5]. Thus, the "negative judgement on the sounds" seems to register a similar subjective response as the simple question for "feeling unpleasant."
|Table 6: Regression analysis for the criterion "negative judgment on the sounds"|
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| Discussion|| |
In this experimental study with real environmental stressors, male and female participants of two different age groups were exposed to a standardized series of vehicle pass-by noises at a given sound level. Physiological, affective and cognitive reactions to the exposure were measured and long lasting biological and psychological factors moderating the reactions were identified. The results show distinct differences in the reactions between four subgroups: Older women have the highest SCL response, feel most unpleasant, evaluate the sounds most negatively and together with the older men, they show the highest arousal and the weakest FPA response, whereas the younger men take the opposite position in all these variables. Only for feeling unpleasant with the noises, the younger women are the counterparts with the lowest values.
Adding personality traits as determinants, the physiological stress reactions to noise, i.e. SCL as stress indicator, are best explained by the female gender and by a low value of the personality trait "sensation seeking." This reflects the dislike of novel, complex, or intense stimuli. In contrast, age alone is predictive for FPA. The affective and cognitive responses however are predicted by personal traits only: The higher the noise sensitivity, the stronger is the feeling of unpleasantness (valence) and the higher the noise sensitivity and the lower the sensation seeking, the stronger is the feeling of activation (arousal).
To sum up, firstly, the two physiological measures do not show much correspondence in the strength of response during noise exposure. Secondly, the physiological responses do not correspond strongly with the affective responses, but only with lasting personal factors such as age, gender and personality traits. That means that there is no homogenous pattern of human response to noise, but the different physiological or affective reactions to noise are moderated differently by personal factors and these mechanisms have to be understood more deeply.
Strengths and weaknesses of the study
The main strength of this study is the systematical analysis of the relations between basic individual factors influencing the individual responses to traffic noise: The sample represents four different sections of the population in terms of age and gender and the selected sound stimuli form an ecologically valid selection of everyday pass-by noises. With regard to the effects of noise, two physiological indicators of activation and stress are registered for which mediatory capacities between exposure and health impact are discussed and additionally affective responses of the subjects as well as judgments on the sounds are assessed by questionnaires.
Variables assessed in the present study are discussed in literature as potential mediators between noise stress and cardiovascular risk. In epidemiological research on CVD, the biological plausibility of a connection between noise and CVD is seen in the general stress model as supported by many experimental studies. ,,, In current models of CVD, physiological changes such as sympathetic activation are part of the psychobiology of acute coronary syndromes besides psychosocial factors related to the social environment, personality characteristics and negative affect. 
However, the weaknesses of the study also have to be mentioned: Regarding the high number of statistically significant interactions between the variables assessed, it has to be stated that a higher number of subjects would have been desirable to emphasize the decisive factors in response to traffic noise.
Secondly, although subjects participating in the experiment already represent a broad age range, it would be of interest with regard to the population at risk by traffic noise to study children and older people, too.
Finally, there was no large variety in experimental noises resulting in a small range of the acoustical environment for which these results are valid. Of course, the sounds in this experiment were selected as representative for traffic noise and they effectively elicited reactions. However, especially with regard to the affective responses and to the influence of noise sensitivity and sensation seeking, a larger scope of sounds as experimental stimuli would allow for a better understanding of the importance of such subjective factors.
Relation to other studies and future research
The assessment of the FPA during noise exposure has a long tradition in experimental noise research because it is a reliable and finely tuned measure of response explained by sympathetic peripheral stimulation due to the auditory stimulus leading to physiological activation. , Thus, the FPA is also included in experimental studies on cardiovascular risks due to noise and shows unambiguous responses to noise stimuli. , A hypothetic, but biologically highly plausible model based on the general stress concept was put forward years ago connecting vascular responses to noise with prognostic conclusions regarding the development of CVDs. 
As expected, the study results show a clear reduction of the FPA for all subjects during the noise exposure. With regard to gender, women have already been reported to present lower vascular responses to noise than men  as seen also in this study, but with regard to age, only cardiovascular reactivity to nocturnal traffic noise has been reported to decrease with older subjects,  whereas vasoconstriction was similar for all groups in that study. Therefore, the outstanding response of the young men with regard to the FPA in the present study needs confirmation and explanation by further studies. Eventually, a reduction of elasticity of the vascular walls due to age might limit the comparability of FPA values decisively. It has to be stated too that the FPA curves of the four groups during the different sound exposures displayed a large variation as compared with the results for the SCL. As expected, there was a habituation of the responses during the course of noise exposure, but especially some older subjects showed considerable variation of their responses during time.
With regard to SCL, the mechanisms by which autonomic sympathetic arousal influences cognition and motivational behavior are understood quite well nowadays.  Consequently, EDA plays an important role as an indicator of the experience of stress and emotional involvement, even as a marker in cardiovascular research.  Regarding the results of the present study, the increase for all experimental groups observed during noise exposure fits well with the general association of SCL with aversive emotional responses to a stimulus in laboratory settings. , Remarkably, the electrodermal response is significantly different between the four experimental groups: The percent increase of the SCL is highest for the group of older women. An explanation might be found in physiological differences of this group. A more intriguing hypothesis would be that older women are under a greater risk of physiological stress due to noise exposure. In epidemiological research, a higher risk for myocardial infarction among women due to long-time residential exposure to traffic noise was reported by one environmental study,  but these results were questioned due to methodological issues.  Anyway, it has to be pointed out that there are other relevant risk factors for coronary heart disease than noise, which modify the influence of gender on susceptibility to CVD. ,
Regarding the differences in physiological response between our four experimental groups, it has to be pointed out that up to now there is very small knowledge on differences in physiological responses in laboratory experiments due to age.  The authors ascertain a "paucity of research examining autonomic arousal among older adults" inviting "a multitude of unanswered questions"  (p. 626), e.g. whether differential physiological responding exists among "subgroups within the very broad older adult category". With regard to EDA, they report controversial findings from the literature. Similarly, a meta-analysis of age-related differences in cardiovascular reactivity to laboratory tasks shows that physiological responses of older adults result from a complicated interaction of bodily changes, level of activation and specific coping strategies.  Thus, the issue of differences in physiological response to noise due to age and gender as emphasized by the present study needs further research.
It might be argued that a valid decision on the influence of age and gender on outcome variables related to health can only be drawn from field research. However, here we find similar contradictions in recent publications: Some studies on CVD report higher risks for men due to traffic noise, ,, whereas other authors do not find any gender effects. ,, Similarly also the effects of age are controversial with some studies reporting strongest effects of traffic noise on the oldest participants in relation to stroke  or myocard infarct, , but other studies found no effects of age with regard to myocardial infarction or CVD. , Recent literature reviews confirm that age and gender are relevant modifiers of noise effects in environmental studies, but with heterogenous results. ,, It might be concluded that laboratory research on specific aspects of these interrelations can still be helpful nowadays to gain more insight in the impact of the respective factors. The situation is similar to research on cortisol, which is studied as a mediator of noise-induced stress response showing a variety of gender effects in the laboratory and field studies. ,
Noise sensitivity has proven a major factor in explaining noise effects ranging from annoyance to smoking habits and even cardiovascular symptoms. , In the present study, noise sensitivity had no significant influence on the physiological parameters, but only on the affective responses of feeling unpleasant and activated. However, the noise sensitivity was highly predictive for the subjective judgments on the pass-by vehicle sounds presented. This finding confirms the strong relationship between noise sensitivity measured by standardized questionnaire and the emotional and cognitive reaction to a specific noise as found in the literature.  The data of the present study underline the necessity of taking noise sensitivity into account when assessing psychological evaluations of sound stimuli because this factor obviously explains the variance between subjects' judgments to a large extent.
With regard to the concept of sensation seeking up to now, there are only a few results in literature related to noise exposure in laboratory settings as already pointed out in the introduction. The two laboratory studies on sensation seeking already mentioned , were to explore the validity of this concept by comparing physiological responses to sensory stimuli of subjects identified as low resp. high sensation seekers. The present study, however, demonstrates with environmental sounds that the degree of sensation seeking is an important predictor of the physiological response in terms of SCL as well as of the subjective experience of activation. As a causal relation between aversion to sensation seeking and dislike of noise is quite plausible, research on noise effects should pay more intention to this factor in future.
| Conclusions|| |
Laboratory studies on noise effects are a helpful tool for explaining or even predicting human responses to noise in real life situations, e.g. physiological responses to noise exposure, which might lead to health-related effects on the long run. The results of the present study underline the importance of taking lasting or slowly changing individual factors as age, gender and personality into account depending on the respective aims of the research. There is still a lack of knowledge concerning the effects of age and gender in response to specific environmental noises as well as the interaction of these factors with important moderators such as noise sensitivity or sensation seeking. Thus, firstly, this study identified older women (in this study 40-55 years) as a subgroup, which might be at higher risk for a sympathetic stress reaction to traffic noise as measured by the SCL. Secondly, it showed that physiological, affective and cognitive reactions to traffic noise are moderated by different patterns of biological and personality determinants. Thirdly, it emphasizes the importance of the concept of sensation seeking in moderating stress reactions (namely increase of SCL and perceived arousal). These results may help to focus epidemiological and intervention studies to those population groups that are at highest risk for the outcome of interest.
| Acknowledgment|| |
The study was supported by the European Research Group on Environment and Health in the Transport Sector (EUGT e.V.), Berlin. The study design was approved by the Ethical Commission of the Medical Department of Heinrich Heine University, Duesseldorf.
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Heinrich-Heine Universität, 40204 Duesseldorf
Source of Support: Financial grant by EUGT e.V. Berlin (Europäische Forschungsvereinigung für Umwelt und Gesundheit im Transportsektor e.V.)., Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]