Laboratory annoyance and skin conductance responses to some natural sounds

Journal of Sound and Vibration (1986) 109(2), 339-345

LABORATORY A N N O Y A N C E AND SKIN C O N D U C T A N C E RESPONSES T O SOME NATURAL SOUNDS E. A. BJORK

Departmdnt of Environmental Hygiene, University of Kuopio, 70211 Kuopio, Finland (Received 23 July 1985, and in revisedform 24 October 1985) The influences of spectral properties of sounds on annoyance and electrodermal activity reactions have been studied. In two laboratory experiments, subjects were exposed to some natural sounds in semi-anechoic conditions. Skin conductance and annoyance reactions were determined. The results suggest that electrodermal activity increases when the A-weighted equivalent sound pressure level exceeds 70 dB(A). It is concluded that the width of the spectrum is relevant, and that the greater the fundamental frequency of the harmonic spectrum the more annoying the sound.

1. INTRODUCTION The fundamental purposes of hearing are to alert and to warn. As a result sound can directly evoke emotions and actions through the inner ear's direct connections to "fight or flight" neural mechanisms via the autonomic nervous system. This defensive response is produced by sounds of sufficient intensity (70-120 dB), significance or duration to be perceived as threatening. The response includes alerting of the cerebral cortex, emotional arousal, and preparation o f the b o d y for action. It appears, e.g., in the form of an increase in the skin electrodermal activity (EDA) [1]. The skin conductance level (SCL) is taken as a gross indicator of the level ofsympathetic activation of the autonomic nervous system [2]. This electrodermal activity is postulated to increase when there is an activation o f the behavioral inhibition system (BIS). The BIS is hypothesized to respond to threatening stimuli. There is also evidence that the orienting response is mediated by the BIS [3]. The unwantedness of a sound depends on the physical parameters of the sounds, on the source of the sound and on the context in which it is experienced. Of the physical parameters the sound pressure level is dominant. Frequency content, tonality and transient character are commonly also considered relevant. H a r m o n i c sound elements have been found to be significant for the evaluation of sounds as well [4]. The investigation described in what follows was undertaken to study the effects of the spectral properties of sounds on annoyance and skin conductance reactions. An ensemble of complex natural sounds was used. 2. METHODS 2.1. SOUND STIMULI Two experiments were carded out. Six test signals in experiment I (see Table 1) were selected from the set of natural sounds used in the experiment of BjSrk [4]. The duration of each recording was about 30 seconds. 339 0022-460X/86/170339+07 $03.00/0 O 1986 Academic Press Inc. (London) Limited

340

E . A . BJORK TABLE 1

Sounds used in experiment I, fundamental frequencies of sound elements (F/), center frequencies ( Fc) and numbers ( N ) of 1/3-octave bands used in calculations of F, LAt LA ~q (dB(A)) - -

Sound b a c d f e

A man reading A baby crying People laughing The bubbling of the surging sea The cries o f b l a c k h e a d e d gulls Song of birds

7 8 12 9 6 6

Ff (HZ)

Fc (Hz)

N

100 450 250 -600 --

1200 1600 2000 2800 3700 4200

18 13 13 12 9 6

TABLE 2

Sounds used in experiment I I , Fc and N as in Table 1, mean ranks for SCR (RscR) and significances of differences between ranks. The numbers preceding each sound indicate the order in the experiment Significances Fc

'-

Sounds

(Hz)

N

Rscn

White noise The scream of a rat The call of a lapwing The bubbling of the sea The vowel ( a : ) of a man 8 The roar of a puma 4 The cry of a baby 1 The tone of 1 kHz

1700 3700 1500 1300

19 1.5 15 13

780 770 1200 1000

12 10 10 3

3 7 5 2 6

Number of cases Kendalrs W P

^

3

7

5

2.19 2.37 3.04 3.35

not not not ** . not

not

3-38 3.56 4.63 5.50

* not ** ***

not not * **

not * * *

2

6

8

4

not not * ***

not not not

not not

not

26 0.21 <0.0001

Wilcoxon Rank Test: *** p < 0.0005; ** p < 0.005; * p < 0.05.

T h e origin a n d s p e c t r a o f the eight s o u n d e l e m e n t s in e x p e r i m e n t I I are s h o w n in T a b l e 2. T h e d u r a t i o n o f e a c h s o u n d e l e m e n t was a b o u t o n e s e c o n d . T h e rise-fall times were a b o u t 25 ms. T h e s o u n d e x p o s u r e levels (SEL) o f s o u n d e l e m e n t s were e q u a l i z e d . T h e s o u n d m e a s u r e m e n t s were c a r r i e d o u t at the a p p r o x i m a t e p o s i t i o n o c c u p i e d b y t h e listener's e a r d u r i n g the e x p e r i m e n t s . T h e A - w e i g h t e d e q u i v a l e n t s o u n d p r e s s u r e level (LAeq), the A - w e i g h t e d s o u n d p r e s s u r e level e x c e e d e d for 1% o f the t i m e ( L M ) a n d the A - w e i g h t e d e q u i v a l e n t s o u n d p r e s s u r e levels o f o n e - t h i r d octave b a n d s f r o m 250 H z to 16 k H z (LA eqi) were m e a s u r e d . T h e relative p e a k level was i n d i c a t e d b y L A I - LAeq. The f r e q u e n c y c o n t e n t o f the s o u n d s was c h a r a c t e r i z e d b y the centre f r e q u e n c y (Fc), d e f i n e d as

Fc = 250 x 2 {(EI•

(Hz),

w h e r e i is the o r d i n a l n u m b e r o f the o n e - t h i r d o c t a v e b a n d . T h e LA ,q i(max) in c a l c u l a t i o n s were 20 d B ( A ) in e x p e r i m e n t I a n d 30 d B ( A ) in e x p e r i m e n t II, a n d negative levels were

ANNOYANCE AND SC RESPONSES TO SOUNDS

341

neglected. The number ( N ) of one-third octave bands used in the calculations o f F~ indicates the width of the spectrum. 2.2. SUBJECTS The test subjects were 30 university employees and students 22-35 years of age, 15 females and 15 males, in experiment I, and 28 students 19-24 years of age, 18 females and 10 males, in experiment II. Experiment II was a demonstration of a psychophysical experiment during a course of environmental psychology. The test subjects reported that they did not have any problems with their hearing. 2.3. PROCEDURES The experiments took place in a semi-anechoic soundproof room of 13 m 2. The subjects sat in the middle of the room at a distance of 1-5 m on the axis of a high quality speaker (Triamp S 30, Genelec) facing the speaker. The skin resistance level (SRL) and the skin resistance response (SRR) were monitored with a polygraph (RP-4, Takei and Company, Ltd.). Electrodes were placed round the second and thlrd finger tips of the left hand o f the subject without any electrode paste. The sensitivity of detection was 20 k f l / c m of pen deflection. In individual cases of skin resistance there are skin resistance responses (SRR) both after increasing the sound li:vel and spontaneously and the SRL has a drift rate. The recording o f the SRL values took place just before the sound level was altered. The spontaneous SRR's were eliminated by taking the SRL value before a spontaneous SRR, if it began less than 10 seconds before the increase of the sound level. In experiment I the sounds were recorded on a loop o f magnetic tape to produce an auditory stimulus of a continuous nature. The recordings were presented re.versed and in a different order to each subject. The initial L g e q of the signals was set at 20 dB(A) and the level was first increased by 10 dB every 30 seconds up to 90 dB(A) and then decreased by 10 decibels every 30 seconds back down to 20 dB(A). The verbal instruction was presented as follows: "You will be presented six sounds in a first ascending and then descending staircase procedure. Each sound will last eight minutes. There will be oneminute silences in the beginning and at the end. You must sit as still as possible during each ten-minute-period". Changing a magnetic tape took about one minute. There were three parts in experiment II, one immediately after another. In the first part the sounds were recorded on a magnetic tape (order shown in Table 1) to produce a sound burst of 80 dB(A) (SEL) every two to three minutes. Every two subjects listened to the sounds in a reverse order. The subjects were asked to sit as still as possible during the 20-minute-period and SRR's were measured. In the second part the sounds were recorded in pairs on loops of magnetic tape to produce continuous stimuli which had sound bursts of 40 dB(A) (SEL) every two seconds. There were 28 such loops. The subjects were asked to choose the more annoying sound burst from each pair supposing a regular basis at home and an acceptable function. The order of pairs was random and every two subjects listened to the pairs in a reverse order. In the third part loops similar to those in the second part were used. Supposing a regular basis at home and an acceptable function the subjects had to call on the author to increase the level of one of the two sound bursts until it was as annoying as the other which was 40 dB(A) (SEL). The listening order of the loops was the same as in the second part and every two subjects adjusted the separate sound of the pairs. Experimental conditions were administered by the author under manual control in the same room behind the subject.

342

E.A. BJORK

2.4. STATISTICS The S R L values were converted to the square root of S C L values before statistical treatment in order to normalize distributions [2]. Mean ranks (R) for each sound, Kendal coefficients of concordance (W) and corresponding chi-square statistics were calculated in experiment II by using log conductance changes and the proportions in'which each sound was chosen or adjusted more disturbing compared with the other sounds, and the sounds were compared with each other by using the Wilcoxon Matched-Pair Signed Ranks Test. 3. R E S U L T S

There is a striking decrease in the S C L during the first three minutes of each listening session. When the stimulus level exceeds 70 dB(A) the S C L curves turn upwards away from the anticipated falling curve. After the maximum level (90 dB(A)) the S C L decreases again. The adaptation of the S C L increase is clearly seen in Figure 1. I

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I I I 50 Sound

I l l t l l 90 level {dB{A))

50

l

Stimulus

Figure 1. Curves of m e a n skin conductance level o f different s o u n d order (1-6).

There were striking differences between the average S C L curves of the first presented sound and other sounds (see Figure 1). Thus the first sound o f every subject was ignored in the comparison o f the different sounds. The SCL's o f different sounds were also normalized to the common mean value at the beginning of stimulus. Figure 2 shows the average S C L curves. At 60-80 dB(A) (increasing level) there are (according to a two-tailed Student's t-test) nearly significant (p <0.05) differences between the sounds a-b and e - f in the SCL. The order o f sounds is nearly the same when ranked, respectively, according

A N N O Y A N C E

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70 90 50 Sound level ( d B { A ) )

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Figure 2. Curves of mean skin conductance level of different sounds (a-f, see Table 1).

to the centre f r e q u e n c y (Fc) a n d to the n u m b e r o f o n e - t h i r d octave b a n d s ( N ) used i n the c a l c u l a t i o n s (see T a b l e 1). I n two cases the SCR was i m p o s s i b l e to d e t e r m i n e as a s p o n t a n e o u s SCR t o o k place j u s t before the s o u n d burst. T h e data o f these two subjects were rejected. The m e a n r a n k s (RscR) for s o u n d bursts are seen in T a b l e 2. The t o n e o f 1 k H z was the least effective a n d the white noise the m o s t effective. T h e o r d e r o f s o u n d s is i n accord with (i.e., inversely as) the n u m b e r o f o n e - t h i r d octave b a n d s ( N ) u s e d in the c a l c u l a t i o n s o f the centre frequency. T h e r e are significant differences b e t w e e n s o u n d s (see T a b l e 2).

TABLE 3

Fundamental frequencies ( Ff ), mean ranks for the choice task (Re) and significances of differences between ranks in experiment II

Sounds A The scream of a rat :B The call of a lapwing C The cry of a baby D The vowel (a:) of a man E The roar of a puma F The bubbling of the sea G The tone of l k H z H White noise Number of case Kendall's W P Wilcoxon Rank Test: * p < 0.05.

F/ (Hz)

Rc

1500 1000 500 100 100 ----

1.44 2.06 3-44 5.00 5.38 5.94 5.94 6.81 8 0.65 <0.0001

A

B

not not not not

not not not

Significances " C D E

not not

F

not not

9 G

344

E: A.

BJORK

TABLE 4

Mean ranks ( Ra) for the adjustment task and significances between ranks Significances ^

Sounds B The call of a lapwing A The scream of a rat D The vowel (a:) of a man E The roar of a puma C The cry of a baby H White noise F The bubbling ofthe sea G The tone of lkHz Number of cases Kendalrs W P

R a

B

1.69 1.81

*

4.37 4-44 4.75 5.44 6.19 7-31

A

* not not not not not not 9 * 9 *

D

E

C

H

* *

not not

not

*

*

*

*

*

*

*

*

F

not

8 0-65 <0-0001

Wilcoxon Rank Test: * p < 0-05. The mean ranks for sounds when the annoyance choice (Re) and adjustment (Ro) data are used are shown in Tables 3 and 4. There are two groups of sounds. The harmonic spectra are the most annoying and the non-harmonic spectra are the least annoying. The sounds without a harmonic s p e c t r u m w e r e nearly significantly (p < 0 . 0 5 ) less annoying in the choice task than the sounds with a harmonic spectrum and the harmonic sounds did not differ significantly from each other. In the annoyance choice the order of ranks o f the harmonic sounds is in accord with (i.e., inversely as) that o f the fundamental frequencies ( F I ) .

4. DISCUSSION In the present study the increase o f SCL from the anticipated course took place at about 70 dB(A). In a very similar preliminary experiment by the author (unpublished) an increase of SCL was also found when LAeq exceeded about 70 dB(A). When the S C L is the indicator of the level of sympathetic activation in these studies (see reference [2]) it may be concluded that in a short-time sound stimulation sympathetic activation increases when LAeq exceeds about 70 dB(A). This change in skin conductivity may be a matter ofdefensive response. Startling and orienting responses are not plausible, while the repeated increases of sound level are well anticipated. Turbin and Siddle [5] did not find any evidence for the differentiation of electrodermal orienting and defensive responses. There were three groups o f s o u n d s which had different stimulating effects on the SCL. There was also nearly the same orderly dif[erence between the frequency contents of these sounds. The order of the groups was not the same at the relative peak level. The S C R seems to correlate with the width of the spectrum but not with the centre frequency or the fundamental frequency. Thus it may be concluded that the width of th e spectrum and the sound level but not the variability and the highness of pitch of a sound are relevant to the skin conductivity. Kryter and Poza [6] have found that wide-band noise is more effective than equally intense high-frequency noise in eliciting a sympathetic nervous system response. It may

ANNOYANCE

AND

SC RESPONSES

TO SOUNDS

345

be c o n c l u d e d that w i d e - b a n d s o u n d s are m o r e effective than n a r r o w - b a n d s o u n d s in activating the sympathetic nervous system which elicits the electrodermal activity. T h e nervous system m a y be the BIS, as described by Fowles [3]. H e U m a n [7] has c o n c l u d e d that a n n o y a n c e is more closely related to loudness than to noisiness. To p r o d u c e the same loudness a n a r r o w - b a n d s o u n d must be more intense than a wide-band s o u n d [8]. In this study a n n o y a n c e was f o u n d to be dependent on the h a r m o n i c structure but not on the width o f the spectrum. The h a r m o n i c structure is c o n c l u d e d to be relevant to the evaluation dimension [4]. So it m a y be concluded that the evaluating factor is n o t less important to a n n o y a n c e than loudness. Furthermore this study indicates that the greater the f u n d a m e n t a l frequency the m o r e a n n o y i n g the sound.

REFERENCES 1. J. C. WESTMAN and J. R. WALTERS 1981 Environmental Health Perspectives 41,291-301. Noise and stress: a comprehensive approach. 2. R. EDELBERG 1972 in Handbook ofPsychophysiology (N. S. Greenfield and R. A. Stembach, editors), pp. 367-418. New York: Holt. Electrical activity of the skin: its measurement and uses in psychophysiology. 3. D.C. FOWLES 1980 Psychophysiology 17, 87-104. The three arousal molel: implications of Gray's two-factor learning theory for heart rate, electrodermal activity, and psychopathy. 4. E. A. BJt)RK 1985 Acustica 57, 185-188. The perceived quality of natural sounds. 5. G. TURBIN and D. A. T. S1DDLE 1979 Psychophysiology 16, 582-590. Effects of stimulus intensity on electrodermal activity. 6. K. D. KRYTER and F. POZA 1980 Journal of the Acoustical Society of America 67, 2036-2044. Effects of noise on some autonomic system activities. 7. R. P. HELLMAN 1985 Journal of the Acoustical Society of America 77, 1497-1504. Perceived magnitude of two-tone-noise complexes: Loudness, annoyance, and noisiness. 8. B. SCHARF 1976 Journal of the Acoustical Society of America 60, 753-755. Acoustic reflex, loudness summation, and the critical band.