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Psychological and Physiological Effects of Low-Level Meaningful Artificial Sounds on Intellectual Tasks

Psychological and Physiological Effects of Low-Level Meaningful Artificial Sounds on Intellectual... The present study aimed to investigate the psychological and physiological effects of low-level meaningful artificial sounds on intellectual tasks. The psychological factors related to the degree of disturbance, concentration, and stress, as measured by subjective evaluation, were compared with the degree of physiological stress, as measured using salivary alpha-amylase activity. The results indicated that human speech and chewing sounds caused similar levels of psychological stress while performing intellectual tasks; however, chewing sounds caused comparatively less physiological stress than did human speech sounds. These findings suggest that depending on the sound stimulus, psychological and physiological stress characteristics may not coincide. Keywords Intellectual task · Auditory stimulation · Psychological and physiological effects of sound on humans · Subjective evaluation 1 Introduction noise with a moderate SPL has been shown to affect cognitive performance [7, 8]. Asakura and Tsujimura [10] found that The coronavirus disease 2019 pandemic has led to a wider household sounds, such as those with much lower SPLs than variety of work styles in various locations, which has road traffic noise, can affect cognitive performance. Further- increased opportunities for office workers to work outside of more, they also reported that these sounds may show an upper traditional office spaces. The environmental characteristics acceptable level of annoyance at SPLs around 40 dB [10], of a home or commercial space differ from those of con- depending on the noise sensitivity of individuals. The effects ventional office spaces. In such differing environments, the of low-level sounds (i.e., 34–45 dB) on intellectual tasks goal is to achieve production efficiency equal to or greater have also been studied. Tamura reported that when sounds than that of conventional workplaces. Numerous studies have with low SPLs are perceived as noise instead of unavoidable examined the impacts of environmental factors on intellec- phenomena, a given task can be quantitatively maintained, tual productivity [1], as well as the effects of the sound but qualitative performance tends to be reduced [11]. On the [2], visual [3], air quality [4] and thermal environments [5]. other hand, no case studies have examined the effects of envi- Among these environmental factors, although the influence ronmental noise with an SPL < 30 dB on human productivity. of various sound sources has been considered a factor of the However, it has been noted that various sounds generated in sound environment, there are generally cases where environ- an office environment can affect work, even if none of the mental sounds such as broadband noise [6], road traffic noise sounds has a significant SPL [12]. [7, 8], and conversation sounds [9] with relatively high sound In the present study, an experimental investigation was pressure levels (SPLs) are present. The impact of broadband conducted to examine the psychological and physiological noise, with a relatively high SPL of around 75–95 dB, has effects of sound environmental stimuli with a low SPL on the been shown to be naturally large [6], whereas even traffic performance of intellectual tasks. The psychological factors related to the degree of disturbance, concentration, and stress, B T. Asakura as measured by subjective evaluation, were compared with t_asakura@rs.tus.ac.jp the degree of physiological stress, as measured using salivary alpha-amylase (sAA) activity. Department of Mechanical and Aerospace Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-Shi, Chiba 278-0022, Japan 123 Acoustics Australia (a) (b) (c) Smartphone Table 12 min 12 min 12 min 12 min 12 min 12 min Participant Stimulus 1 Stimulus 2 Stimulus 3 Stimulus 4 Stimulus 5 Stimulus 6 12 min 12 min 1min 5min 1min 5min 1min 5min A Intellectual UK test B Break A Intellectual UK test Ceiling height: 1900 mm Stimulus 1 Stimulus 2 Unit: mm A: Measuring sAA B: Measuring sAA & subjective evaluation (d-2) (d-3) (e) (d-1) Experimenter Sound source HATS Table Sound sources HATS Experimenter HATS Unit: mm Unit: mm Fig. 1 The experimental flow: (a) the overall flow of the experiment including six auditory conditions and the partial flow of each of the auditory conditions, b the experimental setup showing a participant inside the soundproof room, c the dimensions of the soundproof room, d-1 the measurement situation for each auditory stimulus, d-2, d-3 the spatial relationships between the sound source and the HATS recording device, and e a screen showing the task calculations in the software [14] using the Uchida–Kraepelin (UK) method 2 Methods 5-min break was provided between each experimental con- dition. The order in which the six types of sounds were 2.1 Experimental Procedure reproduced was randomized for each of the participants to reduce the effect of the order. Before the experiment, the The experimental setup and flow are shown in Fig. 1.The participants were also given sufficient practice with the intel- experiment was conducted in a soundproof room to avoid lectual task on the smartphone. Then, instructions were given the contamination of low-level sounds via exterior noise. The for the situations that should be assumed in the experiment, study participants sat at point P inside the room, as shown in as follows. The participants were instructed to carry out the Fig. 1c. intellectual work carefully, as though it involved actual work In this experiment, four types of artificial fluctuating as opposed to a hobby. For the auditory stimuli, artificial sounds and two types of static sounds with equivalent sounds were generated at a distance of 1 m to the left of continuous A-weighted SPLs of 24–29 dB were used the participants. No specific instructions were given as to the as acoustic stimuli. The participants, while exposed to location in which they were supposed to be working. these sounds through headphones (ATH-W1000Z; Audio- Technica, Tokyo, Japan), performed a 5-min intellectual 2.2 Participants task based on the Uchida–Kraepelin (UK) psychodiagnostic test [13] under each experimental condition using Kraepelin The study participants were 20 healthy young male volun- Training free software [14] running on a smartphone (iPhone teers (mean age ± standard deviation [SD]: 21.7 ± 1.3 years, 13; Apple, Cupertino, CA, USA). age range: 20–23 years). Only men were recruited because For the sound playback, the headphones were connected to of the known existence of a gender difference in psycholog- a laptop PC with an audio interface (UR22mkII; YAMAHA ical responses to noise [15]. In accordance with EN 50332-1 Steinberg, Tokyo, Japan). After the task was completed, the and EN 50332-2 proposed by the European Committee for participant evaluated the degrees of disturbance, concentra- Electrotechnical Standardization [16, 17] as sound pressure tion, and stress perceived during the task. Saliva intake was regulations for portable audio players and the university’s measured and sAA analysis was performed before and after ethical guidelines, this experimental study was designed to be the intellectual work, as shown in Fig. 1a. These experimen- noninvasive. Informed consent was obtained from all partic- tal procedures were carried out for all six auditory stimuli. A ipants. The subjects were advised in advance to get adequate 1,200 1843 Acoustics Australia sleep the day before to avoid sleep deprivation on the day of Table 1 SPLs of the auditory stimuli: silence (S–SI), pink noise (S- PN), writing with a ballpoint pen on paper (S-PB), typing and clicking the experiment. The experimental collaborators were briefed (S-TC), TV news (S-TN), and chewing (S-CC).L indicates the equiv- Aeq on the study purpose and methods, as well as the anonymiza- alent continuous A-weighted SPL tion and use of data. Furthermore, prior to the study, all Stimuli S–SI S-PN S-PB S-TC S-TN S-CC participants were asked about their hearing ability, and all assured that their hearing was normal. The participants were L (dB) 20.2 28.5 27.9 25.1 26.9 28.1 Aeq also asked to confirm that they were not in a state of hyper- sensitivity to sound. S-SI S-TC S-TN 2.3 Acoustic Stimuli S-PN S-CC S-PB In this experiment, six types of sounds were used as audi- 10 dB tory stimuli: writing with a ballpoint pen on paper (S-PB), typing and clicking (S-TC) to evoke working sounds in the office, TV news (S-TN), chewing potato chips (S-CC) to evoke the sound of breaks between office work, pink noise without meaning (S-PN), and silence (S–SI). Previous studies have investigated the effects of background noise, including chewing sounds, on the learning efficiency of individuals with highly sensitive misophonia [18], finding that learning efficiency decreased in the presence of gum chewing sounds and increased in a quiet environment [19]. The most typical evoked sounds in misophonia are chewing [20, 21] and repet- itive tapping noises, such as pen clicking [21]. On the other hand, as the prevalence of misophonia has been estimated to 63 125 250 1k 2k 4k 8k be around 20% of the population [22], it is possible that chew- Frequency (Hz) ing sounds may increase annoyance to a small extent, even in relatively healthy individuals. Nevertheless, many evalu- Fig. 2 Frequency characteristics of each of the acoustic stimuli ations of the quality of crispy sounds have been conducted in recent years, and some aspects of these sounds have been accepted positively in terms of improved texture [23]. As that the recorded auditory stimuli were played back using the headphones to reproduce the SPLs shown in Table 1. described above, chewing sounds include various aspects of context; for example, in a place shared with other people, a The frequency characteristics of each of the above stimuli reproduced at the SPLs of Table 2 are indicated in Fig. 2. situation in which people may be working in close proximity to those who are eating and drinking can also be assumed. As indicated in the trend, the S-CC has a relatively higher frequency component, while the other sounds have generally Thus, S-CC was also included as a test sound, as it may have the potential to increase or reduce annoyance. lower frequency. The auditory stimuli were recorded using a head and torso simulator (HATS) system (type 8328A; ACO, Tokyo, Japan) 2.4 Intellectual Tasks in the soundproof room, where the reverberation was sup- pressed by sound-absorbing materials (Fig. 1d). Assuming The participants were presented with a calculation task based an actual office environment, the height of the ear on the on the UK method [13]. This method is used to ascertain the HATS dummy head was set at 1.2 m, which was assumed effects not only of auditory stimulation on the performance to be the height of the ear in the human sitting position, and of intellectual tasks, but also of moderate mental stress on was placed 1 m to the direct right of the person generating the participants and how this stress is affected by the audi- the sound (Fig. 1e). The equivalent A-weighted SPLs of these tory stimulation. It has been used for these purposes in many recorded 5-min auditory stimuli were measured as shown in previous studies [24, 25]. The participants were instructed to Table 1. The background noise inside the room was around add single-digit numbers continuously using the Kraepelin 20 dB, indicated as S–SI. Therefore, the other auditory stim- Training software [14] on the smartphone (Fig. 1e), working uli were measured so that the signal-to-noise (SN) ratio was as quickly and accurately as possible. When a cue was given, > 6 dB, and for (b), the SN ratio was about 5 dB, because the participants were to begin calculations. After 5 min, a the SPL at 1 m was lower than that of the other sounds. The cue for the end of the test was given. For evaluation of the acoustic output level of the audio interface was adjusted so results, the test performance of each participant was assessed Relative SPL (dB) Acoustics Australia in terms of the number of correct answers. While the num- 400 ber of errors was assumed to reflect attentional control [13, 26], the numbers of errors of all the participants were quite small compared with the number of all answers < 1%. One of the reasons for this was that the overall duration of the test was relatively short (5 min). In a previous study [27], the error rate for the UK test was also < 1.0%, even under longer observation. Therefore, the number of errors was not considered in this study. 2.5 Physiological Measurements In this experiment, physiological responses to mental stress S-SI S-PN S-PB S-TC S-TN S-CC were inferred based on information obtained from saliva. Pre- Type of sound vious studies have assessed the degree of stress response in saliva using salivary cortisol [28], amylase [29], or chromo- Fig. 3 Mean and standard deviation for the numbers of correct answers (error bars show 95% confidence intervals) for each auditory stimulus granin A [30]. A comparison of the results of these three methods confirmed that the results are consistent, although gender differences in the statistical trends have been observed were exposed to the auditory stimuli was then evaluated [31]. Regarding gender differences, it was originally noted based on three kinds of indicators: the degrees of concentra- that stress responses differed between men and women [32], tion, stress, and disturbance. The participants were instructed and several studies have found a stronger salivary cortisol to evaluate the three assessment items as they recalled, and response in men than in women in reaction to stressors not to rewrite their evaluations after subsequent reconsid- [33]. On the other hand, Maruyama et al. [34]showed eration. They were also instructed to respond within 1 min, that sAA levels displayed a rapid increase and recovery, which is the required time for sAA measurements. A 10-point returning to baseline levels 20 min after a stressor, whereas Likert-type scale was used to evaluate the three assessment salivary cortisol responses showed a delayed increase that items, with responses from 1  “not disturbed at all” to 10 remained significantly elevated from baseline levels 20 min “strongly disturbed” for the degree of disturbance, from 1 after the stress challenge. Their analyses revealed no gen- “high level of concentration” to 10  “no concentration der differences with regard to the sAA response, but did find at all” for the degree of concentration, and from 1  “very significantly higher salivary cortisol responses in females. stressed” to 10  “not stressed at all” for the degree of stress. Furthermore, they indicated that younger subjects tended to display higher sAA activity. Therefore, in the present study, sAA was used to consider younger age groups in the exper- 2.7 Statistical Analyses iment, which was conducted in men only, in view of gender differences. The sAA levels were measured using a portable A multi-way analysis of variance (ANOVA) was conducted to monitor (DM-3.1; NIPRO, Osaka, Japan). The participants investigate the effects of each auditory factor on the psycho- were carefully instructed about the saliva sampling proce- logical and physiological indicators. If the ANOVA results dure, as described in the manufacturer’s manual (NIPRO). showed significant main effects, the relationship of the mean Next, they collected their own saliva by placing a filter paper values between each group was evaluated in detail through under their tongue for 30 s, and the sAA concentration was multiple comparisons using Bonferroni correction. By con- measured with the monitor. The analysis was initiated by trast, differences between groups in sAA before and after the promptly inserting the saliva chip into the unit, and after auditory stimulation were assessed using a paired t-test. All about 60 s, the sAA was displayed in units of KU/L. The statistical analyses in the present study were performed using above procedure was followed according to the methods used BellCurve for Excel (Social Survey Research Information, by Yamaguchi et al. [35]. Tokyo, Japan), with p values < 0.05 considered significant. 2.6 Psychological Measurements The degree of sound disturbance was adopted as an evalua- 3 Results tion item, referring to a study on sound disturbance during intellectual work using electroencephalography (EEG) sig- The mean numbers and SDs of correct responses obtained for nals [36]. The psychological state of the participants who each of the auditory stimuli are shown in Fig. 3. The results Number of correct answers Acoustics Australia (a) (b) (c) ** ** ** 10 10 10 * * ** 9 * 9 9 ** 8 8 ** 8 ** 7 7 7 6 6 6 5 5 5 4 4 4 3 3 3 2 2 2 1 1 1 S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC Type of sound Type of sound Type of sound Fig. 4 Mean and standard deviation for subjective scores (error bars show 95% confidence intervals) for each auditory stimulus under the conditions of the degree of a disturbance, b concentration, and c stress. *p < 0.05, **p <0.01 (a) 60 (b) 30 : Pre-work sAA ** : Post-work sAA * 30 0 -10 -20 -30 S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC Type of sound Type of sound Fig. 5 Mean and standard deviation for sAA scores (error bars show 95% confidence intervals) for each auditory stimulus: a pre- and post-work sAAs and b sAA, which is the difference between the pre- and post-work sAAs. *p < 0.05, **p <0.01 of the one-way ANOVA with the auditory stimulus as a fac- significant differences in the pairs shown in each figure. In tor showed no significant difference for the main effect of terms of the degree of disturbance, the auditory stimuli S-TN the auditory stimulus. This result is similar to that reported and S-CC showed significantly higher disturbance than did in a previous study on the degree of disturbance during intel- the other four auditory stimuli. In terms of the degree of con- lectual work using EEG signals [36], where no significant centration, the S-TN and S-CC auditory conditions showed difference was found in the main effect of the auditory stimu- significantly lower concentrations than did S–SI. With regard lus when pure tones were used as the auditory stimulus. In any to the degree of stress, the S-TN and S-CC auditory condi- case, the effect of the auditory stimulus on work was small, tions showed significantly higher stress than did S–SI and indicating that it was not reflected in the workload. This was S-PB, respectively. No significant differences were found attributed to the simplicity of the experimental tasks, which between S–SI and S-PB in any of the categories. were easy to carry out even if the participants felt disturbed Next, the physiological results are indicated as follows. by the sound or stressed by the task. The baseline values of sAA described above may have dif- Next, the mean subjective scores and SDs for the degrees fered between each of the subjects due to stress and other of disturbance, concentration, and stress caused by the repro- factors caused by the experimental environment, which is duction of the auditory stimuli are presented in Fig. 4a–c, different from usual for the subjects. Therefore, the pre- and respectively. The results of one-way ANOVAs with auditory post-work sAAs and the difference between pre- and post- stimuli as a factor showed significant differences (p < 0.01) work sAAs (sAA) are shown in Fig. 5a and b, respectively. in the main effects of all auditory stimuli on the degrees of First, a paired t-test of the sAAs measured pre- and post- disturbance, concentration, and stress. The results of multi- work, respectively, showed significant differences (p < 0.01) ple comparisons between each of the auditory stimuli showed Degree of disturbance sAA (KU/L) Degree of concentration sAA (KU/L) Degree of stress Acoustics Australia (a) (b) 10 10 9 9 8 8 7 7 S-TN S-TN 6 6 5 5 S-CC S-PN S-CC S-PN 4 4 3 3 S-SI S-PB S-PB S-SI 2 2 1 1 S-TC S-TC 12 34 5 6 78 9 10 12 34 5 6 78 9 10 Degree of concentration Degree of concentration Fig. 6 Correlation between the subjective scores of a concentration and disturbance, b concentration and stress (a) 15 (b) 15 (c) 15 S-TN S-TN S-TN 10 10 10 S-PN S-PN S-PN 5 5 5 S-PB S-PB S-PB S-SI S-SI S-SI 0 0 0 S-TC S-TC S-TC S-CC S-CC S-CC -5 -5 -5 12 34 5 6 78 9 10 12 34 5 6 78 9 10 12 34 5 6 78 9 10 Degree of stress Degree of concentration Degree of disturbance Fig. 7 Correlation between each of the subjective scores of a disturbance, b concentration, and c stress, and the sAA only for S-PN and S-TN. Next, a one-way ANOVA with audi- S-TN and S-CC indicate almost the same degrees of each of tory stimuli as a factor showed a significant difference (p < the subjective indicators. 0.05) for the main effect of auditory stimuli. As a result of Next, regarding the physiological results of Fig. 5b, only multiple comparisons, a significant difference (p < 0.01) was the S-TN auditory stimulus showed significantly higher found only between S-TN and S-CC, as shown in Fig. 5b. sAA; S-CC, which showed similar subjective rating values to S-TN, showed the lowest values. Then, the relationship between each of the subjective scores of (a) disturbance, (b) concentration, and (c) stress, and the sAA is presented 4 Discussion in Fig. 7. While in all categories except S-CC the sAA increases in some degree in relation to subjective impression, The correlation among each of the subjective scores are indi- it can be seen that the values of sAA differ significantly cated in Fig. 6. As shown in Fig. 6a, the results of the present between S-CC and S-TN despite having almost the same subjective evaluation experiment indicate decreases in con- subjective impression score. This trend appears to be par- centration as the degree of disturbance increased. This is ticularly pronounced in the relationship between stress and consistent with the finding in a previous study that the degree sAA in Fig. 7a. First, as S-TN is a meaningful noise con- of concentration is strongly related to the degree of distur- taining speech, the sense of work disturbance was markedly bance [36]. It is also a natural consequence that the degree increased, and the resultant stress may have increased the of stress increases as observed in Fig. 6b, because reduced sAA. However, the degree of stress caused by S-PB and degrees of disturbance and concentration can be obstacles to S-TC, which may also increase annoyance, was relatively task performance. It should be noted that the conditions of sAA (KU/L) Degree of disturbance sAA (KU/L) Degree of stress sAA (KU/L) Acoustics Australia moderate. On the other hand, S-CC resulted in the same level Thus, it is necessary in the future to examine the effect of of stress as S-TN, but in contrast to S-TN, post-work sAA was longer task durations. the most reduced among all conditions. In other words, the As future research, the effects of auditory stimuli on work sound of chewing crispy chips was subjectively disturbing efficiency should be investigated by controlling the type, and stressful during work, but it did not cause stress physio- duration, and difficulty of tasks and increasing the sound logically. There have been several cases where differences in types and physiological indicators. At this point, it would be stress states have been predominantly detected in sAA-based useful to examine the degree of stress in more detail using analysis results [29, 34]; therefore, the degree of physiologi- EEG signals [37] and heart rate [38] in combination as other cal stress indicated in the present study also seems plausible. physiological indices. Second, the present results are limited Although the participants were instructed to assume they to men in their 20s. It may be possible to draw more general were engaged in office work, it is possible that such chewing conclusions by investigating a wider range of participants, sounds were actually unconsciously recognized as sounds including women and older people. that occur in a more casual setting than in an office, suggest- Acknowledgements The author would like to thank K. Morita for ing that the participants may have consequently performed the technical assistance with the experiments. Informed consent was intellectual work in a state of physiological relaxation. How- obtained from all participants. ever, the participants may have experienced an increase in Funding Open access funding provided by Tokyo University of Sci- subjective stress due to the common knowledge that chewing ence. sounds are perceived as a less favorably accepted artifi- cial action sound and may increase annoyance for a certain Open Access This article is licensed under a Creative Commons Attri- proportion of people. This also suggests the importance of bution 4.0 International License, which permits use, sharing, adaptation, examining the effects of sounds, even those generally con- distribution and reproduction in any medium or format, as long as you sidered to be unpleasant, on people in detail by comparing give appropriate credit to the original author(s) and the source, pro- them not only with subjective impression ratings, but also vide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are with physiological responses. included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in 4.1 Limitations the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a The present study has some limitations. First, sample size copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. was calculated a priori, and the moderate sample size of 20 subjects somewhat restricted opportunities to examine differences between each of the physiological conditions. Specifically, a sample size of 20 participants gave post hoc References power of 35, 79, 36, 26, 75, and 27% to detect differences 1. Mujan, I., Andelkovic, ´ A.S., Muncan, ´ V., Kljajic, ´ M., Ružic, ´ D.: between the pre- and post-work sAA under the S–SI, S-PN, Influence of indoor environmental quality on human health and S-PB, S-TC, S-TN, and S-CC acoustic conditions using a productivity - A review. J. Clean. Product. 217, 646–657 (2019) two-group t-test with a two-sided significance level of p < 2. 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Vitoratou, S., Uglik-Marucha, N., Hayes, C., Erfanian, M., Pearson, O., Gregory, J.: Item response theory investigation of misophonia Publisher’s Note Springer Nature remains neutral with regard to juris- auditory triggers. Audiol. Res. 11(4), 567–581 (2021) dictional claims in published maps and institutional affiliations. 21. Enzler, F., Loriot, C., Fournier, P., Noreña, A.J.: A psychoacoustic test for misophonia assessment. Sci. Rep. 11(1), 11044 (2021) 22. Wu, M.S., Lewin, A.B., Murphy, T.K., Storch, E.A.: Misophonia: incidence, phenomenology, and clinical correlates in an undergrad- uate student sample: misophonia. J. Clin. Psychol. 70, 994–1007 (2014) 23. Endo, H., Ino, S., Fujisaki, W.: The effect of a crunchy pseudo- chewing sound on perceived texture of softened foods. Physiol. Behav. 167, 324–331 (2016) 24. Goi, N., Hirai, Y., Harada, H., Ikari, A., Ono, T., Kinae, N., Hira- matsu, M., Nakamura, K., Takagi, K.: Comparison of peroxidase response to mental arithmetic stress in saliva of smokers and non- smokers.J.Toxicol. Sci. 32, 121–127 (2007) 25. Li, G.Y., Ueki, H., Kawashima, T., Sugataka, K., Muraoka, T., Yamada, S.: Involvement of the noradrenergic system in perfor- mance on a continuous task requiring effortful attention. Neuropsy- chobiol. 50, 336–340 (2004) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acoustics Australia Springer Journals

Psychological and Physiological Effects of Low-Level Meaningful Artificial Sounds on Intellectual Tasks

Acoustics Australia , Volume OnlineFirst – Sep 26, 2023

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Springer Journals
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Copyright © The Author(s) 2023
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0814-6039
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1839-2571
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10.1007/s40857-023-00307-7
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Abstract

The present study aimed to investigate the psychological and physiological effects of low-level meaningful artificial sounds on intellectual tasks. The psychological factors related to the degree of disturbance, concentration, and stress, as measured by subjective evaluation, were compared with the degree of physiological stress, as measured using salivary alpha-amylase activity. The results indicated that human speech and chewing sounds caused similar levels of psychological stress while performing intellectual tasks; however, chewing sounds caused comparatively less physiological stress than did human speech sounds. These findings suggest that depending on the sound stimulus, psychological and physiological stress characteristics may not coincide. Keywords Intellectual task · Auditory stimulation · Psychological and physiological effects of sound on humans · Subjective evaluation 1 Introduction noise with a moderate SPL has been shown to affect cognitive performance [7, 8]. Asakura and Tsujimura [10] found that The coronavirus disease 2019 pandemic has led to a wider household sounds, such as those with much lower SPLs than variety of work styles in various locations, which has road traffic noise, can affect cognitive performance. Further- increased opportunities for office workers to work outside of more, they also reported that these sounds may show an upper traditional office spaces. The environmental characteristics acceptable level of annoyance at SPLs around 40 dB [10], of a home or commercial space differ from those of con- depending on the noise sensitivity of individuals. The effects ventional office spaces. In such differing environments, the of low-level sounds (i.e., 34–45 dB) on intellectual tasks goal is to achieve production efficiency equal to or greater have also been studied. Tamura reported that when sounds than that of conventional workplaces. Numerous studies have with low SPLs are perceived as noise instead of unavoidable examined the impacts of environmental factors on intellec- phenomena, a given task can be quantitatively maintained, tual productivity [1], as well as the effects of the sound but qualitative performance tends to be reduced [11]. On the [2], visual [3], air quality [4] and thermal environments [5]. other hand, no case studies have examined the effects of envi- Among these environmental factors, although the influence ronmental noise with an SPL < 30 dB on human productivity. of various sound sources has been considered a factor of the However, it has been noted that various sounds generated in sound environment, there are generally cases where environ- an office environment can affect work, even if none of the mental sounds such as broadband noise [6], road traffic noise sounds has a significant SPL [12]. [7, 8], and conversation sounds [9] with relatively high sound In the present study, an experimental investigation was pressure levels (SPLs) are present. The impact of broadband conducted to examine the psychological and physiological noise, with a relatively high SPL of around 75–95 dB, has effects of sound environmental stimuli with a low SPL on the been shown to be naturally large [6], whereas even traffic performance of intellectual tasks. The psychological factors related to the degree of disturbance, concentration, and stress, B T. Asakura as measured by subjective evaluation, were compared with t_asakura@rs.tus.ac.jp the degree of physiological stress, as measured using salivary alpha-amylase (sAA) activity. Department of Mechanical and Aerospace Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-Shi, Chiba 278-0022, Japan 123 Acoustics Australia (a) (b) (c) Smartphone Table 12 min 12 min 12 min 12 min 12 min 12 min Participant Stimulus 1 Stimulus 2 Stimulus 3 Stimulus 4 Stimulus 5 Stimulus 6 12 min 12 min 1min 5min 1min 5min 1min 5min A Intellectual UK test B Break A Intellectual UK test Ceiling height: 1900 mm Stimulus 1 Stimulus 2 Unit: mm A: Measuring sAA B: Measuring sAA & subjective evaluation (d-2) (d-3) (e) (d-1) Experimenter Sound source HATS Table Sound sources HATS Experimenter HATS Unit: mm Unit: mm Fig. 1 The experimental flow: (a) the overall flow of the experiment including six auditory conditions and the partial flow of each of the auditory conditions, b the experimental setup showing a participant inside the soundproof room, c the dimensions of the soundproof room, d-1 the measurement situation for each auditory stimulus, d-2, d-3 the spatial relationships between the sound source and the HATS recording device, and e a screen showing the task calculations in the software [14] using the Uchida–Kraepelin (UK) method 2 Methods 5-min break was provided between each experimental con- dition. The order in which the six types of sounds were 2.1 Experimental Procedure reproduced was randomized for each of the participants to reduce the effect of the order. Before the experiment, the The experimental setup and flow are shown in Fig. 1.The participants were also given sufficient practice with the intel- experiment was conducted in a soundproof room to avoid lectual task on the smartphone. Then, instructions were given the contamination of low-level sounds via exterior noise. The for the situations that should be assumed in the experiment, study participants sat at point P inside the room, as shown in as follows. The participants were instructed to carry out the Fig. 1c. intellectual work carefully, as though it involved actual work In this experiment, four types of artificial fluctuating as opposed to a hobby. For the auditory stimuli, artificial sounds and two types of static sounds with equivalent sounds were generated at a distance of 1 m to the left of continuous A-weighted SPLs of 24–29 dB were used the participants. No specific instructions were given as to the as acoustic stimuli. The participants, while exposed to location in which they were supposed to be working. these sounds through headphones (ATH-W1000Z; Audio- Technica, Tokyo, Japan), performed a 5-min intellectual 2.2 Participants task based on the Uchida–Kraepelin (UK) psychodiagnostic test [13] under each experimental condition using Kraepelin The study participants were 20 healthy young male volun- Training free software [14] running on a smartphone (iPhone teers (mean age ± standard deviation [SD]: 21.7 ± 1.3 years, 13; Apple, Cupertino, CA, USA). age range: 20–23 years). Only men were recruited because For the sound playback, the headphones were connected to of the known existence of a gender difference in psycholog- a laptop PC with an audio interface (UR22mkII; YAMAHA ical responses to noise [15]. In accordance with EN 50332-1 Steinberg, Tokyo, Japan). After the task was completed, the and EN 50332-2 proposed by the European Committee for participant evaluated the degrees of disturbance, concentra- Electrotechnical Standardization [16, 17] as sound pressure tion, and stress perceived during the task. Saliva intake was regulations for portable audio players and the university’s measured and sAA analysis was performed before and after ethical guidelines, this experimental study was designed to be the intellectual work, as shown in Fig. 1a. These experimen- noninvasive. Informed consent was obtained from all partic- tal procedures were carried out for all six auditory stimuli. A ipants. The subjects were advised in advance to get adequate 1,200 1843 Acoustics Australia sleep the day before to avoid sleep deprivation on the day of Table 1 SPLs of the auditory stimuli: silence (S–SI), pink noise (S- PN), writing with a ballpoint pen on paper (S-PB), typing and clicking the experiment. The experimental collaborators were briefed (S-TC), TV news (S-TN), and chewing (S-CC).L indicates the equiv- Aeq on the study purpose and methods, as well as the anonymiza- alent continuous A-weighted SPL tion and use of data. Furthermore, prior to the study, all Stimuli S–SI S-PN S-PB S-TC S-TN S-CC participants were asked about their hearing ability, and all assured that their hearing was normal. The participants were L (dB) 20.2 28.5 27.9 25.1 26.9 28.1 Aeq also asked to confirm that they were not in a state of hyper- sensitivity to sound. S-SI S-TC S-TN 2.3 Acoustic Stimuli S-PN S-CC S-PB In this experiment, six types of sounds were used as audi- 10 dB tory stimuli: writing with a ballpoint pen on paper (S-PB), typing and clicking (S-TC) to evoke working sounds in the office, TV news (S-TN), chewing potato chips (S-CC) to evoke the sound of breaks between office work, pink noise without meaning (S-PN), and silence (S–SI). Previous studies have investigated the effects of background noise, including chewing sounds, on the learning efficiency of individuals with highly sensitive misophonia [18], finding that learning efficiency decreased in the presence of gum chewing sounds and increased in a quiet environment [19]. The most typical evoked sounds in misophonia are chewing [20, 21] and repet- itive tapping noises, such as pen clicking [21]. On the other hand, as the prevalence of misophonia has been estimated to 63 125 250 1k 2k 4k 8k be around 20% of the population [22], it is possible that chew- Frequency (Hz) ing sounds may increase annoyance to a small extent, even in relatively healthy individuals. Nevertheless, many evalu- Fig. 2 Frequency characteristics of each of the acoustic stimuli ations of the quality of crispy sounds have been conducted in recent years, and some aspects of these sounds have been accepted positively in terms of improved texture [23]. As that the recorded auditory stimuli were played back using the headphones to reproduce the SPLs shown in Table 1. described above, chewing sounds include various aspects of context; for example, in a place shared with other people, a The frequency characteristics of each of the above stimuli reproduced at the SPLs of Table 2 are indicated in Fig. 2. situation in which people may be working in close proximity to those who are eating and drinking can also be assumed. As indicated in the trend, the S-CC has a relatively higher frequency component, while the other sounds have generally Thus, S-CC was also included as a test sound, as it may have the potential to increase or reduce annoyance. lower frequency. The auditory stimuli were recorded using a head and torso simulator (HATS) system (type 8328A; ACO, Tokyo, Japan) 2.4 Intellectual Tasks in the soundproof room, where the reverberation was sup- pressed by sound-absorbing materials (Fig. 1d). Assuming The participants were presented with a calculation task based an actual office environment, the height of the ear on the on the UK method [13]. This method is used to ascertain the HATS dummy head was set at 1.2 m, which was assumed effects not only of auditory stimulation on the performance to be the height of the ear in the human sitting position, and of intellectual tasks, but also of moderate mental stress on was placed 1 m to the direct right of the person generating the participants and how this stress is affected by the audi- the sound (Fig. 1e). The equivalent A-weighted SPLs of these tory stimulation. It has been used for these purposes in many recorded 5-min auditory stimuli were measured as shown in previous studies [24, 25]. The participants were instructed to Table 1. The background noise inside the room was around add single-digit numbers continuously using the Kraepelin 20 dB, indicated as S–SI. Therefore, the other auditory stim- Training software [14] on the smartphone (Fig. 1e), working uli were measured so that the signal-to-noise (SN) ratio was as quickly and accurately as possible. When a cue was given, > 6 dB, and for (b), the SN ratio was about 5 dB, because the participants were to begin calculations. After 5 min, a the SPL at 1 m was lower than that of the other sounds. The cue for the end of the test was given. For evaluation of the acoustic output level of the audio interface was adjusted so results, the test performance of each participant was assessed Relative SPL (dB) Acoustics Australia in terms of the number of correct answers. While the num- 400 ber of errors was assumed to reflect attentional control [13, 26], the numbers of errors of all the participants were quite small compared with the number of all answers < 1%. One of the reasons for this was that the overall duration of the test was relatively short (5 min). In a previous study [27], the error rate for the UK test was also < 1.0%, even under longer observation. Therefore, the number of errors was not considered in this study. 2.5 Physiological Measurements In this experiment, physiological responses to mental stress S-SI S-PN S-PB S-TC S-TN S-CC were inferred based on information obtained from saliva. Pre- Type of sound vious studies have assessed the degree of stress response in saliva using salivary cortisol [28], amylase [29], or chromo- Fig. 3 Mean and standard deviation for the numbers of correct answers (error bars show 95% confidence intervals) for each auditory stimulus granin A [30]. A comparison of the results of these three methods confirmed that the results are consistent, although gender differences in the statistical trends have been observed were exposed to the auditory stimuli was then evaluated [31]. Regarding gender differences, it was originally noted based on three kinds of indicators: the degrees of concentra- that stress responses differed between men and women [32], tion, stress, and disturbance. The participants were instructed and several studies have found a stronger salivary cortisol to evaluate the three assessment items as they recalled, and response in men than in women in reaction to stressors not to rewrite their evaluations after subsequent reconsid- [33]. On the other hand, Maruyama et al. [34]showed eration. They were also instructed to respond within 1 min, that sAA levels displayed a rapid increase and recovery, which is the required time for sAA measurements. A 10-point returning to baseline levels 20 min after a stressor, whereas Likert-type scale was used to evaluate the three assessment salivary cortisol responses showed a delayed increase that items, with responses from 1  “not disturbed at all” to 10 remained significantly elevated from baseline levels 20 min “strongly disturbed” for the degree of disturbance, from 1 after the stress challenge. Their analyses revealed no gen- “high level of concentration” to 10  “no concentration der differences with regard to the sAA response, but did find at all” for the degree of concentration, and from 1  “very significantly higher salivary cortisol responses in females. stressed” to 10  “not stressed at all” for the degree of stress. Furthermore, they indicated that younger subjects tended to display higher sAA activity. Therefore, in the present study, sAA was used to consider younger age groups in the exper- 2.7 Statistical Analyses iment, which was conducted in men only, in view of gender differences. The sAA levels were measured using a portable A multi-way analysis of variance (ANOVA) was conducted to monitor (DM-3.1; NIPRO, Osaka, Japan). The participants investigate the effects of each auditory factor on the psycho- were carefully instructed about the saliva sampling proce- logical and physiological indicators. If the ANOVA results dure, as described in the manufacturer’s manual (NIPRO). showed significant main effects, the relationship of the mean Next, they collected their own saliva by placing a filter paper values between each group was evaluated in detail through under their tongue for 30 s, and the sAA concentration was multiple comparisons using Bonferroni correction. By con- measured with the monitor. The analysis was initiated by trast, differences between groups in sAA before and after the promptly inserting the saliva chip into the unit, and after auditory stimulation were assessed using a paired t-test. All about 60 s, the sAA was displayed in units of KU/L. The statistical analyses in the present study were performed using above procedure was followed according to the methods used BellCurve for Excel (Social Survey Research Information, by Yamaguchi et al. [35]. Tokyo, Japan), with p values < 0.05 considered significant. 2.6 Psychological Measurements The degree of sound disturbance was adopted as an evalua- 3 Results tion item, referring to a study on sound disturbance during intellectual work using electroencephalography (EEG) sig- The mean numbers and SDs of correct responses obtained for nals [36]. The psychological state of the participants who each of the auditory stimuli are shown in Fig. 3. The results Number of correct answers Acoustics Australia (a) (b) (c) ** ** ** 10 10 10 * * ** 9 * 9 9 ** 8 8 ** 8 ** 7 7 7 6 6 6 5 5 5 4 4 4 3 3 3 2 2 2 1 1 1 S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC Type of sound Type of sound Type of sound Fig. 4 Mean and standard deviation for subjective scores (error bars show 95% confidence intervals) for each auditory stimulus under the conditions of the degree of a disturbance, b concentration, and c stress. *p < 0.05, **p <0.01 (a) 60 (b) 30 : Pre-work sAA ** : Post-work sAA * 30 0 -10 -20 -30 S-SI S-PN S-PB S-TC S-TN S-CC S-SI S-PN S-PB S-TC S-TN S-CC Type of sound Type of sound Fig. 5 Mean and standard deviation for sAA scores (error bars show 95% confidence intervals) for each auditory stimulus: a pre- and post-work sAAs and b sAA, which is the difference between the pre- and post-work sAAs. *p < 0.05, **p <0.01 of the one-way ANOVA with the auditory stimulus as a fac- significant differences in the pairs shown in each figure. In tor showed no significant difference for the main effect of terms of the degree of disturbance, the auditory stimuli S-TN the auditory stimulus. This result is similar to that reported and S-CC showed significantly higher disturbance than did in a previous study on the degree of disturbance during intel- the other four auditory stimuli. In terms of the degree of con- lectual work using EEG signals [36], where no significant centration, the S-TN and S-CC auditory conditions showed difference was found in the main effect of the auditory stimu- significantly lower concentrations than did S–SI. With regard lus when pure tones were used as the auditory stimulus. In any to the degree of stress, the S-TN and S-CC auditory condi- case, the effect of the auditory stimulus on work was small, tions showed significantly higher stress than did S–SI and indicating that it was not reflected in the workload. This was S-PB, respectively. No significant differences were found attributed to the simplicity of the experimental tasks, which between S–SI and S-PB in any of the categories. were easy to carry out even if the participants felt disturbed Next, the physiological results are indicated as follows. by the sound or stressed by the task. The baseline values of sAA described above may have dif- Next, the mean subjective scores and SDs for the degrees fered between each of the subjects due to stress and other of disturbance, concentration, and stress caused by the repro- factors caused by the experimental environment, which is duction of the auditory stimuli are presented in Fig. 4a–c, different from usual for the subjects. Therefore, the pre- and respectively. The results of one-way ANOVAs with auditory post-work sAAs and the difference between pre- and post- stimuli as a factor showed significant differences (p < 0.01) work sAAs (sAA) are shown in Fig. 5a and b, respectively. in the main effects of all auditory stimuli on the degrees of First, a paired t-test of the sAAs measured pre- and post- disturbance, concentration, and stress. The results of multi- work, respectively, showed significant differences (p < 0.01) ple comparisons between each of the auditory stimuli showed Degree of disturbance sAA (KU/L) Degree of concentration sAA (KU/L) Degree of stress Acoustics Australia (a) (b) 10 10 9 9 8 8 7 7 S-TN S-TN 6 6 5 5 S-CC S-PN S-CC S-PN 4 4 3 3 S-SI S-PB S-PB S-SI 2 2 1 1 S-TC S-TC 12 34 5 6 78 9 10 12 34 5 6 78 9 10 Degree of concentration Degree of concentration Fig. 6 Correlation between the subjective scores of a concentration and disturbance, b concentration and stress (a) 15 (b) 15 (c) 15 S-TN S-TN S-TN 10 10 10 S-PN S-PN S-PN 5 5 5 S-PB S-PB S-PB S-SI S-SI S-SI 0 0 0 S-TC S-TC S-TC S-CC S-CC S-CC -5 -5 -5 12 34 5 6 78 9 10 12 34 5 6 78 9 10 12 34 5 6 78 9 10 Degree of stress Degree of concentration Degree of disturbance Fig. 7 Correlation between each of the subjective scores of a disturbance, b concentration, and c stress, and the sAA only for S-PN and S-TN. Next, a one-way ANOVA with audi- S-TN and S-CC indicate almost the same degrees of each of tory stimuli as a factor showed a significant difference (p < the subjective indicators. 0.05) for the main effect of auditory stimuli. As a result of Next, regarding the physiological results of Fig. 5b, only multiple comparisons, a significant difference (p < 0.01) was the S-TN auditory stimulus showed significantly higher found only between S-TN and S-CC, as shown in Fig. 5b. sAA; S-CC, which showed similar subjective rating values to S-TN, showed the lowest values. Then, the relationship between each of the subjective scores of (a) disturbance, (b) concentration, and (c) stress, and the sAA is presented 4 Discussion in Fig. 7. While in all categories except S-CC the sAA increases in some degree in relation to subjective impression, The correlation among each of the subjective scores are indi- it can be seen that the values of sAA differ significantly cated in Fig. 6. As shown in Fig. 6a, the results of the present between S-CC and S-TN despite having almost the same subjective evaluation experiment indicate decreases in con- subjective impression score. This trend appears to be par- centration as the degree of disturbance increased. This is ticularly pronounced in the relationship between stress and consistent with the finding in a previous study that the degree sAA in Fig. 7a. First, as S-TN is a meaningful noise con- of concentration is strongly related to the degree of distur- taining speech, the sense of work disturbance was markedly bance [36]. It is also a natural consequence that the degree increased, and the resultant stress may have increased the of stress increases as observed in Fig. 6b, because reduced sAA. However, the degree of stress caused by S-PB and degrees of disturbance and concentration can be obstacles to S-TC, which may also increase annoyance, was relatively task performance. It should be noted that the conditions of sAA (KU/L) Degree of disturbance sAA (KU/L) Degree of stress sAA (KU/L) Acoustics Australia moderate. On the other hand, S-CC resulted in the same level Thus, it is necessary in the future to examine the effect of of stress as S-TN, but in contrast to S-TN, post-work sAA was longer task durations. the most reduced among all conditions. In other words, the As future research, the effects of auditory stimuli on work sound of chewing crispy chips was subjectively disturbing efficiency should be investigated by controlling the type, and stressful during work, but it did not cause stress physio- duration, and difficulty of tasks and increasing the sound logically. There have been several cases where differences in types and physiological indicators. At this point, it would be stress states have been predominantly detected in sAA-based useful to examine the degree of stress in more detail using analysis results [29, 34]; therefore, the degree of physiologi- EEG signals [37] and heart rate [38] in combination as other cal stress indicated in the present study also seems plausible. physiological indices. Second, the present results are limited Although the participants were instructed to assume they to men in their 20s. It may be possible to draw more general were engaged in office work, it is possible that such chewing conclusions by investigating a wider range of participants, sounds were actually unconsciously recognized as sounds including women and older people. that occur in a more casual setting than in an office, suggest- Acknowledgements The author would like to thank K. Morita for ing that the participants may have consequently performed the technical assistance with the experiments. Informed consent was intellectual work in a state of physiological relaxation. How- obtained from all participants. ever, the participants may have experienced an increase in Funding Open access funding provided by Tokyo University of Sci- subjective stress due to the common knowledge that chewing ence. sounds are perceived as a less favorably accepted artifi- cial action sound and may increase annoyance for a certain Open Access This article is licensed under a Creative Commons Attri- proportion of people. This also suggests the importance of bution 4.0 International License, which permits use, sharing, adaptation, examining the effects of sounds, even those generally con- distribution and reproduction in any medium or format, as long as you sidered to be unpleasant, on people in detail by comparing give appropriate credit to the original author(s) and the source, pro- them not only with subjective impression ratings, but also vide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are with physiological responses. included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in 4.1 Limitations the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a The present study has some limitations. First, sample size copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. was calculated a priori, and the moderate sample size of 20 subjects somewhat restricted opportunities to examine differences between each of the physiological conditions. Specifically, a sample size of 20 participants gave post hoc References power of 35, 79, 36, 26, 75, and 27% to detect differences 1. Mujan, I., Andelkovic, ´ A.S., Muncan, ´ V., Kljajic, ´ M., Ružic, ´ D.: between the pre- and post-work sAA under the S–SI, S-PN, Influence of indoor environmental quality on human health and S-PB, S-TC, S-TN, and S-CC acoustic conditions using a productivity - A review. J. Clean. Product. 217, 646–657 (2019) two-group t-test with a two-sided significance level of p < 2. 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Journal

Acoustics AustraliaSpringer Journals

Published: Sep 26, 2023

Keywords: Intellectual task; Auditory stimulation; Psychological and physiological effects of sound on humans; Subjective evaluation

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