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Background: The aim of this study was to compare noise sensitivity (NS) in schizophrenic individuals with/without hallucinations and healthy individuals. Procedure: A retrospective (causal–comparative) study was conducted in three groups: (i) A group of individuals with schizophrenia and auditory hallucinations (14 participants), (ii) a group of schizophrenic individuals without auditory hallucinations (14 participants) selected by purposive sampling and (iii) a control group (19 participants) selected by convenience sampling. Schutte’s Noise Sensitivity Questionnaire was used to measure NS. Analysis of Variance and Kruskal–Wallis tests were applied to compare the three groups. All the analyses were done using SPSS-20. Results: ANOVA results indicated that the groups were significantly different in terms of NS (p<0.001) and that NS was higher in groups whose participants were schizophrenic (119.64 and 102.36, respectively, in groups with or without auditory hallucinations) compared to that in the group with healthy individuals (94.79). Conclusions: On the basis of this study, it became evident that patients with schizophrenia are more sensitive to noise than healthy individuals. The results also indicated that schizophrenic patients with auditory hallucinations are more sensitive to noise than those without auditory hallucinations.
Keywords: auditory hallucinations, noise sensitivity, psychopathology, schizophrenia
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Noise is an unwanted sound which people try to get rid of completely; it may affect the health and well-being of people. Many individuals are quite sensitive to special noises, but these noises do not affect their daily life. However, some individuals show negative reactions like annoyance, tension, anxiety, or fear when exposed to usual noises, and these reactions affect their lives negatively.[1]
Many definitions of NS relying on different measurements exist, that is, NS measurements had been made before applying proper investigation or proposing a systematic theory.[2] A clear and specific definition which is meant in this research is: NS indicates a tendency to greater levels of annoyance and reaction to noise than in less sensitive individuals[2]; that is, NS refers to any states (physiological, psychological, or related to life style or activities conducted) of any individual which increase their degree of reactivity to noise in general.[2] This definition does not consist of the hyperacusis which is due to decreased sound tolerance[3] but NS indicates that individuals differ in their sensitiveness to or annoyance caused by different noises.[4] NS is a personality trait covering attitudes towards noise in general and a predictor of noise annoyance.[2]
Since noise-sensitive individuals are more affected by noise,[5] they show more involvement and are more likely to show more precise differentiation. They might also perceive noise as a threat and have slower reactions or adaptation to noises.[3]
The reported prevalence rates of NS in previous studies have varied between 20% and 40%[6]; such a prevalent phenomenon is known as an indicator of general vulnerability to stressors combined with environmental threat perception and the lack of control over the environment and is correlated with negative irritability and physiological arousal.[4],[6] NS could associate to some mental consequences.[7],[8] For instance, some studies have shown that individuals with high NS reported clear signs of incompetence, depression, anxiety, isolation tendency, sensitivity, anger, tension, inferiority and nervousness and that these problems have affected their socialization and their presence in society.[4],[6],[9] In addition, the American Psychological Association (APA) has also introduced NS as a soft sign which may result in problems and distress in patients.[10]
It has been shown that NS has Psychological and physiological components. It does aggregate in families and probably has a genetic component too.[5]
Significant differences in heart rate change or heart rate variability (HRV) have been observed between noise-sensitive and noise-resistant groups,[11] that is, sensitive individuals show more HRV and other physiological reactions.
In terms of disturbances in brain functions, as per Kliuchko’s study in 2017, noise-sensitive groups exhibit less sensory gating than the noise-resistant groups, that is, they show less activity in their thalamus to prohibit noise from entering the high-level processing areas of brain. Another physiological investigation of the central auditory processing revealed compromised sound feature encoding and automatic discrimination skills in noise-sensitive individuals.[12],[13] So, these studies show physiological and functional components are effective in the emergence of the problem.[11],[14]
Introversion–extroversion dimension and neuroticism and subjective noise sensitivity (SNS), as psychological factors, have been found to play important role in increasing NS, with neuroticism and introversion–extroversion being the least and the most effective indicators, respectively.[12],[15],[16]
NS is associated with introversion; in fact, introverted people show a low threshold for feeling noise. During mental processing, correlation analysis revealed a highly significant negative relationship between extroversion and noise annoyance.[17]
Neuroticism, as a fundamental trait of general personality, refers to an enduring tendency or disposition to experience negative emotional states.[18],[19] People with such a disposition have displayed worse performance in enduring noise compared to individuals without neuroticism.[17] Interpretation of these findings is very difficult; however, it may be possible that the CNS of individuals with neuroticism is normally under a bigger extent of arousal, so the crucial level of arousal in them could be more easily reached by noise than in people without neurotic tendency.
According to Eysenck, neurotic persons might show enhanced "arousability", that is, their arousal level increases more in stress.[17] Additional unfavorable factors for CNS of people with neuroticism are worrying and anxiety, which might prevent them coping successfully with noise or some other stressors during mental performance.
The third psychological factor is subjective noise sensitivity (SNS). Various criteria have been used to explain individual differences in NS. One of them is auditory acuity, but it seems that there is no significant relation between auditory thresholds as measured by an audiometer and SNS.[17] This favors the assumption that SNS is a function of cognitive processes rather than merely function of a peripheral auditory acuity.
It also has been shown that NS is associated with the structural organization of the brain.[13] It has been observed that NS increases after brain injury[11] and that noise-sensitive individuals have enlarged volumes of the auditory cortical areas and hippocampus as well as thicker right anterior insular cortex.[13] These results suggest that NS is related to the structures involved with auditory perceptual, emotional, and interoceptive processing. Speaking shortly, NS is not merely an auditory phenomenon but instead has underlying neuronal mechanisms.[13],[20],[21]
Despite all the points that were mentioned earlier regarding to causes and effects of NS, its existence in mental disorders or general population has not received sufficient attention, especially in Iran.
A group of individuals who suffer from receiving simultaneous noises and are annoyed by it are patients with schizophrenia.[22]
Schizophrenia is one of the mental disorders that can cause the most severe impairments in different fields of an individual’s functions, with a global prevalence of less than 1%. Hallucinations, delusions (positive symptoms), thought disorders and cognitive impairments (negative symptoms) are its most important symptoms. Hallucinations in schizophrenia could involve different senses; however, auditory system is usually more involved. In fact, among positive symptoms, auditory hallucinations are the most prevalent (82%).[12],[6] But, not all schizophrenic patients experience hallucinations.
Although NS has been associated with some psychiatric disorders, some investigators have suggested that compared to non-patients, schizophrenic patients might be more prone to be affected severely and destructively by stressful noises.[22] Schizophrenia is a heterogeneous disorder and is identified by changes and difficulty in expressing emotions and cognitive processes when facing stressors. These stressors could be interpersonal (like social interactions or occupational demands), biological (such as congenital viruses or neurological insults), or environmental (e.g., urbanization).[23] The likelihood of being diagnosed with schizophrenia may increase by the interplay between these stressors and internal dispositions. Noise could also be considered as a stressor to which schizophrenic individuals may react differently (compared to general population). For instance, schizophrenia is twice more prevalent in urban population than in a villager.[24] In a qualitative study on schizophrenic patients by Londan, Shepherd, McGarry, theedom, Miller,[25] it was indicated that the participants were annoyed because of noise sensitivity; however, they earlier felt that they could not share this problem with health-care professionals or their main care-givers. After speaking about this problem, their concern did not seem as serious. These findings are in line with the brain studies on schizophrenic individuals. In fact, it has been shown that schizophrenic patients and normal individuals have differences in their brains.[10],[26],[27],[28] For instance, due to the reduction in thalamic volume and impairments in thalamus–cortex pathways, these patients receive different stimuli simultaneously and cannot integrate the obtained information properly.[26],[29],[30] Some of the environmental stimuli include noises. Since the pathways of the auditory nerves are impaired in schizophrenic individuals (such as deficient cholinergic neurons in hippocampus, thalamus, or other areas that are responsible for suppressing the irrelevant noises), they receive many stimuli simultaneously and therefore, integration or ignoring the background and intrusive noises becomes a problem.[29],[30] Despite the mentioned studies that have introduced the biological dispositions for NS and over-occupation of the brain in schizophrenic individuals, NS has not been studied systematically or based on evidence in patients with schizophrenia and in the Iranian population. In other words, it is not clear whether NS is different in schizophrenic and healthy individuals. Is NS observed in all schizophrenic individuals or is it related to a specific sub-group of these patients? Therefore, the aim of the current research is to compare the severity of NS in schizophrenic individuals with and without auditory hallucinations and the healthy individuals. According to American Psychological Association, the role of NS in pathology has been neglected despite the distressing nature of this feature.[25],[31],[32] Hopefully, the present study will result in a deeper understanding and identification of NS in schizophrenic patients and the general population and encourage the investigators to propose more practical implications in the fields of prevention or therapy.
ProcedureSubjectives
The current retrospective study (causal–comparative) consisted of three groups: a group of schizophrenic patients with auditory hallucinations, a group of schizophrenic patients without auditory hallucinations, and a group of non-patients. The study population included all schizophrenic patients in the city of Kermanshah in 2018 to 2019. The patients were selected using purposive sampling and the control group was selected by applying convenience sampling among people of Kermanshah. The required sample size for comparing the difference in mean scores of the three groups was determined according to the presented formula:
As a result, 19 participants were needed for each group, and finally, 60 participants were recruited for the three groups.
The inclusion criteria:
The inclusion criteria for the first group: schizophrenic patients with auditory hallucinations
Being diagnosed with schizophrenia according to SCID-I and the confirmation of a psychiatrist.[33]Having experienced auditory hallucinations according to the diagnosis of a psychiatrist.Providing written informed consent for participating in the study by the participants themselves or by their legal guardians.Having at least a secondary school diploma for completing the questionnaires.Falling within the age group 18 to 50 years.Not being diagnosed with other disorders that include auditory hallucinations (schizoaffective disorder, bipolar disorder, drug and medication induced psychosis, and any of the Axis-I disorders with psychotic features).Not having received ECT during the last 2 weeks.The inclusion criteria for the second group, schizophrenic patients without auditory hallucinations, were the same as the first group except that the second group’s participants should not have experienced auditory hallucinations according to the diagnosis of the psychiatrist.
Inclusion criteria for the third group, control group:
Not having been diagnosed with SCID-I psychiatric disorders.Not having immediate family members diagnosed with schizophrenia.Falling within the age-group 18 to 50 years.Having at least a secondary school diploma for completing the questionnaires.Providing written informed consent for participating in the research.At the beginning, the psychiatrist (the advisor of the current project) was asked to introduce the hospitalized schizophrenic patients to the executor of the research project. Afterwards, the patients who were introduced by the psychiatrist and the non-patient participants who were surveyed in the city were invited for the preliminary assessments and the examination of their concordance with the inclusion and exclusion criteria (SCID-I) by the psychiatrist or the psychologist of the project. The eligible participants were given an informed consent form to sign, and were then, included in the study. The sample included 60 participants. According to previous studies, variables like age, income, and occupation were correlated with our dependent variable (NS).[6] Therefore, matching was applied for the three groups in terms of demographic characteristics such as age, income, and occupation. Noise sensitivity of the groups was measured using the Persian version of Schutte’s Noise Sensitivity Questionnaire (NoiseQ).<xps:span class=“xps_endnote”>1 The demographic data were collected by interviewing and reading the medical records of the patients.
Measurements:
Schutte’s Noise Sensitivity Questionnaire
This questionnaire was developed for data collection about NS by Schutte et al. in 2007.[34] This 35-item scale is designed for measuring NS in general and also in five daily life situations, including during leisure time, at work, at home, in society, and during sleep. The items are scored on a 5-point scale from 1 (strongly disagree) to 5 (strongly agree). The general score of NS is calculated by the mean score of all 35 items. When the questionnaire is utilized to measure the general NS, its reliability goes above 0.90. The given data confirm the validity of this scale. The Persian version of this questionnaire was normalized in a study by Ghazavi et al. in 2020, where Cronbach’s alpha was measured to be 0.84. Moreover, the correlation of all the subscales with the total score and with each other was reported to be high and significant. Furthermore, there is a significant convergent validity between this scale and the DASS-21’s interpersonal sensitivity and anxiety components. Factor analysis studies have indicated the acceptable fitness of both 5-factor and single-factor models; however, the 5-factor model has a more suitable fitness.
Structured clinical interview for DSM disorders (SCID-IV)
SCID has two versions, and in the current study, the research version has been used. This version has been designed according to the research criteria of DSM-IV.[10] According to the study of Sharifi, As’adi, Mohammadi, Amini, and Kaviani on 299 patients aged 18 to 65 years, the diagnostic agreement of the SCID test and retest was fair to good for most diagnostic categories (kappas over 0.6). Overall weighted kappa for current diagnoses was equaled 0.52 and 0.55 for lifetime diagnoses.[35] This scale has been utilized in Iranian population, and its test–retest reliability coefficient after 1 week was measured to be 0.95.[35]
Statistical analysis
Descriptive data such as mean, median, and standard deviation were used to describe the studied features. Analysis of Variance and Kruskal–Wallis tests were applied for comparing the three groups. All the analyses were done using SPSS-20. Significance level has been determined for all the tests in the results section.
ResultsThe final sample size of this study included 47 participants, of which 14 were schizophrenic patients without auditory hallucinations, 14 were schizophrenic patients with hallucinations, and 19 were healthy individuals [Table 1].
There was no significant difference between the mean scores of the groups for age (P > 0.01), gender, and marital status (P > 0.05). However, the results of the chi-square test indicated that the educational level is significantly different between the groups. Having a BA or higher educational degrees was significantly more frequent in the non-patient group compared to the groups of schizophrenic individuals with or without auditory hallucinations (P < 0.001) [Table 2].
Table 2 Mean, standard deviation, and ANOVA results for comparing noise sensitivity in three groups of the studyANOVA test results indicated that there is significant difference between the groups in terms of NS (P < 0.001); therefore, regarding the significance in ANOVA test results about noise sensitivity, LSD post-hoc test was applied for pairwise group comparisons [Table 3].
Table 3 The results of LSD post-hoc test for pairwise comparison of the groups in terms of noise sensitivityThe results of the pairwise comparisons after the LSD test indicated that the mean score of noise sensitivity is significantly higher in the group of schizophrenic patients with auditory hallucinations (P < 0.05) compared to non-patients (P < 0.001) or schizophrenic individuals with no auditory hallucinations (P = 0.013).
The mean of noise sensitivity was 7.56 scores higher in schizophrenic patients without auditory hallucinations compared to non-patients; however, this difference was not statistically significant (P = 0.538) [Figure 1].
The results also indicated that there is no significant relationship between noise sensitivity and any of the demographic variables such as age, gender, marital status, and educational level and that none of these variables had a predictive role for noise sensitivity.
DiscussionThe aim of the current study was to compare noise sensitivity in schizophrenic individuals with or without hallucinations and healthy individuals. The results in general indicated that, compared to healthy individuals, schizophrenic individuals were more sensitive to noise; furthermore, the patients with auditory hallucinations were more sensitive to noise in comparison with patients with no auditory hallucinations (P < 0.01). These findings were in line with the investigations of Kelly and Wright. which had highlighted the destructive effects of noise on schizophrenia patients.[22],[23] In fact, these studies suggest that noise can be considered a stressor and that the response of schizophrenia patients might differ from that of other individuals due to their different minds and brain structures and their vulnerability to stressors. Moreover, this finding can be related to the neurological investigations that have suggested the likelihood of the deficient suppression of intrusive noises in pathways of the auditory nerves in schizophrenic individuals and also suggested enlarged volumes of the auditory cortical areas and hippocampus as well as a thicker right anterior insular cortex in people with NS.[13],[20],[26],[29],[30]
Nonetheless, these studies do not determine whether the deficiencies in these pathways cause NS in all schizophrenic patients or not.
The current research suggests that NS is more common in schizophrenic patients (even in those who have not experienced auditory hallucinations) than in healthy individuals. Also, patients with auditory hallucination reported more NS compared to patients without them.
This aspect requires more therapeutic awareness and care, as also modifications in environmental and occupational situations to make them more suitable for these individuals.
The findings of this preliminary study generate more questions that can be answered by the results of the current research; longitudinal studies are, therefore, required for more accurate information. In other words, regardless of all the deductions made on the basis of the results of this study, and more importantly, this investigation further raises these questions: why are schizophrenic patients more sensitive to noise? Is this sensitivity a consequence of the disorder, or is it a predisposition? If it is a consequence, underlying factors and therapeutic methods are required to be studied, and if it is a predisposition, more investigations are needed to determine which schizophrenic symptom is related to noise sensitivity. As a result of exploring solutions to these questions, the vulnerable population will be recognized, and prevention programmes will be improved.
Furthermore, noise sensitivity has been identified in other psychological disorders,[2],[3],[4],[5] but it is unclear how this feature is experienced in other disorders, how it develops in each, or what it leads to. Is there a possibility that a mutual psychological, physiological, or genetic variable in all disorders has led to noise sensitivity? Some studies, for example, have found some mutual physiological and genetic findings in people with NS[5],[20]; are these also true in mental patients, particularly those with schizophrenia?
Moreover, the difference between the two schizophrenic groups with and without auditory hallucinations generates the idea that this variable might have a role in experiencing hallucinations. However, the justification and explanation of this difference and the reasons behind it require further consideration and investigation.
It is suggested that future studies examine this structure with more patients; the low number of participants in the present study was partly due to inclusion criteria, especially “Not being diagnosed with other psychotic disorders such as bipolar disorder, drug-induced psychosis or other disorders” and partly due to the inability of some patients to fill out the questionnaires and cooperate with researchers.
Moreover, this structure can be studied in other disorders as well. It is also suggested that future studies focus on the mutual factors between the different disorders that result in noise sensitivity (as a consequence) or the factors that lead to different effects of NS in different individuals or cause various symptoms in different disorders. Studying the effects of NS on the quality of life of the patients and presenting therapeutic solutions or environmental modifications for reducing these effects also seem to be necessary.
ConclusionsOn the basis of the results of this study, patients with schizophrenia are more sensitive to noise than healthy individuals. The results also indicated that schizophrenic patients with auditory hallucinations are more sensitive to noise than those without auditory hallucinations.
Acknowledgements
The authors would like to thank the associate principal of the research and technology of Kermanshah University of medical science (KUMS) warmly and respectfully for providing the funding of this research.
Financial support and sponsorship
Funding from Kermanshah University of Medical Science (KUMS).Conflicts of interest
There are no conflicts of interest.
References
Correspondence Address:
Youkhabeh Mohammadian
Department of Clinical Psychology, Kermanshah University of Medical Science, postal code: 6714848554, Kermanshah
Iran
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/nah.nah_42_22
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