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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 26  |  Issue : 3  |  Page : 163-167

Comparison of cognitive functions in elderly population with and without hearing loss


1 Department of Speech and Hearing, SOAHS, Manipal Academy of Higher Education, Manipal, Karnataka, India
2 Department of Clinical Psychology, SOAHS, Manipal Academy of Higher Education, Manipal, Karnataka, India

Date of Submission10-Jun-2019
Date of Acceptance03-Jun-2020
Date of Web Publication22-Dec-2020

Correspondence Address:
Dr. Archana Gundmi
Department of Speech and Hearing, MCHP, Manipal Academy of Higher Education, Manipal, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.INDIANJOTOL_65_19

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  Abstract 


Objective: The objective of this study was to investigate the association between hearing loss and cognitive functions in the elderly population. Methods: A cross-sectional study was carried out on 12 elderly individuals with hearing loss (elderly hearing impaired [EHI]) and 20 elderly individuals with normal hearing (elderly normal hearing [ENH]). The participants in the study were aged between 60 and 65 years. The audiological and cognitive tests were performed on both the groups. Results: The data compiled through descriptive statistics and multivariate analysis of variance revealed clinically significant differences between the EHI and ENH on different cognitive tests. This indicates that elderly population associated with hearing loss requires more time to process the tasks as compared to ENH individuals. Conclusion: There is a higher decline in cognitive functions in elderly individuals when associated with hearing loss compared to normal-hearing individuals. Since it is noticed as a comorbid condition, both cognition and hearing loss have to be assessed and treated in these individuals for better quality of life.

Keywords: Cognition, elderly individuals, hearing loss, sensory decline


How to cite this article:
Somnath A, Gundmi A, Bhargavi P G, Rai S. Comparison of cognitive functions in elderly population with and without hearing loss. Indian J Otol 2020;26:163-7

How to cite this URL:
Somnath A, Gundmi A, Bhargavi P G, Rai S. Comparison of cognitive functions in elderly population with and without hearing loss. Indian J Otol [serial online] 2020 [cited 2021 Jan 23];26:163-7. Available from: https://www.indianjotol.org/text.asp?2020/26/3/163/304289




  Introduction Top


Aging is a biological process which has its own dynamics, which is more beyond the human control. In most developed countries, the retirement age, which is approximately 60–65 years, is believed to be the start of an aging process (World Health Organization, 2012). All elderly individuals will experience normal aging alterations in the auditory system. For some people, age-related changes in hearing may result in a significant hearing loss, resulting in a long-lasting sensorineural hearing loss.[1] The deterioration in hearing ability which occurs with age is known as presbycusis. Thus, presbycusis is a slow process affecting both the ears, with progressive hearing loss, and, if left untreated, would affect communication and contribute to depression, isolation, and possibly, dementia.[2]

The reduction in sensory function is also accompanied by a reduction in cognitive performance in elderly individuals.[3] The phenomenon of cognitive aging is a phenomenon of physical aging, which varies from individual to individual. Among the elderly people, because of the age-related neurodegenerative process, there is a negative association between sensory input and cognitive function, and this correlation may increase as age increases.[4] Cognition is a general concept which comprises several mental abilities (e.g., memory, attention, reasoning, etc.) for acquiring knowledge and interacting with the environment. A typical level of cognition is very important for an individual's day-to-day functioning.

Based on the psychometric research, a theoretical framework is often used to describe cognitive aging, which is categorized into two magnitudes of intelligence, namely fluid intelligence and crystallized intelligence.[5] The aptitude to solve problems and think logically in peculiar situations is fluid intelligence which the capability to utilize skills, knowledge, and experiences is crystallized intelligence. This framework is utilized, especially when speculating age-related variations or changes. There is a decrement of fluid intelligence with increasing age, with crystallized intelligence remaining constant or even improving with increasing age. Many psychologists consider that several components of fluid intelligence drive the decline of general cognitive functioning in older adults.[6] The decline mainly comprises processing speed,[7] working memory capacity,[8],[9] and inhibitory control.

Cognitive abilities include mental speed of processing, memory, language, and visuospatial and executive functions. Among them, the most commonly documented cognitive changes associated with old age are decline in memory, attention, and mental speed of processing (executive function). When these abilities are disrupted, elderly individuals take more time to solve problems or make decisions for a faster communication. The younger and older adults performed similarly when memory task was simple.[10] However, its most challenging for older adults is the ability to divide attention and rapidly divert it between simultaneous mental activities[11] and to neglect distracting and irrelevant stimuli.[12]

Individuals with hearing loss are reported to have poorer cognition as compared to the normal-hearing individuals, whether the hearing loss is treated or not.[13] Hearing impairment interferes with cognitive abilities and intellectual functioning. Therefore, due to its long-lasting decline in sensory system, one could expect a decline in cognition as well.[14] Research findings have advocated that hearing loss in older adults is associated with a higher rate of cognitive decline.[15] Thus, the outcome of the current study is presumed to contribute in predicting the relationship between cognition and hearing impairment.


  Methods Top


Study participants

Participants were enrolled in this cross-sectional study consisting of twenty elderly normal-hearing (ENH) and twelve elderly hearing-impaired (EHI) individuals aged 60–65 years with normal middle ear functioning. All the participants underwent both audiometric and cognitive tests. The study was approved by the Institutional Research Committee and Institutional Ethics Committee (IEC) (IEC 590/2016). Participants who gave their consent were taken for further study.

Audiometric examination

All individuals underwent otoscopy, pure-tone audiometry, stapedial reflex recording, and speech audiometry. The tests were performed by a trained examiner. Thresholds measured in decibel (dB) hearing level were obtained from both ears in a sound-treated room. Testing was conducted according to modified Hughson and Westlake procedure using a diagnostic audiometer (Madsen Astera) calibrated to the American National Standards Institute (ANSI) standards (ANSI S3.43-1996). Pure-tone average (PTA) of hearing thresholds at 0.5–4 kHz was calculated for the better ear. Hearing loss was defined as PTA >25 dB.

Cognitive assessment

The participants in the study were administered with digit symbol substitution test (DSST) and N-back tests. DSST was adapted from Wechsler's Adult Intelligence Scale, 1981. It is a nonverbal test of visuomotor coordination, motor persistence, sustained attention, executive function, and mental speed of processing in which participants were made to code a series of numbers with corresponding symbols. Time taken to complete the task was recorded.

The N-back test was originally developed by Smith and Jonides, 1999. This test included two sets: verbal N-back and visual N-back. Each set has two aspects, i.e., verbal N-back 1, verbal N-back 2 and visual N-back 1, visual N-back 2. Complexity varied based on N-back 1 and 2. Scoring was based on the number of hits and errors, which indicates the ability of working memory. For better understanding of the data, percentile scores were also calculated for each hit and error from NIMHANS Neuropsychology battery (Rao, Subbakrishna, Gopukumar, 2004).

Analytic strategy

Descriptive statistics are presented at baseline for all the variables used in the analysis (mean and standard deviation [SD] were calculated). Multivariate analysis of variance (MANOVA) was performed to see the differences between the two groups in each task. Wilks' lambda value was considered for any differences between the groups. The data were statistically analyzed using the Statistical Package for the Social Sciences (SPSS) (version 16) (IBM Corp, Chicago).


  Results Top


The study consisted of 32 individuals with equal number of males and females. The mean age at evaluation for the ENH group was 62.45 ± 1.93 years and 61.50 ± 1.56 years for the EHI group. The mean age of education for the ENH group was 11.7 ± 2.83 and 10.75 ± 2.7 for the EHI group. The ENH group consisted of 35% of businessmen, 15% of retired, 40% of homemakers, and 10% of other varied jobs. The EHI group consisted of 41.7% of businessmen, 8.3% of retired, 41.7% of homemakers, and 8.3% of other varied jobs. All the participants underwent audiological and cognitive evaluation (mental speed of processing and working memory skill).

Audiological findings

All individuals in the ENH group had PTA thresholds ≤25 dBHL. [Table 1] indicates the details of audiological reports of the EHI group.
Table 1: Audiological detail of elderly hearing-impaired group

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Cognitive functions

The current study concentrated on the mental speed of processing and the working memory skills under the domain of cognitive functions in both the groups.

Mental speed of processing

To assess the mental speed of processing, DSST was administered. The results revealed that the mean time for mental speed in the ENH group was 298.10 ± 74.86, while it was 373.08 ± 107.3 for the EHI group. The mean error of the ENH group was 89.05 ± 0.75, and for the EHI group, it was 88.25 ± 1.91. Statistical significance was not observed using MANOVA (F = 3.20; P = 0.05).

Verbal working memory

N-back 1 and N-back 2 were administered to assess the verbal working memory in the ENH and EHI groups. [Table 2] represents the verbal working memory in ENH and EHI.
Table 2: Mean, standard deviation, and percentile score of verbal working memory in elderly normal-hearing and elderly hearing-impaired groups

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Visual working memory

To assess the visual working memory, N-back 1 and N-back 2 sets were administered in the ENH and EHI groups. [Table 3] represents the visual working memory in the ENH and EHI groups.
Table 3: Mean, standard deviation, and percentile score of visual working memory in elderly normal-hearing and elderly hearing-impaired groups

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  Discussion Top


The peripheral hearing threshold is prone to affect the selective attention, working memory, and processing speed. This study provides information on predicting the cognitive decline by considering mental speed of processing and working memory skills. There was a clinically significant difference between the groups during the task of mental speed of processing. The ENH group was able to complete tasks faster with fewer errors when compared to the EHI group. This indicates that EHI individuals took longer time to perform the task when compared to the ENH individuals. In support of the current study, Hoyer and other researchers[9] have observed that individuals with hearing impairment scored poorer when compared with normal-hearing individual on mental processing ability. In EHI individuals, a 40% higher rate of cognitive decline was observed in comparison to normal-hearing individuals.[14] This study supported the “deprivation hypothesis”[3] which postulates that lack of auditory input from an untreated hearing loss can result in altering the neural networks, which in turn would affect the processing speed in individuals with hearing loss. Another remarkable finding from the current study was that both the groups had higher SD on DSST scores. This indicates a high heterogeneity in geriatrics under the current domain. Thus, this warrants the administration of mental processing test on an individual basis to assess the cognitive functions.

Working memory determines the capacity to retain the information in memory during processing simultaneously the same or different information. Currently, N-back is the frequently used instrument to measure the working memory. The task complexity differs in N-back tests. N-back 1 includes easy level and N-back 2 comprises difficulty level. In the current study, N-back tests were administered in two versions, i.e., in auditory modality and visual modality. In verbal working memory, minimal differences were observed between mean hits and mean error, among the ENH and EHI groups of verbal N-back test. In N-back 2, the magnitude of mean hits and mean error difference between the two groups was observed to be more compared to N-back 1. In support of the study, evidences have reported increasing complexity results in poor scores.[16] Clinically significant differences were observed on verbal N-back test between the groups. This is in consensus with the study where EHI individuals reflected lower scores in dichotic verbal memory test compared to normal-hearing elderly individuals.[17]

In visual working memory, results revealed a clinically significant difference in mean hit and mean error scores between the groups and also showed a significant statistical difference between the groups. This indicated that the normal-hearing individuals could perform the task better than EHI. In visual N-back 2 test, the magnitude of mean hit difference was more when compared between the groups. When the task complexity increases, the cognitive performances decrease in hearing-impaired individuals. The similar findings are also observed by Brown et al.[18]

The findings of the current study support the information degradation hypothesis and deprivation hypothesis.[3] According to the deprivation hypothesis, untreated hearing loss leading to lack of auditory input may have a negative effect on the neural networks involved in certain cognitive abilities, and these effects could be permanent in nature. This similar finding has been reported in the information degradation hypothesis where decline in a cognitive performance is related to hearing loss. Cognitive resources are mostly utilized for higher level of comprehension, such as storage of auditory information into memory, selectively attending to a listener, and also processing the auditory information quickly. Just like normal-hearing individuals, these resources must also be used by the individuals with hearing loss to decode and perceive the speech signals. As mentioned before, due to the decline in certain cognitive abilities of such individuals, they are expected to have poor working memory skills compared to normal-hearing individuals.

In this study, differences in the working memory were better projected in visual working memory than verbal working memory. This could be attributed to the simplicity of the task used in verbal working memory (stimulus used syllables). To prove the results further, an advanced neuroimaging studies could have been included comparing cognitive functions with different sensory impairments such as visual versus auditory impairment.


  Conclusion Top


Overall, the results supported higher decline in cognitive functions in EHI individuals compared to normal-hearing individuals. All audiologists should know the abnormal cognitive changes with aging and be aware of their impact on communication. It is important to notice differences by comparing with varying degree of hearing loss and obtaining the correlation between the degree of hearing loss and cognitive impairment. Since it is noticed as a comorbid condition, both cognition and hearing loss have to be assessed and treated in these individuals for better quality of life. This outcome of the study may vary with increased number of participants. This warrants the use of cognitive tests during assessment and rehabilitation in individuals with hearing loss.

Clinical implications included based on diagnostic and rehabilitative processes:

  • During diagnostic process


    • To include questions in audiological history to ask about cognitive functions (memory, depression, and head injury)
    • Consider using cognitive screening tests in the elderly population who may have cognitive impairment
    • Consider hearing difficulty while assessment of cognitive function.


  • During rehabilitation process


    • Consider hearing aid features that reduce cognitive load in older clients (include automatic program changing)
    • Counsel clients and family members regarding the impact of the coexisting cognitive and hearing impairment
    • Recommending auditory-cognitive rehabilitation in an elderly population.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Taljaard DS, Olaithe M, Brennan-Jones CG, Eikelboom RH, Bucks RS. The relationship between hearing impairment and cognitive function: A meta-analysis in adults. Clin Otolaryngol 2016;41:718-29.  Back to cited text no. 13
    
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Lin FR, Yaffe K, Xia J, Xue QL, Harris TB, Purchase-Helzner E, et al. Hearing loss and cognitive decline in older adults. JAMA Intern Med 2013;173:293-9.  Back to cited text no. 14
    
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Gonçalves VT, Mansur LL. N-back auditory test performance in normal individuals. Dementia Neuropsychol 2009;3:114-7.  Back to cited text no. 16
    
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Shahidipour Z, Geshani A, Jafari Z, Jalaie S, Khosravifard E. Auditory memory deficit in elderly people with hearing loss. Iran J Otorhinolaryngol 2013;25:169-76.  Back to cited text no. 17
    
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    Tables

  [Table 1], [Table 2], [Table 3]



 

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