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The Cicadian Rhythm: The Effects of Cicada Sounds on Cognitive Functioning

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Introduction

Figure 1: Brood X Cicada, 2021

Although often unnoticed, insects make a considerable amount of noise. In different locations and times of the year, the presence of noise-producing insects varies, but one of the most notorious loud insects is the cicada (Figure 1). Brood X, the most recent periodical cicada, returned after 17 years and has been documented in almost every Indiana county.1 When in groups, cicadas can reach sound levels up to 100 dB.2 Sound at this level not only damages hearing, but also causes changes to cognitive performance depending on the task chosen to be studied.3

The purpose of this study was to see if Brood X cicada sounds impacted cognitive functioning, as there has been little to no research on the topic. In order to test this, participants were asked whether or not they enjoyed the sounds of Brood X cicadas, and then they were given the Montreal Cognitive Assessment in both quiet and cicada conditions. The score and time were recorded for each section, providing a total score and a total time. I hypothesized that the score for participants who responded that they did enjoy cicada noise would achieve higher scores in a faster time in the cicada environment compared to the quiet environment, and the opposite was hypothesized for those who responded that they did not enjoy the sounds of cicadas.

After analyzing the data by looking at both patterns and using paired t-tests, there was a statistically significant difference for the total score for participants who responded that they did not enjoy the sound of cicadas, as they scored one to three points lower in the cicada trial. Although those who responded yes did not show a statistically significant difference in scores, the scores were one to three points higher in the cicada condition. Finally, there was a statistically significant difference between all participant times for the delayed recall task, but no difference found in total times. Despite these findings, more research would need to be done in order to validate the results, as the sample size for this study was small and not representative of the population. Further research could be done to determine is this shift in cognitive functioning has impacts on daily life, such as causing traffic accidents or changing productivity in the workplace.

Background

Despite the knowledge that cicadas produce a sound that reaches levels that change cognitive performance, there has been little to no investigation into how the sounds produced specifically by cicadas may affect human cognition; therefore, this review will focus on studies that experimented on an aspect of cognition using a different type of sound at different decibel levels, such as environmental, white, or ambient noise. Both the type of sound and the decibel level affect cognitive functioning.

One reviewed study focused solely on attention. The study conducted by O’Malley and Poplawsky experimented with intermittent noise levels of 0, 75, 85, or 100 dB. To test attention, a serial anticipation task was used – four-letter words were shown in the center of a screen and three-letter words were shown on the sides. The results showed that subjects in the two loudest environments learned fewer of the three-letter words than those in the quieter environments, based on a free-recall test. In addition, a Stroop word-color test was used, and subjects in the 85 dB environment performed better than other groups. These results showed that in louder environments, attention is narrowed.4

A later study conducted by Hygee, Bowman, and Enmarker centered on how memory systems were affected by traffic noise and irrelevant speech. 92 high school students were given a variety of different memory tasks, such as text recall, word fluency, or word comprehension tasks. Overall, the results of the experiment showed impaired recall for each of the memory tasks.5 A different study by Angwin et al. provided the opposite result when white noise was used. Participants were sorted into two groups – those in the experimental group were exposed to 70 dB white noise while those in the control group were not. Participants completed five learning phases in which they were shown pictures of aliens and their names. Afterward, each participant completed a recall task in which they were to type the name for each alien presented. The results showed that those in the white noise group had better recall over time, opposite of the study by Hygee, Bowman, and Enmarker.6

By studying multiple aspects, such as attention and memory, a more complete picture of cognition can be ascertained. Multiple studies have tested the effects of noise on cognition or several aspects of it. The first experiment by Gomes, Matinho Pimenta, and Castelo Branco tested if long-term exposure to large pressure amplitude (≥90 dB) and low frequency (≤5500 Hz) affected memory or attention. 40 aircraft technicians and 30 matched controls were tested with the Toulouse-Piéron test and the Weschler Memory Scale (WMS). The study determined that there was no difference in the Toulouse-Piéron test but a significant difference in the WMS, indicating that there was a deterioration of memory but not in attention due to prolonged exposure in loud environments.7 A slightly later study by Hillier, Alexander, and Beversdorf studied cognitive flexibility and memory using 32 adults. Each was tested with three cognitive tests without noise and with 90 dB white noise. Cognitive flexibility was assessed with the compound remote associates (CRA) task, in which three words were provided and the associated word must be identified. Memory was tested using the Hopkins Verbal Learning Test (HVLT) and the Rey-Osterrieth Complex Figure Test (CFT). It was found that the white noise significantly decreased cognitive flexibility performance and increased latency, but it had no effect on memory.8

These studies on multiple aspects of cognition or cognition itself led to the development of experiments on cognitive impairment caused by noise. A study from 2016 by Tzivian et al. performed a cross-sectional analysis of the Heinz Nixdorf Recall Study to determine if mild cognitive impairment can be caused by long-term exposure to air pollution and traffic noise. In the original study, over 4000 participants were given a cognitive assessment. It was found that out of these, 600 participants had mild cognitive impairment, indicated by five neuropsychological tests. The study assessed particulate matter, nitrogen oxide, and traffic noise levels, and a linear regression model was used to identify individual risks. A positive association was shown between air pollution and traffic noise to mild cognitive impairment.9 A previous experiment by Cheng et al. used mice to test for mild cognitive impairment. The mice were exposed to 80 dB white noise for either one, three, or six weeks. The mice were tested using a water maze and a step-down inhibitory avoidance test, which shocked mice when the stepped off a platform onto the ground. The data was analyzed using an ANOVA and t-test, which showed that moderate intensity white noise impaired cognition, and longer exposure to the noise led to more impairment.10

The most similar study to my experiment was performed in 2018 by Van Hedger et al. This experiment focused on studying cognitive performance in urban and natural soundscapes. 63 participants aesthetically rated both the urban and nature soundscapes before being given the dual n-back task and the BDS task. By correlating the cognitive assessment with the aesthetic assessment, the researchers were able to determine if cognitive performance was affected by the type of sound used and if the participant’s rating played a role. They found that the relationship between aesthetic ratings and cognitive performance was not significant, whether the ratings be positive or negative. Overall, the type of noise and the individual’s feelings about that noise did not affect cognitive performance.11

Based on these past studies, each aspect of cognition yields varying results. In addition, the result of a cognitive test depend largely on what type of sound is used. For example, white noise was shown to increase memory systems but also caused mild cognitive impairment. From all of this information, little can be ascertained about how the sounds produced from insects might affect cognition. Many of these experiments focused on how aspects of human cognition are affected by noise, but they failed to use insect noise. Even the two most similar studies failed to completely compare with my intended experiment. The cross-sectional analysis did not involve actual experimentation, but rather manipulation of data. In addition, it looked at long-term exposure, not short-term. The other study used mice instead of humans, it used white noise instead of insect noise, and it tested for mild cognitive impairment using behavioral tests instead of cognitive tests designed specifically for mild cognitive impairments. Although the study most similar to mine did use natural sounds, it failed to focus on insect sounds, specifically the cicada.

Because there is a gap in the research, I studied whether the noise from produced by insects causes a change in cognitive functioning or increased latency depending on the preference for cicada noise.

Methods

The experiment was based on quantitative measures obtained from the Montreal Cognitive Assessment (Figure 2), which provides a score assessing mild cognitive impairment by testing multiple aspects of cognitive functioning and is used in the assessment of different types of dementia.12,13 Qualitative measures were used to determine if there were differences between those who enjoyed the sound of cicadas versus those who did not.

Figure 2: V8.1 of the Montreal Cognitive Assessment

The experiment took place in a quiet setting with no significant distractions, which for many was in my apartment. To begin, the participant took an online hearing test from hearingtest.online to ensure they would be able to effectively hear the cicada noise during the second test. This hearing assessment was chosen because it provided an audiogram for each participant (Figure 3), allowing the description of normal hearing, mild, moderate, or severe hearing loss. If a participant’s results from the online test showed that they had moderate or severe hearing loss, they were disqualified from participating in the study. Moderate and severe hearing loss is described as having difficulty hearing sounds greater than 25 and less than 40 decibels, and greater than 40 and less than 60 decibels, respectively.14 The cicada sound was played at around 85 decibels, so eliminating those who had difficulty hearing sounds near that range helps ensure the sound’s potential effect on cognition is measured accurately.

Figure 3: Audiogram from hearingtest.online

Before beginning the actual quantitative portion of the experiment, the participant was asked a series of questions. First, they are asked their age. This information was used to see if there is a difference between ages, as this could indicate that those who have experienced Brood X a greater number of times are either more or less cognitively affected than those who have experienced it a fewer number of times. Participants were then asked whether they enjoy the sound of the Brood X cicadas. This information was used to determine if those who find the sound more enjoyable perform differently on the test than those who do not.

To begin the quantitative portion of the experiment, the participant was seated and then given Version 8.1 of the MoCA test while the environment was quiet. The participant took the test with a paper and pencil, and I proctored it according to the Montreal Cognitive Assessment’s guidelines. While they took the assessment, I used the MoCA application on an iPad to record the time it took each participant to complete each section. After completion of the MoCA, I scored the exam and uploaded the results to the application. By doing so, both the time of completion of each section and the score were compiled.

After a short break, the participant then completed the second trial. Before starting the assessment, the video “Cicadas in the summer 10 hour loop” from YouTube was played through a speaker. The participant was seated in a position such that the decibel level at their location was approximately 85 decibels, a safe level for exposure during a short time period.15 Brood X cicada noise in Indiana was measured up to 96 decibels in 2004, the last time they were present; however, this sound level can cause hearing loss in as little as two hours, so a level of 85 decibels was chosen because it can be safely heard for up to eight hours.15,16 The participant was given Version 8.2 of the MoCA, and the process listed above was repeated while listening to the video. Afterward, all data from the application was compiled into a spreadsheet.

Once all participants completed the experiment, the scores and the time taken for the assessment were analyzed using patterns and paired t-tests with a p-value of 0.05. A similar experiment in which cognitive functioning was tested in different noise environments for individuals diagnosed with ADHD and neurotypical individuals used paired t-tests and a p-value of 0.05, indicating that this was the correct statistical test and value to use for my data.17

Results/Analysis

After collecting all of the data, the major results were compiled into Table 1 and Table 2. Although there was more data for each individual section of the Montreal Cognitive Assessment, this was not included in the tables unless a clear pattern was present, or a paired t-test was performed on that data.

Table 1: MoCA data
Table 2: MoCA data continued

By looking at the data in Table 1, the total scores for participants who responded “yes” to the cicada preference question were one to three points higher in the cicada trial. For those participants who responded “no,” their scores were one to three points lowers in the cicada trial. The Memory Index Score (MIS) from the Delayed Recall (DR) section was one to six points higher for “yes” participants and two to five points lower for “no” participants in the second trial. For the total time, there were no patterns evident. For the actual delayed recall section, it took participants a longer time to recall the words under the cicada conditions. For the Visuospatial/Executive (V/E) tasks (which involved participants drawing a line, copying a shape, and drawing a clock), the Serial 7 Subtraction (S7) task, and Orientation task, the time decreased for each for the second trial. When looking at age and scores, there was no pattern, meaning that those who have experienced more cicada cycles are not more likely to perform better on the MoCA.

A paired t-test was used because the observations were obtained in pairs, with the comparison coming between participants.18 A p-value of less than 0.05 was considered significant. The p-values of each test and their significance is shown in Table 2.

Table 3: p-values of paired t-tests

Even though there were patterns present in Table 1, many were not statistically significant. There was not a statistically significant difference between the entire group’s scores or between the “yes” participants for the two trials; however, there was a statistically significant difference between the individuals who responded “no” to the cicada preference question, with a p-value of 0.0086. This indicates that an individual who does not enjoy the sound of cicadas is impaired cognitively when asked to function in that environment. There were no statistically significant differences found in any of the Memory Index Scores or the total time. Although the total time was not significant, the amount of time it took to recall words in the Delayed Recall task was found to be significant with a p-value of 0.0440. This indicates that for all participants, it took longer to recall words in the cicada environment than in the quiet environment.

Some participants gave comments after completing the experiment. The most common critiques were that some tasks were easier on one version compared to the other. For example, the participant with the MoCA ID of 12522 said she struggled with the Fluency task of the first version, but not the second. In this task, the participant is asked to list as many words as they can think of that begin with a specific letter. Version 8.1 uses the letter F, whereas Version 8.2 uses the letter S. This participant noted that it was much easier to come up with words beginning with S than F, complicating the comparison between these two versions of the MoCA. After researching this, it is an issue that has yet to be fixed. A study conducted in 2015 by Lebedeva et al. tested five of the tasks within the English MoCA versions, and the difficulty levels of each task did not match from one version to the next.19 While this presents a limitation for the English version, this is not seen in the French and German versions of the MoCA.20,21 The final comment I received was that one participant intentionally sped up during the second trial in order to limit their exposure to the cicada noise; however, this participant had not experienced the cicadas in person and grew up in an environment without many noise-producing insects, especially those as loud as the cicada.

Limitations

There were a few limitations found during my research. First, it has been shown that psychological conditions such as depression and anxiety, along with a low mood, can cause lower scores on the MoCA.22 Although this would not affect the difference between a single participant’s scores in the two trials, as the condition would be present in both trials, it could have an impact on the difference between participants. This may alter the potential correlations between scores and age or cicada preference. I expected that older individuals have lower average scores than younger individuals, so a younger person with a psychological condition could shift this; however, I did not find a correlation between age and score, so this is not of concern to my experiment. It should, though, be considered in future experiments. I also expected that those who enjoy cicada sounds would have higher scores during the cicada test, but this could also be weakened by psychological conditions in those who prefer cicada noise. In both cases as well, it could also make the correlation appear stronger than what may be actually present if the psychological condition were to be in the other individual being studied.

Another limitation of this experiment is that the trials will take place successively. The creators of the MoCA recommend waiting at least one month before retesting, but this is not possible due to the time constraints of this course. In order to avoid the learning effect as much as possible, different versions of the test were used.23 This, however, did not completely prevent the learning effect, as it took participants less time in the second trial to complete tasks that did not change significantly between the versions. Also, as stated above, the different versions of the MoCA are not exactly equivalent in their difficulty level, and this could have impacted the scores and times for the participants.

Another limitation is the sound being used. I was unable to find a file in which the audio only contained the sounds of Brood X. The video I have chosen to use is taken outside in a forest, so it may contain sounds of other species, such as crickets. This should not present a large problem, however, because the sounds of the cicada are so loud, they cover up most, if not all, sounds from other species.

The final limitation is the small sample size used in this study. The sample only included seven individuals, and most of these were college-aged students from Indiana. As a result, this experiment is not representative of the entire population, or even a small fraction, so much more research has to be done before any of these findings can be considered valid.

Conclusion

Cicadas are a somewhat rare increase in biodiversity, but with this increase comes an increase in noise. Cicadas are known to produce very loud sounds when alone and when in groups, and for some, this noise is bothersome. There is currently no research on whether or not the sounds produced by cicadas cause any kind of change in cognitive functioning, and this study begins to fill that gap.

By using the Montreal Cognitive Assessment, a test that provides a score on cognitive functioning and that is used in the diagnosis of dementia, the change in cognitive functioning could be determined between the quiet and silent environments. By also taking into account age and preference for cicada noise, I could analyze the data and determine whether or not either of these played a role.

It was found that although there was an increase in points for those who preferred cicada noise and a decrease in points for those who didn’t, there was only a statistically significant difference for those who did not enjoy the cicada noise. The same pattern was seen for Memory Index Scores, but no significant difference was found for either group. There was no pattern for total time, but there was increased time for the Delayed Recall task and decreased time for the tasks that did not change significantly between the versions, such as the Visuospatial/Executive tasks, the Serial 7 Subtraction task, and the Orientation task.

The limitations include that the difficulty between the versions was not consistent; there was a learning effect seen by the decreased times in similar tasks; the video was not only isolated cicadas; and the sample size was small. For each of these limitations besides the small sample size, a remedy was used to limit the effect of the problem. The only way to remedy the small sample size would be to gather more data by creating a sample that is large and representative of the population. This would allow the data to be valid.

For implications, the sounds of cicadas may cause individuals to lose focus. This is especially important when driving and when working. Further studies could explore each of these issues more in depth to see if there are increased traffic accidents or lower worker productivity during cicada seasons. Exploring this topic further will only continue to fill in the current gap present in the literature.

References

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