Effect of Diurnal Changes on Auditory Stream Segregation Using Spectral Profile Analysis in Young Adults with Normal Hearing

INTRODUCTION

The time of day that affects a person’s capacity to execute both mental and physical tasks is known as a diurnal change. Every individual’s sleep-wake cycle is regulated by a 24-hour internal clock called the Circadian rhythm. These timing processes and the homeostatic physiology regulate the alertness and sleepiness of human beings.¹ Based on the circadian rhythm, individuals can be categorised as morning-type (M-type), evening-type (E-type), or intermediate (those who do not show major morning or evening preferences) based on their circadian rhythm. Individuals who are morning-type are more active in the morning (early in the day), and individuals who are evening-type are more active in the evening (late in the day).² Research indicates that these choices have a major impact on people’s memory, alertness, and attention.³ Numerous studies in the field of audiology have been investigated to determine the distinctions between these preferences by identifying the impacts through behavioural and electrophysiological tests.^4–11

For morning-type people, an electrophysiological test employing P300 to assess diurnal shifts revealed greater amplitude and shorter latencies, while evening-type people exhibited the opposite results.⁵ Literature has shown the effect of diurnal changes in younger adults on various auditory processing abilities, such as dichotic listening tests and temporal processing tests, such as gap detection tests, duration discrimination tests, temporal modulation function tests, and tests of differential sensitivity and temporal resolution.^7–10 Also, auditory working memory and spatial tasks in younger adults revealed similar results.⁴ In contrast, diurnal changes in younger adults on auditory working memory showed no significant effects on the responses of individuals in all three categories, i.e., M-type, E-type, and intermediate category.⁹ Similar findings were reported on screening tests of auditory processing, within-channel auditory gap detection, and recall tasks.^12,13

Auditory stream segregation refers to the cognitive process by which listeners group sounds that share similar characteristics, distinguishing them from other, unrelated sounds.¹⁴ This process, also known as auditory streaming, is crucial for individuals with normal hearing, especially in environments where multiple sound sources are present, helping to prevent the confusion of different auditory signals.¹⁴ One important cue that facilitates auditory stream segregation is spectral profiling. Spectral profiling allows the listener to identify changes in the spectral characteristics of a sound, such as when the amplitude of a component within a complex tone is altered.¹⁵ This alteration results in a change in timbre, which can be analysed to evaluate spectral profiling abilities.¹⁵ Therefore, spectral profile analysis tasks can be used to assess the sensitivity of the auditory system to changes in the spectral composition of sounds.

Moreover, individuals with cochlear pathology or auditory neuropathy spectrum disorder exhibited poorer spectral profile thresholds compared to those with normal hearing.¹⁶ Previous studies have underscored the importance of factors such as participant attention and the timing of testing in influencing the results of audiological assessments.^4,7–10 In particular, research has recommended investigating the diurnal effects—how different times of day might affect audiological test outcomes—for more accurate and generalisable findings.^4,7–10 However, there is still a lack of sufficient research evidence to understand the effect of diurnal preferences on auditory streaming abilities in younger adults. Given this gap, the present study aims to investigate auditory stream segregation abilities through spectral profile analysis in younger adults with normal hearing. Specifically, the study’s objective was to compare the spectral profile thresholds between morning and evening testing sessions across three groups of participants: those who are moderately morning, those with intermediate, and those who are moderately evening.

MATERIAL AND METHODS

RESULTS

Descriptive statistics were used to calculate the mean and standard deviation of the profile analysis thresholds for both morning and evening test conditions across the three groups. The results are illustrated in Figure 1.

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Figure 1:

Mean and standard deviation of profile analysis thresholds for morning and evening tests across all three groups. dB: decibel.

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The findings indicated that individuals in the moderately morning group performed better in the morning compared to the evening, while those in the moderately evening group demonstrated superior performance in the evening. In contrast, the intermediate group showed no significant difference in performance between the morning and evening testing sessions.

To determine whether these differences in performance between the morning and evening sessions were statistically significant, inferential statistics were conducted for all three groups. Given that the data were normally distributed (p > 0.05), parametric paired t-tests were performed to compare the profile analysis thresholds for morning versus evening testing within each group. The results of these inferential statistics are presented in Table 1.

The paired samples t-test results revealed that for the moderately morning group, the profile analysis thresholds were significantly better in the morning (p < 0.05) compared to the evening. Similarly, for the moderately evening group, performance was significantly better in the evening (p < 0.05). However, no significant difference was observed for the intermediate group, as their performance in both morning and evening sessions was similar (p > 0.05).

DISCUSSION

The present study revealed a significant diurnal effect on spectral profile analysis tests. Specifically, profile analysis thresholds were found to be better in the morning for morning-type individuals, while evening-type individuals performed better in the evening. In contrast, the intermediate group exhibited no significant variation in thresholds when tested at different times of the day. These findings are consistent with previous literature, which has documented significant diurnal preferences in various auditory behavioural tests.^4,7–10 Studies have shown that morning-type individuals tend to demonstrate superior auditory temporal processing skills, dichotic listening abilities, and auditory spatial and working memory performance in the morning, while evening-type individuals perform better on similar tasks when evaluated in the evening.^4,7–10 Diurnal effects on speech perception in noise have also been observed in previous studies.¹¹ Furthermore, electrophysiological measures such as P300 latency and amplitude for tonal stimuli have shown similar diurnal effects.⁵

However, some studies have reported no significant diurnal effects in certain auditory processing tasks, such as within-channel auditory gap detection, auditory processing screening tests, and recall tasks.^3,12,13 These differences may be attributed to variations in the nature of the tasks or differences in methodology.

One possible explanation for the diurnal effects observed in spectral profile analysis could be related to individual variations in circadian arousal levels during different cognitive tasks.^6,23–25 Morning-type individuals tend to feel more alert and perform better in the morning, often preferring to engage in work or exercise during this time. Conversely, evening-type individuals generally experience their peak alertness in the late afternoon or evening, leading to better performance in tasks during this period.

Another potential explanation for these diurnal effects is inhibitory control, which plays a crucial role in cognitive functions such as working memory, speech comprehension, and selective attention.²⁶ It is reported that inhibitory control is less effective during off-peak hours, which could contribute to poorer performance on spectral profile analysis tests during these times.²⁶

In contrast, the intermediate group, lacking a distinct peak in arousal, showed no significant diurnal variation in their performance. This suggests that psychoacoustic test outcomes might be influenced by variations in inhibitory control depending on the time of day when testing occurs.^4,7–10,26 Additionally, factors such as sleep patterns, levels of exhaustion, and general alertness at different times of day may further impact the results of psychoacoustic tests.

CONCLUSION

This study aimed to investigate the impact of diurnal variations on spectral profile analysis tests in morning-, evening-, and intermediate-type individuals with normal hearing. The results demonstrated a significant diurnal effect, with morning-type individuals outperforming in the morning and evening-type individuals showing better performance in the evening. No diurnal effect was observed for the intermediate group. The findings suggest that poor cognitive performance and reduced inhibitory control during off-peak hours could account for poorer test scores at those times. Therefore, diurnal variations should be considered as a potential extraneous variable in future research on psychoacoustic tests in younger adults.