Introduction:

Reaction time is the interval between a stimulus and the response generated by the body. It is a fundamental measurement of cognitive performance. An individual’s reaction time is influenced by many factors, including age, gender, fatigue, circadian rhythms, sleep deprivation and time of day (1). The effect of time-of-day has been extensively studied in various contexts, such as driving and work-related tasks. However, only some studies illustrate these effects on athletes (2). Another cognitive function that plays a vital role in an athlete’s overall performance is attention. Attention is a state in which cognitive resources are focused on certain aspects of the environment and the central nervous system is in a state of readiness to respond to stimuli (4). There are mainly four types of attention – Sustained, Selective, Divided, and alternating attention, each having an influence in cognition, and together work to elevate sport performance (3). This literature review explores existing knowledge behind the effect of time of day on reaction time and attention levels of individuals.

Time of day and reaction time:

Reaction time varies depending on the time of day. The circadian rhythm controls the sleep-wake cycle and affects many physiological processes, including cognitive function (5). Many studies have investigated the effect of the time of day on reaction time. The results have shown that the reaction time is fastest during the late morning and early-noon hours and slowest during the early morning and late evening. For example, a study was conducted by Elisabeth et al. (2013) where 14 highly trained male cyclists voluntarily took part in 6 cognitive performance test sessions at 08:30, 10:30, 12:30, 14:30, 16:30, and 18:30. The main results indicated that the reaction time of the cyclists depended on the time of day as there were notable fluctuations in the readings. Four tests were performed: phasic alertness, visual scanning, flexibility, Go/No-go, and reaction time is a component in all 4 of these tests. On assessing the reaction time from these tests, it was evident that reaction time was always the greatest in the morning at 8:30. There is a reduction in reaction time as the hours go by, and the reaction time is always the lowest at 12:30 at the afternoon. There is an upward trend of the reaction time after 12:30, which usually becomes slower as the evening commences (6). On testing 893 white young military men, Simo Taimela (1991) found that RT was slower at 16:00. Though the fluctuation was not too prominent, RT is relatively faster in the afternoon 12:00-14:00 compared to the rest of the day (7).

The Circadian Rhythm is controlled by a complex network of interacting genes and proteins, but most importantly, it is governed by the light from the external environment (8). A study by Camila et al. (2012) aimed to assess the pattern of cognitive functions in totally blind people. The results of the tests are of little concern to this literature review, but the study also had a control group of sighted individuals who participated in the study. The group was subjected to auditory reaction time testing at 2:00, 6:00, 10:00, 14:00, 18:00, and 22:00. The results highlighted the fastest reaction time at 14:00. Slowest reaction time at 2:00. A similar trend was observed where the reaction time improved through the morning, was the slowest in the afternoon and went on to increase through the evening (8).These results are supported by another study by Sana et al. (2013). The study’s objective was to understand the interaction of time of day and sleep deprivation on the cognitive functions of 12 male handball goalkeepers. In a randomized order, the group was subjected to the intervention and reaction time tests at 08:00, 12:00, 16:00, 20:00, and midnight. The results also illustrated that reaction time was the least in the early afternoon at 12:00 and higher in the morning and the later hours of the day (9). 

Additionally, it is also believed that reaction time is affected by an individual’s chronotype or natural tendency towards morning or evening. Morning types tend to have faster reaction times in the morning and slower reaction times in the evening. In contrast, evening types have the opposite pattern (12). A study by Dayane et al (2021), investigated the credibility of chronotypes on cognitive functions such as reaction time. The study was performed on 30 male industrial workers. Based on the Munich Chronotype Questionnaire (MCTQ) results, the subjects were divided into 3 groups: early-type, intermediate-type, or late-type, based on their preference for morning, evening, and night hours respectively. The mean reaction time was taken pre-work (morning) and post-work (night) to assess if cognitive performance is impacted by chronotype. Results show that morning-type people did not have the fastest reaction time in the mornings, and night-type people did not have the fastest reaction time at night. Meanwhile, intermediate-type people had the fastest reaction times in both mornings and evenings, before or after shifts (13). We can see a contrasting result in a study by Elise et al. (2018). The study was done on 56 healthy individuals divided into early-people and late people, depending on their preference towards morning or night, respectively. A strong correlation between chronotypes and reaction times was observed when the whole group was subjected to reaction time tests throughout the day. Morning-type people or early-people had a faster reaction time in the morning and poorer performance as the day went on, while night-type people or late people performed poorly in the morning but better at night (14). Such contrast can be observed while researching the topic; hence the validity of chronotypes still needs to be determined.

Time of day and attention levels

In the realm of attention research, a trichotomy of distinct neural networks known as alerting, orienting, and executive functioning has been recognized in recent studies (15). The relation between the components of this trident is a matter of great interest and many researchers are constantly experimenting with various tests to understand how each of these components are affected by sleep deprivation and time of day. But the more interesting aspect of sleep deprivation and its effect on attention is whether it affects all components of cognitive capacities, or it affects some components of cognition more than others (16). This review also sheds light upon how attention levels are affected by time of day, which tells one whether a person can be alert at various time periods throughout the day (4).

Although it is a crucial cognitive function that underpins various daily activities, such as workplace safety, the natural fluctuations of sustained attention throughout the day have not been fully understood. Therefore, it is important to study how attention levels are affected and change due to time of day. In an experiment by Riley E et al. (2017), participants are instructed to press the space bar when presented with city images and to refrain from responding when presented with mountain images during the gradCPT. Due to the rapid pace of stimulus presentation, accurately distinguishing between the two and inhibiting the response to mountain images is difficult (4). This study identified noteworthy daily fluctuations in sustained attentional control. Group level performance for all sustained attention metrics was highest during the mid-morning hours 9:00 – 11:00 AM, followed by a gradual decline throughout the day and a more rapid decrease during late evening hours.
Performance across all variables was the worst in the early morning hours (3:00-7:00 a.m.) (4).

Results according to the study by Riley E et al. (2017) showed that sustained attention strategy had more subtle daily variation than the ability variables, with the slowest reaction times and most cautious responding between noon and 4:00 p.m. homeostatic sleep pressure is a term that is used by researchers when referring to the build-up of the pressure of sleep as one’s time awake increases. Riley E et al. (2017) found evidence within our large online data set that sustained attentional control is strongest mid-morning and worsens thereafter, likely due to homeostatic sleep pressure (18)

Conclusion:

On reviewing fifteen studies and articles on the influence of time of day on reaction time and attention levels, we infer that reaction time and attention levels are influenced by diurnal changes in the human body. An individual’s reaction time is usually the fastest in the early afternoons and slower during other times of the day. Attention levels are strongest mid-morning and worsens gradually. It is important to focus on variables of cognition and not on attention as one single entity alone. The validity of the influence of chronotypes on reaction time and attention levels is questionable and still needs conclusive evidence.