## 4 Discussion  
The present study investigated the individual differences in sustained attention as measured by the psychomotor vigilance task (PVT), focusing specifically on the influence of age, gender, and time of day. While it has been well documented in prior research that aging is associated with slower reaction times, the impacts of the measurement time and gender differences on attentional performance have not been sufficiently examined in large-scale datasets [1,3]. Our findings contribute new insights into the variability of attention, including its human physiology and ergonomics [26, 27, 28, 29, 30, 31], providing new perspectives on the methodological considerations required when using the PVT in experimental and applied settings. One of the most notable findings of this study was the significant effect of time of day on the reaction time (RT), minor lapses (MNLs), and major lapses (MJLs). Participants tested in the early morning (8:00-12:00) demonstrated significantly slower reaction times and more attentional lapses compared to those tested later in the day (13:00-18:00). This temporal pattern suggests that attentional performance is not uniform throughout the day and is likely influenced by circadian rhythms, which regulate alertness and cognitive performance across time. Although circadian effects have been widely recognized in sleep science, their explicit influence on sustained attention tasks like the PVT has not been adequately integrated into standard experimental protocols. Our findings suggest that time-of-day effects should be taken into account when designing studies or interpreting PVT-based outcomes, particularly in studies seeking to assess fatigue, sleep deprivation, or the impact of long working hours. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**MNL**} & \multicolumn{4}{c}{**Standardized Coefficients**} & \multirow{2}{*}{**T**} & \multirow{2}{*}{\(p\)**} \\ \cline{2-2} \cline{4-6}  & **B** & & & & \\ \hline Constant & 14.7669 & & & & \\ Gender & 6.1711 & 1.557 & 0.2064 & 3.963 & 0.0001 \\ Time period & \(-\)8.6109 & 1.0091 & \(-\)0.4135 & \(-\)8.533 & \(<\)0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Coefficients of the MNL model. Additionally, gender differences were evident in our analyses. Female participants tended to exhibit longer reaction times and a higher frequency of minor lapses, especially during the early morning period. These differences may be partly explained by hormonal or neurobiological variations, but further studies are needed to understand the underlying mechanisms. The interaction between gender and time of day also merits further investigation, as it may indicate differential sensitivity to circadian- or fatigue-related factors between males and females. Importantly, our findings highlight a key methodological issue that has been largely overlooked in experimental design: the timing of cognitive performance assessments. The PVT is often used as an objective measure to evaluate declines in attention associated with fatigue, disrupted sleep, or prolonged work. However, if the baseline attentional performance varies systematically depending on the time of day, this introduces a potential confounder that could affect the validity and interpretation of the findings. For example, a participant tested at 9:00 AM may appear more fatigued than one tested at 3:00 PM, even if both are equally well-rested, simply due to natural variations in alertness. As such, researchers using the PVT should either control for or statistically adjust for the measurement time, or ideally standardize the testing times across participants. This insight is particularly valuable from an experimental methodology standpoint, as it addresses how specific design choices--such as the measurement timing--can significantly influence the data outcomes.