Reaction time is significantly influenced by age, with older participants demonstrating slower responses across all Stroop task conditions, indicating an age-related decline in executive function and cognitive processing speed.
Key Findings
Results
Reaction time in the control condition increased significantly across the three age groups.
Mean reaction time increased from 21.19 ± 6.80 seconds (Group 1, ages 18–30) to 30.38 ± 10.76 seconds (Group 2, ages 31–60) to 45.13 ± 12.69 seconds (Group 3, ages >60–80).
The difference across groups was statistically significant (p < 0.001).
Each age group contained 70 participants (35 male, 35 female).
Total sample size was 210 participants recruited via convenience sampling at Kathmandu University School of Medical Sciences between March and November 2025.
Results
Reaction time in the congruent condition increased significantly with advancing age.
Mean reaction times rose from 20.41 ± 5.32 seconds (Group 1) to 28.34 ± 9.27 seconds (Group 2) to 41.27 ± 9.69 seconds (Group 3).
The difference across groups was statistically significant (p < 0.001).
The pattern was described as 'comparable' to that observed in the control condition.
Results
The most pronounced age-related increases in reaction time were observed in the incongruent (interference) condition of the Stroop task.
Mean reaction times increased markedly from 63.64 ± 30.72 seconds (Group 1) to 104.48 ± 34.25 seconds (Group 2) to 141.32 ± 47.97 seconds (Group 3).
The difference across groups was statistically significant (p < 0.001).
The incongruent condition showed substantially longer absolute reaction times compared to control and congruent conditions across all age groups.
The standard deviations in the incongruent condition were notably larger than in the other conditions, indicating greater variability in performance.
Conclusions
Older participants demonstrated slower responses across all Stroop task conditions, indicating age-related decline in executive function and cognitive processing speed.
The study used a cross-sectional design with participants aged 18–80 years divided into three groups.
Reaction time was measured using a digital stopwatch for each task condition (control, congruent, and incongruent cards).
Each participant was assessed individually.
The authors note that selective attention as assessed by the Stroop test varies with bilingualism, education, gender, and advancing age.
What This Means
This research suggests that the speed at which people can pay attention and process conflicting information slows down considerably as they age. The study used the Stroop test — a well-known cognitive task where participants name the ink color of words that may or may not match the word's meaning (for example, the word 'RED' printed in blue ink) — to measure reaction times in 210 Nepali adults aged 18 to 80. Participants were split into three age groups: young adults (18–30), middle-aged adults (31–60), and older adults (61–80), with equal numbers of men and women in each group.
Across every version of the task, older adults took significantly longer to respond than younger adults. The biggest differences appeared in the hardest version of the task — the incongruent condition — where participants must name the ink color while ignoring the conflicting word meaning. Young adults averaged about 64 seconds to complete this card, middle-aged adults averaged about 104 seconds, and older adults averaged about 141 seconds. Even on simpler reading tasks (control and congruent conditions), older adults were roughly twice as slow as the youngest group.
This research suggests that the brain's ability to filter out distracting information and respond quickly — a set of skills known as executive function — declines meaningfully across adulthood. These findings may have practical implications for understanding age-related changes in everyday tasks that require focused attention, such as driving or multitasking, and could inform the design of cognitive assessments for aging populations.
Jha R, Mishra A, Chaurasiya N, Nepal O. (2026). Changes in Stroop Task Performance Across the Life Span.. Journal of Nepal Health Research Council. https://doi.org/10.33314/jnhrc.v24i01.5311