Reaction time (RT) is defined as the interval between the presentation of a sensory stimulus and the initiation of a voluntary motor response, and it serves as a simple yet remarkably sensitive measure of the integrity and efficiency of sensorimotor and cognitive processing.(1) Because RT reflects the combined function of sensory transduction, central neural processing, and motor execution, it has long been used as a non-invasive physiological tool to assess attention, alertness, and the overall responsiveness of the nervous system across diverse populations, from schoolchildren to elderly adults.(2) Total reaction time can be conceptually divided into three sequential components: sensory transmission of the stimulus, central processing and decision-making, and motor execution of the response. Of these, central processing is understood to constitute the largest proportion of total reaction time, accounting for the majority of variation observed between individuals and across the lifespan.(3) Both visual reaction time (VRT) and auditory reaction time (ART) are commonly studied, as the two modalities differ in their afferent neural pathways and synaptic relay stations before reaching the cortex; auditory stimuli are conventionally reported to be processed faster than visual stimuli, a difference attributed to the shorter neural pathway and fewer synaptic relays required for auditory signal transmission compared with the more complex retinal processing required for visual stimuli.(4) This expected modality difference has been consistently confirmed in comparative studies of healthy young adults, where auditory stimuli reliably elicited shorter reaction times than visual stimuli of comparable salience.(5) Age is among the most consistently identified determinants of RT. In children, RT shows a clear pattern of progressive improvement throughout childhood and adolescence, paralleling the maturation and myelination of central nervous system pathways; ongoing myelination of corticospinal and frontotemporal fiber tracts during late childhood and adolescence increases conduction velocity and supports the refinement of motor and attentional control.(6) This developmental trajectory continues until cognitive processing speed peaks in the third decade of life, coinciding with the completion of prefrontal cortical maturation and maximal myelin efficiency.(7) Beyond this peak, RT begins a gradual age-related decline; cross-sectional studies spanning early to late adulthood have demonstrated that both simple and choice RTs increase progressively with advancing age, with choice RT typically showing more pronounced slowing than simple RT.(8) The physiological basis for age-related slowing in older adults has been the subject of considerable investigation. Early work attributed slowing primarily to declining peripheral nerve conduction velocity; however, subsequent analyses suggested that reduced motor and sensory nerve conduction velocity accounts for only a small fraction of the total age-related increase in RT, with the substantially greater contribution arising from central, premotor processing delays rather than peripheral transmission deficits.(9) More recent neurophysiological research has reinforced this conclusion, showing that aging slows stimulus perception, discrimination, and response selection through increased intrahemispheric and transcallosal transmission times, in addition to delays in motor cortex response generation.(10) Together, these findings indicate that age-related RT slowing is a multifactorial phenomenon involving sensory, central, and motor stages, with central processing delays playing the dominant role. Despite extensive individual investigations into either pediatric development or age-related decline in RT, comparatively fewer studies have examined the full lifespan trajectory of both VRT and ART within a single cross-sectional cohort spanning childhood through late adulthood. Characterizing this complete trajectory is of practical relevance, given the role of RT in everyday tasks requiring prompt sensorimotor responses, such as road safety, occupational performance, and sports participation, across all age groups.(11) The present study was therefore designed to assess and compare simple and choice visual and auditory reaction times across four distinct age groups, from childhood to late adulthood, and to characterize the relationship between age and reaction time performance.

Study Design and Setting This cross-sectional observational study was conducted in the Department of Physiology at a tertiary care teaching institution over a period of eight months. Institutional Ethics Committee approval was obtained prior to commencement of the study, and the study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all adult participants, and informed assent together with parental/guardian consent was obtained for participants under 18 years of age. Study Population A total of 120 healthy volunteers were recruited and divided equally into four age groups of 30 subjects each: Group A (8–15 years), Group B (16–30 years), Group C (31–50 years), and Group D (51–70 years). Inclusion criteria comprised apparently healthy individuals with normal or corrected-to-normal vision and normal hearing on basic screening, and the absence of any known neurological, musculoskeletal, or psychiatric disorder that could affect sensorimotor performance. Exclusion criteria included a history of significant visual or auditory impairment, neurological disease (including stroke, Parkinsonism, or peripheral neuropathy), uncontrolled diabetes mellitus, current use of sedative, stimulant, or psychoactive medication, and recent consumption of alcohol, caffeine, or tobacco within twelve hours of testing. Reaction Time Measurement Simple and choice visual and auditory reaction times were measured using a computerized reaction time apparatus in a quiet, temperature-controlled laboratory between 10:00 a.m. and 1:00 p.m. to minimize diurnal variation. For simple VRT, subjects were instructed to respond as quickly as possible to the onset of a red light by pressing a designated response key; the procedure was repeated using a green light stimulus. For choice VRT, subjects responded with one of two different keys depending on which of two coloured lights appeared, in randomized order. Simple ART was recorded in an analogous manner using high-pitched and low-pitched pure tones delivered through calibrated headphones, and choice ART required subjects to discriminate between the two tones before responding. Each subject completed ten trials per stimulus condition, with the first two trials discarded as practice trials and the mean of the remaining eight trials recorded as the final reaction time for that condition. Statistical Analysis All reaction time values were expressed in milliseconds as mean ± standard deviation. Differences in reaction time across the four age groups were analyzed using one-way analysis of variance (ANOVA), followed by Tukey's post hoc test for pairwise comparisons between adjacent age groups. The relationship between age and each reaction time measure was assessed using Pearson's correlation coefficient and simple linear regression. Differences between visual and auditory reaction times, and between simple and choice reaction times, were assessed using the paired t-test. A two-tailed p-value of less than 0.05 was considered statistically significant. All statistical analyses were performed using standard statistical software.

A total of 120 subjects across four age groups completed the study protocol. Baseline demographic characteristics of each age group are summarized in Table 1. Table 1. Baseline demographic characteristics of the study population by age group Variable Group A (8–15 yrs) Group B (16–30 yrs) Group C (31–50 yrs) Group D (51–70 yrs) Number of subjects (n) 30 30 30 30 Mean age (years) 12.1 ± 2.0 22.6 ± 4.1 41.3 ± 5.8 60.4 ± 6.2 Sex — Male, n (%) 16 (53.3) 15 (50.0) 17 (56.7) 14 (46.7) Sex — Female, n (%) 14 (46.7) 15 (50.0) 13 (43.3) 16 (53.3) Mean BMI (kg/m²) 18.9 ± 2.4 22.4 ± 2.6 24.8 ± 3.1 25.6 ± 3.4 Right-handed, n (%) 27 (90.0) 28 (93.3) 26 (86.7) 27 (90.0) Values are expressed as mean ± standard deviation or number (percentage). BMI = body mass index. The four age groups were comparable in terms of sex distribution and handedness, with an expected progressive increase in mean BMI from the youngest to the oldest group, consistent with normal age-related body composition trends in the general population. Mean values for simple and choice visual and auditory reaction times across the four age groups are presented in Table 2. Table 2. Mean visual and auditory reaction times (ms) across age groups Reaction Time Measure (ms) Group A (8–15 yrs) Group B (16–30 yrs) Group C (31–50 yrs) Group D (51–70 yrs) Simple visual RT (red light) 258.4 ± 28.6 198.7 ± 19.3 224.5 ± 22.1 268.9 ± 31.7 Simple visual RT (green light) 267.1 ± 30.2 204.6 ± 20.5 231.8 ± 23.4 276.3 ± 33.0 Choice visual RT 312.6 ± 34.8 241.3 ± 24.7 279.4 ± 27.6 338.7 ± 39.5 Simple auditory RT (high tone) 231.5 ± 25.9 178.2 ± 17.8 202.6 ± 20.4 244.8 ± 28.3 Simple auditory RT (low tone) 238.9 ± 27.1 183.4 ± 18.6 208.1 ± 21.0 251.6 ± 29.4 Choice auditory RT 289.3 ± 32.0 221.5 ± 22.9 256.0 ± 25.8 312.4 ± 36.1 Values are expressed as mean ± standard deviation, in milliseconds. RT = reaction time. Reaction time followed a distinct U-shaped pattern across the lifespan for all stimulus types: values were highest in the youngest group (8–15 years), decreased to their lowest point in the 16–30 year group, and then increased progressively through the 31–50 and 51–70 year groups. The oldest age group (51–70 years) recorded the longest mean reaction times across all measures, exceeding even those of the youngest group for choice visual and choice auditory reaction time. For every age group, auditory reaction times were consistently shorter than visual reaction times for both simple and choice conditions, and choice reaction times were consistently longer than simple reaction times within the same modality. Results of statistical comparison across age groups, including ANOVA findings and the correlation between age and reaction time, are shown in Table 3. Table 3. Statistical comparison of reaction time measures across age groups RT Measure F-value p-value (ANOVA) Correlation with age (r) R² Simple visual RT 38.7 <0.001 0.71 0.50 Choice visual RT 47.2 <0.001 0.78 0.61 Simple auditory RT 35.4 <0.001 0.69 0.48 Choice auditory RT 43.9 <0.001 0.76 0.58 VRT vs. ART (paired t-test, all groups combined) t = 14.6 <0.001 — — ANOVA = analysis of variance; r = Pearson correlation coefficient between age (treated as a continuous variable within the 16–70 year range) and reaction time; R² = coefficient of determination from linear regression. One-way ANOVA revealed statistically significant differences across age groups for all four reaction time measures (p < 0.001 for all). Choice visual reaction time showed the strongest correlation with age and the highest coefficient of determination, indicating that age accounted for approximately 61% of the variance in choice visual reaction time among adult subjects. The paired t-test comparing visual and auditory reaction time across all subjects confirmed that auditory stimuli were processed significantly faster than visual stimuli (p < 0.001), a pattern that was consistent within every individual age group.

The present study demonstrates that both visual and auditory reaction times vary significantly across the human lifespan, following a U-shaped trajectory characterized by relatively slower responses in childhood, peak performance in young adulthood, and progressive slowing thereafter. This pattern is consistent with the established understanding that reaction time reflects two opposing developmental processes: ongoing neural maturation in youth and progressive sensorimotor decline in later life.(6,7) Our finding that the 16–30 year group achieved the fastest reaction times across all stimulus conditions aligns with evidence that cognitive processing speed continues to improve until the mid-twenties, coinciding with the completion of prefrontal cortical maturation and peak efficiency of myelinated central pathways.(7) The progressive slowing of reaction time observed from young adulthood through the 51–70 year group in our cohort closely parallels the findings of a large cross-sectional study of 120 healthy individuals aged 21 to 60 years, which reported that both simple and choice auditory and visual reaction times increased significantly and progressively across decadal age groups, with strong positive correlations between age and all reaction time measures (r > 0.96 in that cohort).(8) Although the correlation coefficients in our study were somewhat lower, likely reflecting the inclusion of a paediatric group that introduces a non-linear, U-shaped relationship rather than a purely monotonic one, the overall direction and statistical significance of the age effect were consistent with this prior work. Our observation that choice reaction time showed greater age-related slowing than simple reaction time across the adult groups is similarly consistent with classic findings that choice RT is more sensitive to aging than simple RT, a pattern attributed to the additional stimulus discrimination and response selection demands of choice tasks, which engage central processing resources disproportionately affected by aging.(3) Mechanistically, our findings support the now well-established view that age-related slowing of reaction time arises predominantly from central rather than peripheral factors. Early physiological work estimated that declining motor and sensory nerve conduction velocity accounts for only a small proportion of the total age-related increase in reaction time, with the majority of slowing attributable to central, premotor processing delays.(9) This is corroborated by more recent neurophysiological studies demonstrating that aging slows stimulus perception and discrimination and increases intrahemispheric and transcallosal transmission times between sensory and motor cortical regions, while also delaying motor cortex response generation itself.(10) The disproportionate slowing of choice reaction time relative to simple reaction time observed in our older cohort is therefore best explained by age-related changes in these central response-selection and response-generation mechanisms rather than by a simple decline in peripheral nerve conduction. Our consistent finding that auditory reaction time was faster than visual reaction time across all age groups corroborates a substantial body of prior literature. This modality difference is classically attributed to the comparatively shorter and less synaptically complex neural pathway required for auditory signal transmission, in which the cochlea-to-cortex pathway involves fewer synaptic relays than the retina-to-visual-cortex pathway, allowing auditory information to reach the level of conscious perception and motor response generation more rapidly.(4,5) Importantly, this auditory advantage was preserved across every age group in our cohort, including the oldest, suggesting that the relative hierarchy of sensory processing speed is maintained throughout the lifespan even as absolute reaction times slow with advancing age. This study has several limitations. The cross-sectional design precludes direct observation of within-individual change over time and is subject to potential cohort effects, particularly given the wide age range studied. The relatively modest sample size of 30 subjects per age group, while adequate to detect the large effect sizes observed, limits the precision of estimates within narrower age sub-bands and the ability to examine sex-specific interactions in detail. Additionally, formal audiometric and ophthalmological assessment beyond basic screening was not performed, and subclinical sensory impairment in the older age group cannot be entirely excluded as a contributing factor to the observed slowing. Future longitudinal studies incorporating detailed sensory function testing and a broader range of cognitive covariates would help to further delineate the relative contributions of sensory, central, and motor factors to age-related reaction time change.

This study confirms that visual and auditory reaction times vary significantly across the lifespan, following a U-shaped pattern with peak performance in young adulthood, slower responses in childhood reflecting ongoing neural maturation, and progressive slowing from middle age into later adulthood reflecting predominantly central sensorimotor decline. Auditory stimuli were processed faster than visual stimuli across all age groups, and choice reaction tasks proved more sensitive than simple reaction tasks in detecting age-related changes. These findings reinforce the value of reaction time testing as a simple, reproducible physiological tool for assessing sensorimotor and cognitive function across the human lifespan, with potential applications in developmental assessment, occupational screening, and the early detection of age-related neurocognitive decline.

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