Age-related increases in reaction time result from slower preparation, not delayed initiation

Recent work indicates that healthy younger adults can prepare accurate responses faster than their voluntary reaction times would suggest, leaving a seemingly unnecessary delay of 80-100 ms before responding. Here, we examined how the prepa-ration of movements, initiation of movements, and the delay between them are affected by aging. Participants made planar reaching movements in two conditions. The free reaction time condition assessed the voluntary reaction times with which partici-pants responded to the appearance of a stimulus. The forced reaction time condition assessed the minimum time actually needed to prepare accurate movements by controlling the time allowed for movement preparation. The time taken to both initiate movements in the free reaction time and to prepare movements in the forced response condition increased with age. Notably, the time required to prepare accurate movements was significantly shorter than participants' self-selected initiation times; however, the delay between movement preparation and initiation remained consistent across the lifespan (-90 ms). These results indicate that the slower reaction times of healthy older adults are not due to an increased hesitancy to respond, but can instead be attributed to changes in their ability to process stimuli and prepare movements accordingly, consistent with age-related changes in brain structure and function. NEW & NOTEWORTHY Previous research argues that older adults have slower response times because they hesitate to react, favoring accuracy over speed. The present results challenge this proposal. We found the delay between the minimum time required to prepare movements and the self-selected time at which they initiated remained consistent at -90 ms from ages 21 to 80. We therefore suggest older adults' slower response times can be attributed to changes in their ability to process stimuli and prepare movements.

Automated summary

Recent research has shown that healthy younger adults can prepare accurate responses faster than their voluntary reaction times, but a seemingly unnecessary delay occurs before responding. This study examined the effects of aging on movement preparation, movement initiation, and the delay between them. The results indicate that with age, both movement initiation in voluntary reaction time and movement preparation in forced reaction time take longer. However, the time required to prepare accurate movements is shorter than the self-selected initiation times, and the delay between movement preparation and initiation remains consistent across the lifespan.