Visual perceptual processing is unaffected by cognitive fatigue.

Cognitive fatigue (CF) can lead to an increase in the latency of simple reaction time, although the processes involved in this delay are unknown. One potential explanation is that a longer time may be required for sensory processing of relevant stimuli. To investigate this possibility, the current study used a visual inspection time task to measure perceptual processing speed before and after a CF (math and memory) or non-fatiguing (documentary film) intervention. Subjective fatigue and simple reaction time significantly increased following the CF, but not the non-fatiguing intervention, confirming that CF was induced. Conversely, there was no effect of CF on inspection time task performance. It was therefore concluded that the speed of perceptual processing is not significantly impacted by CF, and thus is unlikely to underlie CF-related reaction time increases. Instead, increases in simple reaction time latency in CF may be due to delays in response preparation or initiation.

Slowed reaction times in cognitive fatigue are not attributable to declines in motor preparation.

Cognitive fatigue (CF) can result from sustained mental effort, is characterized by subjective feelings of exhaustion and cognitive performance deficits, and is associated with slowed simple reaction time (RT). This study determined whether declines in motor preparation underlie this RT effect. Motor preparation level was indexed using simple RT and the StartReact effect, wherein a prepared movement is involuntarily triggered at short latency by a startling acoustic stimulus (SAS). It was predicted that if decreased motor preparation underlies CF-associated RT increases, then an attenuated StartReact effect would be observed following cognitive task completion. Subjective fatigue assessment and a simple RT task were performed before and after a cognitively fatiguing task or non-fatiguing control intervention. On 25% of RT trials, a SAS replaced the go-signal to assess the StartReact effect. CF inducement was verified by significant declines in cognitive performance (p = 0.003), along with increases in subjective CF (p < 0.001) and control RT (p = 0.018) following the cognitive fatigue intervention, but not the control intervention. No significant pre-to-post-test changes in SAS RT were observed, indicating that RT increases resulting from CF are not substantially associated with declines in motor preparation, and instead may be attributable to other stages of processing during a simple RT task.

Retrospective composite analysis of StartReact data indicates sex differences in simple reaction time are not attributable to response preparation.

Simple reaction time (RT) can vary by sex, with males generally displaying faster RTs than females. Although several explanations have been offered, the possibility that response preparation differences may underlie the effect of sex on simple RT has not yet been explored. A startling acoustic stimulus (SAS) can involuntarily trigger a prepared motor response (i.e., StartReact effect), and as such, RT latencies on SAS trials and the proportion of these trials demonstrating startle-reflex EMG in the sternocleidomastoid (SCM) muscle are used as indirect measures of response preparation. The present study employed a retrospective analysis of composite individual participant data (IPD) from 25 datasets published between 2006 and 2019 to examine sex differences in response preparation. Linear mixed effects models assessed the effect of sex on control and SAS RT as well as the proportion of SAS trials with SCM activation while controlling for study design. Results indicated significantly longer control RT in female participants as compared to males (p = .017); however, there were no significant sex differences in SAS RT (p = .441) or the proportion of trials with startle reflex activity (p = .242). These results suggest that sex differences in simple RT are not explained by variations in levels of response preparation but instead may be the result of differences in perceptual processing and/or response initiation processes.