Michael B. Steinborn

Mental fatigue and temporal preparation in simple reaction-time performance

Performance decrements attributed to mental fatigue have been found to be especially pronounced in tasks that involve the voluntary control of attention. Here we explored whether mental fatigue from prolonged time on task (TOT) also impairs temporal preparation for speeded action in a simple reaction-time task. Temporal preparation is enabled by a warning signal presented before the imperative stimulus and usually results in shorter reaction time (RT). When the delay between warning and imperative stimuli - the foreperiod (FP) - varies between trials, responses are faster with longer FPs. This pattern has been proposed to arise from either voluntary attentional processes (temporal orienting) or automatic trial-to-trial learning (trace conditioning). The former account suggests a selective RT increase on long-FP trials with fatigue; the latter account suggests no such change. Over a work period of 51 min, we found the typical increase in overall RT but no selective RT increase after long FPs. This additivity indicates that TOT-induced mental fatigue generally reduces cognitive efficiency but leaves temporal preparation under time uncertainty unaffected. We consider this result more consistent with the trace-conditioning account of temporal preparation.

Sequential effects within a short foreperiod context: Evidence for the conditioning account of temporal preparation

Responses to an imperative stimulus (IS) are especially fast when they are preceded by a warning signal (WS). When the interval between WS and IS (the foreperiod, FP) is variable, reaction time (RT) is not only influenced by the current FP but also by the FP of the preceding trial. These sequential effects have recently been proposed to originate from a trace conditioning process, in which the individuals learn the temporal WS-IS relationship in a trial-by-trial manner. Research has shown that trace conditioning is maximal when the temporal interval between the conditioned and unconditioned stimulus is between 0.25 and 0.60s. Consequently, one would predict that sequential effects occur especially within short FP contexts. However, this prediction is contradicted by Karlin [Karlin, L. (1959). Reaction time as a function of foreperiod duration and variability. Journal of Experimental Psychology, 58, 185-191] who did not observe the typical sequential effects with short FPs. To investigate temporal preparation for short FPs, three experiments were conducted, examining the sequential FP effect comparably for short and long FP-sets (Experiment 1), assessing the influence of catch trials (Experiment 2) and the case of a very dense FP-range (Experiment 3) on sequential FP effects. The results provide strong evidence for sequential effects within a short FP context and thus support the trace conditioning account of temporal preparation.

The effect of 40 h constant wakefulness on task-switching efficiency.

This study investigated efficiency of switching between different tasks in 12 male participants (19–30 years) during 40 h of constant wakefulness. As index of task‐switching efficiency, switch costs in reaction time were assessed every 3 h under controlled behavioural and environmental conditions. Overall reaction times and switch costs showed a temporal pattern consistent with the assumption of a combined influence of a sleep homeostatic and a circadian process. An additional analysis indicated that the variation in switch costs could not be attributed to interference of the current task with persisting activation from preceding tasks. We therefore conclude that sleep loss and the circadian system affect the ability to prepare the current task rather than automatic processing of irrelevant stimulus information.

Effects of Sleep Loss and Circadian Rhythm on Executive Inhibitory Control in the Stroop and Simon Tasks

This study assessed the influence of sleep loss and circadian rhythm on executive inhibitory control (i.e., the ability to inhibit conflicting response tendencies due to irrelevant information). Twelve ordinarily diurnally active, healthy young male participants performed the Stroop and the Simon task every 3 h in a 40-h constant routine protocol that comprised constant wakefulness under controlled behavioral and environmental conditions. In both tasks, overall performance showed clear circadian rhythm and sleep-loss effects. However, both Stroop and Simon interference remained unchanged across the 40 h of wakefulness, suggesting that neither cumulative sleep loss nor the circadian clock affects executive inhibitory control. The present findings challenge the widely held view that executive functions are especially vulnerable to the influence of sleep loss and circadian rhythm. (Author correspondence: daniel.bratzke@uni-tuebingen.de)

Distraction by irrelevant sound during foreperiods selectively impairs temporal preparation.

When the interval between a warning signal (WS) and an imperative signal (IS), termed the foreperiod (FP), is variable across trials, reaction time (RT) to the IS typically decreases with increasing FP length. Here we examined the auditory filled-FP effect, which refers to a performance decrement after FPs filled with irrelevant auditory stimulation compared to FPs without additional stimulation. According to one account, irrelevant stimulation distracts individuals from processing time and probability information during the FP (distraction-during-FP hypothesis). This should predominantly affect long-FP trials. Alternatively, the filled-FP effect may arise from a failure to shift attention from FP modality to IS modality (attention-to-modality hypothesis). The first hypothesis focuses on preparatory processing, predicting a selective RT increase on long-FP trials, whereas the second hypothesis focuses on target processing, only predicting a global RT increase irrespective of FP length. Across four experiments, a filled-FP (compared to a blank-FP) condition consistently yielded a selective RT increase on long-FP trials, irrespective of FP-IS modality pairing. This pattern of results contradicts the attention-to-modality hypothesis but corroborates the distraction-during-FP hypothesis. More generally, these data have theoretical implications by supporting a multi-process view of temporal preparation under time uncertainty.

Dynamic adjustment of temporal preparation: shifting warning signal modality attenuates the sequential foreperiod effect.

We examined sequential effects in the variable foreperiod (FP) paradigm, which refer to the finding that responses to an imperative signal (IS) are fast when a short FP trial is repeated but slow when it is preceded by a long FP trial. The effect has been attributed to a trace-conditioning mechanism in which individuals learn the temporal relationship between a warning signal (WS) and the IS in a trial-by-trial manner. An important assumption is that the WS in a current trial (i.e., trial FP(n)) acts as a conditioned stimulus, such that it automatically triggers the conditioned response at the exact critical moment that was imperative in the previous trial (i.e., trial FP(n-1)). According to this assumption, a shift from one WS modality in trial FP(n-1) to another modality in trial FP(n) is expected to eliminate or at least reduce the sequential FP effect. This prediction was tested in three experiments that included a random variation of WS modality and FP length within blocks of trials. In agreement with the prediction, a shift in WS modality attenuated the asymmetry of the sequential FP effect.

Arousal modulates temporal preparation under increased time uncertainty: Evidence from higher-order sequential foreperiod effects

When the foreperiod (FP) is unpredictably varied in reaction-time tasks, responses are slow at short but fast at long FPs (variable-FP effect), and further vary asymmetrically as a function of FP sequence (sequential FP effect). A trace-conditioning model attributes these phenomena to time-related associative learning, while a dual-process model views them as resulting from combined effects of strategic preparation and trial-to-trial changes in arousal. Sometimes, responses are slower in long-long than in short-long FP sequences. This pattern is not predicted from the trace-conditioning account, since FP repetitions should speed up, rather than slow down, responses (due to reinforcement). The effect, however, might indicate the contribution of arousal, which according to the dual-process model, is heightened after a short FP(n-1) but decreased after a long FP(n-1). In five experiments, we examined higher-order sequential FP effects on performance, with a particular emphasis on analyzing performance in long-FP(n) trials as a function of FP length in the two preceding trials, varying temporal FP context (i.e. average FP length) and reaction mode (simple vs. choice reaction). Slower responses in long-long-long (compared with short-short-long) FP sequences were not found within a short-FP context (Exps. 1 & 2) but clearly emerged within a long-FP context (Exps. 3-5). This pattern supports the notion that transient arousal changes contribute to sequential performance effects in variable-FP tasks, in line with the dual-process account of temporal preparation.

The effect of a cross-trial shift of auditory warning signals on the sequential foreperiod effect.

When a warning signal (WS) precedes an imperative signal (IS) by a certain amount of time (the foreperiod, FP), responses are speeded. Moreover, this effect is modulated by the FP length in the previous trial. This sequential FP effect has lately been attributed to a trace-conditioning mechanism according to which individuals learn (and re-learn) temporal relationships between the WS and the IS. Recent evidence suggests that sensory WS attributes are critical to trigger time-related response activation. Specifically, when WS modality is shifted in subsequent trials (e.g., from auditory to visual modality), the sequential FP effect becomes attenuated. This study examined whether the sequential FP effect is reduced only by between-modality shifts or whether this attenuation generalizes to cross-trial shifts of WS attributes within modalities. We compared dimensional (low vs. high tone frequency) and qualitative shifts (pure tone vs. noise) of equal-intense auditory WS events. The results of four experiments revealed that shifts of tone frequency did not, whereas shifts of qualitative tone characteristics did attenuate the sequential FP effect. These results support the view that the WS acts as a trigger cue that unintentionally activates responses at previously reinforced critical moments.

Error reactivity in self-paced performance: Highly-accurate individuals exhibit largest post-error slowing:

Reaction time is typically increased following an erroneous response. This post-error slowing is traditionally explained by a strategic adjustment of response threshold towards more conservative behaviour. A recently proposed orienting account provides an alternative explanation for post-error slowing. According to this account, committing an error evokes an orienting response (OR), which inhibits information processing in the subsequent trial, resulting in slow and inaccurate performance. We tested a straightforward prediction of the orienting account in the context of self-paced performance, adopting an individual-differences approach: Post-error slowing should be larger the less frequent an error is. To this end, participants were classified into three groups differing in overall performance accuracy. Larger post-error slowing and stronger post-error accuracy decrease were observed for the high-accuracy group than for the two other groups. Practice pronounced the post-error accuracy decline, especially for the high-accuracy group. The results are consistent with the orienting account of post-error slowing but are problematic for accounts based on strategic evaluation mechanisms.

Differential effects of prolonged work on performance measures in self-paced speed tests.

Time-related changes in the speeded performance of complex cognitive tasks are considered to arise from the combined effects of practice and mental fatigue. Here we explored the differential contributions of practice and fatigue to performance changes in a self-paced speeded mental addition and comparison task of about 50 min duration, administered twice within one week’s time. Performance measures included average response speed, accuracy, and response speed variability. The results revealed differential effects of prolonged work on different performance indices: Practice effects, being more pronounced in the first session, were reflected in an improvement of average response speed, whereas mental fatigue, occurring in both sessions, was reflected in an increase of response speed variability. This demonstrates that effects of mental fatigue on average speed of performance may be masked by practice effects but still be detectable in the variability of performance. Therefore, besides experimental factors such as the length and complexity of tasks, indices of response speed variability should be taken into consideration when interpreting different aspects of performance in self-paced speed tests.