Impact of one night of sleep restriction on sleepiness and cognitive function: A systematic review and meta-analysis.

Detrimental consequences of chronic sleep restriction on cognitive function are well established in the literature. However, effects of a single night of sleep restriction remain equivocal. Therefore, we synthesized data from 44 studies to investigate effects of sleep restriction to 2-6 h sleep opportunity on sleepiness and cognition in this meta-analysis. We investigated subjective sleepiness, sustained attention, choice reaction time, cognitive throughput, working memory, and inhibitory control. Results revealed a significant increase in subjective sleepiness following one night of sleep restriction (Standardized Mean Difference (SMD) = 0.986, p < 0.001), while subjective sleepiness was not associated with sleep duration during sleep restriction (ß = -0.214, p = 0.039, significance level 0.01). Sustained attention, assessed via common 10-min tasks, was impaired, as demonstrated through increased reaction times (SMD = 0.512, p < 0.001) and attentional lapses (SMD = 0.489, p < 0.001). However, the degree of impaired attention was not associated with sleep duration (ps > 0.090). We did not find significant effects on choice reaction time, cognitive throughput, working memory, or inhibitory control. Overall, results suggest that a single night of restricted sleep can increase subjective sleepiness and impair sustained attention, a cognitive function crucial for everyday tasks such as driving.

Influence of lighting color temperature on effort-related cardiac response.

Higher color temperature refers to a higher proportion of blue spectral components of light, that are known to be associated with higher alertness state in humans. Based on motivational intensity theory (Brehm & Self, 1989), here we predicted that this lighting-induced alertness state should inform about the readiness to perform and this way influence subjective task demand and thus mental effort. To test this, study participants spent 15min under one of four lighting color temperature conditions and then performed a cognitive task. As predicted, effort-related cardiac response, indexed by a shortened cardiac pre-ejection period, decreased with increasing color temperature of light, as indicated by a significant single planned linear contrast. These results demonstrate that spectral properties of light can influence mental effort mobilization.

In a Heartbeat: Light and Cardiovascular Physiology.

Light impinging on the retina fulfils a dual function: it serves for vision and it is required for proper entrainment of the endogenous circadian timing system to the 24-h day, thus influencing behaviors that promote health and optimal quality of life but are independent of image formation. The circadian pacemaker located in the suprachiasmatic nuclei modulates the cardiovascular system with an intrinsic ability to anticipate morning solar time and with a circadian nature of adverse cardiovascular events. Here, we infer that light exposure might affect cardiovascular function and provide evidence from existing research. Findings show a time-of-day dependent increase in relative sympathetic tone associated with bright light in the morning but not in the evening hours. Furthermore, dynamic light in the early morning hours can reduce the deleterious sleep-to-wake evoked transition on cardiac modulation. On the contrary, effects of numerous light parameters, such as illuminance level and wavelength of monochromatic light, on cardiac function are mixed. Therefore, in future research studies, light modalities, such as timing, duration, and its wavelength composition, should be taken in to account when testing the potential of light as a non-invasive countermeasure for adverse cardiovascular events.

Implicit happiness and sadness are associated with ease and difficulty: evidence from sequential priming.

Three experiments tested the hypothesis of implicit associations between happiness and the performance ease concept and between sadness and the performance difficulty concept. All three studies applied a sequential priming paradigm: participants categorized emotion words (Experiment 1) or facial expressions (Experiment 2) as positive or negative or as referring to ease or difficulty (Experiment 3). These targets were preceded by briefly flashed ease- or difficulty-related words or neutral non-words (Experiments 1 and 2) or by happy, sad, or neutral facial expressions (Experiment 3) as primes. As predicted, all three experiments revealed increases in reaction times in the sequential priming task from congruent trials (happiness/ease and sadness/difficulty) over neutral trials to incongruent trials (sadness/ease and happiness/difficulty). The findings provide evidence for implicit associative links of happiness with ease and sadness with difficulty, as posited by the implicit-affect-primes-effort model (Gendolla, Int J Psychophysiol 86:123-135, 2012; Soc Pers Psychol Compass 9:606-619, 2015).

Do sadness-primes make me work harder because they make me sad?

This experiment sought to clarify the potential role of emotional feelings in the systematic impact of implicitly processed affective stimuli on mental effort mobilisation. Participants worked on an attention task during which they were primed with suboptimally presented happiness versus sadness expressions. Before the task, half the participants received a cue for the possible affective influence of "flickers" to be presented during the task. This manipulation usually reduces the impact of conscious feelings on resource mobilisation. As anticipated, sadness primes resulted in higher experienced task demand and higher mental effort (stronger cardiac contractility assessed as shortened pre-ejection period) than happiness primes. Most importantly, instead of reducing the prime effects on mental effort, the cue manipulation significantly increased participants' effort in general, reflecting additional cognitive demand. The results speak against the idea that affect primes influence effort mobilisation by eliciting conscious emotional feelings.