One night of sleep deprivation affects reaction time, but not interference or facilitation in a Stroop task

The Stroop color-naming task is one of the most widely studied tasks involving the inhibition of a prepotent response, regarded as an executive function. Several studies have examined performance on versions of the Stroop task under conditions of acute sleep deprivation. Though these studies revealed effects on Stroop performance, the results often do not differentiate between general effects of sleep deprivation on performance and effects specifically on interference in the Stroop task. To examine the effect of prolonged wakefulness on performance on the Stroop task, we studied participants in a 40-h "constant routine" protocol during which they remained awake in constant conditions and performed a Stroop color-naming task every two hours. We found that reaction time was slowest when the color and word did not match (incongruent), fastest when the color and word did match (congruent), and intermediate when participants named the color of the non-word stimulus (neutral). Performance on all three trial types degraded significantly as a function of time awake. Extended wakefulness did not significantly change the additional time needed to respond when the color and word did not match (Stroop interference), nor did it change the amount of facilitation when color and word matched. These results indicate that one night of sleep deprivation influences performance on the Stroop task by an overall increase in response time, but does not appear to impact the underlying processes of interference or facilitation. The results suggest that the degree to which an "executive function" is affected by sleep deprivation may depend on the particular executive function studied and the degree to which it is subserved by the prefrontal cortex.     

Lack of sleep and unethical conduct

We draw from the Ego Depletion model and research on sleep physiology to predict a relationship between lack of sleep and individuals’ unethical behavior. Laboratory studies showed that sleep quantity is positively related to self-control resources and negative associated with unethical behavior. In a cross-sectional field study examining unethical behavior in a variety of work settings, low levels of sleep, and low perceived quality of sleep, were both positively related to unethical behavior as rated by the supervisor, and cognitive fatigue mediated the influence of sleep quantity. In an experience sampling field study, we found similar effects within-individuals. We discuss the role of lost sleep in better understanding unethical behavior in organizations.     

Changes in processing of masked stimuli across early- and late-night sleep: a study on behavior and brain potentials

Sleep has proven to support the memory consolidation in many tasks including learning of perceptual skills. Explicit, conscious types of memory have been demonstrated to benefit particularly from slow-wave sleep (SWS), implicit, non-conscious types particularly from rapid eye movement (REM) sleep. By comparing the effects of early-night sleep, rich in SWS, and late-night sleep, rich in REM sleep, we aimed to separate the contribution of these two sleep stages in a metacontrast masking paradigm in which explicit and implicit aspects in perceptual learning could be assessed separately by stimulus identification and priming, respectively. We assumed that early sleep intervening between two sessions of task performance would specifically support stimulus identification, while late sleep would specifically support priming. Apart from overt behavior, event-related EEG potentials (ERPs) were measured to record the cortical mechanisms associated with behavioral changes across sleep. In contrast to our hypothesis, late-night sleep appeared to be more important for changes of behavior, both for stimulus identification, which tended to improve across late-night sleep, and for priming, with the increase of errors induced by masked stimuli correlating with the duration of REM sleep. ERP components proved sensitive to presence of target shapes in the masked stimuli and to their priming effects. Of these components, the N2 component, indicating processing of conflict, became larger across early-night sleep and was related to the duration of S4 sleep, the deepest substage of SWS containing particularly high portions of EEG slow waves. These findings suggest that sleep promotes perceptual learning primarily by its REM sleep portion, but indirectly also by way of improved action monitoring supported by deep slow-wave sleep.     

Paranoid delusions and threatening hallucinations: a prospective study of sleep paralysis experiences

Previously we reported a three-factor structure for hallucinations accompanying sleep paralysis (SP). These earlier analyses were, however, based on retrospective accounts. In a prospective study, 383 individuals reported individual episodes online providing further evidence for the three-factor structure as well as clearer conceptually meaningful relations among factors than retrospective studies. In addition, reports of individual episodes permitted a more fine-grained analysis of the internal structure of factors to assess predictions based on the hypothesis that a sensed or felt presence (FP) is a core experience affecting other SP hallucinations. Results were generally consistent with this hypothesis. In particular, associations among, and temporal stability of, sensory hallucinations were largely explained by their common association with FP. The findings are consistent with REM initiation of a threat activated vigilance system with pervasive effects on the SP experience and suggest a potential model for the thematic organization of nightmares and dreams more generally.     

Felt presence: paranoid delusion or hallucinatory social imagery?

Cheyne and Girard characterize felt presence (FP) during sleep paralysis attacks as a pre-hallucinatory expression of a threat-activated vigilance system. While their results may be consistent with this interpretation, they are nonetheless correlational and do not address a parsimonious alternative explanation. This alternative stipulates that FP is a purely spatial, hallucinatory form of a common cognitive phenomenon—social imagery—that is often, but not necessarily, linked with threat and fear and that may induce distress among susceptible individuals. The occurrence of both fearful and non-fearful FPs in a multiplicity of situations other than sleep paralysis attacks supports the notion that FPs are hallucinatory variants of social imagery and that they are not necessarily bound to threat-activated vigilance. Evidence linking FPs with anxiety disorders supports the notion that the distress they evoke may be mediated by a more general affective distress personality factor. To illustrate the predominantly spatial character of FP hallucinations, similarities between FP and phantom limbs are summarized and the possibility that these two phenomena are parallel expressions (self- vs. other-presence) of a mirror neuron system is considered.     

The nature and varieties of felt presence experiences: A reply to Nielsen

Nielsen [Nielsen, T. (2007). Felt presence: Paranoid delusion or hallucinatory social imagery? Consciousness and Cognition, 16(4), 975–983.] raises a number of issues and presents several provocative arguments worthy of discussion regarding the experience of the felt presence (FP) during sleep paralysis (SP). We consider these issues beginning with the nature of FP and its relation to affective-motivational systems and provide an alternative to Nielsen’s reduction of FP to a purely spatial hallucination. We then consider implications of the “normal social imagery” model. We can find only one specific empirical hypothesis articulated within this framework and it turns out to be one that we explicitly addressed in our original paper. We also review our position regarding the possible relation of FP during SP to a number of related anomalous experiences and contrast FP to anomalous vestibular-motor (V-M) phenomena. We review our position that the neuromatrix concept, in the light of available evidence, is more appropriately applied to V-M experiences than FP. Finally, we pursue speculations, raised in Nielsen’s commentary, on the wider implications of FP.     

Dream content: Individual and generic aspects

Dream reports were collected from normal subjects in an effort to determine the degree to which dream reports can be used to identify individual dreamers. Judges were asked to group the reports by their authors. The judges scored the reports correctly at chance levels. This finding indicated that dreams may be at least as much like each other as they are the signature of individual dreamers. Our results suggest that dream reports cannot be used to identify the individuals who produced them when identifiers like names and gender of friends and family members are removed from the dream report. In addition to using dreams to learn about an individual, we must look at dreams as telling us about important common or generic aspects of human consciousness.     

The sleep patterns and problems of clinically anxious children

Childhood sleep problems have been associated with a range of adverse cognitive and academic outcomes, as well as increased impulsivity and emotional disorders such as anxiety and depression. The aim of the study was to examine subjective reports of sleep-related problems in children with anxiety disorders during school and weekend nights. Thirty-seven children with clinically-diagnosed anxiety disorders and 26 non-clinical children aged 7-12 years completed an on-line sleep diary to track sleep patterns across school nights and weekend nights. Anxious children reported going to bed significantly later (p = 0.03) and had significantly less sleep (p = 0.006) on school nights compared to non-anxious children. No significant differences in sleep onset latency, number of awakenings or time awake during the night, daytime sleepiness, or fatigue were found between the two groups. On the weekends, anxious children fell asleep quicker and were less awake during the night than on weeknights. School-aged anxiety disordered children showed a sleep pattern that differs from their non-anxious peers. Although the mean 30 min less sleep experienced by anxious children may initially seem small, the potential consequences on daytime performance from an accumulation of such a sleep deficit may be significant, and further investigation is warranted.     

The effects of total sleep deprivation on recognition memory processes: A study of event-related potential

This study examined the memorization of information after a night of normal sleep and total sleep deprivation (TSD) by means of event-related potentials (ERPs). We expected a disfacilitatory effect of TSD on memory processing. Eighteen subjects were tested twice in a counterbalanced fashion. During the study session, subjects were presented with unfamiliar face stimuli and asked to memorize them for a subsequent memory test. At the test session, the subjects were presented with the studied faces intermixed with “new” faces and asked to indicate the previously presented stimuli. The N100 was used as a covariate to control for the differences in level of vigilance between the two sessions. Sleep deprivation decreased subjects’ ability to discriminate new from previously studied stimuli and decreased the peak amplitude of the early component (N200) to the decrement of performance. In addition, following TSD the amplitude of the late frontal component (LFC), which is thought to reflect contextual processing, was decreased in covariance with the N100 vigilance component. The amplitude of the late posterior component (LPC/P600) was also reduced but was unrelated to the vigilance component of the ERP. Based on prior studies, this LPC reduction can be interpreted to indicate a decrease in information retrieved after TSD. In summary, a night of TSD decreased the amplitude of the ERPs associated with complex episodic memory task stimuli, affected the frontal cortex during episodic retrieval, and prevented the elaboration process. Furthermore, there was an inability to discriminate what is and what is not in memory, possibly due to less local processing of details.     

眼睛运动如何与记忆相关？

很久以来,人们一直在致力于研究人的眼动与心理活动之间的关系,从而揭示其间的奥妙。众多研究表明,睡眠时的快速眼动（RapidEyeMovements,REM）及其周期对记忆的形成与巩固有重要作用。在清醒状态下,人的眼动就是为了获得视觉信息,如果涉及记忆任务,这就是编码阶段的具体行动。另外,问题解决过程也有眼动参与。总体看来,眼动和记忆之间是一种双向的关系,适当的眼动训练或许能够提高记忆成绩。