Does sleep promote false memories?

Memory is constructive in nature so that it may sometimes lead to the retrieval of distorted or illusory information. Sleep facilitates accurate declarative memory consolidation but might also promote such memory distortions. We examined the influence of sleep and lack of sleep on the cerebral correlates of accurate and false recollections using fMRI. After encoding lists of semantically related word associates, half of the participants were allowed to sleep, whereas the others were totally sleep deprived on the first postencoding night. During a subsequent retest fMRI session taking place 3 days later, participants made recognition memory judgments about the previously studied associates, critical theme words (which had not been previously presented during encoding), and new words unrelated to the studied items. Sleep, relative to sleep deprivation, enhanced accurate and false recollections. No significant difference was observed in brain responses to false or illusory recollection between sleep and sleep deprivation conditions. However, after sleep but not after sleep deprivation (exclusive masking), accurate and illusory recollections were both associated with responses in the hippocampus and retrosplenial cortex. The data suggest that sleep does not selectively enhance illusory memories but rather tends to promote systems-level consolidation in hippocampo-neocortical circuits of memories subsequently associated with both accurate and illusory recollections. We further observed that during encoding, hippocampal responses were selectively larger for items subsequently accurately retrieved than for material leading to illusory memories. The data indicate that the early organization of memory during encoding is a major factor influencing subsequent production of accurate or false memories.

Nightmare frequency and femininity/masculinity.

Several large-scale studies showed that women tend to report nightmares more often than men. Despite this robust finding, empirically tested interpretations of these sex differences are lacking. Levin and Nielsen put forward the hypothesis that sex-specific socialization might be one of the risk factors for nightmare occurrence. The present findings of an online survey indicate that expressivity/femininity and instrumentality/masculinity were related to nightmare fre quency and, thus, supported this hypothesis. Since the sex difference in nightmare frequency was not fully explained by these two variables, future studies should investigate other variables--in addition to sex-role orientation--like depressive symptoms, history of sexual and/or physical abuse, ruminative coping styles, and physiological measures of processing emotional stimuli within the brain.

Using the World-Wide Web to obtain large-scale word norms: 190,212 ratings on a set of 2,654 German nouns.

This article presents a new database of 2,654 German nouns rated by a sample of 3,907 subjects on three psycholinguistic attributes: concreteness, valence, and arousal. As a new means of data collection in the field of psycholinguistic research, all ratings were obtained via the Internet, using a tailored Web application. Analysis of the obtained word norms showed good agreement with two existing norm sets. A cluster analysis revealed a plausible set of four classes of nouns: abstract concepts, aversive events, pleasant activities, and physical objects. In an additional application example, we demonstrate the usefulness of the database for creating parallel word lists whose elements match as closely as possible. The complete database is available for free from ftp://ftp.uni-duesseldorf.de/pub/psycho/lahl/WWN. Moreover, the Web application used for data collection is inherently capable of collecting word norms in any language and is going to be released for public use as well.

Tracer: a general-purpose software library for logging events in computerized experiments.

In certain areas of the behavioral sciences, such as cognitive and perceptual psychology, researchers may choose to have their experiments partially or completely driven by software programs, which instruct and guide subjects through the sequence of tasks. Despite distinct advantages of unattended trial execution, on frequent occasions, experimenters may desire to keep track of the progress or to be notified of certain events, such as when the subject has completed a task. The Tracer software library presented here is a lightweight Windows programming interface that provides experimenters the ability to trace events and status notifications on one or more remote computers and log files. With only a few lines of additional code or script code, researchers can monitor the real-time progress of one or more unattended experiments running on remote computers of the local area network or the Internet. This article describes the functionality and usage of the Tracer library. The Tracer binaries, include files, sample code, and documentation files may be downloaded from the Psychonomic Society Archive of Norms, Stimuli, and Data at www.psychonomic.org/archive.

Sleep loss produces false memories.

People sometimes claim with high confidence to remember events that in fact never happened, typically due to strong semantic associations with actually encoded events. Sleep is known to provide optimal neurobiological conditions for consolidation of memories for long-term storage, whereas sleep deprivation acutely impairs retrieval of stored memories. Here, focusing on the role of sleep-related memory processes, we tested whether false memories can be created (a) as enduring memory representations due to a consolidation-associated reorganization of new memory representations during post-learning sleep and/or (b) as an acute retrieval-related phenomenon induced by sleep deprivation at memory testing. According to the Deese, Roediger, McDermott (DRM) false memory paradigm, subjects learned lists of semantically associated words (e.g., "night", "dark", "coal",...), lacking the strongest common associate or theme word (here: "black"). Subjects either slept or stayed awake immediately after learning, and they were either sleep deprived or not at recognition testing 9, 33, or 44 hours after learning. Sleep deprivation at retrieval, but not sleep following learning, critically enhanced false memories of theme words. This effect was abolished by caffeine administration prior to retrieval, indicating that adenosinergic mechanisms can contribute to the generation of false memories associated with sleep loss.

An ultra short episode of sleep is sufficient to promote declarative memory performance.

Various studies have demonstrated that a night of sleep has a beneficial effect on the retention of previously acquired declarative material. In two experiments, we addressed the question of whether this effect extends to daytime naps. In the first experiment we assessed free recall of a list of 30 words after a 60 min retention interval that was either filled with daytime napping or waking activity. Memory performance was significantly enhanced after napping as opposed to waking but was not correlated with time spent in slow wave sleep or total sleep time within the napping condition. The second experiment was designed to clarify the role of total sleep time and therefore included an additional third group, which was allowed to nap for no longer than 6 min on average. In comparing word recall after conditions of no napping (waking), short napping, and long napping, we found superior recall for both nap conditions in contrast to waking as well as for long naps in contrast to short naps. These results demonstrate that even an ultra short period of sleep is sufficient to enhance memory processing. We suggest that the mere onset of sleep may initiate active processes of consolidation which - once triggered - remain effective even if sleep is terminated shortly thereafter.

EQUIWORD:a software application for the automatic creation of truly equivalent word lists.

Word lists are most commonly used in the investigation of human memory. To prevent transfer effects, repeated measures of memory for words require multiple lists of different words. Yet, the psycholinguistic properties of all word lists employed should match as closely as possible to avoid confounding with the independent variable(s) in question. Although comprehensive databases for word norms exist, to our knowledge no tool is available that automates the creation of such equivalent word lists. Instead, matching different lists is often accomplished prima facie. We have therefore developed a Windows program called EQUIWORD that completely automates the creation of word lists that are truly parallel with respect to a wide range of attributes. EQUIWORD takes psycholinguistic databases of different formats as input and computes several coefficients of distance for every possible word pairing. Program output consists of a list of all word pairs sorted according to their distance. On that basis, creating equivalent word lists is simply done by selecting the pairs with the lowest distance coefficients.