SUMMAR Y 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.k e y w o r d s declarative memory, napping, recall, retention, sleep

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.

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.

The present study aimed at investigating the relationship between dream structure, the concept of boundary structure, and the Big Five personality dimensions. Dream structure was assessed with the recently developed Du ¨sseldorf Dream Inventory, which is based on a factorial assessment of dream structure. Dream structure was correlated with boundary structure (Boundary Questionnaire) and personality dimensions (Big Five Inventory) in 1,958 participants in an online study. The results show that boundary structure, openness to experience and neuroticism were associated with dream structure. Participants with thin boundaries had a higher dream recall frequency (DRF), considered their dreams to be personally more significant, exhibited more bizarre and aversive dreams, and more incorporation of elements from waking life. Openness to experience was positively correlated with DRF and personal significance of dreams. Neuroticism was correlated positively with aversive dreams, more incorporation from waking life, and personal significance of dreams. The present results confirm previous correlations between dream structure and personality and identify dream structures that are relevant for these associations.