Memory Processes in Morning Recall after Multiple Night Awakenings

Some episodes of mental sleep experience which are reported after multiple awakenings during sleep are not recalled in the morning. Have they decayed or are they temporarily inhibited to retrieval? Responses of 10 men were recorded for four non-consecutive nights; they were awakened each night four times after 9 win. of REM sleep. Upon each awakening they were asked to report their mental sleep experience, and in the morning they were asked to re-report these experiences. Where subjects were unable to provide a spontaneous morning report they were prompted using a probe, the probe being the first contentful proposition of the corresponding night report. Subjects were aware of this design. All the night and morning reports were subjected to linguistic analysis. Spontaneous morning reports were significantly less frequent than night reports, but the use of the probe significantly increased the frequency of morning reports. Both spontaneous and probed morning reports and their corresponding night reports shared similar linguistic structures, but the probed reports and their corresponding night reports were shorter. The percentage of contents common to night and morning reports was similar for both spontaneous and probed morning reports, as was the stability of the serial position of those contents. We suggest that, with respect to settings with only one night awakening, multiple awakenings increase retrieval difficulty for entire episodes of mental sleep experience but not for single contents.

Consolidation effect of repeated processing of declarative knowledge in mental experiences during human sleep

Sleep may positively influence declarative memory through the processing, which transforms items of declarative knowledge into contents of mental sleep experience (MSE). A prediction from this general hypothesis is that the consolidation level should be higher for the output of items repeatedly processed and transformed into identical or very similar (so-called interrelated) contents of distinct MSEs of the same night rather than for the output of items presumably processed once (that is, all other, non-interrelated contents). Two experiments examined whether and how far the frequency and long-term retention of interrelated contents depend on the repeated processing of given items rather than on the experimental procedure applied for detection of interrelated contents. This procedure entails both multiple awakenings and a verbal report of MSE after awakening. Multiple awakenings could facilitate the re-access and elaboration of some contents into the subsequent (i.e. contiguous) MSE rather than non-contiguous MSEs; verbal reports could enhance the delayed recall of interrelated contents in as much as repeatedly encoded. The first experiment showed that interrelated contents were more frequent and better retained than both non-interrelated and pseudo-interrelated (i.e. by-chance similar or identical) contents, and even more in pairs of contiguous than non-contiguous MSEs collected from the first four periods of REM sleep on each experimental night. The second experiment showed that the frequency and retention rate of interrelated contents, while higher than those of non-interrelated and pseudo-interrelated contents, were not significantly different in pairs of MSEs which were verbally or mentally recalled after awakening provoked during the first four periods of REM sleep in each experimental night. Taken together, these findings indicate that the advantage provided by repeated processing during REM sleep for the consolidation of the output of items of declarative knowledge is conspicuous and largely independent from the experimental procedure, as this only slightly enhances the frequency and retention rate of interrelated contents.

Consolidation effect of the processing of declarative knowledge during human sleep: evidence from long-term retention of interrelated contents of mental sleep experiences

Sleep may partly exert a positive influence on memory through the processing underlying the transformation of items of declarative knowledge into contents of mental sleep experience (MSE). This hypothesis implies that the level of consolidation (and thus, long-term retention) should be enhanced for those items which are repeatedly processed and transformed into identical or very similar (so-called interrelated) contents of distinct MSEs developed over the same night. To test this prediction, we examined accessibility at delayed recall (i.e., the next morning) of the interrelated contents of MSEs reported (immediate recall) by 14 subjects who were awakened during the first four periods of rapid eye-movement (REM) sleep in two experimental nights. Interrelated contents were much more frequent, and at delayed recall much better retained, than other, non-interrelated contents in report pairs of MSEs. Moreover, they were also more frequent and better retained than by-chance similar or identical contents, as estimated in report pairs of MSEs of different subjects. These findings provide partial but coherent evidence in favour of the hypothesis that a generation effect occurs during sleep, with a further consolidation of the input and the output of MSE processing (respectively, the items of declarative knowledge and the contents of MSEs resulting from their elaboration during sleep).

Incorporation of presleep stimuli into dream contents: evidence for a consolidation effect on declarative knowledge during REM sleep?

Presleep stimuli to be retained for further recall is often incorporated into dream contents. To establish whether processing for insertion into dream contents may improve consolidation, we compared the retention rate at delayed recall of contents resulting from incorporation of presleep sentence-stimuli with those of other contents of the same dream experiences. We hypothesized that association with a cognitive task of recall facilitates access to recently acquired items of declarative knowledge such as presleep stimuli, and triggers the deep elaboration of their semantic features, which involves rehearsal. Twelve subjects were given a task of delayed recall for three nonsense sentences delivered once a time before each of the sleep (re-)onsets over an experimental night. After each awakening in rapid eye movement sleep, subjects were asked to report dream experience and recall the sentence to be retained. In the morning, after spontaneous awakening, subjects were unexpectedly requested to again report their dream experiences and to recall the stimuli. Two pairs of judges independently identified possible incorporations of the stimuli, and parsed dream reports into propositional content units. The proportion of night reports with at least one incorporation of the stimulus delivered (i.e. valid incorporations) was higher than that of reports with contents similar to a stimulus(-i) not yet delivered (forward pseudo-incorporations) or delivered prior to an earlier sleep period (backward pseudo-incorporations). The proportion of content units common to night and morning reports (considered to be better consolidated) was significantly higher for incorporated contents than for other contents, including pseudo-incorporated contents. Instead, the retention at morning recall of words of sentence-stimuli corresponding to incorporated contents was not significantly higher than that of other words. The better retention of incorporated contents provides a partial confirmation (that is, limited to the output of the processing) that a generation effect, which benefits retention of actively processed information, is operative during sleep as well as in waking.

Completeness and accuracy of morning reports after a recall cue: comparison of dream and film reports

Our goal was to test the efficiency and accuracy of a complementary morning report, after recall cue, of an experience (having a dream or viewing a film) made and first described during the night. Twenty participants were awakened 10 min after the onset of the second REM sleep. Upon awakening, on one night they described the dream they just had and on the other night they were presented a 4-min video, then had to describe it. A new description requested in the morning after a recall cue yielded an important amount of new information both for the film and the dreams, and for the film, where the accuracy could be checked, 86% of this new information was accurate. Some aspects of the results pointed to an effect of hypermnesia. In conclusion, the morning additional information after recall cue stems from a good access to the memory of the night experience.

The thematic continuity of mental experiences in REM and NREM sleep

In this study the characteristics of interrelated contents in paired reports of mental sleep experience (MSE) were analyzed to obtain insight as to the functioning of processes by which contents previously stored in memory are retrieved and inserted into MSE in rapid eye movements (REM) and non-REM (NREM) sleep. Ten subjects were awakened 3 times on each of 4 nights after 3 min of NREM sleep (in stage II or III before the first REM), of the first phase of REM sleep, and again of NREM sleep (in stage II or III after the first REM). The contents of all the possible pairings of reports were scored by using Clark's (1970) feature-matching model and compared with respect to the factors 'night' (same/different), 'type of report pairs' (1stNREM-REM/REM-2ndNREM/1stNREM-2ndNREM), 'unit interrelated' (lexical/propositional), 'interrelationship' (paradigmatic/syntagmatic). The occurrences of interrelations were greater for same night pairs than for different night pairs, but without significant differences between types of report pairs: these data provide support for the thematic continuity of MSE in both NREM and REM sleep. The units interrelated in pairs of reports were more frequent at a lexical than a propositional level, showing more paradigmatic than syntagmatic interrelationships: these data suggest that the re-elaboration of contents of previous MSEs occurs mainly at a lower level, and that the modality of processing previous contents by insertion into current MSE is similar in NREM and REM sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of positive and negative pre-sleep stimuli on dream experiences

In this study, the emotional and physical content of dreams was examined with post-sleep reports. In the first phase of the study, 45 students were asked to keep a dream diary for a week. The next week, the students were asked to look at a picture with positive, neutral, or negative affect in the evening before going to bed and then to record their dreams the following morning. Results showed that the pictures produced corresponding affect in morning dream reports, though physical elements of dreams and pictorial stimuli were not related to affect.

Recall of Endogenous and Exogenous Material: A Pilot Study

Two reports of the same REM dream, which were collected 5 hr. apart in waking condition, were compared to two film reports, collected under the same conditions. Differences in the addition of content elements and associative sentences between first and second reports of the dream and film materials were analyzed. Keeping the physiological condition constant during the interval between the two reports, the integration of content elements and associative sentences was significantly greater for dream reports than for film reports.

Restructuring Dream-Recall

First and second reports of the same REM dream of 20 male undergraduates were compared, and additions and restructurings analysed. When the interval between the two reports is in the waking condition the additions are more numerous than after an interval of sleep. For other characteristics of the reports (adjacency relations, motivational components) no significant differences between the two conditions were found.

Associative relationships between pre-sleep sentence stimuli and reports of mental sleep experience

The aim of this experiment was to study some linguistic relationships between pre-sleep verbal stimuli and contents of reports of mental experience during sleep. In 4 weekly sessions 16 subjects listened before sleep to a sentence stimulus, which was either semantically acceptable (SEM+) or not (SEM-), and were told to retain it for a recall test after awakening; they were awakened once each night during NREM or REM sleep and asked to report their mental experience during sleep. The relationships between the stimulus and the contents of the reports were classified using Clark's (1970) associative rules. Both pre-sleep sentence stimuli were frequently incorporated into contents of NREM and REM reports, without significant differences between the two types of sleep. The SEM+ sentence led prevalently to incorporations through paradigmatic associative relationships, while the SEM- sentence led to incorporations through both paradigmatic and syntagmatic relationships. It appears that all the features of the lexical constituents of the stimulus may be involved in the processing leading to incorporation.

Employing Review Procedures in Elaboration of Prose Schemata

The effect of review procedures on recall of prose was investigated. After reading a passage, 42 undergraduate volunteers were randomly assigned to one of three conditions, those receiving questions following reading, those receiving interactive questions following reading, and a control. After the review session, subjects in all three conditions completed a free recall of the original passage. One week later, all subjects returned and another free recall was obtained. For repeated-measures univariate analyses of variance showed significant effects for groups, time, and their interaction in logical intrusions. The results support the notion that review procedures elaborate schemata and enhance recall.