Dream Sources, Associative Mechanisms, and Temporal Dimension

Transcription

1 Sleep 10(1):78-83, Raven Press, New York 1987, Association of Professional Sleep Societies Dream Sources, Associative Mechanisms, and Temporal Dimension Corrado Cavallero Department of Psychology, University of Bologna, Bologna, Italy Summary: Using the technique of free association in an experimental setting, this author and colleagues previously found differences in the quality of memory traces involved in the production of REM and sleep onset (SO) dreams. The present study aims to answer two questions raised by those results: (a) Must the associative session be temporally contiguous to the dream production to gain access to the sources of the dream? (b) Are the differences between SO and REM associations due only to differences in structure and content of the two types of dream reports? Free associations with the same dream collected immediately after an experimental awakening were compared with those recalled 2 months later. A first group of results supports the hypothesis that free associations are sensitive to the proximity to the amount of dream production. A second group shows that the differences between SO and REM dreams noted in the previous research are not attributable to differences in formal characteristics of the report. Key Words: REM dreams-sleep onset dreams-free associations-dream sources. The present research deals with some of the cognitive processes involved in dream production, and is one of a series of studies directed toward understanding the processes activated in dreaming rather than the content of individual dreams. Following this approach some preliminary work (1-3) has been done to establish the type of mnemonic material involved in dream production. This research constitutes a first step in the formulation of hypotheses regarding the mechanisms active in the construction of the dream itself. The paradigm used in these studies is the free associative technique, adapted in such a way that the method, of clinical derivation, is suited to the experimental setting (4). The fundamental asssumption underlying the technique is that the contents of the free associations with the dream are elements of memory directly or indirectly involved in the process of dream production. Using the technique of free association, Cicogna et al. (5) recently found a difference in the quality of the memory traces utilized in the production of REM and sleep onset (SO) dreams, in addition to the well-known qualitative and quantitative differences between the two types of dream reports (6-8). That is to say, the dream production Accepted for publication July Address correspondence and reprint requests to Dr. C. Cavallero at Department of Psychology, University of Bologna, Viale Berti Pichat, 5, 40127, Bologna, Italy. 78

2 DREAM SOURCES AND TEMPORAL DIMENSION 79 system, in generating dreams (i.e., oneiric outputs) in different sleep phases, preferentially utilizes different types of mnemonic elements (i.e., oneiric inputs). The difference was assessed by classifying free associations with dreams into those referring to episodic memory and those referring to semantic memory according to Tulving's distinction (9). In addition, a third category, suggested by the nature of the particular material analyzed, was introduced. It includes self-referred, noncontextualized associations that do not fit into Tulving's distinction. The following differences between the two sleep phases were noted: Episodic associative elements were significantly more frequent in SO than in REM. Furthermore, in the SO condition the episodic contents were significantly more frequent than those of the other two types of memory categories. These results, which were obtained by analyzing the associations given by subjects immediately after awakening and after providing the dream report, raise some questions about the relationship between the dream and its mnemonic sources. First, is the relation so tight and univocal that the associative technique may, even after the passage of time, regain access to the mnemonic sources of the dream; or is it rather the temporal proximity to the oneiric production that makes the associative technique suitable for this purpose? Moreover, if the temporal delay between the dream and associations with it has indeed an effect, is this effect the same for dreams generated both in SO and in REM? Second, even if the free associative technique is not able to regain access to the sources of the dream after a temporal delay, delayed associations with SO and REM dreams might still differ from each other by memory categories, just as the immediate associations with the two types of reports do. Such a result would suggest that the differences detected by Cicogna et al. (5) reflect differences in the structure and content of the SO and REM reports rather than in the mnemonic elements involved in the production of the two types of dreams. In the prospect of a dynamic organization of memory traces according to which oneiric production is closely linked to the condition of the dreamer, the hypothesis was formulated that the free associative process is sensitive to the temporal proximity of the stimulus event of the association, and consequently that the associative material provided by the subject after a certain temporal delay will not present the REM/SO differences obtained in the first series of associations. To verify this hypothesis, subjects underwent a second session of free associations with their dreams after a period of time sufficient to minimize the possibility of a direct recall of the associative material produced during the first experimental session. If the hypothesis is correct, the associations obtained after an interval of time should show a low percentage of material retained from the first experimental sessions. Furthermore, the REM/SO differences noted in the previous study should disappear. METHOD Ten male university students, aged years, took part in the first experimental session (Session 1) as subjects. They had previously been trained to provide free associations with their dreams. Each subject slept in the sleep laboratory for 4 nonconsecutive nights under standard electropolygraphic control (two electroencephalographic, two electrooculographic, and one electromyographic channel). Each was awakened once per night, alternately in SO and in REM, in counterbalanced order, for a total of 20 valid awakenings in SO and 20 in REM. Awakenings in SO were carried out in stage Sleep, Vol. 10, No. I, 1987

3 80 C. CA V ALLER 0 2 at 3 min after the appearance of the first sleep spindles. l\wakenings in REM were carried out during the first REM period at 5 min after the appearance of the first burst of rapid eye movements. Upon awakening, mental sleep experience reports were solicited and recorded. Immediately afterward the free associative session took place according to the following procedure: (a) replay to the subject of the whole recording of his dream; (b) replay of the first segment of the dream; (c) request to freely associate with the segment just heard; (d) replay of the next segment and new associative task. The last step of the procedure was repeated until the report was ended. The segment into which the dream report was subdivided corresponded to short thematic units expressing a concept or an action characterized by completeness. A new thematic unit was scored whenever a change in characters, in the prevailing activity, or in the setting occurred in the dream report. The same 10 subjects participated in the second experimental session (Session 2), which took place 2 months later. Each subject lay on the bed in the same room of the sleep laboratory in which Session 1 had been held. Each was asked to provide a second series of associations following the same procedure as in Session 1: (a) replay to the subject of the entire recording of his dream; (b) replay of the segmented dream; (c) request to freely associate with each segment. The thematic units into which the dream was divided were the same as those heard by the subject in Session 1. All of the associative material obtained was classified according to the criteria mentioned below: (a) Strict episodes, i.e., discrete autobiographical events with precise spatiotemporal coordinates (e.g., "It makes me think of the basketball game I played last Saturday"). (b) Abstract self-references, i.e., memory traces referring to the subject's general knowledge of himself and his habits (e.g., "It makes me think that I'm a very curious person," "It makes me think of the fact that I play basketball every Saturday"). (c) Semantic traces, i.e., elements of general knowledge of the world, including episodes from the biographies of others (e.g., "It makes me think of a painting by Leonardo"). The associations obtained in Session 1 and 2 were compared using three independent measures. The following were calculated: (a) the mean number of associations provided during Session 1 and retained in Session 2; (b) the mean percentage of associations belonging to each memory category present in Session 1 in REM and in SO and retained in Session 2; and (c) the mean percentage of associations in each memory category in REM and in SO in Sessions 1 and 2. All of the mean percentages were obtained by averaging individual mean percentages for each subject. The original scoring of the first series of associations was used in data analysis. The scoring of the second series of associations was carried out by two independent judges who were unaware of the hypotheses formulated. Reliability was defined as twice the number of associations scored in common over the total number of associations scored by both judges. Interscorer reliability was 87%. Disagreements were resolved before the final data analysis. RESULTS Statistical analysis of the data on associative material retained in the second experimental session provided the following results: (a) There was a significant difference between the mean number of associations provided in the course of Session 1 and those retained in Session 2 (F 1,9 = 52.72, P < 0.001) (Table 1). (b) There were no significant differences between the two physiological conditions (SO and REM) with Sleep, Vol. 10, No.1, 1987

4 DREAM SOURCES AND TEMPORAL DIMENSION 81 TABLE 1. Mean number of associations provided in the first associative session and retained in the second session Session I Session respect to the percentage of associations, of whatever memory category, retained in Session 2 (F 19 = 2.01) (Table2). (c) There was a significant difference (F 218 = 3.85, p < 0.05) betw~en the percentage of strict episodic, abstract self-referred, ~nd semantic associations retained in Session 2 regardless of the sleep phase (SO or REM). Specifically, strict episodes were retained to a lesser extent than either abstract self-references (p < 0.10) or semantic traces (p < 0.10), while there was no significant difference between the latter two (Table 3). (d) There were no significant differences between SO and REM in the percentages of strict episodic, abstract self-referred, and semantic associations retained during Session 2 (Table 4). Statistical analysis of the data on percentages of the entire associative material provided in the two experimental sessions showed a significant interaction (F 2,18 = 3.52, P < 0.05) between the sleep phase (SO and REM), the nature of the memory traces associated with the dream (strict episodes, abstract self-references, and semantic traces), and the free associative session (1 or 2) (Table 5). In particular: (a) The percentage of strict episodes associated with SO dreams during Session 1 (63.57%) was significantly greater than those with SO dreams in Session 2 (41.55%, p < 0.05), REM dreams in Session 1 (39.67%, p < 0.05), and REM dreams in Session 2 (37.93%, p < 0.05). No significant differences were found in the percentages for SO dreams in Session 2 and REM dreams in Sessions 1 and 2. (b) There were marginally significant differences between the percentage of abstract self-references associated with SO dreams in Session 1 (21.05%) and those with both SO dreams in Session 2 (37.85%, p < 0.10) and REM dreams in Sessions 1 (37.00%, p < 0.10) and 2 (37.93%, p < 0.10). There were no significant differences in the percentages for SO dreams in Session 2 and REM dreams in Sessions 1 and 2. (c) There were no significant diffe~ences between the percentages of semantic traces for SO and REM dreams in Sessions 1 and 2. The absence of significant differences within the second series of associations, together with the differences noted exclusively with reference to the first series of associations with SO dreams, confirms the hypothesis that the temporal distance from the stimulus event has a determining influence on the possibility of access to the mnemonic sources of the dream. TABLE 2. Mean percentages of associations with sleep onset and REM dreams retained in the second associative session Sleep onset REM Sleep, Vol. 10, No.1, 1987

5 82 C. CAVALLERO TABLE 3. Mean percentages of strict episodes, abstract self-references, and semantic traces retained in the second associative session Strict episodes Abstract self-references Semantic traces DISCUSSION The first set of results regarding the retention of associative material across experimental sessions indicates that the dream is generated in an affective-cognitive context closely tied to the hic et nunc of the dreamer. Successive events in a subject's life tend to reorganize the mnemonic elements that contribute to the production of a particular dream. New affective-cognitive connections are established, which are no longer comparable with those existing at the specific moment when the dream was produced. As a consequence of this dynamic reorganization of memory traces, the free associative process may not be able to regain access to the presumed sources of the dream or to strong associates of them: The extremely low level of retention of contents between the first and the second series of associations seems to support this interpretation. From the preceding results and from the comments of the subjects, it further emerges that the dreamer is not only unable to provide the same associations spontaneously, but also he is unable even to recall those provided during the first associative session. From this, it is clear that the free associative process, to provide clues as to the possible generative matrix of the dream, must be temporally near the moment of dream production. The second group of results, regarding the composition of the body of associative material in terms of memory categories, supports the considerations made about the uniqueness of the pattern of mnemonic activation that generates a particular dream. These results also constitute indirect proof of the suitability of the technique of free association as a method for the study of the mnemonic sources of the dream. In fact, the verification, in the second series of associations, that the kinds of mnemonic traces to which there is access are similar for SO and REM dreams implies that the differences noted in the first series are not attributable to different characteristics inherent in TABLE 4. Mean percentages of strict episodes, abstract self-references, and semantic traces retained in sleep onset and REM during the second associative session Memory categories Strict Abstract Semantic Condition episodes self-references traces Sleep onset REM Sleep, Vol. 10, No.1, 1987

6 DREAM SOURCES AND TEMPORAL DIMENSION 83 TABLE 5. Mean percentages of strict episodes, abstract self-references, and semantic traces provided in sleep onset and REM during the first and the second associative sessions Memory categories Strict Abstract Semantic Condition episodes self-references traces Session I Sleep onset REM Session 2 Sleep onset REM the two types of dream reports. Rather, it is likely that the associative process, when close to the moment of dream production, is guided mainly by mnemonic traces activated during the generation of the dream itself. REFERENCES I. Cicogna P. Componenti mnestiche nel processo di produzione onirica. ContribWi del Dipartimellto di Psicologia Universita' di Bologna 1984;2: Cicogna P. Dreams, associations, and the organization of memory. Contribwi del Dipartimento di Psicologia Universita' di Bologna 1984;8: Cicogna P, Cavallero C, Bosinelli M. Mnestic sources of dreams. In: Koella WP, Ruther E, Schulz H, eds. Sleep '84. Stuttgart: Fisher, 1985: Cavallero C, Cicogna P. Models and strategies of sleep mentation research. In: Bosinelli M, Cicogna P, eds. Psychology of dreaming. Bologna: CLUEB, 1984: Cicogna P, Cavallero C, Bosinelli M. Differential access to memory traces in the production of mental experience. 1nt J Psychophysiol 1986;4: Antrobus JS. REM and NREM sleep reports: comparison of word frequencies by cognitive classes. Psychophysiology 1983;20: Bosinelli M, Cavallero C, Cicogna P. Self-representation in dream experiences during sleep onset and REM sleep. Sleep 1982;5: Foulkes D, Schmidt M. Temporal sequence and unit composition in dream reports from different stages of sleep. Sleep 1983;6: Tulving E. Episodic and semantic memory. In: Tulving E, Donaldson W, eds. Organization of memo/yo New York: Academic Press, Sleep. Vol. 10. No. I. 1987