The Invasion of the Concept Snatchers: The Origins, Distortions, and Future of the Continuity Hypothesis
G. William Domhoff
University of California, Santa Cruz
NOTE: If you use this paper in research, please use the following citation, as this on-line version is simply a reprint of the original article:
Domhoff, G. W. (2017). The invasion of the concept snatchers: The origins, distortions, and future of the continuity hypothesis. Dreaming, 27, 14-39.
This article explains the origins and development of the continuity hypothesis in work by cognitively oriented dream researchers. Using blind quantitative analyses of lengthy dream series from several individuals, in conjunction with inferences presented to the individual dreamers to corroborate or reject, these researchers discovered that the same conceptions and personal concerns that animate waking thought are very often enacted in dreams. Other types of studies later supported this finding. The article argues that the cognitive origins and definition of the continuity hypothesis have been distorted by those dream researchers who mistakenly claim that the concept is focused on dreaming as an incorporation of everyday experiences. A review of the literature on experiential and experimental influences on dreams, which includes studies of day residues, the experimental manipulation of presleep events, the incorporation of during-sleep stimuli, laboratory references in laboratory-collected dreams, and the influence of routine daily events, reveals that none of them is very influential and most are trivial. The article concludes that those who study experiential factors should adopt a phrase such as "incorporation hypothesis" to avoid confusion in the literature and make clear that the continuity hypothesis is a central one in an emerging neurocognitive theory of dreams. The intensity of personal concerns and interests, not the events of the day, shape central aspects of dream content. In particular, the frequency of characters or activities reveals the intensity of various concerns, and these concerns can be discovered for individuals through comparisons with normative findings.
The continuity hypothesis put forth in the early 1970s by pioneer dream researcher and cognitive theorist Calvin S. Hall and his coauthor (Bell & Hall, 1971) is widely known and discussed by dream researchers. In its fully developed form, as one key concept in a cognitive theory that has become a neurocognitive theory, the continuity hypothesis states that a large majority of dreams (the exact percentage has not yet been established) express the same conceptions (e.g., of oneself, of specific relatives and friends) and personal concerns (e.g., relationships, avocations) that animate waking thought (Domhoff, 1996, pp. 5, 153; 2001). Building on the working hypothesis that the frequency with which a character, type of social interaction, or activity appears in a series of dreams reveals the intensity of a concern, predictions can be made about the conceptions and personal concerns that are most important for both groups and individuals (Hall & Van de Castle, 1966, pp. 13-14).
More specifically, based on blind quantitative content analyses of a set or series of dream reports, this approach leads to the hypothesis that statistically significant differences between two sets of dream reports, or between an individual dreams series and normative baselines, will relate to the psychologically unique aspects of the dreamers' waking thoughts. Thus, the theory, based on a wealth of past findings, presents a clear statement of what is the most important influence on the frequency of specific types of content in dreams: the intensity of personal concerns.
However, despite the clear meaning that had been established for this concept within the context of a cognitive theory of dreaming by the late 1990s at the latest, it has been repeatedly misstated since that time by more recent dream researchers. The original misguided restatement mistakenly claimed that the essence of the concept is that dreams "reflect" waking-life experiences, with an emphasis on the "incorporation rate" of various types of experiences (Schredl, 2003, p. 26). This formulation is the opposite of dreams as being to a large extent the expression (enactment and dramatization are often used as synonyms) of conceptions and concerns, some of which go back years and decades for many individual dreamers. Despite strong criticisms of this experientialist distortion of the cognitively oriented continuity hypothesis (Bulkeley, 2011, 2012; Domhoff, 2003, 2010b; Domhoff, Meyer-Gomes, & Schredl, 2006), this altered version has been uncritically adopted by many dream researchers without any mention of the original meaning of the concept or of the criticisms of the experiential incorporation version (e.g., King & DeCicco, 2009; Malinowski & Horton, 2011, 2014; Sándor, Szakadát, & Bódizs, 2016; Selterman, Apetroaia, Riela, & Aron, 2014). The problem also has been compounded in a follow-up statement defending and extending the original mistaken article (Schredl, 2012).
The mistaken redefinition of the continuity hypothesis has been translated into a strong indictment by dream researchers who see the continuity hypothesis as a "competitor" to their "threat simulation" and "social simulation" theories, both of which claim that dreams are rehearsals that are useful for dealing with future waking events (see Revonsuo, 2000; Revonsuo, Tuominen, & Valli, 2015, pp. 1, 11, 19, 24, for repeated statements that the continuity hypothesis is in competition with their views). Focusing primarily on the experiential distortion of the continuity hypothesis, they claim that the concept is "too vague and general as a theoretical explanation for the details of dream content," does not "predict in any detail how and why the causal relationship between waking and dreaming works," does not "specify in any detail what counts as a 'continuity' and what would count as a 'discontinuity,'" and "takes almost any similarity between waking life and dream life as a confirmation of the continuity hypothesis" (Revonsuo et al., 2015, p. 10).
In fact, these claims are false. The continuity hypothesis was not presented as a "theoretical explanation for the details of dream content" but as an empirical discovery that has been replicated numerous times, a discovery that can be explained by the idea that most dreams enact and dramatize the same conceptions, personal concerns, and personal interests that animate waking thought. (The word personal is usually connected with the mention of a "concern" or "interest" in this article because the theorists criticized in his article have stretched the original meaning of the term concern to include everyday concerns and passing daily interests.) The original version of the cognitive theory of dreams stated that dreams are the "embodiment of thoughts," and the more recent neurocognitive version states that dreams are embodied simulations that very frequently enact conceptions and personal concerns (Domhoff, 2011b, 2015, in press, Chapters 2-3; Hall, 1953, pp. 273-274). More specifically, perhaps as many as 70% of dreams may be embodied simulations of conceptions and personal concerns (Domhoff, in press, Chapter 2; Domhoff et al., 2006, Table 3, p. 276).
Because of the various misunderstandings and critiques of the continuity hypothesis, it is the purpose of this article to fully explain the origins and evolution of the continuity hypothesis as a key concept in a cognitive, and subsequently neurocognitive, theory of dreams (Domhoff, 1996, pp. 209-212; 2001, 2003, 2011b, in press). The article shows that the concept expresses a major disagreement with the predominant theorists of the clinical era of dream research, who stressed the discontinuities between dreaming and waking thought (Freud, 1900; Fromm, 1951; Jung, 1974). It explains that the concept had its origins in studies of several individual dream series, not in studies based on 2-week dream diaries and questionnaires, which are frequently used by its critics.
Although experimentally oriented skeptics sometimes claim that lengthy dream journals are selective samples that may reflect only the most memorable dreams the person recalls, as in the case of one anonymous reviewer of this article, they overlook the fact that several of these series contain three or more entries per week, which is in the range of the typical rate of dream recall (e.g., Beaulieu-Prévost & Zadra, 2005b; Beaulieu-Prévost & Zadra, 2015; Blagrove & Akehurst, 2000; Schredl, 2008). One of these series, with 2,022 dream reports over a 3-year period, often includes two or more dreams a night, for an average of 13 dream reports per week, far beyond the usual rate in most questionnaire and 2-week diary studies This series, which can be found on DreamBank.net under the pseudonym "Kenneth," leads to the same results that have been found in other studies (Domhoff, in press, Chapter 3; Domhoff & Schneider, 2008, p. 1243).
As noted at the outset, the use of blind quantitative analyses of lengthy dream series makes it possible to develop specific inferences about the dreamers' waking conceptions and personal concerns. These inferences then can be verified or rejected with extant biographical information or direct responses from the dreamers themselves. Because of mistaken inferences in some of the earliest studies making use of the concept, which are examined in the next section, the continuity hypothesis was further refined. It was then supported in later studies of longer dream series that included more detailed analyses and obtained more detailed responses to the inferences from the dreamers, along with testimony from friends of the dreamer in one instance (Bulkeley, 2012, 2014; Bulkeley & Domhoff, 2010; Domhoff, 2003, Chapter 5; 2015; in press, Chapters 3-4).
This defense of the established cognitive meaning of the continuity hypothesis is necessary because the broader definition of the concept downplays its cognitive meaning, opens the door to very loose uses of the term "continuity" by new dream researchers, and creates confusion for all dream researchers. The concluding section of the article suggests that those who include daily events, daily concerns, or episodic daily interests within the purview of their interest in continuity should use a term such as experiential orientation hypothesis, incorporation hypothesis, experiential incorporation hypothesis, or some equivalent term. They should do so because the continuity hypothesis has become an important ingredient in a cognitive tradition that envisions dreaming, along with mind-wandering and daydreaming, as a form of spontaneous, stimulus-independent thought, a tradition that accords little if any weight to everyday daytime experiences (e.g., Antrobus, Singer, Goldstein, & Fortgang, 1970; Domhoff, in press; Foulkes, 1985; Fox, Nijeboer, Solomonova, Domhoff, & Christoff, 2013).
The Origins and Later Refinement of the Continuity Hypothesis
To appreciate the importance of the continuity hypothesis, it is necessary to explain the empirical and theoretical context within which it arose as well as to report the refinements that were made to it, which are seldom or never discussed by those who have altered the meaning of the concept. Such a discussion makes it possible to show how the continuity hypothesis played a key role in the expansion of the original version of Hall's (1953) cognitive theory of dreams into the present-day idea that dreams are embodied simulations that dramatize conceptions and personal concerns (Domhoff, 1996, pp. 209-212; 2007, 2015). In the first statement of his cognitive theory of dreams, as noted in the introduction, Hall (1953, pp. 273-274) claimed that dreams are "the embodiment of thoughts" and then added that thoughts are based on "conceptions," which he explained as follows: "Thinking is a process of conceiving. The end-product of this process is a conception (idea). A conception is an item of knowledge, a formulation of experience that has meaning for a person" (Hall, 1953, p. 274).
Although the cognitive theory of dreams was first stated in 1953, the continuity hypothesis was only developed many years later in a context in which studies attempting to test psychodynamic ideas about dreams through the use of projective or paper-and-pencil measures of personality had led to meager findings. Most of these disappointing results, many of which were reported by Hall's dissertation students at Case Western University in the late 1940s and early 1950s, are summarized in a chapter in a volume on Progress in Clinical Psychology (Hall, 1956). The list of failed or inconclusive studies was updated 40 years later, although there were few or no studies undertaken after 1980 (Domhoff, 1996, pp. 154-156).
In the mid-1960s, in a new introduction to the second edition of his popular book, The Meaning of Dreams, Hall (1953/1966) further reported that he had been very wrong in his inferences in a recent study of the personalities and leadership qualities of 2 of 17 mountain climbers who wrote down their dreams for several weeks as one part of a larger study of the 1963 American Mount Everest Expedition. Although his assessments of most of the men were consistent with those of the psychologists who studied their waking behavior, the two men he thought were the most popular, the most psychologically mature, and the most effective leaders turned out to be "the least liked, the most immature, and had no leadership or morale building assets whatsoever" (Hall, 1953/1966, p. xx). He called it a "sobering experience" to discover "the enormity of the misjudgments that can be made in assessing a person's waking behavior [italics added] from his dreams" (Hall, 1953/1966, p. xx).
Thus, despite Hall's (1954; Hall & Nordby, 1973) admiration for both Freud (1900) and Jung (1963, 1974), and his use of some of their ideas, the meager or negative findings with the standard personality assessments used in psychological research, along with his own mistakes, caused him to amend his blend of cognitive and psychodynamic theory in an even more cognitive direction. However, it was not until he began to study dream series from adults about whom he could obtain autobiographical or biographical information, or who were available to respond to the inferences about current conceptions and personal concerns (based on blind analyses of their dream series), that he made any progress in understanding the specifics of the relationship between dreaming and waking thought and to conceptualize this relationship in terms of "continuity." Although dream series were first used by the early Freudian Wilhelm Stekel (Hall, 1953/1966, p. 236) and Carl Jung (1963, 1968, 1974), their use was novel in terms of empirical dream research based on quantitative content analysis.
The first published scholarly statement related to Hall's gradual development of the continuity hypothesis appeared in a book coauthored with Richard Lind on the Dreams, Life, and Literature of Franz Kafka, which was based on a content analysis of the 37 dreams found in the Kafka diaries that had been published as of the 1960s (Hall & Lind, 1970). After making various predictions about Kakfa's waking conceptions and personal concerns, which derived from a comparison of the content findings for Kafka with the male norms in Hall and Van de Castle's (1966) comprehensive quantitative coding system, Hall and Lind (1970) then turned to a careful reading of Kafka's diaries and letters, which they had purposely ignored up to this point, as well as to a reading of biographies and remembrances of Kafka.
The final chapter, entitled "Realizations," begins by noting that "modern dream theories," for all their differences, emphasize that dreams are "discontinuous with waking life" (Hall & Lind, 1970, p. 89). In other words, Hall thought that Freud, Jung, and most of the neo-Freudians overemphasized the discontinuities between waking thought and dreams in their theorizing. Freud (1900, 1901) did so through the idea that adult dreams are heavily disguised and opaque to the waking mind because they express repressed sexual and aggressive desires that have to be disguised by "the dream-work." This reworking of the repressed wishes by the four cognitive processes that comprise the dream-work makes it necessary for a Freudian-trained expert to find the meaning of any given dream, usually through obtaining free associations to each element of the dream and being alert for what are now called figurative meanings (Gibbs, 1994; Lakoff, 1987).
As for Jung (e.g., 1963, 1974; Mattoon, 1978), he claimed that important dreams were if anything the opposite of waking thoughts because they compensated for the underdeveloped aspects of the person's psyche in very arcane ways (as revealed via symbolism). This theory made expert knowledge about mythology, religious history, and general metaphoric meanings necessary for developing an understanding of dreams. Finally, neo-Freudians, through their emphasis on the alleged metaphoric nature of dreaming, also found it necessary to draw upon myths, fairy tales, and metaphors to understand the underlying meaning of dreams (Fromm, 1951). (There were a few minor dissident neo-Freudians who dissented from the emphasis on discontinuity, but their claims for continuity were based on clinical case studies and had no lasting impact [e.g., French & Fromm, 1964]). Contrary to the well-known clinical theorists who emphasized discontinuity, who far and away predominated for the first 6 decades of the 20th century, Hall and Lind (1970) put their emphasis on the following statement: "This study of Kafka's dreams in relation to his life indicates that dreams are more likely to be continuous with waking life" (Hall & Lind, 1970, p. 89). This conclusion is a frank disagreement with the reigning discontinuity theorists. This point explains Hall's emphasis on "continuity" and puts his choice of terms in the historical context of the past discontinuity theorists. The statement also provides the explanation for a brief, seemingly cryptic sentence that appears in the discussion of the continuity hypothesis in a coauthored popular book with his research assistant: "The dream world is neither discontinuous [i.e., Freudian] nor inverse [i.e., Jungian] in its relationship to the conscious world" (Hall & Nordby, 1972, p. 104). However, the concept of a "continuity hypothesis" was not introduced in the book on Kafka's dreams.
The Kafka book was followed a year later by Hall's study of 1,368 dreams that a child molester wrote down over a 4-year period between 1963 and 1967 for his own reasons; only later did he give them to a clinical psychologist, Alan Bell, who interviewed him at the prison mental hospital in which he was incarcerated (Bell & Hall, 1971). Because of the huge sample size, Hall was able to make many inferences that were for the most part supported by personality assessment instruments and clinical materials collected by Bell at the facility as well as through the dreamer's written replies to questions formulated by Bell and Hall (1971, Chapter 2).
In this study Hall drew on the earlier discovery that the frequencies of an element in a series or set of dream reports reveal the relative intensity of waking concerns (Hall & Van de Castle, 1966, pp. 13-14). This finding adds a quantitative precision to the concept of "concerns," which should not go unremarked here because it makes it possible to rank personal concerns and demonstrate in yet another way that dreams are not based on incorporations from everyday waking life. For example, if a man dreams far more frequently about his mother than is the case for the male norms, or than any other character in a dream series, as this dreamer did, "it is inferred that the mother plays an important role in his life," as was indeed the case in this instance (Bell & Hall, 1971, p. 117). There then follows the first mention of the continuity hypothesis, with the italics in the original: "This may be called the continuity hypothesis because it assumes there is a continuity between dreams and waking life" (Bell & Hall, 1971, p. 117).
It is also important to add that the quoted sentence is followed by a qualifying statement showing that further work was needed to refine the concept: "There are difficulties with this hypothesis as we have seen, but first let us reconsider some of the kinds of information that dreams provide" (Bell & Hall, 1971, p. 117). The "difficulties" that Hall alludes to concern the fact that the continuity is not always with both waking thought and behavior, but sometimes with waking thought only, which is one of the key reasons why the emphasis came to be on waking thought, not behavior, in later refinements of the concept (Domhoff, 1996, 2003). That is, a behavioral concomitant may or may not be present, but the same concern expressed in the dream reports is always present in waking thought.
The child molester study, although a major advance over the Kafka study, nonetheless had deficiencies, partly because Bell, reasonably enough, wanted to foreground the projective tests, paper-and-pencil personality tests, interviews, and clinical information he had collected to construct a portrait of the child molester's personality (see Bell & Hall, 1971, p. 8 for the different interests and the division of labor between the two authors). More importantly, however, the analysis was presented within a Freudian framework, which led among other things to Hall's inference that the complete absence of the dreamer's father from the dream reports must mean that his conceptions and concerns in relation to his father had been repressed (Bell & Hall, 1971, p. 73). He then concluded that this claim was supported by the child molester's belief that he had been sexually abused by his father at age 4 (Bell & Hall, 1971, pp. 24, 76-77, 90).
However, this is the kind of memory of the past that is difficult if not impossible to confirm, as shown by the numerous later studies of the fallibility of memory (e.g., see Bauer, 2013; Garry & Hayne, 2007, for overviews). This is perhaps even more the case with highly troubling "recovered" memories from childhood, most if not all of which prove to be inaccurate, and especially so if they are allegedly from before the age of 5 or 6 (e.g., Foley, 2013; Howe, 2000; Howe & Knott, 2015). They are constructed in various ways through the imaginative reworking of memories and suggestions, which are often due to pressures from legal investigators of alleged molestations or through interactions with therapists who believe that child molestation is widely prevalent and is perpetrated even by women working in nursery schools (e.g., Ceci, Bruck, & Battin, 2000; Hyman & Loftus, 2002; Loftus, Joslyn, & Polage, 1998; Loftus & Ketcham, 1994; Ofshe & Watters, 1994; Ornstein, Ceci, & Loftus, 1998; Strange, Clifasefi, & Garry, 2007).
Thus, later cognitive dream researchers minimized or entirely abandoned any inferences and questions about long-ago events that allegedly happened to the dreamer. In terms of the inferences that they do make, the focus is on ongoing personal concerns. At the same time, it was never doubted by cognitive theorists that many of these personal concerns were persistent ones that the dreamers believed to go back many decades, especially in terms of past relationships with parents and siblings (Domhoff, 1996, Chapters 7-8; 2003, Chapter 5). Therefore, they rejected any claim that past concerns had been repressed, only to be recalled much later with the help of hypnosis or psychotherapy and then labeled a recovered memory. By the same token, the zero-frequency hypothesis put forth in the case of the child molester, based on the concept of repression, for which there is no systematic empirical evidence, was also discarded by later cognitive dream researchers (Loftus et al., 1998; Loftus & Ketcham, 1994; Mazzoni & Loftus, 1998; Mazzoni, Loftus, Seitz, & Lynn, 1999; Ofshe & Watters, 1994).
The first complete statement of the continuity hypothesis was put forth in a popular book in 1972: "The wishes and fears that determine our actions and thoughts in everyday life also determine what we will dream about [italics added]" (Hall & Nordby, 1972, p. 104). Hall then did several other studies related to the continuity hypothesis, adding new wrinkles and evidence, until shortly before his death in 1985; most of these studies were not published. On the basis of these studies, his final published statement on the continuity hypotheses used the phrase "concerns and preoccupations" instead of "wishes and fears," which reflected his gradual distancing from the language of the two major psychodynamic theorists, Freud (1900) and Jung (1974): "The continuity hypothesis states that dreaming is continuous with waking life. That is, people will manifest in their dreams the concerns and preoccupations of their waking life [italics added]" (Hall, Domhoff, Blick, & Weesner, 1982, p. 193).
Hall's further development of the continuity hypothesis, and the changes in it by cognitive theorists, is traced out in greater detail in a chapter in Finding Meaning in Dreams entitled "The Continuity Between Dreams and Waking Life" (Domhoff, 1996, Chapter 8). In particular, this chapter spells out the mistaken inferences Hall drew and the lessons that he and later cognitive dream researchers learned from them. They are important in understanding how the concept evolved into a fully cognitive one, with no remnants of the psychodynamic elements in Hall's earlier theorizing.
For example, in the case of the child molester, Hall inferred (based on several dreams in which the dreamer was masturbating) that he was a frequent and compulsive masturbator. However, the dreamer said this was untrue and noted that he was able to resist urges to masturbate for weeks at a time. He thought masturbation was wrong and often felt depressed after he masturbated (Bell & Hall, 1971, pp. 25, 94). He worked hard to overcome his preoccupation with his body and was very interested in spirituality and meditation. Bell and Hall (1971, p. 96) therefore concluded that "an analysis of the dream content reveals very little about his defensive maneuvers," which means that he was able to resist masturbating in waking life. This distinction is a very useful one that was taken into account in future studies by those who followed in Hall's path. It is one of many pieces of evidence that refutes the claim that the continuity hypothesis has any necessary relationship to waking behavior. This evidence includes a more recent study also concluding that the frequency of sexual dreams was related to the frequency of waking sexual fantasies, but not to the frequency of masturbation or sexual relations (Schredl, Desch, Röming, & Spachmann, 2009).
Hall also did a study of 58 dreams from a neurotic patient in psychotherapy in which his 42 inferences were corroborated or rejected by the psychotherapist (Domhoff, 1996, pp. 171-176; Moss, 1970, Chapter 3). Most of his inferences proved to be correct, but it is his mistakes that were the most useful. In particular, he wrongly inferred on the basis of only one dream, a dream in which the patient and his brother were trapped in their mother's apartment (i.e., she was not actually present in the dream), that the dreamer had a negative relationship with his mother. This inference proved to be quite wrong. In effect, Hall overgeneralized, as he explained: "I figured that anyone who had such poor relations with women, including his wife, and then has a dream in which he is trapped in her [i.e., his mother's] apartment, must also have poor relations with his mother" (Domhoff, 1996, p. 175). The lesson here is that hostility toward a general category, such as women, should not be presumed to include specific significant others who are included in that category unless there is hostility toward them as well. In effect, Hall relied on psychodynamic theory in making this inference, as can be seen in his sentence quoted earlier in this paragraph, rather than relying on specific portrayals of interactions within several dream reports.
Hall performed a very informative study of an engineer in his early 30s, Karl, who sent him more than 1,000 dream reports and mailed him detailed answers to his inferences (Domhoff, 1996, pp. 178-181; Hall & Nordby, 1972, pp. 119-126). Once again, Hall's inferences were mostly correct, but it is the mistakes that are useful. First of all, Karl had many highly aggressive dreams, especially toward his father, so Hall inferred that he occasionally provoked fights and harbored generally angry feelings. However, Karl reported that he never engaged in fights and regarded himself as being a friendly, warmhearted, and peaceful person. In this instance, Hall made the opposite type of mistake to the one made with the neurotic patient. With the neurotic patient, Hall used hostile interactions with various women to infer that the dreamer disliked his mother, and he was wrong. With Karl he used hostility toward Karl's father (and mother and wife) to infer aggressive interactions with a wider range of people, and he was wrong again, this time because Karl's dream reports do not reveal that he is in general an angry, violent person. On the other hand, Karl repeatedly told Hall that he harbored great anger toward his father, mother, and wife; therefore, the general point once again is that inferences drawn from the analysis of dream reports concerning continuity with waking thoughts and personal concerns should focus on specific people and not on generalities.
On the basis of these and a few other studies discussed in the synthesis chapter, the continuity hypothesis was updated to include both conceptions and personal concerns, which more firmly links the emphasis on conceptions in Hall's (1953) original formulation of a cognitive theory of dreams to his later discovery of how well the frequency of various elements in a person's dream reports tracks her or his waking personal concerns:
In all, the findings presented in this chapter are good evidence for our claim that the conceptions and concerns found in dream content appear to be the same ones operating in waking life. The waking mind and the dreaming mind seem to be one and the same, which is a strong argument for the idea that there is meaning in dreams. (Domhoff, 1996, p. 189)
Studies beginning in the late 1990s fully demonstrated the new, fully cognitive conception of the continuity hypothesis. The largest and most detailed of these studies is based on 3,115 dream reports written down by a divorced woman ("Barb Sanders") over a period of nearly 37 years. However, the first 106 dreams were written down only sporadically during the first 19 of those years; thus, the analysis is for the most part based on 3,009 dreams documented over a period of 18 years and 4 months. This means that she averaged 3.5 dream reports per week during the later time period, when she had the time and motivation to document every dream she recalled. Therefore, she can be classified as a typical dream recaller. In addition to numerous Hall and Van de Castle (1966) content analyses, the study included interviews with the dreamer and four of her friends. The friends were included to serve as "judge and jury" if there were any differences between the investigator's inferences and the responses by the dreamer (in the event, there were very few in this case; Domhoff, 2003, Chapter 5). This study also reintroduced the idea that there are "discontinuities" in dream reports as well as continuities. However, they were not the kind of discontinuities claimed by the various psychodynamic discontinuity theorists of the past. On the basis of an examination of many of the discontinuities in this dream series, discontinuities were hypothesized to be related to possible figurative constructions, which remained poorly studied as of the end of 2016, and/or to possible cognitive glitches, which remain completely unstudied.
The original Barb Sanders study was later extended in various ways, including the addition of more than 1,000 of her subsequent dreams for some new analyses, but so much has been written about the overall results that little more will be said here (Bulkeley, 2009; Domhoff, 2010a). However, a highly original network analysis comparing her waking social networks and her network of dream characters, based on 4,254 dream reports documented over a 41-year period, is well worth noting (Han, 2014). It revealed that the social networks in her dream reports were small-world networks similar to those found in waking life, but her network of dream characters differed from those in her waking life. The people who were emotionally closest to her in waking life tended to appear in dreams together although they were not in the same social networks in waking life (Han, 2014, pp. 50, 67). These results, which appear to take the continuity hypothesis to a more abstract and quantitative level, along with the other findings based on the Barb Sanders series, including her constant rehashing of past relationships and other disappointments, belie any emphasis on the influence of daily events on dreaming and support the conclusion that dreams are not a mere incorporation of everyday waking activities.
It is also relevant to any discussion of the continuity hypothesis that studies of dream series using 40 standardized word strings (Bulkeley, 2012, 2014; Bulkeley & Domhoff, 2010) have lent independent support to the concept, which answers any criticisms of studies of dream series based on the Hall and Van de Castle (1966) coding system by critics of the cognitive version of the continuity hypothesis (Schredl, 2012, pp. 4-5). To take one good example from a comprehensive blind analysis that led to numerous correct inferences, a young woman who wrote down 223 of her dreams as a teenager, and another 63 in her early years of college, had more frequent (and upsetting) dreams about her parents and brother during her first year or two in college than she previously had. This led to the correct inference that she experienced more worry and stress relating to her family while in college than she previously had. As she explained in response to this inference:
My first semester at college was very difficult and I was extremely homesick. I also had a spike in my anxiety, which led me to seek counseling through the college. I ruminated and worried a lot, missed my family, and was sure that now that I was away at school, something bad would happen. (Bulkeley, 2012, p. 245)
As the investigator concluded, This finding highlights an important point about the continuity hypothesis: "Dreams accurately reflect emotional concerns but not necessarily actual events" (Bulkeley, 2012, p. 248). This researcher uses the word reflect, but the crucial difference from the incorporation theorists is that he stresses the reflection of concerns, not the reflection of various waking events.
Although the original studies that led to the continuity hypothesis were based on individual dream series, an impressive longitudinal study in which the investigators studied the participants in 1991 and 2000-2001 demonstrated considerable continuity between waking well-being measures and aspects of dream content (Pesant & Zadra, 2006). Then, too, in a study comparing 30-day dream diaries from 35 professional musicians and 30 nonmusicians, which also included a daily questionnaire concerning their involvement with music during the day, the musi- cians dreamt twice as often about music as did the nonmusicians, and the frequency of their musical dreams was greater if they became involved in music as young teenagers or earlier. Even more significant in terms of this article, the frequency of their musical dreams did not relate to the degree of their waking musical activity during the days they kept the dream diary; therefore, the musical dreams did not reflect current waking reality (Uga, Lemut, Zampi, Zilli, & Salzarulo, 2006). These two studies are important because they minimize or eliminate any concern that possible selection biases in self-motivated dream series account for the evidence for the continuity hypothesis.
On the other hand, the possibility that evidence for the incorporation of everyday experiences and passing daily concerns into dreams might be found in controlled studies has received no support. This conclusion first of all rests on a series of three studies using both laboratory-collected and home-collected dream reports to compare daytime concerns with dream reports collected that night. In the initial study, eight participants spent 8 nights each in the sleep laboratory and reported dreams from awakenings after the first rapid eye movement (REM) period of the night. The several judges could not match the dream reports with either the general thought samples or the expressions of significant concerns of that day, which the participants provided before falling asleep (Roussy et al., 1996). A second laboratory study involved 13 women participants who reported dreams after awakenings from three of the first four REM periods on each of 4 laboratory nights. Once again, judges were unable to match the dream reports with either waking thought samples or lists of five significant concerns from earlier in the day that were obtained before the participants went to sleep (Roussy, 1998). The third study simulated everyday conditions by asking 13 women students to write down, on 6 separate days, the events of the day before going to bed, and then to document any dreams they recalled upon awakening the next morning. Using a less complex matching task than in the first two studies, 14 independent women judges could only rarely match the thought samples with the dream reports (Roussy et al., 2000). It is also noteworthy in regard to the experiential incorporation hypothesis that two longitudinal laboratory studies of the dreams of children and adolescents found that they rarely dreamed of their most frequent daytime activities, watching TV and reading, writing, and learning in a classroom setting (Foulkes, 1982, 1999; Strauch, 2005).
In concluding this discussion of what the continuity hypothesis actually involves, it is far more specific, empirically developed, and refined over time than is understood by those who claim that the continuity hypothesis is about the influence of events from waking life on dreaming. As shown in this section, the initial studies leading to this new concept were based on personal dream journals, which are regarded as unobtrusive and nonreactive measures by researchers in personality, social, and community psychology (e.g., Allport, 1942; Baldwin, 1942; Johns, Coady, Chan, Farley, & Kansagra, 2013; Schwartz & Sechrest, 2000, pp. xi-xix; Webb, Campbell, Schwartz, Sechrest, & Grove, 1981; Whitley & Kite, 2013). They are more valuable than many experimentally oriented dream researchers seem to appreciate because they have not been influenced by the demand characteristics, expectancy effects, and social desirability effects that were shown decades ago to vitiate the results of many experimental studies to a far greater extent than many current experimentalists seem to remember (e.g., Kihlstrom, 2002; Orne, 1962; Rosenthal & Ambady, 1995; Rosenthal & Rosnow, 1969). That said, this section also has shown that two studies not based on self-motivated dream series support the continuity hypothesis as well (Pesant & Zadra, 2006; Uga et al., 2006).
Looking for Continuity in All of the Wrong Places
Although it was widely known by the late 1990s that the continuity hypothesis is narrowly focused on the continuity between conceptions and ongoing personal concerns in dreams and waking life, this point is completely ignored in the first full-length article that misunderstood its meaning (Schredl, 2003). The problems started in the first sentence of the abstract, which begins with the pejorative "so-called continuity hypothesis" and then proceeds to incorrectly define it, as shown in the following quotation. The second sentence in the quotation then criticizes this inaccurate and newly created definition of the concept as "very broad and vague:"
The so-called continuity hypothesis of dreaming states that waking experiences are reflected [wrong] in dreams. The formulation of the continuity hypothesis is very broad and vague [wrong], however, so that it seems necessary to investigate factors which might affect the incorporation rate of waking-life experiences [which is completely off base and irrelevant because the hypothesis says nothing about 'incorporation']. (Schredl, 2003, p. 26)
The first two sentences of the main body of the article then mistakenly link the origins of the continuity hypothesis to Freud's concept of the "day residue," which concerns the (usually minor) event from the previous day that Freud (1900, pp. 127, 366-368) claimed to be the starting point for every dream:
Already in 1900, Freud (1) reported that day residues (recent waking-life experiences) are common in dreams. This observation and subsequent empirical studies (overviews: 2-5) have led to the so-called continuity hypothesis of dreaming which states that waking experiences are reflected in dreams; in other words: dreaming is in continuity with waking life. (Schredl, 2003, p. 26)
Thus, in the space of just four sentences, the continuity hypothesis has been stood on its head. Dreams do not "reflect" waking-life experiences; for the most part they express (enact, embody, dramatize) personal conceptions and ongoing personal concerns relating to the important people and activities in the dreamers' waking lives. This hypothesis is not "very vague and broad" but was made so by the critic through a mischaracterization of it. Nor did it have its origins in Freud's (1900, p. 127) claims about the day residue; it says nothing about day residues and represents a major departure from the Freudian theory of dreams.
After wrongly summarizing the established continuity hypothesis, the article then proceeds to review the literature on the influence of (a) day residues, (b) the experimental manipulation of presleep events, and (c) laboratory references in dreams collected in sleep laboratories. It also examines (d) the degree to which ordinary daytime experiences are incorporated into dream content. However, all of these alleged incorporations are relatively rare, and some of them are trivial, as overviewed in the next section. In addition, the failure to find connections between the events of the day and dream reports in the three studies discussed at the end of the previous section is not addressed (Roussy, 1998; Roussy et al., 1996, 2000). Instead, one of those three studies is mentioned in a table concerning the frequency of references of the laboratory setting in REM dream reports collected in a sleep laboratory (Roussy et al., 1996; Schredl, 2003, p. 34).
Surprisingly, the critical review does not cite any of the original work on the continuity hypothesis by Hall and his coworkers (Bell & Hall, 1971; Hall & Lind, 1970; Hall & Nordby, 1972). Although it briefly mentions Finding Meaning in Dreams (Domhoff, 1996) as one of four sources providing "overviews" of "empirical studies" (Schredl, 2003, p. 26), it does not indicate that the definition of the concept in that book and the empirical evidence that it cited are completely at odds with its account. Nor is there any mention of the large body of work on dream series that is presented in detail in Finding Meaning in Dreams (Domhoff, 1996). Despite these many problematic aspects to Schredl's (2003) original critical article, there is no criticism of any of the many omissions and distortions in it, or even any mention of them, by any of the authors who had cited it and made use of its redefinition of the continuity hypothesis by the end of 2016 (e.g., King & DeCicco, 2009; Malinowski & Horton, 2011, 2014; Revonsuo et al., 2015; Sándor et al., 2016; Selterman et al., 2014).
In response to criticism of his first analysis of the continuity hypothesis (e.g., Bulkeley, 2011; Domhoff, 2011a), Schredl (2012, p. 1) quotes four paragraphs from the popular book by Hall and Nordby (1972), which he had originally ignored, to claim that the authors "clearly indicate that the continuity hypothesis was defined very broadly and clearly goes beyond the notions of conceptions and concerns suggested by Domhoff as the most important aspects of continuity." Although these four paragraphs include the original psychodynamic definition of the continuity hypothesis that was cited earlier in this article ("The wishes and fears that determine our actions and thoughts in everyday life also determine what we will dream about"), which renders his other (often mistaken) claims irrelevant, the crucial point in terms of making any theoretical advances is that the concept had been refined and improved in the ensuing decades (Domhoff, 1996, Chapter 8), as demonstrated in the previous section. By resorting to a debatable exegesis of an outdated text instead of formulating one or more new alternative hypotheses, such as an experiential incorporation hypothesis, this kind of analysis obscures the fact that the present-day cognitive version of the continuity hypothesis abandons some of Hall's original claims and builds in part on work by other cognitive theorists (e.g., Antrobus, 1978; Domhoff, 1996, pp. 7, 209-212; Foulkes, 1982, 1985; Klinger, 1971).
Schredl (2012, pp. 4-5) goes further astray by criticizing the coding categories for emotions in the Hall and Van de Castle (1966) coding system because they allegedly underestimate the frequency of emotions in dreams and overstate the percentage of emotions that are negative. Although there are strong methodological and empirical reasons for doubting this claim (e.g., Domhoff, 2005, in press, Chapters 1 and 6; Foulkes, Sullivan, Kerr, & Brown, 1988), the important point here is that none of the studies of personal concerns was based on emotion codings. Some of the studies included codings for aggressive and friendly interactions, but aggression and friendliness are not among the five to seven basic emotions that are generally agreed upon by research psychologists (e.g., anger, apprehension/fear, sadness, disgust/contempt, surprise, love, and joy; e.g., Ekman, 1992, 2016; Shaver, Schwartz, Kirson, & O'Connor, 1987). On the basis of these points, it can be seen that any emphasis on the incorporation of waking emotional experiences into dreams is an offshoot of Schredl's (2006, 2012) experiential incorporation hypothesis, which could be called the emotion assimilation hypothesis to distinguish it from the continuity hypothesis (e.g., Malinowski & Horton, 2014, 2016; Schredl, 2006; van Rijn, Eichenlaub, & Blagrove, 2016).
A year after Schredl's (2003) original summary article modifying and criticizing the continuity hypothesis appeared, Schredl and Hofmann (2003) repeated the same inaccurate claims about the definition of the continuity hypothesis in the context of a study that led to many similar studies by several dream researchers. It is based on 2-week dream diaries that were kept by 133 participants (104 women and 29 men). At the end of the 2 weeks, the participants were asked via a questionnaire to estimate the amount of time they had spent during the previous 2 weeks in
a variety of daily activities such as using a computer for working, playing computer games, making telephone calls, spending time with the spouse, reading (divided into leisure time and occupational/studying), driving a car, watching TV, riding a bus/tramway, walking, doing a job, calculating, talking with friends, writing, and being in nature. (Schredl & Hofmann, 2003, p. 301)
It apparently did not seem relevant to these researchers that accurate after-the-fact assessments of the time spent on these activities over a 2-week period would be a considerable feat of memory, although one of the coauthors later acknowledged that this approach "suffers from possible recall problems" (Schredl, 2012, p. 5).
On the basis of 443 dream reports from the 133 participants, the investigators found a range of correlations between the amount of time spent in various waking activities and the frequency with which those activities appeared in the dream sample. They explain their mixed and generally negative findings on the basis of the generality of the continuity hypothesis (without saying that one of the coauthors had created this general, vague, and inaccurate definition) and various methodological problems. They raise these criticisms without even mentioning the unlikelihood that a retrospective questionnaire can provide anything but vague guesswork if modern-day memory research by psychologists has any merit. They then conclude that "the continuity hypothesis in its present general form is not valid [italics added] and should be elaborated and tested in a more specific way" (Schredl & Hofmann, 2003, p. 299).
The conclusion that the continuity hypothesis is not valid is then added to the bill of particulars put forth by dream theorists who focus on the possibility that dreams are a kind of social rehearsal as threat simulations (Revonsuo, 2000) and/or as social simulations (Revonsuo et al., 2015). However, in doing so they ignore the original definition of the continuity hypothesis by claiming it states that dreaming is a "passive mirroring of recent waking life" and therefore can be tested by assuming that "dreams represent a random sample of recent waking experience (or a random sample of their memory representations)" (Revonsuo et al., 2015, p. 10). Nor do the simulation theorists (or the two-dozen other investigators who cite the Schredl & Hofmann, 2003 study) offer the slightest criticism of it, not even for the use of a retrospective questionnaire.
Furthermore, the simulation theorists do not adequately comprehend the implications of the findings on consistency in a person's dreams over months, years, and decades, based on nearly two dozen studies, which reveal that people tend to differentially dramatize (not passively reflect) the same ongoing concerns about interpersonal relationships and favorite avocations on a very regular basis (Domhoff, 1996, Chapter 7; 2010a; Hall & Nordby, 1972, Chapter 5). The detection of repeated patterns, especially in instances involving frequent dreams about failed past relationships, or about deceased love ones, is a major addition to the already strong evidence that calls into question any claim that dreams are primarily a reflection of recent events (Domhoff, 1996, Chapter 7; 2003, Chapter 5; 2015; in press, Chapter 3).
The inadequacies of the Schredl and Hofmann (2003) study, and the simulation theorists' misuse of it, to one side, studies based on retrospective estimates of time spent in waking events continued to be the predominant basis on which Schredl and his coworkers studied experiential incorporations. In a backward step from the Schredl and Hofmann (2003) study, many of these studies did not even involve keeping a dream diary. For example, in a study of 82 truck drivers that was said to support the experiential distortion of the continuity hypothesis, the participants were asked to estimate the amount of time they spent driving a truck each week, the frequency with which they dreamt, and the percentage of their dreams that were about truck driving (Schredl, Funkhouser, & Arn, 2005, p. 181). Another study asked 131 college students, some of who were athletes, to estimate the frequency with which they dreamt, the amount of time they spent playing sports and reading, and the percentage of their dreams that involved sports or reading (Schredl & Erlacher, 2008, p. 268-269). Still another study was said to support the continuity hypothesis because the students who replied on a questionnaire concerning typical dreams that they had killed someone in a dream had higher hostility scores on a personality test (Schredl & Mathes, 2014, p. 178).
In a questionnaire study of music and dreams, 144 students, including music students, estimated the time they spent in music-related activities in waking life and the frequency with which they dreamt about music. The investigators found that "the amount of time invested in music activities during the day is directly related to the percentage of music dreams, thereby confirming the continuity hypothesis" (Vogelsang, Anold, Schormann, Wübbelmann, & Schredl, 2016, p. 132). However, they then note the "possible recall biases regarding retrospective measures" and suggest future studies using dream diaries (Vogelsang et al., 2016, p. 132). Because there is already a dream-diary study showing that the amount of time involved in music during the day did not relate to daily estimates of the frequency of music dreams for musicians (Uga et al., 2006), a study the authors duly cite, it seems unlikely that their music study, based as it is on estimates in response to a retrospective questionnaire, or any of the studies cited in the previous paragraph, can be taken seriously as studies of the continuity hypothesis, even for their version of it.
Questionnaire studies that ask for estimates about dream recall frequency, dream content, and time spent in various waking activities are simply correlational studies of various dimensions of waking thoughts and beliefs. Because very few people have any detailed knowledge of their dreams, studies of the current beliefs that people have about them are probably based on a combination of cultural stereotypes, personality variables, dreams recalled within the previous few days, selective recall of a few memorable dreams, and the whims of the moment (e.g., see Beaulieu-Prévost & Zadra, 2005a, 2005b, 2007, 2015; Bernstein & Belicki, 1996; Bernstein & Roberts, 1995).
The Rarity of Everyday Influences on Dreaming
According to cognitively oriented dream researchers, the appearance of daily events in dreams is a relatively minor matter because dreams are dramatic simulations based on the human ability to imagine (e.g., Antrobus, 1978, 2000; Foulkes, 1985, 1999; Hall, 1991; Reinsel, Antrobus, &Wollman, 1992). Their claims are fully supported by the three careful studies of the issue discussed in an earlier section (Roussy, 1998; Roussy et al., 1996, 2000). They are also supported by the rarity of any evidence for the influence of daily experience on dream content in many other kinds of studies.
For example, in the case of day residue, five detailed studies from decades ago, one of which involved a study of a lengthy dream series that included mentions of day residues, demonstrated that only approximately half of dreams contain even the slightest day residue that can be identified by the dreamer (Botman & Crovitz, 1990; Harlow & Roll, 1992; Hartmann, 1968; Marquardt, Bonato, & Hoffmann, 1996; Nielsen & Powell, 1992).
As far as stimulus-incorporation studies, early laboratory dream researchers found that it is very difficult to influence dream content with either presleep stimuli, such as fear-arousing or sensual movies, or with concurrent stimuli administered during REM periods, such as sounds or the whispering of the names of significant people in the dreamers' lives (e.g., Berger, 1963; Dement, 1965; Dement, Kahn, & Roffwarg, 1965; Foulkes, 1996; Foulkes & Rechtschaffen, 1964). Moreover, the impact of external stimuli on dreams may be exaggerated because the criteria for incorporation were very loose in several studies; sometimes, alleged metaphoric expressions of the stimulus, which are notoriously difficult to validate, were counted as correspondences (see Arkin & Antrobus, 1991, for a critical review).
Suggestions during sleep related to the dreamer's current concerns (which may or may not be very personal or long felt) fared no better in a laboratory study. In this carefully controlled study, seven young adult men each slept in the laboratory for 4 consecutive nights: 1 night for adaptation and 3 for studies of their incorporation of recorded words that were played several times during different REM periods. Some of the stimulus words related to their current concerns, as ascertained via a questionnaire, and some did not (Hoelscher, Klinger, & Barta, 1981, p. 89). Fifty-six of 59 REM awakenings yielded a dream report. Independent judges concluded that there were only five instances of incorporated current concerns, a very meager return (Hoelscher et al., 1981, p. 90).
One exception to these generalizations about the small impacts of external stimuli can be found in a pilot study in which the researcher used a rough equivalent of a blood-pressure cuff to apply increasing pressure during REM periods to the legs of four acquaintances of the researcher who agreed to participate; this somatosensory stimulation was frequently incorporated as simple, direct sensations of pressure or squeezing (Nielsen, 1993). Another exception may concern the influence of the smell of rotten eggs on dream content (Schredl, Atanasova, et al., 2009; Schredl, Hoffmann, Sommer, & Stuck, 2014). Contrary to what these investigators seem to believe, their studies using extraordinary stimuli, which are rarely if ever encountered in ordinary daily life, reveal just how unlikely it is that the events of the day are incorporated into dreams.
On the basis of a consideration of the laboratory dream research literature over a period of nearly 40 years, a dream researcher who did several studies that tried to influence dream content later concluded that
Probably the most general conclusion to be reached from a wide variety of disparate stimuli employed and analyses undertaken is that dreams are relatively autonomous, or 'isolated,' mental phenomena, in that they are not readily susceptible to either induction or modification by immediate pre-sleep manipulation, at least those within the realm of possibility in ethical human experimentation. (Foulkes, 1996, p. 614)
Nor have more recent studies of laboratory incorporations shown any higher percentages, and some of them suggest that personal concerns are the key reason for these few incorporations. The rarity of incorporations, even during the sleep-onset period, is demonstrated in a study in which participants played a computer game (Tetris) for 7-9 h a day for 3-4 days in a row (Stickgold, 2003, pp. 10-14). Although 64% of the 27 participants reported at least one incorporation after being "automatically and repetitively prompted for mentation reports during the first hour of attempted sleep," the actual number of incorporations was only 9.8% of all probes for 12 novice players and 4.8% for 10 experienced players; it was 7.2% for 5 participants suffering from profound amnesia, who were included because they might report imagistic evidence of playing the game although they could not remember they had played it (Stickgold, 2003, pp. 10-11). Although the investigator was gratified by the differences among the three groups because he thinks they support his theoretical assumptions, the crucial point as far as this article is concerned is that these figures are reminiscent of the low levels of incorporations found in earlier studies and once again are based on an experimental manipulation that far exceeds the bounds of everyday life (Arkin & Antrobus, 1991).
In a study in which 50 participants took part in a task in which they individually learned how to negotiate a virtual maze on a computer screen and then took a nap, only 4 of them reported thoughts and images after awakenings that related to the task they had learned. Three of them "reported task-related mentation at sleep onset (following at least one minute of continuous sleep), whereas the fourth reported a maze-related dream after awakening from stage 2 sleep at the end of the nap period" (Wamsley, Tucker, Payne, Benavides, & Stickgold, 2010, p. 850). Once again, this is a very meager amount of incorporation for an intense daytime experience (a difficult learning task) that had taken place not long before their naps. Moreover, tasks such as the Tetris game and the virtual maze negotiation may be incorporated on rare occasions because they are "related to concerns about pre-sleep task performance," which is consistent with the original cognitive meaning of the continuity hypothesis (Blagrove, Ruby, & Eichenlaub, 2013, p. 609). Put another way, many people feel personally threatened when they are asked to perform a challenging task.
Similar conclusions seem to follow from a study in which four students (a very small sample size) taking a 6-week second-language immersion class in French each slept in the laboratory 4 times (once before the class began, twice during the 6 weeks of instruction, and once after the class ended). The dream reports mentioning the attempt to learn French portray frustration and failure in grappling with what the person was trying to learn, not a simple incorporation of the participants learning French in the classroom and speaking French in the dormitory and dining hall. As the researchers who performed this work put it, the findings "support the notion that incorporations of learning experiences into dreams that contain frustration and anxiety do not appear to be associated with the learning process [italics added] but instead may be a reflection of obstacles encountered" (De Koninck, Wong, & Hébert, 2012, p. 190). In other words, they are about a frustrating waking concern, a new personal concern they have developed in an unusual and challenging environment in which the expectations as far as learning are very high.
Turning to studies of the appearance of the laboratory setting in dreams collected in the sleep laboratory, Schredl (2003, p. 35) is mistaken in claiming that "the experimental setting strongly affects dream content" and that "participation in a laboratory experiment is 'real' stress." In fact, after one or two adaptation nights, during which portions of the left hemisphere are now known to be more alert than on later nights in a new place (Tamaki, Bang, Watanabe, & Sasaki, 2014, 2016; Tamaki, Nittono, Hayashi, & Hori, 2005), the percentages for incorporation then decline to a low level because the participants know what to expect. However, he may be right that "the incorporation rates are higher than those for experimental manipulation of the pre-sleep situation" (Schredl, 2003, p. 35).
In the best-controlled early study of the effects of the laboratory on dreaming and dream content, it was determined that only 10.6% of the dream reports from 11 college male participants included any portion of text, however brief, that related to the experimental situation. This figure did not vary from the first night they were awakened, after 3 adjustment nights in which they were not awakened, until the end of the participants' involvement in the study; furthermore, only 6.2% of the dream reports contained a significant amount of laboratory-related content, a fact that is also reported in Schredl's (2003, p. 34) assessment of the evidence for everyday incorporations (Hall, 1967, pp. 200, 202-206). Of 32 dream reports with laboratory elements, 13 contained anxiety or hostility in relation to the experiment or the investigators (40.6%), which suggested negative concerns. Surprisingly, the investigator found that the participants who developed the most interest in the study (as evidenced by the questions they asked before and after experimental nights) dreamed most frequently about the laboratory setting, which suggests a positive concern with the study on their part (Hall, 1967, p. 198).
Ironically, this study also provided inadvertent support for the not-yet-formulated continuity hypothesis in that several participants dreamt very frequently about their major waking interests, dwarfing the handful of dreams that included laboratory elements. For example, 30% of the 50 dream reports from a participant preoccupied with sports cars included a sports car; a person focused on a small singing group to which he belonged dreamt about it in 40% of 35 reports; and a person whose chief avocation involved airplanes dreamt about them in 32.3% of his reports (Hall, 1967, pp. 204-205).
Nor is there any evidence that the laboratory situation is continuously stressful even for children ages 4-10, as shown through careful monitoring of their prebedtime behavior and sleep patterns in both longitudinal and cross-sectional studies (Foulkes, 1982; Foulkes, Hollifield, Sullivan, Bradley, & Terry, 1990). The 14 preschool children in the longitudinal study were rated as calm or relaxed on 79% of the nights and as extremely anxious on only 5.4% of the nights. Their median time to fall asleep was 20 min; the same children took only 12 min when they returned 2 years later. The median number of spontaneous night awakenings was 1 or 0, and the median time awake during the night was 8 min or less (Foulkes, 1982, pp. 33-34). In a cross-sectional study involving 80 children within a month of their fifth through eighth birthdays, the participants scored low on a 5-point anxiety scale that was administered on each visit and on average fell asleep 12.5-14.5 min after the lights were turned out (Foulkes et al., 1990, p. 454).
Finally, there are well-designed studies of the degree to which everyday daily life is reflected in dream reports. In these studies the participants kept 1-week or 2-week records of the major daily events, major waking concerns, and personally significant events in their waking lives, as well as of any dreams they recalled. Therefore, these studies may be more accurate than the numerous studies based on retrospective estimates of time spent on a certain activity. However, they involve a different kind of judging task that has its own methodological difficulties, leading to a complex mix of findings that will need to be sorted out in future replication studies before they can be used to balance out the overwhelmingly negative results in relation to the experiential incorporation hypothesis. Specifically, in these studies the participants are asked at the end of the data-collection phase to go through the dream diaries and their record of daily events to make judgments on the correspondences they see between dreams and waking concerns and experiences and whether the concerns and experiences are from the same day as the dream occurred or from any of the days before the dream occurred (e.g., Henley-Einion & Blagrove, 2014; van Rijn et al., 2015).
These studies sometimes show some evidence for the inclusion of recorded events from the same day as the dream (day residue) and for the appearance of recorded events in dreams that occur 5-7 days later (the "dream-lag effect"). However, the results vary depending on whether participants "give a single rating to the degree of correspondence between each dream report and each diary record" or "rated separately the intensity of as many correspondences as they could identify between each dream report and each diary record" (Henley-Einion & Blagrove, 2014, p. 71). In the single-rating design, it is uncertain as to "how participants were making these global judgments"; as for the methodology using multiple correspondences, any statistically significant evidence of incorporations disappears, perhaps because some participants "have an excessive propensity to connect events" (Henley-Einion & Blagrove, 2014, pp. 72, 87).
However, it was then found that there is a statistically significant day-residue effect for the group of participants who identify less than the median number of overall correspondences, but why this would be so is not clear. Thus, this unanticipated finding for below-median responders needs to be replicated, and then further studies would be necessary to understand why low-responding participants would be more accurate than those who provide an above-median number of overall correspondences (Henley-Einion & Blagrove, 2014, p. 72).
In short, methodological issues make it uncertain as to whether statistically significant inclusions of thoughts, events, and experience from daily life have been demonstrated in these more recent and well-designed studies. Moreover, there are some indications that any incorporations that do occur in these more recent studies lend support to the cognitive version of the continuity hypothesis. In one of the most complex and best-controlled studies of this type, based on both laboratory and home-collected REM dream reports, the presence of the dream-lag effect "is dependent on the salience or personal importance of waking life events" (van Rijn et al., 2015, p. 107). This type of finding is also reported in a study of 2-week dream diaries and daily events diaries from 32 participants by two researchers who adhere to the emotion assimilation hypothesis; they conclude that "major daily activities were included significantly less than the combination of personally significant experiences, major concerns, and novel experiences" (Malinowski & Horton, 2014, p. 31).
As this overview shows, these studies reveal that daily events and experimental manipulations have very little influence on dream content. Metaphorically speaking, it is as if highly sophisticated statistical investigators reported after performing an exhaustive multivariate regression analysis that they had explained approximately 5-7% of the variance. However, if the most recent incorporation studies (Henley-Einion & Blagrove, 2014; Malinowski & Horton, 2014; van Rijn et al., 2015) can be replicated, then the small number of personally significant experiential incorporations would be a useful augmentation to the version of the continuity hypothesis that is consistent with recent theorizing by cognitive psychologists (Domhoff, 2003, in press; Foulkes, 1985, 2017; Foulkes & Domhoff, 2014).
As this article fully documents, the continuity hypothesis is a precisely defined cognitive concept focused on a person's conceptions and concerns, with concerns referring to a person's primary personal interests and preoccupations of both a positive and negative variety, many of which may extend back to their college years in the case of some adults that have been studied (Domhoff, in press, Chapters 3-4). As such, this concept is an important part of the effort to develop a neurocognitive theory of dreams that envisions dreaming as a form of spontaneous thought, far removed from the theoretical tradition of stimulus-response psychology, a tradition that naturally leads to a focus on the incorporation of events from daily life (e.g., Antrobus, 1978; Antrobus et al., 1970; Domhoff, 1996, pp. 210-212; 2010b; Domhoff & Fox, 2015; Foulkes, 1985, 1999; Foulkes & Domhoff, 2014; Fox et al., 2013; Reinsel et al., 1992). Therefore, the continuity hypothesis should be distinguished from the broadly defined "experiential incorporation hypothesis" created by Schredl (2003) and endorsed by many others (e.g., Malinowski & Horton, 2014; Revonsuo et al., 2015; Sándor et al., 2016; Selterman et al., 2014), which encompasses day residues, stimuli-induced incorporations within the laboratory setting, incorporations of the laboratory setting into dream reports collected in a sleep laboratory, and the appearance of everyday experiences from recent daily life.
Because of the very different theoretical orientations and methods that experiential incorporation theorists (e.g., Schredl, 2003; Schredl, 2012) and social rehearsal/simulation theorists (Revonsuo, 2000; Revonsuo et al., 2015) use in studying the relationship between waking and dreaming, and out of respect for the difficulties of developing a new theory in any research field, these dream researchers should adopt another label for the hypothesis they favor over the cognitive version of the continuity hypothesis. The concept of a continuity hypothesis owes its provenance to the cognitive tradition of dream researchers, who are trying to develop a new theory of dreams; therefore, the concept should not be redefined and diluted, which generates lack of clarity and confusion. The cognitively oriented dream theories are as independent from the psychodynamic discontinuity theories of the prelaboratory era as they are from the experiential incorporation and emotion assimilation hypotheses that flourish at the present time.
It may seem unusual that a dream researcher whose work is being critiqued in this article would be a coauthor of an article that directly states that his view of the continuity hypothesis is incorrect. However, he is a coauthor on that 2005-2006 article because he kindly provided the set of dream reports that is the basis for the empirical analysis in that article. Although he had the opportunity to read and comment on a draft version of it, he did not comment. The critique of the emphasis on experience in the article reads as follows, with the italics in the original published article:
More theoretically, the comparison of dream content with waking life suggests that dreams express our conceptions of the people and activities that concern us in waking life (Domhoff, 2003), not merely our experiences in waking life. This distinction between conceptions and experiences is a crucial one because Hall and Nordby's (1972) evidence and line of reasoning lead to a cognitive theory of dreams, whereas an emphasis on experiences in waking life implies a more environmentalistic or behavioristic theory. (Domhoff et al., 2006, p. 277)
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The author thanks Richard L. Zweigenhaft for his critical reading of the first draft of this article, which led to several changes; to Kelly Bulkeley for very helpful suggestions to make the manuscript more focused; and to David Foulkes for two readings of subsequent drafts of the article, which led to even more changes.
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