Dream Study Intro -
The Threat Simulation Theory (TST) of dreaming accounts for the high frequency of negative typical dream themes by proposing a biological role for dreaming, taking an evolutionary-psychology perspective (Revonsuo, 2000). The TST describes dreaming as a biological mechanism with specific adaptive purpose, a threat detection and avoidance system which allows humans to practice handling the types of threats encountered in the prehistoric environment.
As noted by the originators of the TST, the causal relationship between environmental pressures and evolutionary adaptation by way of fitness cannot be directly tested. Rather, the propositions made regarding what traces such a system would leave, if it were selected for over the millennia, can be studied. Six such propositions were put forth which, when given credence, would make up the scaffolding supporting the TST: Dreams are a simulation of waking experience but biased toward representing particular events; the bias of the dreaming system is to over-represent threatening events in comparison to waking experience; only encounters with real threats while awake will fully activate the dream-threat system; behaviors and perceptions in dreams are realistic rehearsals of how we might deal with events if they were to really occur; mental action simulations can improve physical performance even if such rehearsal is not explicitly recalled; and the ancient environment included frequent and severe threatening scenario cues which activate the dream threat system (Revonsuo, 2000).
The first study testing the TST analyzed 592 dreams from 52 University of Turku students (34 female, 18 male; age M = 23.3, SD = 3.7) (Revonsuo & Valli, 2000). The students were instructed on how to record their dreams and did so after awakening, for four weeks, sans any knowledge of hypotheses regarding the study. A rating scale which came to be known in subsequent studies as the Dream Threat Scale (DTS) was devised to categorize threatening dimensions in dreams, including the nature of the threats, the target and severity of threats, the source of the threatening events, etc. Kappa tests were computed between three raters, where applicable, and an acceptable inter-rater agreement was obtained with the DTS. The average dream had 1.2 threatening events (SD = 0.43), with no significant gender difference. Of all the dream reports, 66.4% had at least one threat, and no participant had zero reports with at least one threat. Average report length was 140 words, and 34% of Total Recall Count (TRC) described threats. The most typical type of threat was aggression, and when combined with escapes and pursuits, 42% of threats types were accounted for. The only gender differences in any of the rating scales were in direct physical aggression, which men reported twice as often as females. The dream self, followed by significant others, was the most common target of threats.
A second study used the DTS to replicate the first study, in a Swedish university population, analyzed by new judges (Revonsuo & Valli, 2000). Again, all participants supplied at least one dream report with one or more threats, and 77% of all reports had at least one threat description. To compare dream threats to a waking baseline of threatening experiences, a third study had 39 Finnish university students record their waking life in daily journals and also write down their dreams during the same time period, in addition to being interviewed concerning the threatening events which could be recalled from long-term memory (Valli, Strandholm, Sillanmaki, & Revonsuo, 2008). The TRC in dream reports for threatening descriptions was 37.1%, and 72.8% of the Finnish student’s dream reports included at least one threat, while only 15% of daily log reports did so, and the dream threats were more severe than were the waking threats. Averaging these first three university population studies together, participants recalled on average 3.57 (SD = 1.6) dreams per week, of which 72.1% (SD = 5.3) included one or more threatening events (Valli & Revonsuo, 2009).
Two studies used the DTS to compare dream threat frequencies between traumatized and non-traumatized child populations (Valli & Revonsuo, 2009). In one of these studies, 64 severely traumatized and 52 less traumatized Kurdish children and 70 nontraumatized Finnish children supplied a total of 763 dreams using a semistructured dream and sleep journal. The Finnish children had the lowest threat incidence of any population analyzed thus far with the DTS (TRC = 20.1%). Of the Kurdish children who did not directly experience trauma but were likely close to those who had, average TRC of threat description was 42.1%. The highly traumatized Kurdish children, in contrast, had the highest number of dream reports with threats and average TRC threat percentage of any child or adult sample population studies so far with the DTS, at 79.5% and 61.1%, respectively. In the other study testing the TST in a child population, traumatized and non-traumatized (but again, likely close to persons having experienced trauma) Palestinian children had a TRC of threatening description at 38.0% and 58.7%, respectively.
Recurrent dreams and nightmares have also been analyzed with the DTS to test the TST prediction that these dreams are exemplary cases of the threat simulation system at work (Zadra, Desjardins, & Marcotte, 2006; Desjardins & Zadra, 2004). These data were collected with retrospective questionnaires for the recurrent dream study and 2- to 4-week dream diaries for the nightmare study, prior to being intended for use within the TST paradigm. Although threat frequencies were not higher than in normative dreams (recurrent dreams including at least one threat = 65.5%, nightmares = 63%), the quality of the threats were more severe (Valli & Revonsuo, 2009).
At a frequency of 42% of all threats in the university population dreams analyzed with the DTS, aggression (pursuit, attack, etc.) is the most common threat type; in children’s dreams this percentage is even higher (53-76%) (Valli & Revonsuo, 2009). In the university students’ dreams, failures accounted for slightly more and accidents and misfortunes for slightly less than one-quarter of dream threats. Catastrophic events were rare (3-6%), and disease or illness was even less common (0-11%). In all samples tested, dream threats were predominantly directed against the dreamer (69-94%), followed by significant others, and 40-70% of dream threats would endanger the reproductive success of the dreamer had they occurred while awake.
The Threat Simulation Theory for the function of dreaming has been critiqued as being too narrow in its focus on the various types of dream content reported in dream research. Bulkeley (2004), for example, faults Revonsuo (2000) for appointing the chasing nightmare as the paradigmatic dream, and downplaying “the multiplicity of dreams.” In an attempt to broaden the adaptive value of dreaming, Bulkeley compares dreaming to play, in that both occur in a quasi-real, relatively safe environment and involve strong emotions, and both draw raw material from survival concerns, with a tendency toward exaggeration while the rules that govern daily life are suspended, allowing for experimentation. By placing the role of dreaming in this ludic context, the pluralistic nature of dreaming which the TST supposedly cannot account for is, possibly, contained. Although it is sound to attempt to broaden the function(s) of dreaming to make sense of all the content and themes which people do dream about, even to admit that several adaptive functions, or modules, may surface and find expression in dreaming, the TST does cast a wide net in its definition of what constitute threat. The chasing dream is given its elevated status by virtue of this theme consistently being exposed as the most common dream around the world and throughout time (Garfield, 2001), however, the TST also addresses the other physical and nonphysical aggressions in dreams, as well as failures, accidents, and misfortunes.
Yet, even highly vivid and memorable dreams may not always contain threatening events. Flying dreams can arouse a euphoric sense of freedom. Interactions with deceased loved ones can offer placation to a much-sought desire for reunion. And lucid dreams, in which the dreamer is aware of her being inside of a dream, can provide an unparalleled opportunity for play unlike anything available during waking life. These are only a sample of dream scenarios which do not necessarily provoke a sense of threat, although they can. For example, although highly positive feelings are usually emphasized in the literature of flying dreams (Domhoff, 1996), these dreams can also be accompanied by strong sensations of effort to stay afloat or feelings of a haunting presence, or may even be precipitated by being chased, realized as an attempt to escape (Schronhammer, 2000).