Of the theories that are directly applicable to dreaming, we have already addressed the Continuity Hypothesis (CH) in our target article (Revonsuo et al. this collection). As we say there, it has never been formulated in a sufficiently precise manner such that risky, testable predictions can be derived from it. The CH, largely because of its vagueness, might actually be consistent with simulation theories. The particular contents of dreams are neither selected through an active process, nor do they reflect any function(s); they are selected through a passive and more or less random mirroring of the experiences that have been lived through. Further, CH does not consider how to deal with potential anomalies for the theory: the relatively frequent cases where either something very alien to our waking world (and thus entirely discontinuous with it) appears, or where something very common in our waking life fails to appear in our dream contents. Can the theory be regarded as falsified when evidence of such blatantly discontinuous dream contents appear over and over again in dream data? One version of the CH, presented by Foulkes (1985) states that the mnemonic sources of dream contents are random and unpredictable; thus dream contents are unselective random samples of our memories; but the general form of dreams as world simulations as such is highly predictable—thus the function of dreaming would be more related to the general form than to the specific contents of dreams. However, as we have argued, dream contents are not random, but selective, and in particular they select threatening and social events into dreams. Thus, the basic assumption behind Foulkes's version of CH has turned out to be empirically false. The CH thus does not look very promising. But, as we argued in our target article (Revonsuo et al. this collection), some testable predictions can and should be derived from CH, to render its predictions as the null hypothesis “no selectivity, no functionality”, and thereby directly test its predictions against those derived from TST and SST.
Another major functional theory of dreaming, the Emotion Regulation Theory (ERT; also reviewed by Dresler this collection), also seems relatively weak as a scientific theory. It has been presented by many different authors in many different formulations (e.g., Cartwright et al. 2006; Hartmann 1996; Kramer 1991). There seems to be no standard, detailed, or shared version of this theory among its supporters; thus it also suffers from a vagueness similar to that of CH. The shared core in all of the different versions appears to be the idea that dreaming works with and processes difficult, unpleasant emotions and events, and through this dream processing makes us get over them and feel and function better in our lives. An often-used analogy compares dreaming with psychotherapy (Hartmann 1995; Walker & van der Helm 2009).
Again, when looking at the evidence it is important to separate sleep from dreaming. When it comes to emotional processing during sleep, the analogy to psychotherapy gains some support (Walker & van der Helm 2009). But when applied specifically to dreaming and dream contents, the idea runs into difficulties. Its theoretical roots appear to originate predominantly from the clinical tradition, and more specifically from the idea that the function of dreaming is to protect sleep from strong surges of emotion and to solve emotional problems. The negative contents of dreams originate from interpersonal conflicts and current concerns, thus being consistent with the continuity between dreaming and waking, in fact so much so that the CH coupled with the ERT could perhaps be seen to form one specific paradigm of dream theorizing. Perhaps one of the core differences between the ERT+CH paradigm and the simulation paradigm is their relationship to biological explanations. The ERT+CH favours psychological-level explanations and emphasizes recent individual experiences (learning, nurture) as proximate explanations of dreaming. The simulation paradigm emphasizes biological explanations of the form and contents of dreaming, and links dream consciousness to both the underlying neurophysiological levels as well as the ontogenetic and phylogenetic, ultimate biological history of dreaming as explanations of the form and contents of dreaming. A further core difference between these paradigms is that the psychological paradigm sees the function of dreaming as contributing to our psychological well-being and psychological adaptation to our lives, whereas the biological paradigm sees the origin of dreaming in its ability to increase fitness in all mammals and in humans during their evolutionary history; but dreaming need not necessarily contribute to our psychological well-being in order to fulfill its original biological function.
As these approaches represent different paradigms with differing core ideas, it might not be possible to integrate them, in the manner that Dresler (this collection) suggests, into one overall multifunctional theory of dreaming. Some of the core assumptions of ERT are inconsistent with TST, especially when it comes to the function(s) of dreaming and to the explanation of nightmares and bad dreams. According to TST, post-traumatic dreams, recurrent dreams, nightmares, bad dreams, and the earliest dreams in childhood are the best and strongest manifestations of the function of dreaming, when the function is fully at work and typically activated by ecologically valid threat cues and dangerous events observed in the environment, often displaying universal threat scripts consistent with evolutionarily relevant threats. In parasomnias the threat-simulation system can be overactivated, or activated in an inappropriate context and therefore seen as psychologically dysfunctional, so that it might in actuality either decrease the well-being of the individual or hamper with other functions of sleep and dreaming, even though it at the same time carries out its original biological function perfectly. By contrast, according to ERT, such highly negative dreams are malfunctions and failures of the core function of dreaming itself, because such dreams disturb sleep and make us feel negative emotions. Nightmares cause psychological suffering and sleep disturbances, thus they are like a failed psychotherapy session that increases the individual's psychological distress, instead of calming the individual down. As such, very large and important categories of dreams (and their functionality) are explained in squarely opposing ways by the two paradigms.