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A recent paper published in Sleep Medicine Reviews in November 2018 discusses the phenomenon of “white dreams” — the feeling of having dreamt without having any recall for the content of the dream. According to prior research, up to one-third of awakenings are associated with “white dreams.”
Many people assume that white dreams are simply cases where we have had a dream, but have forgotten it by the time we wake up. Even in dream studies, researchers will often group white dreams into the category of not remembering a dream, and so they are simply disregarded.
The authors of the current paper attempted to explore other possible explanations for white dreams and argue that these dreams can be informative for our knowledge of how dreams occur in our mind and brain.
To classify three types of dream experience, as per Fazekas et al. (2018): Contentful dreams are those dreams which we can recall upon awakening as having specific content that can be described in detail. White dreams are those instances where there is a distinct feeling of having dreamt, yet being unable to recall any specific details. No-dream experiences are those cases where we have no sense of having dreamt at all prior to awakening. One study found that after about 45 percent of awakenings, subjects recalled contentful dreams, white dreams account for 33 percent of awakening reports, and 22 percent of awakenings were associated with no recall of experiences (Siclari et al., 2017). Contentful dreams occurred more often following REM sleep, whereas white dreams occurred more following NREM sleep.
There are two interpretations to white dreams: 1) White dreams are contentful dreams which have been forgotten, either through the awakening process, or perhaps due to their not being encoded in memory while experienced. 2) White dreams are conscious experiences that lack any perceptual or image qualities to remember them by; in other words, they are a minimal form of subjective experience without any specific sensory detail.
In the second case, the white dream experience still entails some form of phenomenal self-experience: We experience a sense of presence and time, but without any other spatial or perceptual awareness. The authors distinguish this from dreamless sleep in that, during dreamless sleep, there is the lack of any sense of self or temporal duration at all, and we have no recall of any experience after awakening. (The case of dreamless sleep itself, though, is still a contentious point among experts, as it could again be a case of a lack of recall even if some conscious experience does occur.)
As described in a previous post, dream science typically involves the study of dreams within the sleep laboratory (see previous post), where researchers measure brain activity through EEG and collect dream reports following awakening, asking participants to report any dream experience they can recall. One recent study analyzed the EEG activity of the brain that corresponds with white dreams (Siclari et al. 2017); they assessed EEG activity 20 seconds prior to awakenings that were associated with contentful, white, or no dream recall. The authors found that in cases where participants could not remember any dream experience at all, there were more slow waves in the posterior region than in cases where participants recalled white dreams or contentful dreams. So it seems that in the case of no dream recall, the power of slow wave activity in the posterior region of the brain inhibits the generation or recall of dreams. Slow waves are most abundant during deep sleep, and are less common in lighter stages of sleep, which corresponds with findings that we have lower dream recall when awakened from deep sleep stages.
The authors then analyzed fast brain activity, which is more like wakeful brain activity, and found that participants who reported contentful dreams had more fast activity in the frontal and parietal areas of the brain than those who reported white dreams. If we consider fast activity to be an indication of wakefulness, we could understand this to mean that when there is more wakeful activity in frontal areas of the brain, we are more likely to remember contentful dreams.
The authors of the current paper draw a connection between these neural findings and similar findings from the waking literature, namely that in studies of waking perception, the quality of conscious experience directly correlates with the quality of neural representation.
For example, all types of waking perceptual experiences (e.g., visual, auditory) can be classified along a continuum according to their vividness, specificity, and stability. These characteristics of conscious experience seem to arise directly from patterns of neural firing. To illustrate, to perceive an object as vivid, clear, and stable depends on underlying neural representation of sufficient intensity, specificity, and maintenance over time.
These qualities diverge dramatically in dreaming. For instance, in dreaming, the vividness of imagery varies; some dreams may encompass our entire visual field saturated with color and brightness, whereas other dreams may simply consist of a small, faded image off in our periphery, even lacking any color or light. In dreaming our perception is also markedly discontinuous, images may change fluidly into other objects over time. And finally, dreaming can lack clarity, we may see something that looks like a dog or maybe a sheep, or is it a horse or some other animal?
Already it is quite common to ask participants upon reporting their dreams to rate their dream images along these scales, and thus white dreams would fall at the very bottom of the spectrum, having no vividness, clarity, or stability outside of an ephemeral sense of experiencing. This novel perspective contrasts with prior assumptions that white dreams are simply cases of forgetting contentful dreams.
Finally, the authors draw a parallel to studies of waking visual perception. For example, in a visual masking paradigm, participants are shown visual objects which are gradually masked by a filter. When the stimulus is nearly completely masked, participants often report what is termed a "weak glimpse," where they have the experience of having seen an object, but cannot identify or remember what it is. This weak glimpse is strikingly similar to the white dream.
The authors underscore the fact that degraded perceptual experiences in waking life are characterized by reduced neural activity, and they propose that the reduced fast activity corresponding with white dream as compared to contentful dream reports supports their interpretation that white dreams are low quality dream experiences (and not simply forgotten contentful experiences).
References
Fazekas, P., Nemeth, G., & Overgaard, M. (2018). White dreams are made of colours: What studying contentless dreams can teach about the neural basis of dreaming and conscious experiences. Sleep medicine reviews.
