The default view in philosophy of mind and cognitive neuroscience has long been that the very notion of phenomenal experience occurring during dreamless sleep is nonsensical and involves a conceptual contradiction.[1] In this view, consciousness is „that which disappears in dreamless sleep and reappears when we wake up or dream” (Thompson 2015, this collection, p. 1), and dreamless sleep is simply characterized by the absence of conscious experience.[2] In his target article, Evan Thompson casts doubt on this view. Drawing from classical Indian philosophy as well as evidence from sleep and dream research, he argues that dreamless sleep experience is a theoretically coherent and empirically tractable target for future research. Yet, in order to even begin to make sense of dreamless sleep experience, a more fine-grained taxonomy of sleep states and new experimental protocols integrating disciplined first-person reports as well as neuroscientific methods are needed.
Here, I take up this challenge and attempt to sketch the outlines of a positive account of dreamless sleep experience. This commentary has three main aims. The first is to propose that Thompson’s case for dreamless sleep experience can be strengthened by constructing a rough analogy between the historical Indian debate on dreamless sleep and contemporary Western debates from scientific dream research and philosophy on the epistemic status of dream reports. Based on this analogy, I argue that the default view is inconsistent with the methodological background assumptions of scientific sleep and dream research. This internal inconsistency lends additional urgency to Thompson´s demand for a more fine-grained taxonomy of sleep states. I then use the Indian debate as a foil to sketch the outlines of an integrated theoretical position on the trustworthiness of first-person reports of dreams and dreamless sleep experience. I take this approach to be in the spirit of the type of cross-cultural approach recommended by Thompson and hope to show that valuable lessons can be learned on both sides.
My second aim is to sketch the outlines of a positive account of dreamless sleep experience. Here, my key claim is that dreamless sleep experience can be described as pure temporal experience. By this I mean phenomenal states that aside from their temporal structure are devoid of any further intentional content and characterized only by the subjective experience of time. Pure temporal experience (or pure subjective temporality, as I will also sometimes call it) is not structured around perceptual objects, events or emotions; it is the experience of being just in time.[3] This account of dreamless sleep experience is attractive, or so I claim, because it offers a way of spelling out not just what is distinctive about dreamless sleep experience, but also how dreamless sleep experience can be integrated into a broader theoretical framework describing different kinds of sleep experiences, including dreams. The key idea is that while even the simplest forms of dreaming are characterized by phenomenal selfhood, or the experience of being or having a self, the transition from dreaming to dreamless sleep experience occurs when even this minimal form of phenomenal selfhood is lost. While the analysis of dreaming can help identify the conditions for minimal phenomenal selfhood, the analysis of dreamless sleep experience may provide a glimpse of an even simpler (and perhaps even minimal) form of phenomenal experience. In the final part of the commentary, I identify what I take to be the three most promising candidates for a future research program on dreamless sleep experience. These are lucid dreamless sleep, white dreams, and sleep-state misperception of the type most commonly seen in subjective insomnia. These examples broaden the scope of the target phenomenon by suggesting that the theoretical and experimental investigation of dreamless sleep experience extends beyond the case of expert meditators discussed by Thompson.