So far, we have applied TDI to Stage 1 (also called NREM1 or N1) sleep, which is the first stage of sleep. During sleep onset, hypnagogia (a special state occurring in the transition from wakefulness to sleep) occurs. Sleep onset is characterized by a gradual, piece-by-piece descent into sleep, as opposed to a sudden, binary on/off switch from wakefulness to sleep which some people imagine occurs. In fact, there are nine separate substages of sleep onset. In the middle of this gradual transition from wakefulness to sleep, the brain maintains sensitivity to outside stimuli (for example, people can still hear sounds and smell scents in the space around them) even as the brain enters a more dream-like state, both in terms of physiology and mental experience.
In our work, we use a TDI protocol with auditory stimulation to guide sleep onset (N1) dreams. We carry out our TDI protocol with the Dormio system (read more on Dormio here), but TDI can be carried out with any combination of tools that can track sleep stages, play stimuli, and record dream reports. A person wears Dormio and lies down to fall asleep. The Dormio system tracks sleep onset. Once sleep onset is detected, a timer of a few minutes is started. At the end of the timer, an audio recording is played to ask the user for a dream report, bringing the wearer back into wakefulness briefly. We record everything the user says during their dream report, to avoid them forgetting a potentially useful idea. Following their dream report, the system then plays an audio cue, reminding the wearer to think of certain words (like "fork" or "rabbit"), with the aim of integrating the cued topic into their next set of dreams. The user then drifts back to sleep, with the cue in mind. In our laboratory testing, we have found that the cued words reliably entered the hypnagogic dreams of our users. The system continues to track the state (awake or asleep) of the user, repeating the process described above of waking them up after a few minutes of sleep to collect a dream report. This protocol is carried out repeatedly to guide dreams and collect dream reports.
To better understand how our auditory stimulus makes its way into people’s dreams, just consider “a lion playing volleyball underwater.” This phrase, even written, conjures a mental image. The creation of a mental image from words also happens at sleep onset. Words heard by the napper just as they fall asleep serve as a seed for mental images/thoughts, allowing the ideas to slip into their dream. We wake the subject up after a few minutes and request a dream report in order to avoid them slipping into a deeper sleep, at which point the likelihood they forget their dream would increase.
We began this work using the Dormio device for tracking sleep so we could incubate dreams. Since then we have also used the Masca, the Hypnodyne, and even typical polysomnography to enact TDI and produce targeted dreams. We emphasize that our TDI protocol can be carried out using a variety of technologies to track sleep, play, and record audio. We are working on new ways to do low-tech dream incubation, such as through just an online timer interface: https://christinatchen.github.io/dormio/timer.