Last month, for the first time in over a year, I had lucid dreams for two nights in a row. A lucid dream, or realizing that you’re dreaming while still inside of the dream, is not an unusual experience: most people will have at least one lucid dream in their lives.
An occasional lucid dreamer myself, I’ve never developed the degree of control that some master lucid dreamers have, who can bend, Matrix-like, the fabric of their dreams to their will, night after night. Instead, my own version of lucid dreaming tends to consist on being in the midst of some horrifying nightmare, then having the thought that “this is just too awful to be real, so I must be dreaming,” and eventually grasping that that’s indeed the case. When that happens, I typically use my newfound awareness to wake myself up at once and be done with the whole thing. But in these two recent instances, I had an altogether different experience. Critically, I figured out that I was dreaming while having a neutral sort of dream, so I wasn’t compelled to seek an immediate exit. So my understanding of my unusual situation was a lot more matter-of-fact than in the majority of my prior lucid dreaming episodes.
On each consecutive occasion, I immediately decided on flying. I had had dreams of flight before, but never intentionally. Now I could soar with purpose. I ascended at vertiginous speeds over the Manhattan skyline, and as soon as the clouds enveloped me I dove down, superhero-style, unafraid of gravity. Rising up again, I darted around buildings and billboards with ballistic accuracy. I briefly joined a flock of birds, then left them behind.
The experience felt as real as life, and my oculomotor system probably opined the same. A new study on lucid dreaming, published in Nature Communications last month, has found that we make certain kinds of eye movements when we dream that also occur when we view actual objects, but not when we imagine them.
The eye movements in question are called “smooth pursuit,” and as their name indicates, we use them to track objects in motion: a ball rolling on a playground, a boat sailing against the horizon, or a flock of birds flying in formation. One fascinating aspect of smooth pursuit eye movements is that you can’t fake them. You can use smooth pursuit to track an actual moving object, but not an imagined one. You can convince yourself with a little experiment, which you can perform on your own or with the assistance of a partner, as follows:
Raise your index finger at an arm’s length in front of your eyes and move it slowly from left to right, and then back. Do this several times and notice (or have your partner observe) that your gaze follows your finger on a smooth path, with a continuous fluid motion. That’s your smooth pursuit system at work. Now try to replicate the same eye motion while imagining the trajectory that your finger described previously, without seeing an actual finger. You will find (or your partner will verify) that your eyes are no longer moving smoothly, but are instead performing tiny frog jumps from side to side along the imagined path. These little eye jumps are not controlled by your smooth pursuit system (which is inactive in the absence of motion in the visual field), but by your saccadic system (‘saccade’ is French for jolt), which you use to explore the visual scene around you.
A team of researchers at Stanford University and the University of Wisconsin-Madison realized that–because people can’t perform smooth pursuit eye motions in response to imagined trajectories—they could track the eye movements of lucid dreamers to discover if dream imagery is more similar to our perception of actual objects (which can generate smooth pursuit movements) or to our imagination (which cannot). The question goes back to Aristotle, but had remained unresolved until now.
To find out, Stephen LaBerge, Benjamin Baird, and Philip G. Zimbardo recruited experimental participants with demonstrated ability to have lucid dreams in the sleep laboratory. Each participant spent between 1 and 8 nights in the lab during the course of the study, sleeping while the researchers obtained their EEG and gaze measurements (via electro-oculogram).
While asleep, participants indicated the moment in which their dreams became lucid by “LRLR eye movement signals,” that is, they quickly moved their eyes all the way to the left, and then all the way to the right for two consecutive times, to signal to the scientists that they were now aware that they were dreaming.
Once dream lucidity was communicated to the researchers in this way, participants had to visualize previously agreed-upon dream objects and follow them with their eyes, while the researchers tracked their eye motion. The eye movement data showed that smooth pursuit tracking during lucid dreaming was highly similar to the smooth pursuit that occurs during waking perception, while being qualitatively different from the saccadic tracking that takes places during imagination. The scientists concluded, based on these results, that the visual imagery that occurs during sleep is more similar to perception of real objects than to imagination.
The data moreover showed that the neural circuitry of smooth pursuit can be activated by dreamt imagery in the absence of retinal stimulation from actual visual objects.
Plus, it suggests that the eye movements I performed while chasing birds and planes during my oneiric acrobatics were likely much the same as they would have been in real life—had I been able to perform similar superhuman feats.