The Revolution of Optic Flow
Our culture typically equates movement with exercise.
My piece on the wonderful new studies on movement anomalies in depression confirmed what most of us know intuitively: movement is so much more than exercise.
Yet medical professionals still urge us to “get exercise.” This, and the injunction to “do yoga,” are blunt tools. They don’t address the full capacity of movement and yoga to offer precise and powerful therapeutic tools.
I look forward to a time in the not-too-distant future when we’ll be able to determine the specific types of movements that are therapeutic for each of us, the contexts in which to use them, and the emotional benefits of doing so.
Today, I’d like to unpack optic flow, a form of movement you already do that has profound therapeutic potential.
I’ll cover what optic flow is, how it happens, and why it benefits us beyond the neurological level.
The Basics of Optic Flow
Optic flow describes the distribution of local movement trajectories as they cross our visual field. Its a pattern of visual motion is caused by our own movements. (Let’s put a bookmark in that and return to it later.) Simultaneously, it signals to us our own movement through the world, which is a vital part of our sense of body-in-the-world, which you can also think of as a node of embodiment.
But what exactly is it? On a visceral level, optic flow refers to the unique sensation that happens when you perceive your environment actively moving in relationship to your body’s movements. We all experience it; we’re just so used to it that we rarely give it a second thought.
As you walk, bike, run, skate, or swim, objects in your environment appear to move. As you approach, they grow larger; this lets you know you’re getting closer.
While you swim, for example, you perceive the bottom of the pool, lake, or ocean, moving beneath you, or objects on the side moving as you turn your head to breathe. Typically, these objects approach, arrive, and recede. (If you were to walk, run, or skate backwards, you’d see objects recede a little differently, which is a reason to go backward regularly.)
You can also get some optic flow by walking indoors, e.g. throughout your home.
But moving outside (walking, running, biking, skating, swimming, kayaking, etc.) is an ideal way to get your light exposure and optic flow at the same time. (I talk a lot elsewhere about the benefits of light exposure, particularly in the morning.)
It’s practical, too: You can get optic flow on the way to the train or bus, taking out the trash, or circling your block once or twice each day.
Your body’s movement provides the key mechanism for optic flow. A car, train, or motorcycle may give you pleasure and transportation, but won’t boost your optic flow. A treadmill, stationary bike (even the kind that simulates an approaching environment), yoga, or other forms of indoor fitness won’t offer the continuous forward movement that characterizes optic flow, even though they are beneficial in other ways.
If you walk at night, as I also do after dinner, you’ll find it less effective at generating optic flow. You’ll also find that movement feels more effortful at night: When you move in the dark, you see only objects that are close to you. This decreases the speed of optic flow, causing the sensation that you’re working harder and going farther. (That’s OK; we don’t need walks to do everything! Plus, night walks can be beneficial, particularly to offload glucose and help digest your last meal of the day; this promotes deeper sleep.)
In optic flow your eyes move, continually updating your brain on your location. But it doesn’t depend on vision. For blind people, optic flow occurs aurally, through sound.
With the impetus of optic or aural flow, your brain can tell whether you’re moving, or whether something in the environment is moving instead. It calculates what direction you’re moving in, whether you’re turning or dropping, how far away objects are from you, and how to regulate yourself in the space around them so as not to collide. Proprioception and peripersonal space come into play here too.
But that’s not all optic flow does for you; it also helps with stress resilience, trauma recovery, and myriad other issues. Let’s meet the person who discovered this, and changed the landscape of trauma-sensitive therapy.
Optic Flow + EMDR
We know about the strong relationship between vision (or audition), optic flow, and stress management not just because of neuroscience, but thanks to the tireless efforts of Francine Shapiro.
One sunny May afternoon in 1987, Shapiro found herself troubled by disturbing memories of a past trauma. A graduate student in psychology, Shapiro went for a walk in a nearby San Diego park when she made an accidental and astonishing discovery.
While recalling the traumatic incident, her eyes moved rapidly from side to side. Afterward, the disturbing memories were markedly less intrusive. Shapiro summoned another traumatic memory and moved her eyes in the same way; amazingly, the memory became less disturbing. She knew with the acuity that comes from relentless searching for tools and that trauma survivors and other neurodivergent people employ that she was onto something groundbreaking.
After writing her Ph.D. thesis on the effect of these eye movements, Shapiro founded the field of EMDR (Eye Movement Desensitization and Reprocessing). Despite detractors and skeptics, Shapiro worked hard to legitimize the technique. In 2013, the World Health Organization approved EMDR for use in treating PTSD and other mental health disorders. And independent researchers have demonstrated its efficacy with PTSD.
And that leads us to the link between optic flow and emotional resilience.
Optic Flow + Nervous System Elasticity
Your eyes are part of our nervous system. This means that your visual system links closely with (read: is part of) your autonomic nervous system.
Activating the sympathetic (fight-or-flight) nervous system ignites the stress response. Your eyes have a role in that response: your pupils dilate, narrowingy our field of focus.
When your parasympathetic, or rest-and-digest system comes online, activates, your pupils do the opposite: they constrict, expanding your field of focus.
Narrowly focused vision, the kind you employ when concentrating on work (or, say, a computer screen or phone) dilates your pupils and ignites sympathetic activation. This gives us the mild arousal you need to pay attention. (Visual focus plays a key role in sustained focus and attention. (And in Attention-Deficit Hyperactivity Disorder, a little eustress—the good kind that you control—helps with distraction control and focus.)
However, If you stay locked in high-focus visual perception for too long, you can experience feelings of anxiety, stress, hypervigilance, and irritability. (Or you’ll encounter the kind of agitation that comes after too-long periods of hyperfocus in ADHD.)
When you look at the horizon or at a broad vista without focusing narrowly and while taking in your periphery, your pupils constrict. This activates your parasympathetic (rest-and-digest) nervous system, and vice versa.
Perhaps more importantly. as your eyes move from left to right and up and down and forward in optic flow (panoramic vision), the brain’s stress response quiets. It’s like a bit of home-grown EMDR.
Benefits of Optic Flow for Embodiment
Self-generated optic flow also gives you moment-to-moment updates on where your body is located in space. It provides input on the orientation, coordination, and balance of your body as you move. It informs you about balance, postural control, and the spatial layout of your environment.
In these ways, optic flow strengthens proprioception, your sixth sense. (You can read more about proprioception here.)
To help organize my reflections on the inner senses stimulated by optic flow, I reached out to Alexander Borst of the Max Planck Institute. His lab does groundbreaking work on optic flow. He described a still-vivid memory of a visit to a neurology department. He sat inside a turning drum, and the vivid impression of being rotated as though inside a washing machine.
Borst mentioned the importance, in optic flow, of distinguishing between self-generated movement and other-generated movement that is directed by a force that is not us. (Remember how a couple of weeks ago, in the article linked above on new insights in depression and movement, I mentioned that people with depression (and those with Parkinson’s) have fewer internally-generated movements?)
That got me thinking.
My strong personal conviction: Because its effects are strongest and most therapeutic when movement is initiated and maintained by us, optic flow supports body agency, the ability to initiate movement in a way that matches our intentions.
Optic flow allows us to feel the impact of our actions on the world around us—a key element of the sense of agency.
Because of this, optic flow is vital to the process of recovery not just for trauma, but for other “diseases of disembodiment” involving agency, such as depression, anxiety, obsessive-compulsive disorder, schizophrenia, eating disorders, and more. It is also vital to lifting depression and to alleviating seasonal affective disorder. And it helps boost agency and slough off agitation for people with ADHD.
Aligning with the Journey as well as the Destination
Often, the wellness and spiritual worlds represent the outcome (destination) and process (journey) as a binary, as though we ought not to focus on outcomes at all. But in practice, it’s possible to do both, and to learn to hew closer to the one that comes less easily to you.
I tend to have a destination-oriented ethos that can creep in to my love of movement. I might inadvertently think about where my walk will take me, the endpoint of a swim, or getting a strength training session “in” at the gym.
When I immerse myself in optic flow, I feel the way speeding up my movements helps me walk up a hill more easily, or slowing down my movements. This boosts proprioception and my sense of agency.
At the same time, I can also feel the way speeding up increases the velocity of approaching objects. This adds to the optic flow aspect, and resets my nervous system. It often gives me a tiny hit of joy and self-determination, which I can infuse into the rest of my evening.
A walk, a run, a swim, a bike session may inherit the weight of obligation, of mere “exercise.” But optic flow is so much more. It’s a powerful therapeutic tool that allows us to access many aspects of embodiment at the same time, and to reanimate the relationship we have with the world around us.
The Bottom Line
This is one of the many ways that practicing something on a bodily level reverberates not just physiologically, but neurally, mentally, emotionally, and in a way that nourishes the bodily self and its place in the world.
Tip: Mindfulness helps. When you walk, bike, swim, or run, take time periodically to check in with your vision, and the interplay between your movements and the objects moving toward you or receding away from you. Consider promoting deliberate awareness of optic flow every so often—it’s easy and fun! (When I swim indoors in fall, winter, and spring, the bottom of the pool sometimes appears stationary; I take a moment, when turning my head, to register the side of the building “moving” as I go past.)
If you love to listen to podcasts while you move outdoors, check to see that your gaze is panoramic rather than focused, at least for a chunk of time. If it’s too focused, consider taking your earbuds out every so often. Also, since optic flow can happen aurally, taking an earbud break can help you boost it; plus, you’ll be able to hear the sounds of nature, too.