It’s theoretically possible to place a brain in a vat filled with a nutrient-rich liquid, connect it to a computer, provide it with electrical impulses similar to the ones it would normally receive, and have it fully believe it’s experiencing reality as if it were placed in a skull connected to a body.

This is the brain in a vat thought experiment, and it’s an updated version of René Descartes’s famous thought experiment. It asks the question: how do we know what is real life? After all, the world as we perceive it isn’t the world as it exists. It’s our brain’s best guess of what’s going on, based on prior experiences and sensory input. And that brain can be tricked.

The advent and technical improvements of virtual reality have made this question more relevant than ever. Anyone who has ever tried VR knows how fully and how immediately your brain is tricked into believing it’s somewhere else. This is called presence: the subjective feeling of being somewhere. But how does VR actually achieve presence? How does it trick our brain?

Stereoscopic Vision

Visual cues alone are sufficient to have at least a degree of presence. A VR headset emulates how our eyes work. Humans have 3D vision because our eyes are around two inches apart from each other. This separation means that each eye sees the world from a slightly different perspective.

You can test this out right now: hold your thumb out in front of you and alternate looking at it with one eye. See how it jumps left and right? The closer you move it to your eyes, the more it’ll jump. The brain fuses those slightly different views to create a sense of depth. It understands how far an object is from the distance that the object jumps between both eyes.

VR isn’t any different. Through an HDMI cable connected to the headset or through a smartphone, two feeds that are slightly offset are sent to one display or two displays (one per eye). Along with autofocus lenses between the screen and your eyes, which can be adjusted to match the distance between your eyes, your brain will create 3D images that are similar to how our eyes view the world.

Additionally, the brain uses past experiences to build a set of rules to create our world. What we identify as the sky is up. The ground is down. We have an internal model of gravity. The vestibular system in our ears helps us with gravity. We have an internal idea of where our body parts are too, something called proprioception. VR emulates this as best as possible.

Combine this with the fact that a VR headset blocks out the external world entirely, and with the fact that our head movements are tracked along the X, Y, and Z axis, and we immediately achieve a strong feeling of presence.

Latency

But this feeling of presence will quickly collapse if there’s too much latency between our real movements and the movements as reflected in VR. Latency needs to be less than 20 milliseconds to trick the brain. Although latency is influenced by many variables, from the power of your CPU to how well data transfer down your HDMI cable, an important variable to decrease latency is the refresh rate of the display. The refresh rate is the frequency at which the images on a screen are refreshed. It’s measured in Hertz (Hz).

You want to make sure your screen’s refresh rate is consistent with your GPU’s frame rate. The frame rate is how fast your GPU can process images per second. If your framework is inconsistent with your refresh rate, you can experience VR screen tearing, which makes the images break apart. This can be countered with VSync, which limits your GPU frame rate to your screen’s refresh rate.

The displays in modern VR headsets have improved significantly over the last few years. The latest version of the Oculus Rift now has a 90Hz display, and the PlayStation VR headset even gets to 120Hz, although it has a slightly lower resolution than its competitors.

The Other Senses

Of course, reality is more than what we see. We can dramatically increase our feeling of presence by involving the other senses as well. One such example that’s already included in some VR headsets is spatialized audio, which is the placement of sound in a 3D environment. Something happening in VR behind you will sound like it’s actually happening behind you.

Another promising area is touch. Imagine you can feel the digital world you’re immersed in. You crouch and pick up an entirely fictional rock, but it looks and feels as if you’re holding a rock. Sounds like sci-fi? It’s already possible. In fact, we’ve written a whole blog post on VR haptics. Suffice to say it will be another big factor in making us feel present in a virtual world.

What Are the Implications?

The fact that VR can trick our brain into believing we’re somewhere else explains why VR has so many applications in different industries. In healthcare, for example, VR is being used to treat phobias, such as fear of heights or fear of spiders. Research has also shown that people can become more emphatic towards elderly people when being placed in an elderly body in VR, showing the power that embodiment has on our brain.

The brain is capable of changing much more and much faster than previously thought, even through adulthood. VR allows us to redefine how we think about the brain and, by extension, how we think about what’s real and what’s not.