VR R&D and design practice: "Embodiment" is more important than "immersion".

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(XR Navigation Network March 18, 2024) Synapse, which was a finalist for Best AR/VR Game at the 2023 TGA and Best VR Game at the Golden Rocker Awards, is a community favorite. Players in this VR action shooter can experience left and right, wielding fierce firepower as well as raging thoughts with abandon. You'll take on the role of an agent who breaks through thought defenses, wielding a deadly weapon in one hand and exaggerated Nenbi skills in the other, triggering chaos in the minds of your enemies, breaking through chilling defenses and penetrating deep into hostile mindspaces.

A few days ago, the development team nDreams introduced a key concept in VR game development with Synapse: Embodiment.

Definition of embodiment

So what is embodiment and why talk about it instead of talking about the cool shooters, shocking explosions, and clever design of the game? This concept will help us understand why specific design decisions work so well in Synapse.

Embodiment is a term used to describe the sense of physical presence in a VR experience, as if you were actually standing in the world depicted by the experience.

Now your reasonable response is, "But aren't we already using the word Immersion immersion to describe it?"

In layman's terms, of course, that's what people would use, but I want to make an important distinction between "immersion" and "embodiment".

"Immersion," for the purposes of our discussion, is when something captures your full attention. When the story of a movie is so compelling, in that moment you don't notice anything outside of the movie theater at all; it's as if they've all disappeared into thin air. But even with the most immersive movie you've ever seen, do you feel like you're actually inside the movie? Of course not.

This is where "embodiment" comes in. For the sake of clarity, I will define immersion as attention. Embodiment, on the other hand, is your physical presence and how it relates to the world around you.

So I think it's important to recognize that all VR games get immersion for free. By taking over your senses of sight and sound, they largely take over your full attention automatically. The moment you put on the headset, you're immersed.

But some VR games take us a step further. Not only do they capture our attention, but they can make us feel like our entire body is transported into the virtual world. Like if you reach out and touch them, you'll seem to feel their exact presence.

Immersion is attention and embodiment is the feeling of being there.

To be clear, embodiment is a spectrum, not a binary. Some VR games have a slight sense of embodiment, others have a very strong sense of embodiment. But what exactly makes the difference?

That's exactly why we're talking about Synapse.

You can feel the bunker.

At first glance, Synapse seems like a pretty generic VR shooter, but there are a couple of intentional design decisions that drive a strong sense of embodiment. The first thing I'd like to mention is the bunker system.

Every VR shooter has cover. You can walk behind a wall and it will provide you with cover. But other than that, the wall has no real physical connection to your body because you're never actively touching it. It's just a stationary object.

But Synapse makes walls and other cover interactive, allowing you to lean your hand against a wall and use the force to rise out of cover. This feels very natural and works very well for the game as well.

And because you're the one moving you in relation to the wall, rather than just moving it back and forth through the controller, the wall starts to become more real. Specifically, it feels more real because when you grab the wall and use it as an anchor point for movement, you subconsciously treat it as part of your proprioceptive model.

Understanding Ontology

Let's take a moment to explain proprioception below, because this term comes up many times when we talk about tricking our body into thinking we are somewhere else.

The clearest example of proprioception is this video clip. Watch closely as this cat approaches the table, not thinking too much about moving his ears away at just the right time and effortlessly.

This is proprioception at work. It's a model of how your body relates to what's around it. In order for a cat to know exactly when and where to move its ears to avoid the table without looking at it, it must have some innate sense of the space occupied by its ears and how it relates to the space occupied by the table.

Using the bunker system in Synapse as an example, you can visualize that "when I lean my hand against a wall and move my hand to the right, my body moves to the left."

Thus, walls are no longer just "what's visible", but more important objects. They relate to you in a more meaningful way because you can directly engage with them and influence your body position. In doing so, your brain begins to pay more attention to the walls in relation to your body. They begin to become more real. By extension, your own body begins to feel more present in the simulation and you feel more "embodied".

cartridge clip

In Synapse, walls can be used as more than just cover. You can use them to stuff magazines into your weapons.

Synapse is a run-and-gun shooter, so the developers went with a faster-paced but still attractive reloading system. The magazines don't nag the player about inventory; they'll simply eject and float there. To reload, just shove them back into the weapon. It may seem silly, but it works great in the sci-fi context of the game, reducing the complexity of reloading while keeping it fun.

Now we can see how this works perfectly with the bunker system.

The game's bunker system requires one of your hands for use. So how do you reload? Instead of using your other hand to rest the clip into the weapon, a straight downward slam will allow the clip to enter the gun, the perfect solution to allow players to use both systems at the same time.

But guess what? It's not just a really clever design, it's also another way for you to interact with the wall as if it's actually there. If you're going to load with it, you need to know if your arm is close enough to the wall. So, your brain starts to incorporate the walls and their proximity into your proprioceptive model. You start to really feel the space between your body and the walls.

So those two things make the walls feel more real because you can get up close and personal and interact with them in a meaningful way.

As the world around you begins to become more real, you begin to feel more convinced that you are really there. This is embodiment. Remember: virtual worlds are always "immersive" because they have to capture our full attention. But embodiment goes beyond what we see; it's about what we feel.

Synapse takes its incredible telekinesis system to a whole new level when it comes to contacting the world.

Expand your reach

Synapse may have a lot of shooting content, but you actually have powerful telekinesis abilities that allow you to remotely grab and manipulate entities in the world. You can throw enemies into the air and smash them to the ground. You can crush people with crates or use them for cover. You can even move platforms.

Exploding barrels add explosive fun to the game, but the developers have added a very clever little detail at the same time. When maneuvering the explosive barrel, you only need to hold the trigger halfway, as squeezing the trigger all the way causes the barrel to explode. This is very useful for blowing it up in front of enemies, but at the same time is a cool way to force the player to balance their aggressiveness and intent.

If you hastily raise an explosive barrel with your mind in the middle of a fight without thinking and pull the trigger hard enough, the barrel will explode.

But if you keep a cool head, you can use exploding barrels to very good effect.

Okay, but what does this psychic telepathy have to do with embodiment?

Remember how I said that items you can physically interact with start to feel more real because your brain incorporates them into the proprioceptive model? The same thing applies to items you control with telekinesis.

Even though you are interacting with them from a distance, the fact that they are able to respond to your natural movements makes all the difference.

When it comes to shooting, pulling the trigger to kill a bad guy in the distance is a very "objective" interaction. The process is so fast that you barely realize the parameters of how the interaction happens.

On the other hand, when performing Nimble Control with your own arm and hand movements, you feel very proactive even if the item is some distance away. It feels like you have a superpower, rather than just pointing at enemies and pressing the trigger a couple times to shoot them.

《Synapse》的念力感觉像是超能力的另一个原因是，游戏使用了PSVR 2的eye tracking功能来检测你想要抓住的物品。所以可能有三到四个有效的物品摆在你面前，但你可以通过注视来找出正确的物品。

In practice, it feels really, really natural, almost like the game is reading minds. It makes it feel like you really do have this ability.

summarize

Synapse has several clever design choices to enhance the game's embodied feel. But assuming you're not making a bunker shooter or a game with telekinesis capabilities, how should we utilize the team's experience?

First, the more you need to move your actual body, the more you can feel the presence of embodied sensations. Second, near-field interaction, i.e. objects within reach, is a powerful way to absorb the virtual world into the brain's proprioceptive model.

Again, this model records the position of objects in space in relation to your body. So when we activate said model in our brain, this of course makes us more integrated into the game world.

Before concluding, I'd like to add that those of you who follow the field of XR design closely may be familiar with a concept called "presence". You may have noticed that the definition of embodiment in this article sounds like presence. You're right, they are essentially the same thing.

I tend to use the term embodiment because presence is a more common term that overlaps too much with the colloquial sense of "immersion". I find it hard for people to distinguish between them, which makes discussions like this one less clear. So I prefer the term "specificity" because it is more distinct from "immersion" than "presence".