Rats Master the Art of Slaying Demons in DOOM

Photo credit: Viktor Tóth
Viktor Tóth began down this path a few years ago with a simple question: can rats figure out how to navigate the levels of a classic video game? He tried setting up something similar in New York a while back, with rats running on a large ball that logged their every move. As the rat ran back and forth on the spot, sensors detected its motion and turned it into forward movement within DOOM II. Every time the rat reached a specific point, a tube would appear and feed it a delectable drop of sugary water to keep it motivated and moving down those interminable halls.

The rats quickly caught on, named after gaming legends such as Romero and Carmack, and began racing towards rewards, dodging virtual walls, as well as reacting to demons on screen like pros. Tóth used a modified version of the game through a platform called ViZDoom, which made it extremely simple to connect real-world activities to in-game replies. Early sessions were all straight courses, but the rats quickly learned to negotiate curves and dead ends with ease.

Shooting proved to be more challenging to teach. Tóth devised a method in which the rats would raise their heads and pull a lever, triggering the shotgun. The system would gently assist them at first, giving them just enough nudge to guarantee they triggered it, and then sort out the prize once a demon was defeated. After months, some rats began tearing it down, blasting imps that stood in their way without assistance.

It had been a while, but public interest has revitalized the initiative. Tóth and some engineers (Sándor Makra was on the crew this time) set to work on a new and improved version that was far more advanced than the first. The new setup is very slick; it has a lightweight aluminum frame with a smooth ball that can spin freely, as well as optical sensors all around to detect every movement the rat makes. The motors on the ball will start the thing automatically to move the rat in the appropriate direction without requiring any pushing. A fold-down AMOLED screen wraps around the rat’s head, providing a superb view of the gaming environment, much like a widescreen cinema presentation from the rat’s perspective. Virtual walls feel close up, and enemies appear directly in their face. There is still some room around the margins for whiskers to roam freely.

Shooting is also made easier now, thanks to a special lever placed right into the rat’s paw. When the rat pulls it, a sensor transmits a firing command to the game. If you wish to educate the rat how to do it, the system can move the lever to demonstrate which actions result in a reward. The new sytstem can prepare a specific sugary drink (just 10 microlitres) and deliver it to the rat exactly when it needs it. They even timed it perfectly for game events like reaching a checkpoint or whacking an enemy. Other fascinating additions include small puffs of air near the rat’s whiskers to alert it when it hits a wall, allowing the rat to learn its boundaries without being damaged.

A computer runs the DOOM environment (the same game but with a few modifications), while a smaller board handles all of the real-time tasks, such as reading sensors and distributing rewards on time. You can even manually control it or automate sequences in which the system moves the ball or lever to show the rat what to do step by step.
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