AI can learn real-world skills from playing StarCraft and Minecraft
Virtual gaming worlds are good test-beds for exploring, responding and adapting
Dario Wünsch was feeling confident. The 28-year-old from Leipzig, Germany, was about to become the first professional gamer to take on the artificial intelligence program AlphaStar in the rapid-fire video game StarCraft II. Wünsch had been professionally playing StarCraft II, in which competitors command alien fleets vying for territory, for nearly a decade. No way could he lose this five-match challenge to a newly minted AI gamer.
Even AlphaStar’s creators at the London-based AI research company DeepMind, which is part of Alphabet, Inc., weren’t optimistic about the outcome. They were the latest in a long line of researchers who had tried to build an AI that could handle StarCraft II’s dizzying complexity. So far, no one had created a system that could beat seasoned human players.
Sure enough, when AlphaStar faced off against Wünsch on December 12, the AI appeared to commit a fatal mistake at the onset of the first match: It neglected to build a protective barrier at the entrance to its camp, allowing Wünsch to infiltrate and quickly pick off several of its worker units. For a minute, it looked like StarCraft II would remain one realm where humans trump machines. But AlphaStar made a winning comeback, assembling a tenacious strike team that quickly laid waste to Wünsch’s defenses. AlphaStar 1, Wünsch 0.
Wünsch shook it off. He just needed to focus more on defense. But in the second round, AlphaStar surprised the pro gamer by withholding attacks until it had amassed an army that once again crushed Wünsch’s forces. Three matches later, AlphaStar had won the competition 5-0, relegating Wünsch to the small but growing club of world-class gamers bested by a machine.
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Researchers have long used games as benchmarks for AI smarts. In 1997, IBM’s Deep Blue earned international acclaim by outwitting chess champion Garry Kasparov (SN: 8/2/97, p. 76). In 2016, DeepMind’s AlphaGo famously overpowered Go champion Lee Sedol (SN: 12/24/16, p. 28).
But board-based contests like chess and Go can only push AI so far. These games are still pretty simple — players take turns and can see every piece’s position on the board at all times. When it comes to making an AI that can deal with real-world ambiguity and fast-paced interactions, the most useful tests of machine cognition will probably be found in games played in virtual worlds.
Building AI gamers that can trounce human players is more than a vanity project. “The ultimate idea is to … use those algorithms [for] real-world challenges,” says Sebastian Risi, an AI researcher at IT University of Copenhagen. For instance, after the San Francisco–based company OpenAI trained a five-AI squad to play an online battle game called Dota 2, the programmers repurposed those algorithms to teach the five fingers of a robotic hand to manipulate objects with unprecedented dexterity. The researchers described this work online at arXiv.org in January.
DeepMind researchers similarly hope that AlphaStar’s design could inform researchers trying to build AIs to handle long sequences of interactions, like those involved in simulating climate change or understanding conversation, an especially difficult task (SN: 3/2/19, p. 8).
Right now, two important things that AIs still struggle with are: coordinating with each other and continually applying new knowledge to new situations. The StarCraft universe has proved to be an excellent testing ground for techniques that make AI more cooperative. To experiment with methods to make AIs forever learners, researchers are using another popular video game, Minecraft. While people may use screen time as an entertaining distraction from real life, virtual challenges may help AI pick up the skills necessary to succeed in the real world.
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When AlphaStar took on Wünsch, the AI played StarCraft II like a human would: It acted like a single puppeteer with complete control over all the characters in its fleet. But there are many real-world situations in which relying on one mastermind AI to micromanage lots of devices would become unwieldy, says artificial intelligence researcher Jakob Foerster of Facebook AI Research in San Francisco.
Think of overseeing dozens of nursing robots caring for patients throughout a hospital, or self-driving trucks coordinating their speeds across miles of highway to mitigate traffic bottlenecks. So, researchers including Foerster are using the StarCraft games to try out different “multiagent” schemes.
In some designs, individual combat units have some independence, but are still beholden to a centralized controller. In this setup, the overseer AI acts like a coach shouting plays from the sidelines. The coach generates a big-picture plan and issues instructions to team members. Individual units use that guidance, along with detailed observations of the immediate surroundings, to decide how to act. Computer scientist Yizhou Wang of Peking University in China and colleagues reported the effectiveness of this design in a paper submitted to IEEE Transactions on Neural Networks and Learning Systems.
Wang’s group trained its AI team in StarCraft using reinforcement learning, a type of machine learning in which computer systems pick up skills by interacting with the environment and getting virtual rewards after doing something right. Each teammate received rewards based on the number of enemies eliminated in its immediate vicinity and whether the entire team won against fleets controlled by an automated opponent built into the game. On several different challenges with teams of at least 10 combat units, the coach-guided AI teams won 60 to 82 percent of the time. Centrally controlled AI teams with no capacity for independent reasoning were less successful against the built-in opponent.
AI crews with a single commander in chief that exerts at least some control over individual units may work best when the group can rely on fast, accurate communication among all agents. For instance, this system could work for robots within the same warehouse.
But for many machines, such as self-driving cars or drone swarms spread across vast distances, separate devices “won’t have consistent, reliable and fast data connection to a single controller,” Foerster says. It’s every AI for itself. AIs working under those constraints generally can’t coordinate as well as centralized teams, but Foerster and colleagues devised a training scheme to prepare independent-minded machines to work together.
In this system, a centralized observer offers feedback to teammates during reinforcement learning. But once the group is fully trained, the AIs are on their own. The master agent is less like a sidelined coach and more like a dance instructor who offers ballerinas pointers during rehearsals, but stays mum during the onstage performance.
The AI overseer prepares individual AIs to be self-sufficient by offering personalized advice during training. After each trial run, the overseer simulates alternative possible futures and tells each agent, “This is what actually happened, and this is what would have happened if everyone else had done the same thing, but you did something different.” This method, which Foerster’s team presented in New Orleans in February 2018 at the AAAI Conference on Artificial Intelligence, helps each AI unit judge which actions help or hinder the group’s success.
To test this framework, Foerster and colleagues trained three groups of five AI units in StarCraft. Trained units had to act based only on observations of the immediate surroundings. In combat rounds against identical teams commanded by a built-in, nonhuman opponent, all three AI groups won most of their rounds, performing about as well as three centrally controlled AI teams in the same combat scenarios.
The types of AI training that programmers test in StarCraft and StarCraft II are aimed at helping a team of AIs master a single task, for example, coordinating traffic lights or drones. The StarCraft games are great for that, because for all their moving parts, the games are fairly straightforward: Each player has the singular goal of overpowering an opponent. But if artificial intelligence is going to become more versatile and humanlike, programs need to be able to learn more and continually pick up new skills.
“All the systems that we see right now that play Go and chess — they’re basically trained to do this one task well, and then they’re fixed so they can’t change,” Risi says. A Go-playing system presented with an 18-by-18 grid, instead of the standard 19-by-19 game board, would probably have to be completely retrained on the new board, Risi says. Changing the characteristics of StarCraft units would require the same back-to-square-one training. The Lego-like realm of Minecraft turns out to be a better place for testing approaches to make AI more adaptable.
Unlike StarCraft, Minecraft poses no single quest for players to complete. In this virtual world made of 3-D blocks of dirt, glass and other materials, players gather resources to build structures, travel, hunt for food and do pretty much whatever else they please. Caiming Xiong, an artificial intelligence researcher at the San Francisco–based software company Salesforce, and colleagues used a simple building full of blocks in Minecraft to test an AI designed to continually learn.
Rather than assigning the AI to learn a single task through trial and error in reinforcement learning, Xiong’s team staggered the AI’s education. The researchers guided the AI through increasingly difficult reinforcement learning challenges, from finding specific blocks to stacking blocks. The AI was designed to break each challenge into simpler steps. It could tackle each step using old expertise or try something new. Compared with another AI that was not designed to use prior knowledge to inform new learning experiences, Xiong team’s AI proved a much quicker study.
The knowledge-accumulating AI was also better at adjusting to new situations. Xiong and colleagues taught both AIs how to pick up blocks. While training in a simple room that contained only one block, both AIs got the “collect item” skill down pat. But in a room with multiple blocks, the discrete-task AI struggled to identify its target and grabbed the right block only 29 percent of the time.
The knowledge-accumulating AI knew to rely on a previously learned “find item” skill to locate a target object among distractions. It picked up the right block 94 percent of the time. The research was presented in Vancouver in May 2018 at the International Conference on Learning Representations.
With further training, Xiong and colleagues’ system could master more skills. But this design is limited by the fact that the AI can only learn tasks assigned by the human programmer during training. Humans don’t have this kind of educational cutoff. When people finish school, “it’s not like, ‘Now you’re done learning. You can freeze your brain and go,’ ” Risi says.
A better AI would get a foundational education in games and simulations and then be able to continue learning throughout its lifetime, says Priyam Parashar, a roboticist at the University of California, San Diego. A household robot, for example, should be able to find navigational work-arounds if residents install baby gates or rearrange the furniture.
Parashar and colleagues created an AI that can identify instances in which it needs further training without human input. When the AI runs into a new obstacle, it takes stock of how the environment is different from what it expected. Then it can mentally rehearse various work-arounds, imagine the outcome of each and choose the best solution.
The researchers tested this system with an AI in a two-room Minecraft building. The AI had been trained to retrieve a gold block from the second room. But another Minecraft player had built a glass barrier in the doorway between the rooms, blocking the AI from collecting the gold block. The AI assessed the situation and, through reinforcement learning, figured out how to shatter the glass to complete its task, Parashar and her colleagues reported in the 2018 Knowledge Engineering Review.
An AI faced with an unexpected baby gate or glass wall should probably not conclude that the best solution is to bust it down, Parashar admits. But programmers can add additional constraints to an AI’s mental simulations — like the knowledge that valuable or owned objects should not be broken — to inform the system’s learning, she says.
New video games are becoming AI test-beds all the time. AI and games researcher Julian Togelius of New York University and colleagues hope to test collaborating AIs in Overcooked — a team cooking game that takes place in a tight, crowded kitchen where players are constantly getting in each other’s way. “Games are designed to challenge the human mind,” Togelius says. Any video game by nature is a ready-made test for how much AI know-how can emulate human cleverness.
But when it comes to testing AI in video games or other simulated worlds, “you cannot ever say, ‘OK, I’ve modeled everything that’s going to happen in the real world,’ ” Parashar says. Bridging the gap between virtual and physical reality will take more research.
One way to keep simulation-trained AI from overreaching, she suggests, is to devise systems that require AIs to ask humans for help when needed (SN: 3/2/19, p. 8). “Which, in a sense, is making [AI] more like humans, right?” Parashar says. “We get by with the help of our friends.”