Figure 1. The Pac-Man game and the performance of the monkeys.

(A) The monkeys used a joystick to navigate Pac-Man in the maze and collect pellets for juice rewards. Also in the maze, there were two ghosts, Blinky and Clyde. The maze was fixed, but the pellets and the energizers were placed randomly initially in each game. Eating energizers turned the ghosts into the scared mode for 14 s, during which they were edible. There were also fruits randomly placed in the maze. The juice rewards corresponding to each game element are shown on the right. (B) The monkeys were more likely to move toward the direction with more local rewards. The abscissa is the reward difference between the most and the second most rewarding direction. Different grayscale shades indicate path types with different numbers of moving directions. Means and standard errors are plotted with lines and shades. See Figure 1—figure supplement 1 for the analysis for individual monkeys. (C) The monkeys escaped from normal ghosts and chased scared ghosts. The abscissa is the Dijkstra distance between Pac-Man and the ghosts. Dijkstra distance measures the distance of the shortest path between two positions on the map. Means and standard errors are denoted with lines and shades. See Figure 1—figure supplement 1 for the analysis for individual monkeys.

Figure 1—figure supplement 1. The performance of Monkey O (left) and Monkey P (right).

(A, C) Probability of monkeys moving toward the largest reward. The monkeys were more likely to move toward the direction with more local rewards. The abscissa is the reward difference between the most and the second most rewarding direction. The colors indicate the path types in which different numbers of moving directions are possible. Means and standard errors are plotted with lines and shades. (B, D) Probability of monkeys moving toward ghosts. The monkeys escaped from the normal ghosts and chased the scared ghosts. The abscissa is the distance between Pac-Man and the ghosts. The colors and the line types indicate the ghosts and their modes. Means and standard errors are plotted with lines and shades.