It works a lot like how humans judge motion with their eyes, except bats do it with sound. To a bat, this would make echoes feel as if the world were moving faster or slower than it really is. When the panels moved against the bat’s direction of flight, the echoes came back with stronger Doppler shifts. They read the overall pattern of sound moving around them. Professor Marc Holderied adds that this flow of sound tells bats both how fast they are moving and how close they are to obstacles.