By using decades’ worth of data from human motion perception studies, researchers have trained an artificial neural network to estimate the speed and direction of image sequences.
The new system, called MotionNet, is designed to closely match the motion-processing structures inside a human brain. This has allowed the researchers to explore features of human visual processing that cannot be directly measured in the brain.
Their study, published in the Journal of Vision, uses the artificial system to describe how space and time information is combined in our brain to produce our perceptions, or misperceptions, of moving images.
The brain can be easily fooled. For instance, if there’s a black spot on the left of a screen, which fades while a black spot appears on the right, we will ‘see’ the spot moving from left to right – this is called ‘phi’ motion. But if the spot that appears on the right is white on a dark background, we ‘see’ the spot moving from right to left, in what is known as ‘reverse-phi’ motion.”
The researchers reproduced reverse-phi motion in the MotionNet system, and found that it made the same mistakes in perception as a human brain – but unlike with a human brain, they could look closely at the artificial system to see why this was happening. They found that neurons are ‘tuned’ to the direction of movement, and in MotionNet, ‘reverse-phi’ was triggering neurons tuned to the direction opposite to the actual movement.
The artificial system also revealed new information about this common illusion: the speed of reverse-phi motion is affected by how far apart the dots are, in the reverse to what would be expected. Dots ‘moving’ at a constant speed appear to move faster if spaced a short distance apart, and more slowly if spaced a longer distance apart.
“We’ve known about reverse-phi motion for a long time, but the new model generated a completely new prediction about how we experience it, which no-one has ever looked at or tested before,” said Dr Reuben Rideaux, a researcher in the University of Cambridge’s Department of Psychology and first author of the study.
Image: Driving in fog
Credit: Yaopey Yong on Unsplash
Reproduced courtesy of the University of Cambridge