-By Nikita Vijay Biliye
Human eyes allow us to judge moving objects with an accuracy that allows us to catch a ball thrown at us, estimate depth or decide the safety to cross the road. However, there are many aspects of human motion perception that are still not understood.
The researchers at the University of Cambridge have studied the properties of motion perception in biological systems. Using the previous data from the studies of human motion perception, the researchers developed an artificial neural network. This network will help evaluate the speed and direction of the image sequences.
The system is named MotionNet, designed to meet the motion-processing structures inside the brain. With the help of MotionNet, researchers explored features of human visual processing that our brain is not capable of measuring. The computer network operates equivalent to a human brain and enables new insights into how our brain processes moving images. The system is also capable of explaining some of the intricating optical illusions.
Their study described in the Journal of Vision uses the artificial system to explain how our brain combines space and time information to produce perceptions or misperceptions of the moving image. For instance, if we see a black spot on the left of the screen that eventually fades and appears on the right side – we will see that the spot is moving from left to right – This is called the phi motion. If a white spot appears on the right side of a black background, we will see that the spot is moving from right to left – This is called the reverse-phi motion.
By reproducing the reverse-phi motion in the MotionNet system, the researchers found that the system made the same mistakes as a human brain regarding perceptions. But unlike the human brain, the artificial system was able to show why this was happening. The system showed that reverse-phi was triggering the neurons tuned to the opposite direction of the actual movement.
The system MotionNet also revealed other new information about this common illusion. The researchers were able to investigate the mysteries behind optical illusions and how they fool the human brain. The distance between the dots, the reverse of expected, affects the speed of reverse-phi motion. The dots moving at a fixed speed having short space between each, appear to move faster and slower if the space between them is longer.
One of the researchers, Dr. Reuben Rideaux, stated the new system as a completely new prediction of the reverse-phi experience of the human brain. He says MotionNet can measure what goes on inside the human brain when we perceive motion which even the best medical technology could not show.
Thoughts of things moving at a different speed than they actually are can create disastrous issues. For example, humans tend to misjudge their driving speed in foggy conditions, as the foggy sceneries are dimmer and appear to move past slower than they really are. In past studies, researchers showed that neurons in our brains favor slow speeds. Due to low visibility, the neurons tend to guess that the objects are moving more slowly than they are.
The researchers are confident that the system MotionNet will help fill many more gaps in the understanding of how the human brain perceives motion. Predictions made by MotionNet need to be validated by biological experiments. But the system will help in realizing which part of the brain to focus more and thus save a lot of time.
- Reuben Rideaux, Andrew E. Welchman. Exploring and explaining properties of motion processing in biological brains using a neural network. Journal of Vision, 2021; 21 (2): 11 DOI: 10.1167/jov.21.2.11