A friend knows you are taking this class. One day, they ask you: "why don't the objects in my visual field appear to move each time I slowly move my eyes?"

In lecture and textbook, you learned that if we are staring at something that is stationary, such as a couch, or a mountain range, our brain does not detect any motion even if our eyes are moving. How can you explain this to them? (Hint: consider Sherrington and Helmholtz's theories, as well as the function of the motion detectors)