If we think of the brain as a sophisticated biological computer, then the eye, with its image forming optical system and two-dimensional sheet of light-sensitive tissue called the “retina” at the back, is more like a video camera than a monitor in basic design.
Both video cameras and eyes can be characterized in terms of sensitivity to light (how bright a scene has to be to be recorded), spectral sensitivity (responses to color), density of photosensitive elements (“grain” of the image), and how fast it responds to change. The retina’s array of light-sensitive photoreceptor cells sends signals to your brain when stimulated by light. The position of each of the photoreceptor cells is electrically mapped on your brain, so that a spatial picture forms in your mind corresponding to the image of the outside world projected on the retina. When an object moves across this visual “field”, it excites the photoreceptors. Our brains cannot track objects that move faster than about 16 “frames” per second. When you go to the movies, you are actually watching still pictures that are flashed before your eyes faster than your brain can interpret them as “stills”, so the pictures appear to move.
Another proof that we cannot track very rapid movement is illustrated by watching spokes on moving wheels. As the wheel turns more and more rapidly, its spokes appear to slow down, and may even seem to be rotating backwards! This is how our brains misinterpret the rapidly changing images of the wheel that reach our eyes. Interestingly, some animals are much better at detecting rapid changes in the visual field than we are. The humble housefly, for example, can actually see the alternating current that flows through florescent lights. These lights flicker 120 times per second, too quickly to bother us, but perhaps annoying to the fly, which can track objects moving at up to 300 frames per second!
Ph.D. Cornell University
Development of sensory systems and ecological physiology of precocial vertebrates
Two daughters, Marina and Fredrika Loew, and husband Ellis Loew, Professor of Physiology in the department of Biomedical Sciences at Cornell.
Family, scuba, sailing, gardening, painting
Candor High School
Candor High School