1Visual system, Auditory system, Vestibular system, Tactile system, Kinesthetic (proprioceptive) system, Olfactory system, Gustatory system. These are some of the sensory systems in humans.23Vision is very important for human survival. It involves many important and complex tasks.4Visual pathway of the macaque monkey, whose visual system is very similar to the human visual system. Note that the visual areas take up a very large percentage of the monkey’s cortex. In humans it is a smaller percentage but still very substantial. The optic nerves contains 2/3 of all sensory neurons in humans.5Major neural connections between the visual areas in the previous map of the macaque monkey’s visual pathway. This diagram hints at the complexity of the perceptual systems.6Chromatic contrast and assimilation. The orange rings in a and b are identical. The blue-green rings in e and f are identical.7The table tops are parallelograms of exactly the same dimensions.8Twisted cord illusion. The twisted cord is not a spiral but a series of concentric circles. Even seemingly simple tasks such as judging the curvature or slant of contours involve complex processing.9Another twisted cord illusion. The letters are not tilted.10Demonstration of active perceptual grouping mechanisms by J.L. Marroquin. One sees a fluctuating collection of circles of various diameters. Vision involves active, complex subconscious processes.11Demonstration of local adaptation effects. Note the close connection of the effects to eye movements.12Complex natural scenes that have never been seen before are quickly and accurately interpreted by the visual system.13Famous painting by Bev Dolittle (The Forest Has Eyes) demonstrating how good humans are a detecting meaningful structure in images.14Most natural tasks involve dealing with one or more of these difficult general problems. Furthermore, the solutions that the visual system can come up with in natural tasks are constrained by various fundamental biological factors.15Natural example of importance of solving the context problem in order to recognize familiar