In the bright sunny days, if you keep your eyes closed, you can still see through your eyelids. You can walk around, perceiving just the different intensities of light. This is the primordial visual mechanism, the one that the oldest creatures had, crawling towards the sun. It is almost indistinguishable from the sense of touch, for what is an eye if not a patch of skin that can feel the touch of light? There is also a heightened awareness of the sound, which lets the mind drift away and imagine things.