Many years ago when I was in school, the subject the interest me the most is how our eyes perceived the world. After taking some classes I have come to a realization that seeing believing! Our eyes play tricks some us sometimes.
Did you know we have a blind spot in each eye? To do a simple test, just hold a blank piece of paper with a small black dot on it. Cover one eye and keep looking straight ahead. As you move the paper out slowly to the side you will notice that the black dot disappear at one point. This is where our blind spot lies in our visual field. The brain makes up the blind spot by filling in what you see at the surrounding. Isn’t it crazy?
Do you also know that we can produce an after image? If you fixate at an image for 30 second, the retina produces an after image. This after image is usually in opposite color of what you just saw! For example if you stare at the black and white stripe, your after image will be a white and black stripe. If you stare at a green and red stripe, the after image of yours will be red and green. Try it out. Have fun.
Have you heard of the Hermann Grid? If you look at these grids you will notice some dark spots at the intersection of white horizontal and vertical stripes. Although they are vivid, every spot you see is illusionary. These illusionary spots are the products of center/surround antagonism within the receptive field of the ganglion cells. To understand it more, I will prepare an article for you to read about how the receptor cells work in the eye.
One day you should check out an ambiguous figure. This is the type of picture that can be perceived as two different pictures. The stimulus information reaching the eye remained unchanged but the perception of the picture is flipping. Presumably the neural events responsible for the spontaneous change in the figure arises higher level of visual processing beyond the visual cortex.
Have you heard of the Ames room? Size affects our perceived distance. Objects that are closer appear to be larger. This phenomenon can be perceived by having the same size object but different distance. The Ames Room creates an illusion which the construction is different and the windows have been distorted to make the room appear rectangular. Take care look at the picture and you will be amazed!
Our eyes always wonder! By this I mean our eyes actually never stand still. This involuntary movement is important for our eyes because this is what allows our eyes to focus. If you try very hard to fixate on a black dot for 30 seconds and you will find that the black dot gets blurry after a while. This shows that a stabilized retinal image will fader and disappear. This may not be a bad thing because we have many blood vessels in front of the retina that cast shadow in front. We don’t see it because the shadows are stabilized retinal image and fade over time. To demonstrate this is true is to just simply hold a small flashlight at the corner of your eyes with your eyes closed. Rock the small flashlight back and forth gently and you will see some after image of what look like branch of trees. These are the shadows of the blood vessels. Once you get a view, stop moving the flashlight and the branches will disappear as the retinal image return to a stabilized condition.