Perceptual Illusions Essays - Sensory Systems, Perception

Perceptual Illusions Many of us take our vision for granted. We seem to accurately use our properties of vision with little effort or thinking at all. At times we often see things with our eyes and wonder how can this be possible? Physicist Richard Feyman once wrote, Its quite wonderful that we can see or figure it out so easily. Someone whos standing at my left can see somebody whos standing at my right that is the light can be going this way across or that way across, or this way up, or that way down; its a complete network. Some quantity is shaking about, in a combination of motions so elaborate and complicated the net result is to produce an influence which makes me see you, completely undisturbed by the fact that at the same time there are influences that represent the guy on my left side seeing the guy on my right side. The lights there anywayit bounces off this, and it bounces off that all this is going on, and yet we can sort it out with this instrument, our eye (Introduction to Perception [Online]). As you can see by this quote, sight is a very complicated process that is easily controlled by our eyes. However, perceptual illusions need a little more explaining. Take an instant to observe the world around you. If you tilt your head, the rest of the world does not tilt along with you. If you close on of your eyes, you dont suddenly lose your depth perception. Shades of color seem to vary under different levels and types of illumination. When you move around an object, the shape you see changes, yet the object remains stable (Introduction to Perception [Online]). Just take a peek at the Perceptual Illusions on last page of this report. Even though you may know that you are being fooled, it does not stop the effect from continuing to trick you. This indicates a split between the sensation of seeing it, and the way in which you perceive it. In many cases your cognitive abilities can not influence your perceptions. For any given retinal image, there is an infinite variety of possible three-dimensional structures that can lead to it. Our visual system, however, usually settles for the correct interpretation (Introduction to Perception [Online]). I t is when a mistake is made in the interpretation that an illusion occurs. Perceptual illusions are anything that may seem to cause something to become perceptually confusing. These illusions have a distinct manner of confusing our normal perceptual processes. The Muller-Lyer Illusion and the Ponzo Illusion may be the two most commonly studied perceptual illusions in psychology. Stephen R. Jackson states in his Feb. 2000 article in Journal of Experimental Psychology that appropriate indications such as linear perspective and relative size can exert a powerful effect on the perception of objects. The illusory effects such as those of the Muller-Lyer and Ponzo illusions demonstrate this fact (Jackson 2000). In the Muller-Lyer Illusion (fig. 1), there are two objects, both having one line and two lined triangles at their ends. When the objects are placed parallel to each other, the line from the top object looks longer than the line from the lower object. Why does it appear to be longer when the two are actually the same length? This has to do with the direction of the two triangles or arrows at the end of the lines. On the lower figure, the open ends of the triangles are facing inward, causing the line to appear shorter than it is. And on the upper figure, the open ends of the triangles are facing outward, causing the line to appear longer than it actually is (Online. Retrieved on October 11, 2000 at http://www.epsychlopedia.net/concepts/sensationAndPerception/index.php?id=sensandperc8). The Ponzo Illusion (fig 2) has four lines. There are two horizontal lines parallel to each other and two diagonal lines approaching each other on either side of the parallel lines. The top line appears to be longer than the bottom line. This is a result of our perception thinking that the top horizontal line is father away from us, resulting in our brain telling us that the top line is longer than the bottom one. (Online.