Illusions and Psychology
When something goes wrong in either the physical or the mental world, the underlying reasons for the mishap may be more easily seen than when everything is running srnoothly. For this reason we can learn something regarding the process of perception from a study of illusions. An illusion is a surprising error of perception. We ence illusions when a stimulus is so misleading that we fall trap and get a false meaning from the signs received by our organs.
You can easily demonstrate one of the oldest of illusion shutting your eyes, crossing two fmgers, and running a pencil tween the fingers. Your perception will such that you are aware of two pencils being run over your fingers instead of one. This occurs because, in the past, when the fingers were stimulated on their outside edges, the stimuli came from two objects, not from one. In other words, this il due to habit and familiarity derived from prior experience. You should be reminded at this point of our earlier discussion about th portance of past experience in shaping all our perceptions.
Familiarity and habit give rise to what is known as the" reader's illusion." In learning to read, we respond to larger and larger patterns-words, sentences, paragraphs. Once these habits a lished, they persist in the face of error. This means that a word perceived as such even when it is spelled incorrectly. The re for the meaning, responds to a few cues and reads on, not notiel: printer's error. If the word as printed has enough resemblance t right word, it arouses the same response. In the effort to print perfectly, proofreaders are employed whose job is to look specific for printer's errors. This means that the proofreader must ig tendency to perceive whole units and must concentrate on th ments. But so deeply ingrained is the old habit that even the professional falls into the trap of the proofreader's illusion and makes errors.
An illusion familiar to everyone is experienced at the moives. Actually, not pictures in motion but ext are projected on the screen. The seen the viewer; in other words it must be the can readily demonstrate apparent motion about 3 inches in front of your nose and looking at it while blinking first one eye and then the other. To the one side and to the right eye, more to closing one eye and simultaneol\sly seems to move across your field of v illustration of the general tendency to trying to combine successive stqt!o whole, the observer creates a sense of movement between the stimulated unmoving points.
There is a variety of common visual illusions. In the Poggendorf illusion the continuity of a line is interrupted by narrow strips laid across it at an anlgle. You can easily see what effect is given to the character of the line. An interesting error occurs in the ring segments illusion. The two arcs are drawn with lines of the same length, but the misleading effect of the spatial separation of one from the other is clearly apparent.
Illusions are extreme instances of the difference between what is "out there" and what we perceive to be "out there." Illusions dramatically illustrate that perception can play tricks on us. The point to be remembered is that the world as people see it is not necessarily the world as it really is. We must be concerned with what people see ill addition to what we show them; with what they hear besides what we say to them. Whether we feel hot or cold depends largely on us, not on the thermometer.
