This thread reminds me of a distinction I have either read or hear about many years ago with respect to illusions: Optical vs. those that are purely perceptual. As I recall, the main difference between the two types of illusions lies in the source of the error. When the error stems from light that is already distored before entering the eye, it should refer to as an optical illusion (e.g., the broken pencil-in-a-glass-of-water illusion) whereas when the error is in our heads (e.g., vertical-horizontal illusion, Müller-Lyer illusion and most other so-called geometrical illusions) the illusion would be labeled perceptual. I suppose that mirages, such as the common oasis-in-the-middle-of-the-desert mirage (shimmering from heat rising in the horizon that appears as a body of water) and perhaps other like illusions are a combination of the two, optical and perceptual. In the case of the mirage, the percipient may be so confused from dehydration and exhaustion and so thirsty that s/he ends up believing that the distortion created by the shimering is an oasis, thus both elements are present in this illusion.
I have not done a systematic review of S & P sections of textbooks, but my sense is that most authors tend to use both terms interchangably. I wonder whether the distinction is a valid one and whether anyone who has heard of it knows the original source (Gibson? Richard Gregory? Irv Rock?). Also, if you subscribe to this separation of illusory phenomena, what type of illusion would the Escher water wheel and similar ones that have been posted under this thread be classified under? Miguel --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=8876 or send a blank email to leave-8876-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
