Distance and Size Perception
Monocular Cues to Distance Perception
Interposition (Overlap)
Known Size Cues
Texture Gradient
Linear Perspective
Atmospheric Perspective
Shading (Attached and Cast Shadows)
Link - Dan Kersten (University of Minnesota) has provided a page of demos, including a nice demonstration of the impact of shadow on perceived depth in motion.
Height Cues
Motion Parallax
Kinetic Depth Effect
Gilbert, S. (1991). A new kinetic depth illusion for introductory psychology and sensation and perception courses. Teaching of Psychology, 18, 55-56.
Representing Three-Dimensional Space in Two Dimensions
Link - You'll find helpful information about viewiing a 3D world at Vision3d.com (Rachel Cooper).
Link - Victor Vasarely is an artist who created a sense of a 3D world on a 2D canvas. Vega Nor (1969) is one example.
Binocular Cues to Depth Perception
Theories of Distance Perception
Perceiving a Three-Dimensional World
Factors Influencing Size Perception
Link - Dan Kersten (University of Minnesota) has provided a page of demos, including a nice demonstration of the impact of perceived distance on size perception.
Size Constancy
Illusions of Distance and Size
Illusions Involving Line Length or Distance
Link The Exploratorium has a number of online exhibits of interest, but for our purposes, you should look at Changing Illusions.
With the Pulfrich Phenomenon, you'll perceive a swinging object (moving back and forth in the same plane parallel to your eyes) as moving closer and farther away (i.e., moving in depth). To produce the phenomenon, you need to place a dark filter over one eye. You can experience the phenomenon yourself (with the appropriate lens/filter) using Mark Newbold's site. You can see a visual explanation of the phenomenon here. You can also achieve this illusion of motion in depth using the filter over one eye and looking at a television showing "snow" (i.e., no video signal).
Explanations for Line-Length and Distance Illusions
Illusions Involving Area or Size
Context is very important for perception. For instance, the picture on the left below depicts an Adirondack Chair. (The chair itself may be found in the Kingsbrae Garden at St. Andrews-by-the-Sea, Canada.) Note that in this context, you probably see the chair as "normal." The actual size of the chair is more readily apparent when it is occupied, as in the picture on the right below.
Photos by M. A. Foley
Thomson Higher Education has published two very useful CD-ROMs. John Baro (Polyhedron Learning Media) has developed Insight: A Media Lab in Experimental Psychology [see Measuring Depth Perception and 3D Pictures] and Colin Ryan (James Cook University) has developed Exploring Perception [see Module 4].
Lafayette Instruments The Depth Perception Apparatus lends itself to several demonstrations and even simple experiments that the students themselves might conduct. The Illusionator Set contains several illusions, but the Ames rotating trapezoidal window is always a winner! You might also try constructing a special rotating "window" by taping together two trapezoidal windows at the wide end, as demonstrated by Julian Hochberg at one EPA conference. After viewing the regular trapezoidal window, see if your students can accurately predict the perceived motion of the double window. (Fineman's book shows how to construct the original trapezoidal window, so just double the recipe on your photocopier.) You can find an online version of the Ames Rotating Trapezoidal Window at the Exploratorium exhibit site.
ViewMaster by Fisher-Price. If you don't have access to an old stereoscope, this child's toy (ahem) is an excellent means of illustrating the effectiveness of binocular disparity.
Al Seckel has put forth a number of compilations of visual illusions as well as a web site (with links to his books).
Walter Beagley (Alma College) has developed Eye Lines, which still works on non-Intel Macs and PCs. The package may be used for a variety of purposes, including using classical psychophysical methods to assess the magnitude of illusions. Keep your eyes open for a forthcoming revision to the program.
Beagley, W. K. (1993). Eye Lines: Generating data through image manipulation, issues in interface design, and the teaching of experimental thinking. Behavior Research Methods, Instruments, & Computers, 25, 333-336.
Wurst, S. A. (1994). Generating stereoscopic displays with Eye Lines: Applications in instruction and research. Behavior Research Methods, Instruments, & Computers, 26, 148-150.Link - If you are interested in demonstrating SIRDS (autostereograms), a good starting point is the Magic Eye site. If you'd like to create your own (as well as anaglyphs), you can use 3D Maker by Sandy Knoll Software. Stuart Inglis has produced a page of FAQs about SIRDS. There's also Vern's SIRDS Gallery for your viewing pleasure.
Link - Michael Bach has created a site of visual illusions that contain some illusions of distance and size.
Link - A number of artists create realistic works that capture 3-D space on a 2-D canvas. However, you'll likely enjoy these two atypical artists who manage to create trompe l'oeil art (at least when seen from a particular perspective): Julian Beever and Kurt Wenner.
Link - You will find a very extensive set of illusions, including illusions of size and distance, at SandlotScience.
Link - Take a look at Mark Newbold's Stereo 3-D Stuff. And you already know that Necker Cubes are wonderful demonstrations, but wait until you (and your students) see Mark's Necker Cube animation.
Link - The Smith-Kettlewell Eye Research Institute maintains a research page that contains relevant links.
Julesz, B. (1995). Dialogues on perception. MIT.
Patterson, R. & Martin, W. L. (1992). Human stereopsis. Human Factors, 34, 669-692.
