The Ames Trapezoid is a trapezoid when continuously rotated about its vertical axis is supposed to look like it is oscillating about its vertical axis. This effect, in person, works when the viewer is 6 feet or more from the device. The purpose of this exercise was to see if shading effected the perception of the Ames Trapezoid. There was only one other example online that I could find with motion. This example seems to force the viewer into believing that it oscillates back and forth because of the false three dimensionality that is has. When the window frame is at its max width it looks like it should have depth; however when it is at its minimum width it has no depth to it whatsoever.

How people perceive the Ames Trapezoid illusion varies from ‘civilized’ to ‘uncivilized’ culture. In cultures were they aren’t exposed to vanishing points, and don’t have very much exposure to rectangles in general they are less apt to see the illusion. However in our culture where we have been exposed to vanishing points and have much exposure to rectangle we see the illusion very easily. Slack, in his paper ‘Critique on the Interpretation if the Cultural Difference in the Perception of Motion in Ames’s Trapezoidal Window’ hypothesizes that if there was someone who came from a very trapezoidal culture would not see the illusion because they are used to seeing trapezoids in all of their forms and motions.

For my VRML (Virtual Reality Markup Language) trapezoids I experimented with 3-D and 2-D representations of the trapezoid, I found both to be equally ineffective. Every person that showed the Ames Trapezoid to no matter what variation of it was thought that it was rotating, not oscillating. I think that it may be artifact of proximity of the viewer to the screen or the 2 dimensionality of the medium. But this would require further investigation. The examples below are the 2-D representations, I found then to be easier to rotate and to apply colors.

There are six different trapezoids posted, all of them rotate independently and are shaded differently. The last two are slightly different than the other five. I changed the slope of the top and bottom legs of the trapezoid so that it was less severe in hopes that it may be easier to see the optical illusion. In all of my tests subjects they were still unable to see the optical illusion.

Gray Ames Trapezoid

Shiny Gold Ames Trapezoid

Red Ames Trapezoid

Rainbow Colored Ames Trapezoid

Less Sloped Gray Ames Trapezoid

Less Sloped Colored Ames Trapezoid

In order to properly view the files you will need to download a VRML viewer. Go to the NIST website they have a number of VRML plug-ins to choose from. I have used Cortona3D, and it works well with both Internet Explorer and Firefox.