If you walk around the stairs clockwise, you proceed infinitely downstairs, and if you walk counterclockwise, you go upstairs forever without gaining in altitude.
|"Scholar's Stairway," Oil on board, 12 x18 inches.|
To find out, I asked vision scientist Greg Edwards, president of Eyetools, Inc., to run some eye tracking tests using this image as the subject.
Dr. Edwards had fifteen subjects look at my pictures on a computer screen for fifteen seconds each while a sensor tracked their eye movements in real time. Below is the eye track of one subject's experience. The colored line shows the pathway of the eyes, beginning randomly at the green circle. The numbers in the black squares show where they eye traveled at each second of the fifteen second session.
One can’t know for sure without a follow-up interview, but evidently this particular observer didn’t notice the optical illusion.
The second image shows the "heatmap," which aggregates data from all fifteen observers. The red and orange blobs are the areas of the image received nearly 100% of people's attention. The rider on the brachiosaur took attention away from the central illusion. The dark blue and black areas received almost no attention.
What can we conclude from the heatmap image? Viewers definitely looked at the figures, wherever I placed them. Beyond that, we can't say much because we didn't design a very thorough experiment. I would love to work with a larger sample size and to gather followup interview data, and ideally collect simultaneous fMRI data set to see if we could correlate cognitive behavior with eye movement. That way we could understand better what happens when people "get" the illusion. If there's any vision scientist who has the equipment and wants to try an experiment like this, please contact me.