This post concerns what is probably the most frequently encountered visual illusion in the United States--and possibly the world--yet most people don’t know that it is there.
If you have not yet seen this illusion, then be prepared, because once it is pointed out to you, you will see it all the time and, perhaps, wonder how you could possibly have missed it.
What to notice: Look at the FedEx logo and see if you can find the image of the arrow embedded in the letters. Give up? Click on the button and the arrow will appear as yellow outlined by blue. Click the button again to make the yellow arrow go away.
(Credits: The image of the back of the Fed Ex truck was taken by my brother, Chuck Shapiro; the Flash movie was made with the assistance of my nephew, Sam Shapiro. I do not know who created the FedEx logo. I think the logo is absolutely brilliant, and I would love to know its history.)
Comments: The FedEx logo is a reversible image, like Edgar Rubin’s famous Face/Vase image, and the M.C. Escher-like bird image shown below. As in these images, the logo can be interpreted either as an “EX” or as an arrow, depending on what we see as “figure” and what we see as the background.
Reversible images are tremendously fun because even though the image doesn’t change, our perceptions of it do. Our brains, therefore, must somehow or other switch the interpretation, even though nothing physically has changed. Vision scientists have asked many questions about reversible images: What causes them to “switch”? Why is it that we typically don’t see both interpretations at the same time? To what extent does the image depend on where we look? What can the perceptual switch tells us about consciousness? etc.
To me, the most striking aspect of the FedEx illusion is that even though people see the image thousands of times, few will notice the arrow until it is pointed out to them. Personally, I did not perceive the arrow until the Society for Neuroscience Annual meeting in Atlanta in 2006 (it was pointed out to me by Eric Altschuler’s son, who must have been about eight years old).
Why should the arrow be so difficult to see? First, there is a question of how we segment the scene. The arrow is made from the same color as the background, which extends behind the letters. It is therefore easy to see the letters as the figure, and the arrow as part of the background. To notice the arrow, we must do the double task of ignoring the letters, and treating the parts between the letters as if they were separate from the background field.
The effect of the background can be seen in the image below. The arrow and the background have different colors, and as a result, the arrow stands out. Notice that the color of the arrow and the color of the area immediately surrounding the arrow have not changed from the original image.
Second, visual images contain a lot of information. In order to sort through that information, the brain seems to form expectations concerning what we are about to encounter in the world. These expectations can greatly influence how we perceive ambiguous images. In this case, we see letters and a logo; therefore, why should the visual system “work” to create an interpretation of an arrow? To see some classic examples of the effects of perceptual expectations, visit this site on “perceptual sets,” which was posted by Saul McLeod as part of Simply Psychology.
Take-home message: our visual system has a number of properties that make it quite good at finding the things we expect to see in the environment. However, if we do not work to find other interpretations, we miss the arrow.
I am still on the road. My guess is that I will not be able to post again until early August.