Finding Your Blind Spot and Perceptual Filling-in

1. Stimulus Design

1. Open a blank white page in a slide editor (PowerPoint or Keynote will suffice).
2. Near the right edge of the page, make a circle about as large as penny, when the slide is printed. This will be the fixation point.
3. Near the left edge of the page, make a small star (or any other shape), so that when you print the slide, the shape is about the size of a penny This slide is the left eye blind spot stimulus.
4. Duplicate the slide, and switch the positions of the fixation point and the shape. This makes the right eye stimulus.
5. Print the stimuli.
6. Figure 1 shows what these stimuli should look like when printed on an 8.5 x 11 piece of standard white paper.

Figure 1. Stimuli for finding the blind spot in each eye. The stimuli should each occupy an 8.5 x 11 in. piece of paper with the star about the same size as a penny, when printed.

2. Procedure for finding the blind spot

1. Explain the procedure first for the left eye, then how to adjust it for the right eye. This procedure can be performed on one's self, or recited to an observer to perform.
2. Hold the left eye stimulus sheet at arm's length with the shapes facing you.
3. Now close or patch your right eye. With your left eye, fixate the circle on the right side of the page. You will still probably see the star on the other side.
4. Slowly move the page to the left or to the right, up or down, closer and farther. At some point, the star will disappear from the corner of your eye.
5. Once you have made the star disappear, move the page around in very small increments. You should be able to make the star appear and re-appear through small adjustments.
6. The place where the star is when you cannot see it is your blind spot.
7. Repeat the procedure with the right eye stimulus, closing your left eye this time.

3. Using the blind spot to study perceptual filling-in

1. With slightly more complicated stimuli, the blind spot provides a powerful demonstration of how the brain creates, even at times invents, our perceptual consciousness.
2. Generate three additional blind spot stimuli by placing the star shape among some kind of pattern-this can be as simple as a colorful background or within a continuous line segment. Figure 2 shows three example stimuli.
3. Repeat the procedure in 2.2-2.7. This time though, ask the participant what they see when the star stimulus disappears.

Figure 2. Blind spot stimuli for demonstrating properties of perceptual filling-in. In these images, when the star occupies an observer's blind spot, their brains fill-in the missing stimulation to conform to the properties of the surrounding image.