A reason that one typically does not notice a blind spot in the visual field is that

Estimated time to complete lab: 20 minutes

Background

Your eyes contain a dense set of receptors that are sensitive to light energy. These receptors convert light energy into electrical energy, which eventually is transferred to your nervous system and your brain. These receptors, however, are not distributed evenly across your eye. There is a central location, called the fovea, where the receptors are very densely packed. Generally, when you stare at an object you are arranging your eyes so that the object's image falls on the foveae of your eyes. There are fewer receptors outside the fovea. In fact, in some places there are no receptors at all.

There is a place in each eye where the optic nerve exits the back of the eye to send information to the brain. This "hole" is called the optic disk. It contains no light sensitive receptors. As a result, any light that falls on this part of the eye is undetected and invisible to you. Functionally, this location on the eye is called the blind spot.

You have probably never noticed your blind spots (one in each eye). There are several reasons for this. First, each blind spot is far away from its eye's fovea. Because the fovea is typically where you are "looking," you would not generally notice that something has disappeared into a blind spot. Second, when you view the world with two eyes, one eye can compensate for the other eye's blind spot. Light that falls into the blind spot of one eye generally does not fall on the blind spot of the other eye. Third, your brain only processes the presence of information, not the absence. Your brain does not notice a "hole" in the information it receives from the eye. It simply works with the information it receives. In a similar way, the brain does not observe that we are unable to view ultraviolet light. It has no knowledge about missing information.

With the proper experiment, however, it is possible to identify and map the blind spot, which is the purpose of this experiment. There are many demonstrations of the existence of the blind spot (Miles, 1928a,b). You will probably be surprised at how large the blind spot is. It covers a large part of your visual field. The experiment used here is similar to a test used by eye doctors to identify visual scotomas (damaged spots in the retina of your eye). Should you consistently find "holes" in your data other than the blind spot, you may want to see an eye doctor.

Instructions

If you have logged in, you'll see a black rectangle below and a small blue square on the left side of the rectangle. Make sure that you can see the full area before you begin the lab.

The experiment is designed to map the blind spot of your right eye. In order for this lab to work, you will need to follow the instructions carefully.

Close your left eye (or cover it with your hand or a patch). Arrange your screen/display so that you can comfortably place your head so that your right eye is directly in front of the small blue square and is about 11 inches/28 cm from the screen. This is the same as a US letter-size piece of paper and approximately the same as an A4 piece of paper. If your eye is too far away from the screen, your blind spot will not fall within the black rectangle.

When you start a trial, two things will happen simultaneously: The blue square will turn green and a yellow dot will appear somewhere on the screen near the green square. One second later, the dot will start to move to the right. Your task is to report if the dot disappears and re-appears, all while keeping your right eye fixed on the fixation square and keeping your head still.

It is very important that during a trial, you do not move your right eye: stay focused on the fixation point. It is also important that you do not move your head. If you do either of these, it will change the location of your blind spot relative to the screen.

There are a total of 19 trials. You can take a break if you wish, but try to stay in the same position when you resume the experiment. If you move around, your blind spot will move with you and the data will be a mix of the two positions you take. Most importantly, keep your right eye 11 inches/28 cm from the display directly in front of, and constantly focused on, the small blue/green square.

Tablet Specific Details

If you are using a tablet, tap the Start Next Trial button to begin. A dot will appear and will start moving to the right. If it disappears, tap the Disappeared button. When you tap this button, it is relabelled as Reappeared. If the dot does reappear, tap this button again. When the green square turns blue again, that's the end of the trial.

Computer Specific Details

If you are using a computer, click the Start Next Trial button to begin. A dot will appear and will start moving to the right. If it disappears, click the Disappeared button. When you click this button, it is relabelled as Reappeared. If the dot does reappear, click this button again. When the green square turns blue again, that's the end of the trial.

Lab

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Global data

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