Blind Spot Demos

The optic disc blind spot is the region of each retina where the optic nerve passes out of the eye en route to the optic chiasm. In this region there are no photoreceptors, and hence no visual information. But the brain quietly fills in this absence so that it is almost never noticeable.

1. Existence

This first demo will (hopefully) enable you to observe the existence of this blind spot, as the filled in visual information fails to contain an object that you know is there.

Close one eye and look at the letter corresponding to the open eye — ie, on the opposite side of the visual field to that eye — in the box below. Adjust your head position until the other letter disappears — this should be when your eye is about 3 times further away from the screen than the distance between the letters. You may or may not find it helpful to tilt your head slightly away from horizontal in the direction you are looking.

2. Sneakiness

In this second demo, you are presented with a similar setup, but the stimulus on each side is more complex, and it's continuous with the surrounding region. In this case you will likely not really be able to see the blind spot, even though the information from that region is still not being received. The brain is able to interpolate the content based on the information it is receiving from the neighbouring areas.

Once again, close one eye and look with the other towards the centre of the circle on the opposite side of the box. Adjust your head position until the centre of the other circle is in your blind spot. This may be slightly trickier than before, but you should still be able to find a position where you are aware that the centre is sort of not there, but there will probably not be any noticeable gap in the converging lines.

When you are finished, return to the lab page.