| ISLE | Chapter 3
| Letters and the Fovea
The human fovea is densely packed with cones. It looks like a little pit on the retina because the cells that are above the retinal surface, such as retinal ganglion cells, horizontal cells, and amacrine cells, are swept away so that the cones are at the surface. Because of the layers that are swept away, there is less scattering of light in the fovea, allowing for the visual acuity to be higher in the fovea. It is the foveae of the retinae that give humans our excellent visual acuity. By visual acuity, we mean the clarity of vision. Thus, the visual image of the word you are reading right now is falling on the fovea of your retina. Words you have just read or have not yet read are tailing off into the periphery of the retina. When you move your eyes to read the next part of a sentence, it is your fovea that is directed toward the new stimulus. This is why it is said that the fovea represents the direction of your gaze. The fovea is quite a small part of the retina, which means that you only see a little bit of the world with our excellent acuity. Try this demonstration to illustrate this fact.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Font Size: change the font size of the sentence on the screen (when available).
Slope: change how fast the letters get larger as they move into the periphery (when available).
Number Pad: can use to enter the number of letters you can see clearly; numbers on a keyboard also work.
Done: Indicate when done entering how many letters you see; changes stimulus from a sentence to a ring of letters getting larger.
Pressing this button restores the settings to their default values and changes the screen back to the sentence.