Background

Our visual system can perceive objects in the world that move, but, of course, we move as well. We can move our eyes, our heads, and our bodies. We can track motion just by moving our eyes, or we can follow the direction of a moving object by walking or running. In this activity, we are concerned with eye movements that direct our eyes from one location to another in the visual world. This contrasts this discussion of eye movements with vergence (see more here). Eye movements serve a great many functions, the most significant being the ability to direct the gaze of our foveae on whatever stimulus in the world attracts our attention. Eye movements allow us, for example, to read. We make small discrete movements along the page to ensure that our foveae are directed at whatever it is we want to read right now. When we watch moving print, such as the credits at the end of a movie, we make small eye movements from left to right and up and down. In this activity, we will discuss the two most common voluntary eye movements that allow us to look around.

Saccades are the most common and rapid of eye movements. They are used to look from one object to another.

Smooth-pursuit eye movements are the voluntary movements we use to track moving objects. We can make smooth-pursuit eye movements only when there is an actual moving object in the environment.

Use this activity to explore these two eye movements.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Object Position X: Moves the objects closer or farther from the eyes. (will cause vergence)
Object Position Y: Moves the objects up and down the screen. (will cause smooth pursuit)
Eye Separation: Makes the eyes closer or farther apart. The farther the separation, the greater the vergence change.
On the drawing:
Clicking or touching one of the dots will cause the eyes to make a saccade to that dot.
Draging your mouse or finger up and down the screen will do the same as the Object Position Y slider.

Reset

Pressing this button restores the settings to their default values.