• Background
• Instructions
• Settings
• Illustration
• Quiz

## Background

The motion aftereffect, first discussed by Aristotle, is also known as waterfall illusion (Verstraten, 1996; Wade, 1996). An aftereffect is a sensory experience that occurs after prolonged sensory exposure to one stimulus that alters how we experience other stimuli after the prolonged exposure. Another way to observe this illusion at home is to watch the credits at the end of a movie without taking your eyes off of the television screen. After watching the credits for two minutes, have a friend or family member hit the pause button. You will see an illusion of the movie credits moving up the screen even though you know the video is now stopped. Aristotle observed this by looking at nonmoving surfaces after watching the downward motion of waterfalls.

## 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

On the Illustration tab, click or touch (if you have a touch screen) anywhere on the grating to start the motion of the grating.
Stare in the middle of the grating while it moves. After the motion stops, notice your perception of the still grating. You can even look around the room at other objects to see if you experience the same effect.

### Settings Tab

On the Illustration tab, you can adjust these parameters:

Adaptation Duration: you can see how long the grating moves to create the motion aftereffect from 10 to 60 seconds.

Direction of the grating the grating is either vertical or horizontal.

Direction of Motion: choose the direction grating moves during adaptation.

Type of Grating: choose Squarewave: alternating black and white bars or Sinewave: fuzzy bars.

Grating Size: proportion of the vertical screen drawing area. So a grating size of 0.25 will have four bars on the screen.

Grating Speed: how fast the grating moves in cycles/second. So a grating speed of 2 means that the grating will move the distance of two cycles in a second (one black and one white bar = 1 cycle). Thus, the larger the bar, the faster it moves for the same grating speed setting.

### Reset

At the top of the settings page is a Reset button. Pressing this button restores the settings to their default values.

### Settings for Motion Aftereffect Illustration

Change the settings below to alter how the motion aftereffect illustration operates.