Perception experiment

This experiment asks you to report on aspects of a an afterimage that you may see. You are to report on what you see after looking at a sequence of images.

Start a trial by pressing the space bar. On each trial you will see the following: (1) A black and white horizontal bar grating, shown for one second. (2) A second stimulus that is either a grating of a blank gray screen. If the stimulus is a grating, it will flicker. (3) A blank gray screen of variable duration. (4) A square shaped random dot pattern.

Your task is to report the dominant orientation of what you see during the blank gray screen in (3) just before the random dot pattern in (4) appears. Your choices are:

  1. Horizontal: press the h key.
  2. Vertical: press the v key.
  3. Nothing: press the n key.

When you press a key, you will receive text feedback on your selection. There are no correct or incorrect selections, just report on what you saw during that trial. You can change your selection by pressing the other key. When you are satisfied with your selection, press the space bar to start the next trial.

After the first trial, there is a 15 second delay between the end of one trial and the start of the next trial. A counter tells you how many seconds remain before the next trial starts. During the intertrial countdown, a random dot pattern will appear on the screen but if you wish you can relax and look around the room. Just be prepared for the next trial when the counter gets into only a few seconds remaining because the next trial starts automatically.

There are a total of 63 trials. Each trial takes approximately half a minute, so the experiment will last about 30 minutes. On each trial you just report on the dominant orientation of what you saw just before the square-shaped random dot pattern appears. If your percept changes during the presentation of the blank gray screen, report what was last seen.

Interpreting the results