Background

Masking refers to the difficulty in seeing one stimulus, the target stimulus, when it is quickly replaced by a second stimulus that occupies the same or adjacent spatial locations. In masking, a briefly-shown and to-be-detected stimulus that would normally be visible is rendered invisible by the presence of a second stimulus, here called the masker. This masker stimulus occurs in the same location immediately or that surround the test stimuli. Usually the masker stimulus persists after the test stimulus disappears (Enns & Di Lollo, 1997).

Use this activity to explore one type of visual masking, called backward masking. The target stimulus will occur first and will be a small circle. The masker will be a big circle that will surround the target stimulus. The masker will be presented after the target stimulus has been removed. Even though the masker does not happen at the same time or location as the target, it can still, if the settings are correct, reduce or prevent your perception of the target stimulus.

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:

Start or clicking or touching the stimulus area: start a trial. This button or action starts a trial. The fixation mark, a plus, will be presented. Look at it. Then the fixation mark will be removed and replaced by the target stimulus, a small circle. Then after the stimulus is removed the masker will be presented if selected.
Stimulus Level: How much darker is the target stimulus than the background. Adjust this till the circle is visible but still faint.
Show Masker (Annulus): Have the masker, an annulus that surrounds the central stimulus, turn on or not.
Interstimulus Interval (ISI)(ms): the time betwen the removal of the target stimulus and the presentation of the masker, in milliseconds. Usually shorter intervals are better for masking.
Stimulus Size: the size of the target stimulus, relative to the height of the drawing area.
Stimulus Duration: how long will the stimulus be presented, in milleseconds.
Gap Size between Stimulus and Annulus: the separation between the outside of the stimulus, the target, and the annulus, the masker. A value of 0 means that the outside of the circle meets the inside of the annulus. A negative value means that the annulus partly overlaps the target stimulus. Values are relative to the height of the drawing area.
Masker Duration (ms): the time period that the masker is on, in milleseconds.

Reset

Pressing this button restores the settings to their default values.

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