Typically, we attend to a particular location in space by directing our gaze to that location. Thus, when reading, you are directing your gaze at the words on the page, and when you glance up at the baseball game, you direct your gaze to the television screen. In almost all situations, what is being represented in our foveae is what we are attending to. If our attention shifts, so does our gaze. A question we can ask, however, is whether it is possible to attend to spatial locations other than the location we are looking at.
Michael Posner and his colleagues investigated this phenomenon in a series of interesting experiments in the late 1970s and early 1980s (see Posner, 1980). In this paradigm, a participant is directed to look at a central fixation light. The participant then sees an arrow pointing either to the right or the left. This arrow is a cue, which directs the participant’s attention in visual space. The task of the participant is to maintain fixation on the center point, but direct his or her covert attention in the direction of the arrow. Then a light appears on either the same side as the cue indicates or the opposite side the cue indicates. When the light occurs on the same side as the cue, it is said to be a valid cue, but when it occurs opposite the cue, it is said to be an invalid cue.
In this experiment you can try the original or any of several variations on the basic design to see if you can replicate the original results.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On this tab you can adjust the type of stimulus and the various parameters of the motion of the stimulus to see how this might effect the aftereffect. The settings include the following:
Dot Diameter: The diameter of the dot in pixels.
Dot Position: The distance the dot is from the fixation mark, as a proportion of the available area.
Dot Luminance: intensity of the dot (in the basic intensity values of the screen). The dot values are differences from this level.
Background Level: brightness of the background against which the dot is to be detected (in the basic intensity values of the screen).
Duration of Cue: the duration of the cue stimulus (ms).
Time between cue and stimulus: the period of time between the cue going of and the stimulus coming one, the interstimulus interval or ISI (ms).
Reset At the top of the settings page is a Reset button. Pressing this button restores the method settings to their default values.
On this tab you can adjust how the method will work. The settings include the following:
Number of Trials: How many trials in the experiment.
Percentage of Trials Valid (of trials with a cue): the percentage of trials with an arrow cue where the cue is valid. (Invalid cues will be 100-% valid).
Percentage of all Trials Neutral: Percentage of all trials where only a line and not an arrow will be presented. When an line is presented, there is a 50% chance the cue is to either side.
Reset At the top of the settings page is a Reset button. Pressing this button restores the stimulus settings to their default values.
On the Experiment tab, press a space button or the button on the screen to start the experiment.
Keep your eyes fixated on the red plus sign in the middle of the screen. This red plus sign will be
followed by an arrow or a line. If the arrow is presented, the dot will be to the side pointed to
by the arrow the percentage of time set on the Percentage of Trials Valid slider (default
and originally 80). On the other trials, the dot will be to the opposite side. If the line is presented
the dot will be to either side 50% of the time.
After the arrow or line are removed, there will be break and then the dot will be presented. Your job is to repond as quickly as you can after the dot has been presented. You can respond by selecting the Yes button at the bottom of the screen or with the space bar.
You data will presented on this tab. On the x-axis will be the three cue conditions. On the y-axis will be the reaction time to the dot in each the three cue conditions. To display the data as values Show Data button.
Change the settings below to alter the stimulus parameters in this experiment.