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In this experment you can measure the duration that items can be held in working memory using the classic methodology of Brown (1958) and Peterson and Peterson (1959) now called the Brown-Peterson experiment.

In this experment you will be presented a 3 letter string and and a 3 digit number. There will be a period of time before you are asked to recall the letters, called the retention interval. During this time there will be a tone beeping at a regular interval and you are to count backwards from the presented 3 digit number by 3. It is vital that you focus on this counting task and not try to repeat the letter string during the retention interval. At the end of the retention interval you will be asked to enter the letter string. Press the space bar to go to the next trial.

The counting backwards is designed to interfer with your rehearsal activities so that the losing of information from working memory can be more clearly observed. It was found in both experiments that as the retention interval increased, retention accuracy decreased over the first 15 seconds about until the results seemed to be at a chance level.

Brown, J. (1958). Some tests of the decay theory of immediate memory. Quarterly Journal of Experimental Psychology, 10(1), 12-21.
Peterson, L., & Peterson, M. J. (1959). Short-term retention of individual verbal items. Journal of experimental psychology, 58(3), 193-198.

Setup Instructions

You can adjust several parameters to design your own version of the experments. The settings are discussed below.

Settings for the Stimuli

You can adjust several parameters to design your own version of the experments. The settings are discuss below.

Stimulus Type: What type of letter string, either only consants (CCC) or two consonants with a vowell in between (CVC).

Duration of Stimulus (ms): how long the stimulus is presented. Sperling (1960) used 50 ms but that his hard for most monitors to reproduce well. He used a tachistoscope.

Font Size: choose the font size of the letters. The bigger the letters the farther the outside letters will be from the fovea.

Background Gray Level : the brightness of the background, in basic display units. This variable alters the contrast between the letters and the background.

Duration of Fixation (ms): how long the fixation mark is on (ms).

Stimulus Delay (ms from end of fixation): how long after the fixation mark is removed till the beginning of the stimulus. This number needs to be big enough for any arrows that occur before the stimulus (the negative numbrer includes the duration of the stimulus). Reset Stimulus At the top of the settings is a Reset Stimulus button. Pressing this button restores the method settings to their default values.

Experimental Method Settings

Press the space bar to go to the next trial.: this is the principle independent variable during the experiment. This is the retention interval between the removal of the string and when you will be asked to enter the string.

Use Interference: Use or not the counting task during retention interval.

Metronome Rate: so-called because it was a metronome that Peterson and Peterson (1959) used. This is how long of time between beeps to indicate how fast you should try to count backwards by 3.

Number of Trials/Delay: how many trials at each level of delay.

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


Settings for the Stimuli

Change the settings below to alter the stimulus parameters in this experiment.

Experimental Method Settings

Change the settings below to alter the parameters of the experimental method.

Instructions for Experiment

Below, press the spacebar or the Open Experiment Window button on the screen to open the window where the experiment will run. When this screen opens, press the spacebar or click the "Start" button to begin the experiment. There are instructions above the "Start" button. Read them to know how to perform the experiment. Keep your eyes fixated on the red plus sign in the middle of the screen.

Results Tab

Your data will be presented on the results tab. The x-axis will have the retention intervals. The y-axis will show the percent correct for each delay. To see your trial-by-trial, press the Show Data button. To see the summary data press the Show Summary button. This data can be copied and saved.

Your Results