Saturday, October 6, 2012

Sternberg's Memory scanning Test: PEBL Test Battery Test

Saul Sternberg, image from
http://www.psych.upenn.edu/~saul/
New in version 0.13 of the PEBL Test Battery is Saul Sternberg's famous memory scanning test (e.g., see Sternberg, S. (1966). High-speed scanning in human memory. Science, 153(3736), 652–654, which has been referenced more than 2000 times)  This task is notable for illustrating how one can probe their short-term memory for letters or numbers, with interesting results regarding how long it takes, with the counter-intuitive results of serial exhaustive search, and also a lesson in advancing the methodology of mental chronometry beyond the subtraction logic to one that uses additive factors.



The task, frequently simply called "The Sternberg Task",  requires a participant to remember a short series of numbers, letters, or other stimuli, and then repeatedly probes them about whether particular elements were members of the set.

In PEBL, the task works by giving lists of 2, 4, or 6 consonants to remember.  In Sternberg's original, this set was at times varied for each trial, but in the current implementation we will use a single set for the entire block.  To the left shows  screenshot examples of the learning screen for a  two-character set.  Below is an example learning screen for a  a six-character set.  Responses are made with the left and right shift keys, and the participant is allowed to study the sequence until they are ready to begin.







Whenever an error is made, the original stimulus will be displayed to the screen again, giving the participant another chance to memorize it.
The test takes only a few minutes to complete, and so in its current form is best suited for an in-class demonstration.  In the task, 50 trials are given at each length, with 25 probes actual items from the set, and 25 not members.  These options can be changed of course, and probably 50 trials is on the low side, especially without doing practice.  The script is actually set up to allow multiple sessions--if you enter a subject code that has already been used, it will ask if you want to use it by appending to the current data.  During the task, the stimulus is given on-screen and a keyboard response is required.

At the end of the test, some simple statistics are computed, as seen below. These statistics are also saved in a .txt file in the participant code directory for later reference.  Without practice, without strong incentives for low errors rates, and with only 50 trials per condition, you are unlikely to find the precise results described by Sternberg.  But with specific rewards and additional practice, you should get fairly close.   The sternberg task is distributed in Version 0.13 of the PEBL test battery, in the battery\sternberg folder.


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