In the peterson and peterson study, participants saw three sets of random letters (for example, mtz, pwh, kql) and then counted backward by 7 from a numeric prompt (for example, 358) for set time intervals of three to eighteen seconds. finally, participants recalled as many letters as possible. in this test of the duration of short term memory, the purpose of counting backward by 7 is:

Keeping the short term memory busy.

Explanation:

The technique given in the example Peterson and Peterson study is named "Brown Peterson Technique" where the participants are given a small amount of information that they are asked not to forget and then the counting task is performed which is done for the purpose of keeping the participants from memorizing the earlier information. After they are done counting, the participants are asked to recall the first information, the letters that they were given. This experiment proves that when a new learned information is not rehearsed while it is in the short term memory, it is deleted after a period of approximately 18-20 seconds.

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the vibration from the sound waves messed with the glass and it shattered.

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