Which task prevents rehearsal by requiring numerical subtractions after recalling a letter trigram?

The correct answer is the Brown-Peterson task, a well-known psychological experiment designed to study short-term memory and the effects of rehearsal on retention. In this task, participants are presented with a trigram consisting of three consonants (for example, "JFG") and then asked to recall the letters after a short delay. To prevent rehearsal—the process of repeating information to keep it in short-term memory—participants must perform a distracting task, such as numerical subtractions (for instance, counting backward from a number).

This distraction is critical because it eliminates the opportunity for participants to rehearse the trigram mentally. Consequently, the design of the Brown-Peterson task allows researchers to examine how quickly information is lost from short-term memory when rehearsal is not possible, thereby providing insights into memory retention and interference.

The other tasks listed do not involve the specific requirement to perform mathematical subtractions to prevent rehearsal, which is a defining feature of the Brown-Peterson task.