In the 1970s psychologists became interested in testing the role rehearsal played on the primacy effect. In 1972 psychologist Phillip Marshal tested whether eliminating rehearsal would affect the primacy effect. He did this by engaging his participants with a word-sorting task while presenting a list of 18 common nouns. Participants were not asked to learn the nouns in this experimental condition but were still tested on recall accuracy. Being unaware that researchers were going to test the participants’ memory meant that there was no need for rehearsal. Marshal found that eliminating rehearsal also eliminated any significant primacy effect. Which proved that rehearsal accounted for the existence of a primacy effect. 