Superior memory for stimuli presented at the end of a sequence is called the recency effect. One possible explanation for the better memory for words at the end of the list is that the most recently presented words are still in STM.
To test this idea, Glanzer and Cunitz had their participants count backward for 30 seconds right after hearing the last word of a list. This counting prevented rehearsal and allowed time for information to be lost from STM.
The result was what we would predict: The delay caused by the counting eliminated the effect
Glanzer and Cunitz therefore concluded that the recency effect is due to storage of recently presented items in STM