Muhammad has been in his school cafeteria hundreds of times. It is a large room, and there are nine free-standing pillars that support the roof. One day, to illustrate the nature of forgetting, Muhammad’s teacher asks him how many pillars there are in the cafeteria. Muhammad has difficulty answering the question, but finally replies that he thinks there are six pillars. What memory concept does this example illustrate?

a. Storage decay

b. Retrograde amnesia

c. Proactive interference

d. Retroactive interference

e. Encoding failure