John and Susan find a penny, and Susan says, "I bet you can't tell me what is on the penny". John thinks about it, and realizes he can't describe the penny. It appears that
John can't describe a penny because he never learned what one looked like in the
first place. John's inability to describe the penny is an example of
1) simply forgetting.
2) a failure to encode.
3) retroactive interference.
4) proactive interference.