While driving in a new city, you briefly see a road sign that you think marked the exit you are looking for, but after a few seconds you can't remember what the sign said. this illustrates the quick decay of memory?

I believe the answer is: Iconic memory
Iconic memory refers to the type of memory that taken from one of our senses which last on a very short period of time before it fades.
Iconic memory happens because of the mix-up between short-term memory and long-term memory and would explain weird psychological occurrences such as De javu.

The correct answer is b