Final answer:
The best illustration of a person remembering only the first and last steps of instructions read a week prior is the serial position effect, not related to encoding failure or retrograde amnesia.
Step-by-step explanation:
A person who can remember the first and last steps of a procedure a week after reading the instructions, but not the middle ones, is experiencing the serial position effect. This phenomenon occurs because people tend to remember information at the beginning (primacy effect) and at the end (recency effect) of a list better than the information in the middle. It is not indicative of encoding failure, which is an inability to store information in the first place, nor retrograde amnesia, a loss of memory for events that occurred prior to a brain trauma. It also is not related to repression or social facilitation, which have different psychological implications.