Final answer:
German psychologist Hermann Ebbinghaus conducted self-experiments on memory in 1885, creating the famous forgetting curve showing significant loss of memorized information over time.
Step-by-step explanation:
The person who studied memory and forgetting by testing only himself was the German psychologist Hermann Ebbinghaus. In 1885, Ebbinghaus experimented with memorization of nonsensical syllables and tracked how much he retained over various time spans. His research gave birth to the famous forgetting curve, which demonstrates how information is lost over time due to storage decay, showing that around 50% of memorized information can be forgotten after 20 minutes and 70% after 24 hours.