Hermann Ebbinghaus was the first person to conduct scientific studies of memory, using himself as a subject.  He invented nonsense syllables and tried to memorize them. He memorized hundreds of lists of nonsense syllables over thousands of repetitions, then tested his memory of these lists after various time intervals. He graphed his retention and forgetting over time (the famous forgetting curve depicted on the next slide).  Current research suggests that this curve is unusually steep, probably due to the fact that Ebbinghaus was using meaningless material. When people memorize more meaningful material, the curve is not nearly so steep.
	To study forgetting empirically, psychologists must measure it precisely. To measure forgetting, we must measure memory.
	Retention refers to the proportion of material retained (remembered). In measuring retention, scientists study both recall, which involves requiring subjects to reproduce information on their own without any cues, and recognition, which involves requiring subjects to select previously learned material from an array of options (multiple-choice vs. essay exams).