To study how recognition memory decreases with time, the following experiment was conducted.  The subject read a list of 20 words slowly and aloud and then at different time intervals was shown a list of 40 words, containing the 20 words that had been read.  The percentage of words recognized (second column) was recorded as a function of the time elapsed in minutes (first column).  This shows the averages for 5 different subjects.

Adapted from "Quantitative Methods in Psychology" by D. Lewis, McGraw-Hill, New York, 1960.