In September 1959, psychology researchers Lloyd and Margaret Peterson tested how quickly people forget information. The researchers asked their study participants to remember a random trigram, a three-letter group (e.g., KHZ). Next, the researchers gave the participants a three-digit number (e.g., 375). The participants were then instructed to count backward from the number by subtracting three (e.g., 372, 369, 366, etc.).