Iconic Memory and Sperling's Experiments
What Is Iconic Memory?
Iconic Memory is a very brief memory store with a massive capacity. This is where visual information viewed with the eyes is stored for around one third of a second, which is just long enough for the visual information to be processed.
The Iconic Memory provides a stream of visual information to the brain all the time when your eyes are open, and is constantly 'refreshing' the visual information presented to it. If the iconic memory did not clear itself quickly, conflicting information about a scene would overlap, causing it to be very confusing! For example, you may be in a room with a friend, who is walking across the room towards you. Your iconic memory would be receiving visual information about her movements, processing that information (this is when you'd think "Oh, she's moving), and then discarding that information in under a second. You then would receive a continuous stream of information as she continued to walk towards you, all of which is quickly processed and discarded. If it were not discarded, your brain would have conflicting information about her whereabouts in the room as the processed information built up, and you would get confused.
George Sperling, an American psychologist, was the first to demonstrate the existence of a sensory register for visual information. To do this, he used a tachistoscope to briefly present participants with a set of 12 letters, presented in three rows of four letters. The random letters would then be projected onto a screen for around one-twentieth of a second. The participants then would recall as many letters as they could. Most participants could recall four or five letters, although they said that they had seen all the letters. Sperling concluded that all the letters had been registered, but the memory had faded too quickly for all of the letters to be recalled.
Sperling later conducted a second experiment in order to test if the iconic memory was actually retaining all of the letters after they had been flashed on the screen. Sperling presented participants with another set of twelve letters, with four letters in each of the three rows. He sounded a tone just after the letters were flashed onto the screen, and participant had been instructed to recite the letters in the top row if they heard a high tone, letters in the middle row for a medium tone and letters in the bottom row for a low tone.
Participants were able to recall the letters in the row indicated by the tone used by Sperling without any problems, suggesting that the iconic memory did indeed register all twelve letters.