Iconic memory is the term for when the human brain remembers an image after briefly being shown the visual. Sensory memory refers to any memory of any of the senses. Iconic memory refers only to the memory of sight. The word icon means a picture or image, hence the term for this short-term type of memory. From experiments, scientists learned that a witnessed image is stored briefly without the brain spending much time processing.
Sensory stores, also called sensory buffers, save a visual image for the very short term. Echoic memory, the auditory memory, remembers sounds for under four seconds, while iconic memory is gone in less than a second. With these memory tests, the human brain does not have much time to decide what to process. Each sense remembers information for a different length of time. The transference of information from the eye to the brain is preserved just long enough for the eye to move to the next point.
The idea was introduced by George Sperling in the early 1960s. Using a tachistoscope, Sperling showed his test subjects letters arranged to form a box shape, three letters tall and four letters across. The tachistoscope, invented in 1859 and used to increase memory or reading speed, is a projector apparatus that flashes images on a screen for only a fraction of a second. Sperling recorded how many blocked letters subjects could read during the visual flash. Generally, participants could read three or four letters during the iconic memory test.
Sperling then added sound to the projected images 250 milliseconds after the letters appeared. The sounds were different tones: high, medium and low. Subjects were instructed to read high, medium or low letter rows depending on which tone they heard. Typically, the subjects heard the tone then read three or four letters from any row. These experiments proved subjects were seeing a memory of all the letters for one-fourth of a second then reading from that iconic image once they heard the tone.
Later, in 1967, Ulric Neisser coined the phrase iconic memory. He wanted the term to indicate a preservation of an image's duplicate being apparent to the retina. In the 1990s, findings from iconic memory were used to conduct further experiments about how the human brain registers visual images. Experiments are being conducted to learn how quickly people can detect changes in a group of visually presented items.