Why is it that you can park your car at a huge mall and find it a few hours later without much problem, or make your way through a store you have never been to before?
The answer may lie in our ability to build up visual memories of a scene in a short period of time, according to a Rutgers study published in today's issue of the journal Nature.
The study, "Persistence of Visual Memory for Scenes," authored by David Melcher, a graduate fellow in the department of psychology of Rutgers' Faculty of Arts and Sciences-New Brunswick, counters current thinking that visual memory is generally poor and that people quickly forget the details of what they have seen.
Melcher proved that even with very limited visual exposure to a scene, people are able to build up strong visual memories and, in fact, their recall of objects in the scene improved with each exposure.
Over the past two years, Melcher tested subjects in Psychology Professor Eileen Kowler's Eye Movements and Vision Laboratory at Rutgers, using hundreds of three-dimensional, computer-generated scenes of rooms that contained 12 unrelated objects such as an apple, a plant, a toy and a lamp.
The scenes were randomly selected and shown to subjects for as little as a quarter of a second to a maximum of four seconds. Immediately after, the subjects were asked to name as many of the items in that scene as they could recall.
Melcher found that after viewing a scene, a subject might recall four objects and, when shown the scene again, might recall six. The more times a particular scene was shown, the more objects the subject could recall and identify. Subjects also were able to recall the same number of objects after two brief one-second exposures as after one longer two-second exposure.
"Surprisingly, subjects continued to build memory for the scene as if it had never left their sight, despite the fact that each view of a particular scene was separated by many other scenes over a period of several minutes," observed Melcher.
"My research shows that the build up of visual memory over time is much better than widely thought and may underlie the successful performance of real world visual and cognitive tasks that require people to keep track of objects in their immediate environment."
According to Melcher, these images aren't stored in short-term or long-term memory; they are preserved in medium-term memory, which lasts for a few minutes and appears to be specific to visual information as opposed to verbal or semantic information.
"Medium-term memory depends on the visual context of the scene, such as the background, furniture and walls, which seems to be key in the ability to keep in mind the location and identity of objects," he explained. "These disposable accumulated visual memories can be recalled in a few minutes if faced with that scene again, but are discarded in a day or two if the scene is not viewed again so they don't take up valuable memory space."
He also noted that when the objects in a scene were replaced with words, such as the word "apple" for an image of an apple, subjects lost the ability to build up memories; frequency of exposure in this case did not increase the number of words recalled.
In addition, if subjects were shown a scene that had an identical background to one previously viewed, but the objects or their location was changed, interference between the two scenes developed. As a result, subjects remembered fewer items than when seeing a totally new scene.
"What this means is that medium-term memory can be helpful, enabling us to quickly identify our surroundings without having to constantly visually scan our environment, but it can also be equally harmful to memory if the locations of objects are changed frequently," he said.
"So, if you put your car keys on the dresser tonight and then on the kitchen table tomorrow and someplace else the next day, these previous memories of where you put the keys will begin to interfere with each other and cause confusion," he added. "What was great about this research is that it provided me with scientific reasons why I remembered things or didn't. Now I put my keys in the same place every day."
The research was funded by a grant from the Air Force Office of Scientific Research, which supports basic research in vision and cognition.
Melcher is a National Institutes of Health predoctoral fellow and a Ph.D. candidate in psychology at Rutgers. He earned a master's degree in psychology from Rutgers' Graduate School-New Brunswick, and holds a bachelor's degree in psychology from Transylvania University, Kentucky. - By Joseph Blumberg
[Contact: David Melcher, Stacey B. Hersh, Joseph Blumberg]