Our cheatin' brain: The brain's clever way of showing us the world as a whole

October 29, 2008

Whether we choose to admit it or not, we all experience memory errors from time to time. Research suggests that false memory may be a result of having too many other things to remember, especially over long periods of time. However, previous studies have indicated that a specific type of false memory known as "boundary extension" occurs for different reasons. Boundary extension is a mistake that we often make when recalling a view of a scene-we will insist that we saw more of the scene than was shown, falsely remembering having seen beyond the boundaries of the view. Although this error is very common and occurs in people of all ages (from infants to the elderly), few studies have been done examining how quickly boundary extension occurs. That is, how long must a view of a scene be disrupted before people are convinced they saw more than they actually did?

Psychologists Helene Intraub and Christopher A. Dickinson from the University of Delaware were interested in this effect and wanted to test how quickly boundary extension can occur in a group of volunteers. The researchers made two photographs of the same scene-one showed a close-up view and the other showed a wider view that revealed more of the scene. In the first experiment, volunteers were shown one view, interrupted for a brief interval (in some cases for less than 1/20th of a second) by a "mask" (an unrelated, meaningless display) followed by the same photograph or the other version of the photograph, which remained on the screen. Volunteers were then asked to report whether the picture they were looking at was the same, or showed more or less of the scene compared to the first photograph. The second experiment had a similar set up except that the first and second photographs were shown on opposite sides of the monitor forcing the volunteers to shift their eyes from one image to the other so that the interruption included an eye movement.

The results, reported in the October issue of Psychological Science, a journal of the Association for Psychological Science, showed that boundary extension occurred in both experiments-although the volunteers knew exactly what would be tested and their view of the scene was disrupted for as little as 42 milliseconds, when the second view was identical, they often failed to recognize this, reporting instead that the second view showed less of the scene. Even though the interruption was briefer than an eye blink, they were confident that they had seen more of the scene in the first photograph! The results of the second experiment (requiring an eye movement) indicate that boundary extension also occurs during visual scanning and not just during more simple tasks that use a mask alone (as in Experiment 1).

Based on these results, the authors suggest a new concept of scene perception, one that is not based solely on visual input. Rather, they suggest that other inputs are also involved, including amodal perception (the ability of the brain to automatically "fill in" blank spaces for us) and spatial perception (providing the viewer with a sense of space beyond the image). Therefore in this study, during the interruption, when the visual input was gone what was remembered reflected memory not only of that visual input, but the other inputs as well, thus causing the volunteers to remember seeing more of the scene than was actually shown.

The researchers suggest that errors in boundary judgment may actually be beneficial because the end goal is a logical view of the world as a whole. The authors conclude, "The rapidity of this error would be advantageous rather than harmful, because the goal of the visual system is not to represent the spurious boundaries of each fleeting view, but to incorporate those views into a coherent, continuous representation of a surrounding world."
For more information about this study, please contact: Helene Intraub ( intraub@psych.udel.edu)

Psychological Science
is ranked among the top 10 general psychology journals for impact by the Institute for Scientific Information. For a copy of the article "False Memory 1/20th of a Second Later: What the Early Onset of Boundary Extension Reveals About Perception" and access to other Psychological Science research findings, please contact Barbara Isanski at 202-293-9300 or bisanski@psychologicalscience.org.

Association for Psychological Science

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