Compression of space in visual memory.

Human observers had to point to the location of a briefly presented target by means of a mouse after a brief delay following target offset. It was found that observers systematically mislocalized the target closer to the center of gaze, and to visually salient markers in the visual display. A perceptual judgment task revealed that these errors in localization were independent of whether or not eye movements were made, and even of planning for them, thereby demonstrating that the effect was a perceptual phenomenon, not a sensorimotor one. Further experiments demonstrated clearly that the magnitude of the time interval between target presentation and judgment regarding its spatial location was the critical parameter. A longer time interval between the event and its report enhanced significantly the amplitude of compression, thus establishing this phenomenon as a visual memory effect. We conclude that visual memory of spatial location is distorted over time in a systematic, monotonic fashion as a result of the sustained fixation of the observer on a fixed location during and shortly after target presentation, or by the continual presence of stable, salient landmarks in the environment.