Limited capacity in iconic memory for contour curvature

摘要

We measured the difference threshold for contour curvature in iconic memory by using the spatially cued discrimination method. In Experiments, the study stimulus consisting of 2 to 6 curved contours was briefly presented, followed by red and green lines as cues. The cue delays were 0 ms and 300 ms in Experiments 1 and 2 respectively, and 50 ms before the study offset in Experiment 3. Participants judged if the red-line-cued contour had greater curvature than the green-line-cued contour. Clear set-size effects in Experiments 1 and 2 indicate that iconic memory has a limited capacity. Small difference in set-size effects between Experiments 1 and 2 suggest that iconic memory lasts for at least 300 ms. Set-size effect in Experiment 3 indicates that perception itself has a limited capacity, even while the study stimulus is physically present. These properties of iconic memory at threshold level are contradictory to the traditional view that iconic memory has a high capacity, and a rapidly decaying memory both at suprathreshold and categorical levels. A more efficient method of examining iconic memory is to display a single study stimulus with cues.