Capacity Limitation in Short-Term Visual Memory for Contour Curvature

I measured the difference threshold for contour curvature in short-term visual memory (STVM) using a two-interval forced-choice partial discrimination task. In experiments 1 and 2, the study stimulus consisting of 1 to 4 curved contours was briefly presented. It was followed by a single contour stimulus after a retention interval. The subjects judged if the test stimulus had a higher or lower curvature than the corresponding study contour. The results of experiment 1 showed that the Weber fraction increased monotonically with increasing set size. The results of experiment 2 clarified that the set-size effect was not due to a temporal limitation in encoding resulting from the short exposure time. In experiment 3, the study stimuli always consisted of 4 items, but the numbers of memorised items were different in each condition. Nevertheless, the results showed the set-size effect, which indicated that its occurrence depended largely on the capacity limitation in short-term visual memory (STVM) storage. Otherwise, the Weber fraction was not hugely higher for set size 4 compared with set size 1. It was concluded that only 1 object could be retained in STVM with high fidelity, but that at least 4 objects could be retained in STVM with some degree of fidelity.