Response classification analysis of the maintenance of contrast for an object

摘要

Previously Shimozaki, Thomas and Eckstein (1999, JEP:HPP) found that an object's contrast is affected by its previous contrast. In that study observers perceived two moving squares across two intervals through apparent motion. Observers were told to judge the contrast of one square only in the second interval; despite this instruction, contrast changes in the target square from the first to the second interval led to worse performance. This study assessed the spatio-temporal dynamics of this effect through response classification. Three observers performed a yeso contrast discrimination of 1?° uniform central squares (30% signal contrast) presented for 90.9ms (2 frames, 45.4ms/frame) on pedestals varied for each observer for near-threshold performance (15-25%).A non-judged interval of 318.2ms (7 frames, 45.4ms/frame) preceded the judged interval, with two 1?° squares (1?° apart) in the upper left and right with abutting corners to the target square. Another square (1?°) in the second interval (1?° to the right or left of the target) led to apparent motion of two squares, either left or right. The contrasts of all squares were randomized (either the pedestal or signal contrast), as well as direction of motion (left or right). For response classification, stimuli were presented in Gaussian-distributed image noise, independently sampled for each frame. The behavioral results replicated the previous study; despite instructions to judge only the second interval, performance was significantly worse when the target contrast changed from the first to second interval (change in da?2: 0.788 to 0.991). The classification movies during the second (judged) interval found that the target contrast in the second interval affected the judgments, as expected, with the second frame having a larger effect. The classification movies during the first (non-judged) interval found that the effects of the target square were distributed throughout the 7 frames (318.2ms), and began with the second frame at 45ms.