Backward masking of visual targets with internal contours

Detection thresholds were obtained using a staircase procedure coupled with a forced-choice indicator response to test the hypothesis that a visual target would become increasingly less susceptible to backward masking as the amount of its internal contour increased. Relative maskability of each of several targets was expressed as a ratio of threshold under masking to threshold under nonmasking conditions. The hypothesis was confirmed, some earlier results were verified, and an unan ticipated backward “facilitation” effect was indicated for the target with the most extensive internal contour (a disk composed of 16 black and white segments).