After reviewing the works of Porterfield, Schmidt, Muncke, Valentine, Aubert, and Bourdon, the authors decided to examine the effect, noted by Aubert, that minimal liminal values for visual motion were obtained "when the movement was viewed for several seconds." The apparatus consisted of a black screen (67 x 84 cm.) with a movable white dot 2 mm. square at the center. The screen was 240 cm. from the S, placed in a dark room. At this distance the dot subtended an angle of 2' 42". The screen was illuminated by a 100 watt daylight Mazda lamp above the S's head, flashed on only for the exposure periods. The S's head was in a head-rest with one eye covered. The movement of the dot was controlled by an endless thread which passed over a rotating drum, which also served as an interval timer. The three S's used the constant process method with exposures of 0.5, 1, 2 and 4 seconds. The judgments asked were "whether the white dot moves, and if so, in what direction" and also "describe the criteria on which you base your judgment." The lower limen for motion, in sec. of arc per sec., decreases as the exposure time increases. For the shorter exposures the values are identical with those of the minimal space limen. The perceptions appear to be simple integrations of extents, in the case of the shorter exposures simultaneous, in the longer case successive. Duration enters simply as the stimulus factor that modifies these extents. (PsycINFO Database Record (c) 2006 APA, all rights reserved)