Measures of displacement and type of background in apparent motion with random-dot cinematograms

The primary purpose of the studies presented was to determine whether stimulus displacement in random-dot cinematogram apparent motion should be measured in terms of relative or absolute distance, while taking into account the effect of number of displaced elements. Support for each measure has been reported in the literature (Braddick, 1974; Lappin & Bell, 1976). A secondary purpose was to test a basic assumption about the generalizability of results in the random-dot cinematogram literature by determining whether the same results may be obtained using cinematograms with a constant-background field as with cinematograms with a varied-background field. For varied-background cinematograms, the clarity of apparent motion decreased as relative displacement increased. The number of elements in the target square was also found to affect the ratings. These findings support a global rather than strictly local process for perceptually segregating areas of random-dot texture based upon motion. For constant-background cinematograms, factors different from those affecting varied-background cinematograms determined the clarity of apparent motion.