A recent investigation (McDermott, i965) One of the problems in studying the effect of distance information on the perception of size may be in the manner in which these experiments are conducted. Under reduction conditions (dark room, 5 isolated from the stimuli. reduced viewing conditions) the relationship in space between the 5 and the stimulus is undefined. For example, with interposition as the available distance cue, the 0 has information about the distance of one object relative to another but no information about the absolute distance between himselfand either object is available. In the absence of such absolute distance information the 5 is in a sense forced to respond to the only stable perceptual experience available to him, i.e., the retinal image. Rock and McDermott ( 19(4) have shown under certain reduction conditions the retinal image is a stable perceptual experience to which Ss can respond with a minimum of intersubject variability. Another problem in these kinds of experiments may be that a single distance cue may simply not provide enough information. Or perhaps the information a single distance cue does provide may be so unstable that the 5 again must respond to the only stable experience available to him, the retinal image.Perceived size is believed to depart from constancy as the amount of available distance information decreases (Chalmers, 1952;Hastorf & Way, 1952;Holway & Boring, 1941; Lichten & Lurie. 1950; McDermott, 1963 McDermott, , 1965 Rock & McDermott. 19(4). Characteristically experiments examining the effect of distance on size perception manipulate the distance information by changes in the viewing conditions rather than by manipulating the distance cues themselves. For example, reducing the viewing condition to a monocular condition results in the loss of distance information supplied by convergence and retinal disparity. Adding an artificial pupil eliminates accommodation. Each change results in size perception departing from constancy in ever increasing amounts until finally With the addition of the artificial pupil retinal image size matches arc made. In a recent study (McDermott, 19(5) each of the distance cues referred to above as well as linear perspective, movement parallax and interposition were systematically studied one at a time and their individual effect on size perception was measured. It was found that size matches in the presence of single cues to distance were made in terms of retinal image size. These findings supported the earlier work in accommodation and convergence (Adams, 1955; Gogel. 1962a, b: Heinemann, 1961Heinemann, Tulving & Nachmias, 1959;Woodworth & Schlosberg, 1954). The surprising finding of retinal image size matches in the presence of other individual cues to distance once again points to weakness in the size-distance invariance hypothesis consistent with previous findings (Epstein, Park, & Casey, 19(1).In order to extend knowledge about the effect of distance information on size it was decided to investigate the effect of distance cues ...