In Experiment I, the tactile adjustment of a comparison bar was used to measure the change in the rod-and-frame illusion as a function of the stereoscopic position of the rod relative to the frame. A vertical rod was presented at a near, a middle. or a far distance, with a single frame tilted counterclockwise at the near distance. a single frame tilted clockwise at the far distance. or two frames of opposite tilt presented simultaneously at the near and far distances. When only one frame was present. displacement of the rod in front of the far frame but not behind the near frame significantly reduced the illusion. When both frames were present. the illusion was determined mainly by the frame at the apparent distance of the rod. In Experiment II. the tactile method of measuring perceived tilt was validated for the range of perceived tilts encountered in Experiment I. The results of Experiment I are discussed in terms of the perceptual resolution of the conflict between relative and absolute cues of tilt.

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Two methods of measuring perceived distance are contrasted. One of these, called a direct method, accepts the observer's direct response to perceived distance as a valid measure of the distance perceived. The other, called an indirect measure, uses the observer's direct response to a perception that is not perceived distance but which has a known relation to perceived distance in order to calculate the distance perceived. There are indications that the direct measure of perceived distance provided by the verbal report sometimes will be modified by cognitive factors. A procedure and apparatus for an indirect measure is suggested which is likely to be free of the cognitive effects found in verbal reports of distance. This apparatus adjusts the distance around which the line-of-sight to the object pivots as the head is moved laterally. The pivot distance at which no apparent motion of the object occurs with head motion is a measure of the perceived distance of the object.

The introduction of misleading size cues between binocularly presented objects can result in a distortion of the binocular visual field. The effect of this primary distortion upon the perceived depth of extraneous objects (objects not used in generating the primary distortion) was studied when both the primary distortion and the extraneous objects involved vertical separations. It was found that the perceived depth between the extraneous objects (the secondary distortion) was affected by the presence of the primary distortion. From the present and previous studies it can be concluded that the secondary distortion is directly related to the primary distortion for either horizontal or vertical separations of the objects in both the distortions. This result is discussed as an example of the “adjacency principle.”

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