Walter C. Gogel

Depth adjacency in simultaneous contrast

The Gelb phenomenon, as an example of whiteness contrast, was investigated with three amounts of separation in depth between the test and induction disc. The cue of binocular disparity was used to vary the perceived depth between the discs. It was found that the magnitude of the contrast effect decreased with an increase in the perceived depth between the two discs. This change was regarded as an instance of the adjacency principle. The problem of whether the binocular disparity cue per se or perceived depth was the significant variable was discussed. The consequences of the results were considered with respect to the relation between whiteness constancy and whiteness contrast and the problem of neural localization of the contrast effect.

An indirect method of measuring perceived distance from familiar size

Two methods of measuring perceived distance as a function of familiar size were compared in five experiments. The method which uses the perception of motion concomitant with a motion of the head, unlike the method of verbal report, is considered to provide a measure of perceived distance that is unaffected by factors of cognitive distance. The results of the experiments indicate that although the perceived egocentric distance of an object can vary somewhat as a function of the cue of familiar size, the larger variation often found with verbal reports of distance is based upon cognitive, not perceptual, information. The cognitive information is interpreted as resulting from the perception of the object as off-sized and the observer’s assumption that the perceived size of an object will vary inversely with its physical distance.

Scalar Perceptions with Binocular Cues of Distance

Under reduced conditions of observation, the perception of egocentric distance is determined by a composite of the tendency to see objects as near (the specific-distance tendency) and residual oculomotor cues of distance. The resulting perceived distance-the egocentric reference distance-was found to affect the perceived relative depth produced by binocular disparity between two points of light: the more distant light was positioned in apparent depth near the egocentric reference distance, with the scalar perception of the depth between the lights related to the magnitude of the reference distance. Implications for the scaling of relational perceptions are discussed.

Relative motion and the adjacency principle

The perception of motion of physically moving points of light was investigated in terms of the distinction between absolute and relative motion cues and the change in the effectiveness of the latter as a function of the frontoparallel separation between the points. In situations in which two competing relative motion cues were available to determine the perceived path of motion of a point of light, it was found that the relative motion cue between more adjacent points was more effective than the relative motion cue between more separated points. In situations in which only one relative motion cue was available to determine the perceived motion of a point it was found that the effectiveness of this cue as compared with the absolute motion cue decreased with increased separation. These results are predictable from the adjacency principle which states that the effectiveness of cues between objects is an inverse function of object separation. Some consequences of the study for the theory of motion perception are discussed.

Measuring Attention Using Induced Motion

Attention was measured by means of its effect upon induced motion. Perceived horizontal motion was induced in a vertically moving test spot by the physical horizontal motion of inducing objects. All stimuli were in a frontoparallel plane. The induced motion vectored with the physical motion to produce a clockwise or counterclockwise tilt in the apparent path of motion of the test spot. Either a single inducing object or two inducing objects moving in opposite directions were used. Twelve observers were instructed to attend to or to ignore the single inducing object while fixating the test object and, when the two opposing inducing objects were present, to attend to one inducing object while ignoring the other. Tracking of the test spot was visually monitored. The tilt of the path of apparent motion of the test spot was measured by tactile adjustment of a comparison rod. It was found that the measured tilt was substantially larger when the single inducing object was attended rather than ignored. For the two inducing objects, attending to one while ignoring the other clearly increased the effectiveness of the attended inducing object. The results are analyzed in terms of the distinction between voluntary and involuntary attention. The advantages of measuring attention by its effect on induced motion as compared with the use of a precueing procedure, and a hypothesis regarding the role of attention in modifying perceived spatial characteristics are discussed.

The Effect of Object Familiarity on the Perception of Size and Distance

The perceived sizes and perceived distances of familiar objects were investigated in two experiments in which images of familiar objects were presented monocularly, one at a time, in an otherwise dark field of view. It was found that the angular size of the objects as well as their familiar size determined reported size. Reported distances were increasingly underestimated as a function of increasing simulated distances of the objects. The results are consistent with the conclusion that, as a function of the retinal size of the objects, the observer perceives the familiar objects as off-sized, and, that as a consequence of these off-sized perceptions, the observers judgements of the object distances reflect inferential rather than perceptual processes.

The organization of perceived space

SummaryPerceptions tend often to be proportional to proximal stimuli with reduced conditions of observation and proportional to distal stimuli under multicue conditions. Two explanations of this phenomena are examined. One, termed the core context hypothesis, postulates that the response to the proximal stimulus (the core) is modified by distance information (the context). The second, termed invariance hypotheses, postulates an interaction between two or more perceptions, one of which is often perceived distance. In order for invariance hypotheses to be valid it is necessary that a perceived distance occur under reduced cues of distance. It is asserted that perceived distance under these conditions is supplied by observer tendencies termed the specific distance and equidistance tendency. Perceptual interactions occur in situations other than those relevent to invariance hypotheses and the evidence for perceptual interactions is discussed in relation to perceived motion, perceived depth from exocentric cues, the adjacency principle, and other phenomena. It is suggested that the analysis of many perceptions in terms of perceptual interactions is parsimonious in that the effect of the independent perception, e.g., perceived distance, upon the dependent perception, e.g., perceived size, motion, or depth, is the same regardless of the cues by which the particular value of the independent perception is achieved.

The adjacency principle and induced movement

The apparent movement of a stationary point of light was investigated as a function of the apparent distance of the point of light with respect to the inducing frame of frames. When two frames were presented simultaneously, they were at different distances and physically moved at opposite phase in frontoparallel planes. When one frame was presented alone, it was positioned at different times at each of the two distances. The point of light was presented stereoscopically at the distance of either the near or far frame or midway in depth between these distances. With the single frame, it was found that the magnitude of the induced movement decreassed as the point of light was increasingly far in front of a frame but decreased less or remained approximately constant for distances be hind a frame. With the two frames presented simultaneously, it was found that as the depth between a particular frame and the point of light decreased, the contribution of that frame to the induced movement increased. The results illustrate the interaction of perceptions, in this case perceived depth and perceived motion, and are consistent with the adjacency principle.

An indirect measure of perceived distance from oculomotor cues

The sensitivity of an indirect method of measuring perceived distance was compared in two experiments with the direct procedure of eliciting verbal reports of distance. Perceived distance was varied by varying the oculomotor cues to object distance. The indirect method, called the “adjustable pivot method,” uses an apparatus that physically moves the stimulus object laterally concomitantly with the lateral motion of the head. The magnitude and direction of this concomitant motion determines the distance of the point around which the direction of gaze to the object rotates (the pivot distance) as the head is moved. The pivot distance at which the object appears stationary with head movement measures the apparent distance of the object. Both types of measures were found to vary systematically with the oculomotor distance of the object for points of light (Experiment 1) and extended objects (Experiment 2). A previous study has shown that the adjustable pivot method avoids cognitive errors that can distort verbal reports of distance. The present study, by demonstrating the discriminative capability of this method under conditions in which differences in perceived distance were expected to occur, provides clear evidence that the adjustable pivot method is a sensitive and useful procedure for measuring perceived distance.

The effect of perceived distance on perceived movement

Equations were developed to predict the apparent motion of a physically stationary object resulting from head movement as a function of errors in the perceived distances of the object or of its parts. These equations, which specify the apparent motion in terms of relative and common components, were applied to the results of two experiments. In the experiments, the perceived slant of an object was varied with respect to its physical slant by means of perspective cues. In Experiment I, O reported the apparent motion and apparent distance of each end of the object independently. The results are consistent with the equations in terms of apparent relative motion, but not in terms of apparent common motion. The latter results are attributed to the tendency for apparent relative motion to dominate apparent common motion when both are present simultaneously. In Experiment II, a direct report of apparent relative motion (in this case, apparent rotation) was obtained for illusory slants of a physically frontoparallel object. It was found that apparent rotations in the predicted direction occurred as a result of head motion, even though under these conditions no rotary motion was present on the retina.