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Biomedical subjects

W C Gogel

Publications and source records attributed to W C Gogel.

At least 19 recordsLinked to original sources
PubMed1992

Determinants of the perception of sagittal motion.

This study examines the change in the perceived distance of an object in three-dimensional space when the object and/or the observer's head is moved along the line of sight (sagittal motion) as a function of the perceived absolute (egocentric) distance of the object and the perceived motion of the head. To analyze the processes involved, two situations, labeled A and B, were used in four experiments. In Situation A, the observer was stationary and the perceived motion of the object was measured as the object was moved toward and away from the observer. In Situation B, the same visual information regarding the changing perceived egocentric distance between the observer and object was provided as in Situation A, but part or all of the change in visual egocentric distance was produced by the sagittal motion of the observer's head. A comparison of the perceived motion of the object in the two situations was used to measure the compensation in the perception of the motion of the object as a result of the head motion. Compensation was often clearly incomplete, and errors were often made in the perception of the motion of the stimulus object. A theory is proposed, which identifies the relation between the changes in the perceived egocentric distance of the object and the tandem motion of the object resulting from the perceived motion of the head to be the significant factor in the perception of the sagittal motion of the stimulus object in Situation B.

Adult↗
PubMed1992

Absence of compensation and reasoning-like processes in the perception of orientation in depth.

When errors are present in the perceived depth between the parts of a physically stationary object, the object appears to rotate as the head is moved laterally (Gogel, 1980). This illusory rotation has been attributed either to compensation (Wallach, 1985, 1987) or to inferential-like processes (Rock, 1983). Alternatively, the perceived distances of and directions to the parts of the object are sufficient to explain the illusory perceived orientations and perceived rotations of the stimulus. This was examined in three experiments. In Experiment 1, a perceived illusory orientation of a stimulus object extended in depth was produced by misleading binocular disparity and was measured at two different lateral positions of the head under two conditions. In the static condition, the head was stationary at different times at each of the two measurement positions of the head. In the dynamic condition, continuous motion of the head occurred between these two positions. In Experiment 2, static and dynamic conditions of illusory stimulus orientation were observed with the head stationary. In Experiment 3, a perspective illusion instead of binocular disparity produced the errors in perceived depth. In no experiment did the perceived orientation of the object differ for the static and dynamic conditions. In the absence of head motion, neither compensatory nor inferential-like processes were available. It is concluded that these processes are not needed to explain either illusory or nonillusory perceptions of the orientation or rotation of stimuli viewed with a laterally moving head.

Adult↗
PubMed1990

A theory of phenomenal geometry and its applications.

The geometry of perceived space (phenomenal geometry) is specified in terms of three basic factors: the perception of direction, the perception of distance or depth, and the perception of the observer's own position or motion. The apparent spatial locations of stimulus points resulting from these three factors thereupon determine the derived perceptions of size, orientation, shape, and motion. Phenomenal geometry is expected to apply to both veridical and illusory perceptions. It is applied here to explain a number of representative illusions, including the illusory rotation of an inverted mask (Gregory, 1970), a trapezoidal window (Ames, 1952), and any single or multiple point stimuli in which errors in one or more of the three basic factors are present. It is concluded from phenomenal geometry that the size-distance and motion-distance invariance hypotheses are special cases of the head motion paradigm, and that proposed explanations in terms of compensation, expectation, or logical processes often are unnecessary for predicting responses to single or multiple stimuli involving head or stimulus motion. Two hypotheses are identified in applying phenomenal geometry. It is assumed that the perceptual localization of stimulus points determines the same derived perceptions, regardless of the source of perceptual information supporting the localizations. This assumption of cue equivalence or cue substitution provides considerable parsimony to the geometry. Also, it is assumed that the perceptions specified by the geometry are internally consistent. Departures from this internal consistency, such as those which occur in the size-distance paradox, are considered to often reflect the intrusion of nonperceptual (cognitive) processes into the responses. Some theoretical implications of this analysis of phenomenal geometry are discussed.

Attention↗
PubMed1989

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.

Adult↗
PubMed1979

Induced motion as a function of the speed of the inducing object, measured by means of two methods.

Induced motion is illustrated by the apparent motion imparted to a stationary disc by the horizontal motion of an enclosing frame. The present study examined the effect of frame speed, with a constant extent of frame motion, on the magnitude of induced motion for average frame speeds varying from 0.17 to 2.85 deg s-1. The induced motion was measured by two methods. (i) The observer adjusted the horizontal distance between comparison posts to indicate the extent of the horizontal induced motion in a physically stationary disc. (ii) The observer adjusted the slant of a comparison rod to indicate the apparent path of motion of the disc physically moving straight up and down in phase with the horizontal motion of the surrounding frame. The latter method requires the observer to integrate two apparent components of motion of the disc, one from its physical vertical motion and the other from its induced horizontal motion. The results from both methods show that substantial amounts of induction occurred at all of the frame speeds. The vector addition of apparent motions from real and from induced motion obtained from the second method, and the substantial amounts of induction found with the high frame speeds are interpreted to indicate that the processes underlying the perception of real and induced motion are essentially the same.

Adult↗
PubMed1979

Depth adjacency and induced motion.

Induced motion was investigated as a function of the stereoscopic separation of the test and inducing object and the instructions to attend to or to ignore the inducing object. It was found that stereoscopically displacing the test object from the inducing object with both kinds of instructions resulted in a decrease in the magnitude of induction particularly with crossed disparity. These results are consistent with the adjacency principle and with the ability of attention as well as adjacency to modify the magnitude of the induced motion.

Attention↗
PubMed1977

Eye fixation and attention as modifiers of perceived distance.

An error in the perceived distance of a physically stationary object results in an apparent horizontal motion of the object if the head is moved horizontally. Procedures have been developed to use this apparent motion to measure the apparent distance of the object. Research also has indicated that the apparent distance of an object will tend to be displaced toward the distance at which the eyes are fixated. In the present study head-motion procedures were used to measure the effect of eye fixation and attention upon the apparent distance of a point of light in two experiments. Substantial errors in perceived distance occurred in the predicted direction as a function of fixation distance. Attending to an object at a distance other than the distance of the fixated point of light had a much less effect upon the apparent distance of the point. It is concluded that the apparent conomitant motion which occurs in a variety of situations as a function of the distance of fixation indicates that substantial errors in perceived distance are common in most environments.

Attention↗
PubMed1976

An apparatus for indirect measurement of perceived distance.

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.

Cognition↗