Identity imposition and its role in a stereokinetic effect

Lines of constant curvature, a circle or a straight line, have no distinguishable parts. Yet they are perceived as if they did. When they move and intersect, they are perceived to slide across each other as if one of them had parts that can be seen to move in relation to the other line. With no such parts present in stimulation, they are products of perception. It was found that a third line of constant curvature, the helix, is also seen to slide when two helixes intersect and are in motion. Another manifestation of perceived identical parts is that rotating circles and similar shapes are perceived not to rotate even when cues for rotation are present. Furthermore, changes between merely perceived identical parts can result in apparent depth. Evidence is presented that such depth, known as the stereokinetic effect, results from kinetic depth-effects that are based on perceived identical parts instead of on actually identical parts, and that depth is seen when the intervals between such perceived parts change length and orientation simultaneously.     

Rapid adaptation to a prismatic distortion

Among several shape distortions caused by a wedge prism is one where a pattern of evenly spaced lines that are parallel to the prism base reaches the eye with distances seen through the base region contracted and distances seen through the apex region expanded. Rapid partial adaptation to this distortion was obtained by having subjects who wore the prism in vertical orientation move the head up and down during the exposure period. The head movements caused the distortion to shift up and down through the line pattern. When, with subjects’ heads stationary, the distortion was made to shift up and down by artificial means, rapid adaptation failed to develop. It is proposed that head movements are here needed for adaptation to develop, because the covariance between them and the shifting of the distortion serves as a signal that the distortions are not objective facts and causes the initiation of the adaptation process.     

Vector analysis and process combination in motion perception

Experiments are reported supporting an altered explanation of the vector analysis that occurs in certain motion displays discovered by Johansson (1950). What seemed the result of a perceptual vector analysis is ascribed to the outcome of two different, independent stimulus conditions to which such displays can give rise because of external vector analysis. The different stimulus conditions are configurational change on the one hand and one of the subject-relative stimulus conditions on the other. In two of Johansson's displays, conditions for configurational change were altered by adding stationary reference points in the surround of the displays. Veridical perception of the displays resulted in a majority of instances. We also found that the different motions that result from configurational change and from subject-relative stimulation may combine to form unitary perceived motions and that this happens quite frequently under some conditions.     

Coercive uses of mandatory reporting in therapeutic relationships

Mandatory reporting legislation was enacted with little consideration of its consequences for ongoing therapeutic relationships. One consequence is the unanticipated and coercive uses of the law in mental health settings. Thirty therapists and 25 child protective service workers were interviewed about their experiences with mandatory reporting in therapy relationships. The interviews revealed unanticipated as well as coercive uses of mandatory reporting in therapeutic relationships, including prompting crisis in family systems to promote change, and using reporting or threats of it to enforce attendance and engagement in therapy. Therapists'd anger and view of reporting as a form of power or tool for social control also related to coercive uses of mandatory reporting. The special case of coercion in mandated cases resulting from mandatory reporting legislation is discussed as well.     

How does speed change affect induced motion?

The nature of a recently reported effect of speed on induced motion was investigated. Wallach and Becklen (1983) had found that the extent of induced motion decreases linearly with increases in presentation speed. We found that this speed effect occurred only in induced motion and not under conditions in which configurational change, which is responsible for induced motion, operated veridically. It took place whether configurational change was in conflict with ocular pursuit or with image displacement, and seemed to consist in diminished effectiveness of configurational change when it competed with one of these subject-relative stimuli.     

Adaptation in motion perception: Alteration of induced motion

Prolonged exposure to a condition that causes induced motion was found to diminish this effect. The extent of a horizontal induced motion was measured by obtaining estimates of the direction of the apparent oblique path that resulted when a spot was visible on a horizontally moving pattern and was therefore in horizontal induced motion and, at the same time, moved vertically. Because the horizontal component of the perceived motion path represented the induced motion, the slope of the path measured the extent of the induced motion. After a 10-min exposure to induced motion, the apparent motion path was steeper; the mean change corresponded to a 15% smaller extent of the induced motion. Results were obtained that argue that this effect is not due to a diminished horizontal motion of the pattern but amounts to a smaller motion-inducing effect. The experiments were meant to support the view that the perceptual process that underlies induced motion is learned.