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PubMed1988

Relation of mobility-fixity to the interpretation of pictorial stimuli.

A group of 61 students who had previously (in 1986) been classified by Hansson, Rydén, and Johnsson in terms of perceptual fixity-mobility using a "free" Rod-and-Frame Test, were investigated regarding their interpretations of a nonfigurative stimulus shown repetitively at short exposure-times, and their characterization of two pictures each portraying two soldiers in intensive interaction--one man apparently attacking the other in the first picture and apparently rescuing or taking care of the other man in the second. Mobile subjects on the free Rod-and-Frame Test reported a larger number of different interpretations of the nonfigurative stimulus and construed it more frequently in terms of human themes than did the fixed subjects; in rating the pictures of soldiers, they used more extreme and complex characteristics. It appeared that, when confronted with ambiguous stimuli, the mobile individual moves both "horizontally", as it were, along the surface of objective reality, and "vertically", from present to past realities, thus conjoining subjective-emotional and objective-analytic aspects of perception. This interpretation agrees with Werner's model of mobility-fixity which implies that the mobile individual operates on different developmental levels of perceptual functioning.

Attention↗
PubMed1992

Rectangles may appear to reverse like trapezia when they rotate at an uneven rate.

A 1983-1985 theory by Mitchell and Power predicts that, when rotating rectangles undergo certain kinds of speed fluctuation, they should appear to reverse just as trapezia do. The prediction is partially confirmed. One of two 'mimic' rectangles underwent apparent reversals more often than a control rectangle undergoing even rotation and in the same places as rotating trapezia. However, its reversal frequency was less than those of the trapezia, and a second 'mimic' slowed an inappropriate distribution of reversals round the cycle. These anomalies call for some modification to Mitchell and Power's theory, but minor qualifications may be sufficient.

Adult↗
PubMed1994

Apparent depth threshold for the Benussi effect.

Using the single staircase psychophysical method, the apparent depth threshold for the Benussi effect was determined for 5 observers. The threshold occurred at an eccentricity of 2r/3, where r equals the radius of the larger circle expressed in millimeters.

Depth Perception↗
PubMed1995

A size illusion from simultaneous changes in length and direction of a line pattern.

A circle was attached to one of three lines which were changing in length and direction simultaneously. This configuration of moving lines had been found previously to induce the perception of depth. Of 26 observers 20 reported that the moving circle appeared smaller in size than a physically equal stationary circle which was located outside the changing, depth-inducing configuration.

Depth Perception↗
PubMed1999

Representational momentum in children: dynamic information and analogue representation.

Two groups of children and a control group of adults completed a visual memory task previously shown to produce representational momentum in adults. In the task, a computer-animated target was shown moving either horizontally or vertically, and the target vanished without warning. After the target vanished, observers indicated the location at which it had vanished. Both children and adults exhibited representational momentum, i.e., indicated locations slightly beyond where the target actually disappeared, and the magnitude of representational momentum was larger for younger children than adults. Implications of the results for issues of sensitivity to dynamics and for reliance on analogue representation are discussed.

Adult↗
PubMed2001

Time course of amodal completion revealed by a shape discrimination task.

We measured the extent of amodal completion as a function of stimulus duration over the range of 15-210 msec, for both moving and stationary stimuli. Completion was assessed using a performance-based measure; a shape discrimination task that is easy if the stimulus is amodally completed and difficult if it is not. Specifically, participants judged whether an upright rectangle was longer horizontally or vertically, when the rectangle was unoccluded, occluded at its corners by four negative-contrast squares, or occluded at its corners by four zero-contrast squares. In the zero-contrast condition, amodal completion did not occur because there were no occlusion cues; in the unoccluded condition, the entire figure was present. Thus, comparing performance in the negative-contrast condition to these two extremes provided a quantitative measure of amodal completion. This measure revealed a rapid but measurable time course for amodal completion. Moving and stationary stimuli took the same amount of time to be completed (approximately 75 msec), but moving stimuli had slightly stronger completion at long durations.

Discrimination Learning↗
PubMed2004

Geometrical haptic illusions: the role of exploration in the Müller-Lyer, vertical-horizontal, and Delboeuf illusions.

This article surveys studies of the occurrence, in the haptic modality, of three geometrical illusions well known in vision, and it discusses the nature of the processes underlying these haptic illusions. We argue that the apparently contradictory results found in the literature concerning them may be explained, at least partially, by the characteristics of manual exploratory movements. The Müller-Lyer illusion is present in vision and in haptics and seems to be the result of similar processes in the two modalities. The vertical-horizontal illusion also exists in vision and haptics but is due partly to similar processes (bisection) and partly to processes specific to each modality (anisotropy of the visual field and overestimation of radial vs. tangential manual exploratory movements). The Delboeuf illusion seems to occur only in vision, probably because exploration by the index finger may exclude the misleading context from tactile perception. The role of these haptic exploratory movements may explain why haptics is as sensitive as vision to certain illusions and less sensitive to others.

Form Perception↗