Ebbinghaus illusion: effect of figural similarity upon magnitude of illusion when context elements are equal in perceived size.

The magnitude of the Ebbinghaus illusion has been reported to be greater when test element and context elements are figurally similar as opposed to figurally dissimilar. In the current investigation with 16 observers, illusion magnitude was greater for a figurally similar configuration even though the context elements of the figurally similar configuration were perceived as smaller than the context elements of a figurally dissimilar configuration. Hence, figural similarity appears to have a prepotent effect in the Ebbinghaus illusion.

Benussi effect as an integration of disparity by motion.

It was hypothesized that the apparent depth of the Benussi effect could be elicited using stimuli corresponding to retinally disparate images. When such stimuli were presented rapidly and successively in a manner approximating apparent motion, 21 of 22 observers reported apparent depth.

The Benussi effect with rectangles?

The perceived depth of the Benussi effect is usually demonstrated by presenting a configuration of nonconcentric circles on a rotating disc. However, in the current investigation with 21 undergraduates the Benussi effect was elicited by presenting an eccentric configuration of rectangles. Depth was reported when the configuration of eccentric rectangles was alternated rapidly and successively with its mirror image. As is characteristic of the Benussi effect, there was an increase in apparent depth with an increase in the eccentricity of the rectangles.

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.

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.

Motion parallax, relative size, and Benussi effect.

Many observers perceive depth when a configuration of nonconcentric circles is rotated on a disc. While it has been suggested by a number of investigators that motion parallax has a role in generating this phenomenon, the supporting data are equivocal. The current study proposed that the ambiguity regarding the role of motion parallax may have arisen because there are contradictions between relative size cues and motion parallax cues in the configuration of rotating circles. However, with 17 undergraduate observers, apparent depth was no more reliably reported with consistent cues of motion parallax and relative size than when these cues were contradictory.

Is the Benussi effect a kinetic depth effect?

Rapid, successive presentations of an eccentric circle pattern and its mirror-image elicited apparent depth and, as has been previously demonstrated for the Benussi effect, there was an increase in apparent depth with an increase in circle eccentricity. Taken together, these data were interpreted as contravening Wallach, Adams, and Weisz's account of the Benussi effect as an instance of the kinetic depth effect.

Attenuating Necker cube depth reversals.

Rapid, apparent, to-and-fro (right-left) rotation of the Necker cube sharply reduced reversals in depth for 10 undergraduates. This finding was considered consistent with the satiation theory of Necker cube reversals.

Blackness enhancement.

Since apparent brightness increases as an intermittent luminous source decreases from flicker fusion to approximately 10 cps, the phenomenal blackness induced by an intermittent annulus should also increase as a result of brightness contrast. However, data from 5 observers showed the phenomenal blackness occurring with a 10-cps inducer was greater than that expected on the basis of brightness contrast.