Reduction of the Zöllner illusion with motion of inducing figure

The magnitude of the Zöllner illusion was measured when the inducing lines moved rightward or leftward and were tracked by subjects. Motion of the inducing lines significantly reduced the magnitude of illusion, as in the Poggendorff illusion. Increasing velocity markedly increased the reduction, and, again, this effect was not significantly different from that obtained with the Poggendorff illusion. The current evidence seems to support the suggestion outlined earlier in relation to the Poggendorff illusion, that is, moving and stationary figures are processed by separate channels and, therefore, the interaction between them is reduced.     

Effects of orientation-selective adaptation on the Z?llner illusion

The model of inhibitory interaction between orientation detectors was examined by prolonged presentation of grating patterns (which was expected to induce orientation-selective adaptation) before measurement of the Z?llner illusion. Adaptation effects were measured under conditions which excluded intrusion by the tilt aftereffect. In experiment 1, illusion magnitude greatly decreased only when the orientation of the adapting grating was the same as that of the inducing lines, which confirmed the first prediction deduced from the model. There was no effect of adapting grating when it was oriented more than 20 degrees away from the inducing lines. In experiment 2, adaptation effects were selective not only to orientation but also to spatial frequency. In experiment 3 it was shown that illusion reduction was mediated neither by lowered apparent contrast of the inducing lines nor by retinal adaptation. The results are discussed with respect to the nature of adaptation and possible physiological correlates.     

Depth separation and the Ponzo illusion

The Ponzo illusion refers to an apparent change in length of objectively equal parallel lines induced by enclosure within an acute angle. The present study investigated this illusory change in stimulus extent as a function of the relative depth positions of the parallel lines and the inducing angle. To permit facile and unconfounded manipulation of apparent depth, the stimuli comprising the Ponzo configuration were stereoscopic contours formed from dynamic random-element stereograms. The main results were: (1) apparent depth separation exerted a strong influence on illusion magnitude; (2) this influence was asymmetrical in that illusion magnitude decreased when the inducing angle appeared in depth behind the parallel lines and increased when the inducing angle appeared in depth in front of the lines. These data are consistent with a general theory of space perception that assumes that information about depth position is processed prior to information about stimulus characteristics.     

Size contrast as a function of conceptual similarity between test and inducers

In four experiments, the effect of the semantic relationship between test and inducing stimuli on the magnitude of size contrast in an Ebbinghaus-type illusion was explored. In Experiments 1 and 2, the greatest illusion was found when test and inducing stimuli were identical in shape and differed only in size. Decreased size contrast was found when inducing stimuli were drawn from the same category as the test stimulus, but were not visually identical. Even less size contrast was found when inducing stimuli were from a near conceptual category, with the least effect when they were drawn from a completely different category. In Experiment 3, it was demonstrated that even if test and inducing stimuli are drawn with identical geometric elements, the size contrast illusion is greatly reduced if they represent apparently different conceptual categories (through the manipulation of orientation and perceptual set). In Experiment 4, any geometric or spatial confounds were ruled out. These results suggest that size contrast is strongly influenced by the conceptual similarity between test and inducing stimuli.     

Similarity of the perimeters in the Ebbinghaus illusion

Coren and Miller (1974) and Coren and Enns (1993) argued that the magnitude of the Ebbinghaus illusion is a function of the rated or conceptual similarity of the inducing objects to the test object. In three experiments, we examined the convergence between conceptual similarity and illusion magnitude. The first failed to find support for this parallel. Two further experiments yielded support for an alternative hypothesis that the magnitude of the Ebbinghaus illusion is a function of the similarity of the perimeters of the inducing object to the test object. The similarity of the centers had no effect. These results suggest that the information used to estimate size is computed earlier in the visual system than suggested by Coren and colleagues and apparently does not involve the use of conceptual information.     

Three elemental illusions determine the Zöllner illusion

We have discovered an apparent contraction illusion of acute angles in a special form of the Z?llner figure at the intersecting angles between 36 degrees and 83 degrees (i.e., a reversal of the Z?llner illusion). The necessary condition for this illusion is that inducing lines are long enough and the induced line (test line) is single. When an illusory line is used as the induced line, the magnitude of contraction increases. Short inducing lines give no illusion or a slight expansion of acute angles at the intersecting angle of 45 degrees. We have ascertained that the source of this expansion is the narrow region in the vicinity of the induced line, whereas the source of the contraction is much broader regions. Furthermore, we have discovered another expansion mechanism, which is generated by the symmetrical configuration of the standard Z?llner figure.     

Three elemental illusions determine theZöllner illusion

We have discovered an apparent contraction illusion of acute angles in a special form of the Zöllner figure at the intersecting angles between 36° and 83° (i.e., a reversal of the Zöllner illusion). The necessary condition for this illusion is that inducing lines are long enough and the induced Une (test line) is single. When an illusory line is usedas the induced line, the magnitude of contraction increases. Short inducing lines give no illusion or a slight expansion of acute angles at the intersecting angle of 45°. We have ascertained that the source of this expansion is the narrow region in the vicinity of the induced line, whereas the source of the contraction is much broader regions. Furthermore, we have discovered another expansion mechanism, which is generated by the symmetrical configuration of the standard Zöllner figure.     

Apparent equivalence between perception and imagery in the production of various visual illusions

The ability of high and low imagers (as assessed by the Vividness of Visual Imagery Questionnaire) to utilize imagery in the production of a visual illusion was examined in three experiments. In Experiment 1, subjects were to imagine noninducing elements oi the Ponzo figure. In Experiment 2, subjects were asked to imagine the inducing angle of the Ponzo figure. Subjects were requested to imagine the inducing diagonals of the Hering and Wundt figures in Experiment 3. Regardless of which figure was presented, high imagers consistently reported an illusion whether it was produced by real or imagined lines. Also, the imagery-produced illusion was equivalent in magnitude to the actual illusion (when all lines are physically present). Low imagers reported an illusion only when lines were physically present. These results were interpreted in terms of Finke’s (1980) equivalence theory.     

The effect of structure and degree of tilt on the tilted room illusion

The effect of structure and angle of tilt on the magnitude of the tilted-room illusion and its relationship to the illusion produced by a tilted-line field were examined in two experiments. In Experiment L, nine groups of 13 Ss were tested under three conditions of room tilt in the frontal plane (22.5, 45, and 67.5 deg) and under three conditions of structure (empty room, room with a back wall of stripes, and room with furniture). The results indicate that, while magnitude and direction of the illusion vary with degree of room tilt, structure increases the magnitude of the illusion only at a 45-deg room tilt. In Experiment 2, a field of lines was presented through a circular reduction tube to three groups of 13 Ss under three conditions of line tilt (22.5, 45, and 67.5 deg). An illusion occurred that was much smaller in magnitude and functionally different for the three tilt conditions when compared with the tilted-room illusion.     

The role of apparent depth and context in the perception of the Ponzo illusion

The role of apparent depth features and the proximity of the test lines to the adjacent contours in the actuation of the Ponzo illusion was examined. Six versions of the Ponzo figure were employed: a standard Ponzo figure and five modified figures in which the test lines varied in orientation (horizontal or vertical) and in location (inside or outside the converging contours). Both manipulations resulted in a significant decrease in the magnitude of the illusion in comparison to the standard Ponzo figure. The results suggest that the Ponzo illusion is significantly affected by contextual factors.     

The Relationship Between Visual Illusion and Aesthetic Preference – an Attempt to Unify Experimental Phenomenology and Empirical Aesthetics

Experimental phenomenology has demonstrated that perception is much richer than stimulus. As is seen in color perception, one and the same stimulus provides more than several modes of appearance or perceptual dimensions. Similarly, there are various perceptual dimensions in form perception. Even a simple geometrical figure inducing visual illusion gives not only perceptual impressions of size, shape, slant, depth, and orientation, but also affective or aesthetic impressions. The present study reviews our experimental phenomenological work on visual illusion and experimental aesthetics, and examines how aesthetic preference is influenced by stimulus factors determining visual illusions including anomalous surface and transparency as well as geometrical illusion. Along with line figures producing geometrical illusions, illusory surface figures inducing neon color spreading and transparency effects were used as test patterns. Participants made both of psychophysical judgments and of aesthetic judgments for the same test pattern. Both of geometrical illusions and aesthetic preferences were found to change similarly as a function of stimulus variables such as the number of filling lines and the size ratio of the inner and outer figural components. Also, following specific stimulus variables such as lightness contrast ratio and spatial interval between inducing figural elements (so called ``packmen''), strong effects of color spreading and transparency were accompanied with strong preferences. It seems that the paradigm to investigate aesthetic phenomena along with perceptual dimensions is useful to bridge the gap between experimental phenomenology and experimental aesthetics.     

Perception of the Ponzo illusion by rhesus monkeys, chimpanzees, and humans: Similarity and difference in the three primate species

In Experiment 1, 3 rhesus monkeys and 1 chimpanzee were tested for their susceptibility to the Ponzo illusion. The subjects were first trained to report the length of the target bar presented at the center of the computer display by touching either of the two choice locations designated as “long” or “short.” When inverted-V context lines were superimposed on the target bar, the subjects tended to report “long” more often as the apex of these upward-converging lines approached the target bar. The perception of the Ponzo illusion was thus demonstrated. In Experiment 2, the same 3 rhesus monkeys and 2 new chimpanzees were tested using two types of context lines that provided different strengths of linear perspective. The subjects showed a bias similar to that found in Experiment 1, but there was no difference in the magnitude of the bias between the two types of context in either species. This failed to support the classic account for the Ponzo illusion, the perspective theory, raised by Gregory (1963). In Experiment 3, the magnitude of the illusion was compared between the inverted-V context and the context consisting of short vertical lines having the same gap as the former in the same 3 rhesus monkeys and 2 of the chimpanzees from the preceding experiments. While the chimpanzees showed the illusion for both types of stimuli, the monkeys showed no illusion for the latter. In Experiment 4, 6 humans were tested in a comparable procedure. As in the nonhuman primates, the illusion was unaffected by the strength of linear perspective. On the other hand, the humans showed considerably larger illusion for the context consisting of vertical lines than for contexts consisting of converging lines. Thus, there was a great species difference in the effect of the gap itself on the magnitude of the Ponzo illusion. Similarity found at first turned out to be no more than superficial. Possible sources of this species difference are discussed.     

Displacement effects caused by converging lines and dots

Changes induced in orientation were examined under conditions of a dot or full-line version of a stimulus consisting of a test and inducing line. 44 subjects visually extended the test line to the surrounding circle on 11 trials and indicated their response by a mark on the circle. Magnitude of illusion was reduced by 54% for the dot version compared with the full-line form, but both produced an illusion significantly greater than zero. A significant practice effect was obtained with full lines but not with the dot form. Results are discussed in terms of lateral inhibition theory and related research.     

The tilt illusion: Length and luminance changes of induction line and third (disinhibiting) line

Direct effects (acute-angle expansion) and indirect effects (acute angle contraction) aspects of the tilt illusion were reduced by reductions in the length as well as the luminance of the induction line, and also by the addition of a third line to the display. When this third (disinhibiting) line was also reduced in length and luminance, the reduction in the illusion became less and the illusion increased in magnitude. The illusion size was also changed by increasing the orientation difference between the disinhibiting line and the induction line. It is argued that these effects are mediated by (lateral) inhibition and disinhibition between mechanisms responsible for orientation coding in the visual system.     

Two-dimensional tilt illusions induced by orthogonal plaid patterns: effects of plaid motion, orientation, spatial separation, and spatial frequency

Tilt illusions occur when a drifting vertical test grating is surrounded by a drifting plaid pattern composed of orthogonal moving gratings. The angular function of this illusion was measured as the plaid orientation (and therefore its drift direction) varied over a 180 degrees range. This was done when the test and inducing stimuli abutted and had the same spatial frequency, and when the test and inducing stimuli either differed in frequency by an octave, or were spatially separated by a 2 deg blank annulus, or both differed in frequency and were also separated by the annulus (experiments 1-4). The obtained angular function was virtually identical to that obtained previously with the rod and frame effect and other cases involving orthogonal inducing components, with evidence for illusions induced both by real-line components and by virtual axes of symmetry. Although the magnitude of the illusion was very similar in all four experiments, there was evidence to suggest that largest real-line effects occurred in the abutting same-frequency condition, with a pattern of results similar to that obtained previously with the simple one-dimensional tilt illusion. On the other hand, virtual-axis effects were more prominent with gaps between test and inducing stimuli. A fifth, repeated-measures, experiment confirmed this pattern of results. It is suggested that this pattern-induced tilt effect reflects both striate and extrastriate mechanisms and that the apparent influence of spatially distal virtual axes of symmetry upon perceived orientation implies the existence of AND-gate mechanisms, or conjunction detectors, in the orientation domain.     

Modal completion in the Poggendorff illusion: support for the depth-processing theory

The Poggendorff illusion is one of the most prominent geometrical-optical illusions and has attracted enduring interest for more than a hundred years. Most modern theories explain the illusion by postulating various kinds of distortion of the "test" component of the figure by the context or the inducing component. They make no reference to the importance of processes involved in three-dimensional scene perception for understanding the illusion. We measured the strength of the Poggendorff illusion in configurations containing solid inducing surfaces as opposed to the usual parallel lines. The surface, oblique-line, and background luminances were manipulated separately to create configurations consistent with modal completion of the obliques in front of the surface. The marked decrease in the size of the illusion in conditions favoring modal completion is consistent with claims that perceived spatial layout is a major determinant of the Poggendorff illusion.     

Planning to reach for an object changes how the reacher perceives it

Three experiments assessed the influence of the Ebbinghaus illusion on size judgments that preceded verbal, grasp, or touch responses. Prior studies have found reduced effects of the illusion for the grip-scaling component of grasping, and these findings are commonly interpreted as evidence that different visual systems are employed for perceptual judgment and visually guided action. In the current experiments, the magnitude of the illusion was reduced by comparable amounts for grasping and for judgments that preceded grasping (Experiment 1). A similar effect was obtained prior to reaching to touch the targets (Experiment 2). The effect on verbal responses was apparent even when participants were simply instructed that a target touch task would follow the verbal task. After participants had completed a grasping task, the reduction in the magnitude of the illusion remained for a subsequent verbal-response judgment task (Experiment 3). Overall, the studies demonstrate strong connections between action planning and perception.     

The influence of optical aberrations on the magnitude of the Poggendorff illusion

The amount of blurring of the retinal image can be reduced by proper selection of an artificial pupil and a chromatic filter. Reduction of the amount of blurring due to optical aberrations by viewing through a 1-mm artificial pupil and an interference filter in the eye, results in a concomitant reduction in the magnitude of the Poggendorff illusion. The magnitude of the reduction is smaller, however, than would be expected if the illusion was predominantly determined by blur due to optical aberration.     

Ponzo错觉解释的合理性：倾斜恒常性理论的局限

倾斜恒常性理论是一种新的解释Ponzo错觉的理论,但是似乎存在一些局限。本研究采用调节法通过两个实验考察了四种Ponzo错觉版本在各种条件(视角和水平线段间距)下的错觉量情况,以此来检验倾斜恒常性理论。实验一中,对称Ponzo错觉变异版本在50mm时的错觉量情况和Prinzmetal(2001)的结果相似,但是在85mm和120mm时得到了较多的错觉量,这和倾斜恒常性理论的理论预期不符。实验二对不对称Ponzo错觉的考察得到了和实验一类似的结果,只有50mm时的情形符合倾斜恒常性理论预期。通过以上实验得到水平线间距和视角因素都是产生Ponzo错觉的重要因素,而倾斜恒常性理论过分强调了背景线的倾斜诱导效应,忽略了其他结构因素对Ponzo错觉的影响,所以倾斜恒常性理论具有一定的局限性,不能有效地解释Ponzo错觉的产生机制。     

Spatial factors of brightness illusion in the Ehrenstein figure

The strength of brightness illusion in an Ehrenstein figure has been examined as a function of two variables--inducing line length and gap size--by a two-alternative forced-choice procedure. The results show an interaction between the two variables; the length of the inducers and gap size are both involved in the formation of the brightness illusion, with gap size as the stronger factor. A spatial limit (corresponding to a gap size of 2.4 deg) was found, below which the illusion is always present regardless of the length of the inducers. An area ratio, defined as the ratio of the area of the ring formed by the four inducing lines of an Ehrenstein figure to the area of the illusory surface, takes into account the different spatial factors studied in the experiment and the global size of the Ehrenstein figure. The strength of the illusion was found to increase linearly with increasing values of the area ratio.