Contrast and assimilation in the Baldwin illusion

Four experiments were conducted to investigate the role of "large" squares on the occurrence of assimilation and contrast in the Baldwin illusion. In Exps. 1 and 2, in which subjects reproduced the length of the test line, large squares induced illusions of assimilation. In Exp. 3, reproduction of the entire length of the test line also resulted in illusions of assimilation but bisection of the test line and reproduction of one-half the length of the test line resulted in contrast. Exp. 4 replicated the findings involving judgments of one-half the length of the test line. Over-all, the results indicate that judgments of one-half the length of the test line result in contrast, whereas judgments of the entire extent result in assimilation.     

Auditory illusion analogous to the Baldwin figure in vision

An auditory illusion was demonstrated in which there was perceptual shortening of the temporal interval contiguous to a low frequency (large) tone and/or perceptual lengthening of the temporal interval contiguous to a high frequency (small) tone. This auditory analogy to the Baldwin figure was demonstrated after first determining that there was a symmetrical expansion of perceived time during the auditory filled-duration illusion.     

Lack of sex differences on the Stroop Color-Word Test across three age groups

The present study investigated recent reports of sex differences on the Stroop Color-Word Test by age. Present results indicate no sex differences at 7-8 years, 9-10 years, and 18-24 years. The two school-age samples reported similar amounts of interference and significantly more than the college-age sample. Inconsistencies in the literature may be a function of response modality rather than interference.     

The effects of location,orientation, and cumulation of boxes in the Baldwin illusion

Three experiments were conducted on variants of the Baldwin illusion. Experiment 1 showed that placing a box on each side of the standard line produced a larger illusion than placing both boxes on the same side of the line. These results failed to support the assimilation theory proposed by Brigell, Uhlarik, and Goldhorn (1977). In Experiment 2, the side of a rectangular box was varied when that side was either parallel or perpendicular to the standard line. The parallel rectangle produced a function that was similar to the one found with the classical Baldwin figure, but the perpendicular boxes produced a monotonically decreasing function with a reversal of illusion evident at the large sizes. The latter function did not support any version of the assimilation theory. The findings of Experiment 3 replicated previous findings that showed that cumulating contours as box size increased had no effect on the illusion. These findings explain two longstanding puzzles about the Müller-Lyer illusion: why a multifinned form is not the sum of its single-finned parts and why the shrinkage form produces a smaller effect than does the expansion form.     

Lack of evidence for a tactual Poggendorff illusion

Lucca, Dellantonio, and Riggio (1986) reported large distortions in a tactual analogue of the visual Poggendorff illusion. They also reported large effects in the direction opposite to the visual illusion, which they termed "inversions." However, their evidence for such effects is questionable; they used what we consider to be inappropriate measurement and analysis procedures. In attempting to replicate their experiment, and in conducting four additional experiments, we found no evidence at all for their alleged tactual analogue of the visual Poggendorff effect. Instead, we demonstrated that "inversions" are likely due to the use of a raised stimulus display that causes artifactual mistracking, which is totally unrelated to normal mechanisms of alignment judgment. We also discuss the possible role of intersensory factors in the generation of tactual illusions.     

Sex differences in susceptibility to the Poggendorff illusion

This study presents experimental results indicating that there are sex differences in the susceptibility to a geometric optical illusion. Participants (57 male and 39 female undergraduate students) performed 3 trials on a test involving the Poggendorff illusion. Analysis indicated that the magnitude of the illusion diminished significantly with each trial and that the percent perceived error was significantly larger for women than for men. This finding is consistent with the numerous studies which have indicated better visuospatial abilities for men than for women.     

Cultural and learning differences in the Judd illusion

In the present study, we examined whether individual differences in the perception of illusory Judd drawings point to variability in the pickup of informational variables. Two sources for these individual differences were addressed: culture and learning. East Asian (n = 24) and Western (n = 24) participants made perceptual judgments of the midpoint of the shaft of various Judd figures in a pretest–practice–posttest design. During practice, half of the participants received feedback about the actual midpoint after each trial, while the other half did not receive feedback. The results showed differences among perceivers of different cultures in judging the midpoints of the shafts of Judd figures, particularly with respect to their propensity to improve perceptual accuracy after repeated practice and feedback. For most participants, changes in illusory bias as a consequence of learning were shown to reflect either a change in what informational variable they exploited or a rescaling or calibration of the perception to the informational variable. However, the individual differences in illusory bias related to culture could not be unequivocally attributed to either of these perceptual-learning processes.     

Visual field differences in the magnitude of the Oppel-Kundt illusion vary with processing time

Three experiments were performed to investigate hemispheric differences in susceptibility to the Oppel-Kundt illusion presented tachistoscopically to the two visual hemifields. Experiment 1 used a successive comparison mode, in which 16 undergraduate students indicated whether the second of two successive extents looked shorter or longer than the first. Experiment 2 (20 under-graduates) and Experiment 3 (1 commissurotomy patient) required judgments of two extents presented simultaneously. The first experiment found no significant visual field differences, although females were more susceptible than males. In the second experiment, the illusion magnitude was greater in the left visual field, and in the third experiment, it was greater in the right visual field. Post hoc analyses resolve the conflicting results and show that in all three experiments, the susceptibility of the right hemisphere declined more than that of the left hemisphere during illusion processing. An interpretation is offered in terms of two parallel processes, one that is fast, uses feature extraction, and is performed more effectively in the left hemisphere, and one that is slow, uses visuospatial analysis to compute distances between parts of the illusion figure, and is performed more effectively in the right hemisphere.     

Sex differences in the Poggendorff illusion: identifying the locus of the effect

Extensive research has identified individual differences associated with sex in a range of visual task performances, including susceptibility to visual illusions. The aim of this study was to identify the locus of sex differences within the context of the Poggendorf illusion. 79 women and 79 men participated within a mixed factorial design. Analyses indicated that sex differences were only present in the stimulus context with the full inducing element present. This finding replicates recent research and provides qualifying evidence as to the locus of the effect. The findings are discussed within the functional framework of perceptual processes involved in extrapolating 3-dimensional characteristics from 2-dimensional visual stimuli.     

The geometric illusion and induced differences in perceived time

Just as circle-size induces differences in the perceived extent of a line which interconnects the circles of the Baldwin illusion, it is demonstrated that circle-size induces differences in the perceived duration of a time interval which intervenes between circles of different sizes.     

How the Thatcher illusion reveals evolutionary differences in the face processing of primates

Face recognition in humans is a complex cognitive skill that requires sensitivity to unique configurations of eyes, mouth, and other facial features. The Thatcher illusion has been used to demonstrate the importance of orientation when processing configural information within faces. Transforming an upright face so that the eyes and mouth are inverted renders the face grotesque; however, when this “Thatcherized” face is inverted, the effect disappears. Due to the use of primate models in social cognition research, it is important to determine the extent to which specialized cognitive functions like face processing occur across species. To date, the Thatcher illusion has been explored in only a few species with mixed results. Here, we used computerized tasks to examine whether nonhuman primates perceive the Thatcher illusion. Chimpanzees and rhesus monkeys were required to discriminate between Thatcherized and unaltered faces presented upright and inverted. Our results confirm that chimpanzees perceived the Thatcher illusion, but rhesus monkeys did not, suggesting species differences in the importance of configural information in face processing. Three further experiments were conducted to understand why our results differed from previously published accounts of the Thatcher illusion in rhesus monkeys.     

Local and global visual mechanisms underlying individual differences in the rod-and-frame illusion

The role of local and global visual mechanisms in individual differences in the rod-and-frame (RF) effect was investigated. Field-dependent and field-independent observers, selected on the basis of Witkin and Asch’s (1948) classical procedure, were submitted to the small RF test (Coren & Hoy, 1986). Four frame tilts and two gap sizes were used. As expected, direct effects (i.e., rod settings in the direction of frame tilt) were observed at small degrees of frame tilt, while indirect effects (i.e., rod settings in the direction opposite that of frame tilt) were observed at larger frame tilts. Fielddependent observers showed larger direct effects in the case of the small gap. Indirect effects were comparable in both field-dependent and field-independent subjects, regardless of gap size. Following the model proposed by Wenderoth and Johnstone (1987), these findings indicate that low-level visual mechanisms, responsible for local orientation interactions, have a different gain in fielddependent and field-independent individuals. In contrast, global visual mechanisms, presumably acting     

Individual differences in the rubber-hand illusion: Predicting self-reports of people's personal experiences

Can we assess individual differences in the extent to which a person perceives the rubber-hand illusion on the basis of self-reported experiences? In this research, we develop such an instrument using Rasch-type models. In our conception, incorporating an object (e.g., a rubber hand) into one's body image requires various sensorimotor and cognitive processes. The extent to which people can meet these requirements thus determines how intensely people experience and, simultaneously, describe the illusion. As a consequence, individual differences in people's susceptibility to the rubber-hand illusion can be determined by inspecting reports of their personal experiences. The proposed model turned out to be functional in its capability to predict self-reports of people's experiences and to reliably assess individual differences in susceptibility to the illusion. Regarding validity, we found a small, but significant, correlation between individual susceptibility and proprioceptive drift. Additionally, we found that asynchrony, and tapping rather than stroking the fingers constrain the experience of the illusion.     

The influence of age, sex, and specialized training on the vertical-horizontal illusion

With the aim of investigating the perceptual processes responsible for perceptual illusions, we have studied the influence of age, sex and specialized training on two forms of the vertical-horizontal illusion. In Figure A, the vertical is a short distance away from the horizontal; in Figure B, the vertical meets the horizontal segment at its mid-point. Both figures were presented in brief (0-2 second) and long (I-o second) tachistoscopic exposure, and in unlimited exposure.

When time is unlimited. Illusion A increases up to 9-10 years and then remains constant and Illusion B decreases as a function of age and chiefly as a function of the degree of scientific training. The illusions are stronger in tachistoscopic perception than under conditions of umlimited exposure. Both illusions also increase in tachistoscopic perception with age except for science students. Under condition of unlimited time, women have stronger illusions than men. This difference does not occur in tachistoscopic perception.

These results may be interpreted in terms of the interaction of three processes: interaction among the elements of a figure (field effects); perceptual activity which makes possible the passing from syncretism or multiplicity to organized perception; and the activity of measuring the elements relatively to each other. This latter activity develops with cultural level and especially with scientific training. It is more effective with men than with women, due, it is suggested, to the spatial factor being higher in men.