The occlusion illusion: partial modal completion or apparent distance?

In the occlusion illusion, the visible portion of a partly occluded object (eg a semicircle partly hidden behind a rectangle) appears to be significantly larger than a physically identical region that is fully visible. This illusion may occur either because the visual system 'fills in' a thin strip along the occluded border (the partial-modal-completion hypothesis) or because the partly occluded object is perceived as farther away (the apparent-distance hypothesis). We measured the magnitude of the occlusion illusion psychophysically in several experiments to investigate its causes. The results of experiments 1-3 are consistent with the general proposal that the magnitude of the illusion varies with the strength of the evidence for occlusion, supporting the inference that it is due to occlusion. Experiment 4 provides a critical test between apparent-distance and partial-modal-completion explanations by determining whether the increase in apparent size of the occluded region results from a change in its perceived shape (due to the modal extension of the occluded shape along the occluding edge, as predicted by the partial-modal-completion hypothesis) or from a change in its perceived overall size (as predicted by the apparent-distance hypothesis). The results more strongly support the partial-modal-completion hypothesis.     

The octave illusion revisited: suppression or fusion between ears?

The octave illusion occurs when each ear receives a sequence of tones alternating by 1 octave but with the high and low tones in different ears. Most listeners perceive these stimuli as a high pitch in one ear alternating with a low pitch in the other ear. D. Deutsch and P. L. Roll (1976) interpreted this phenomenon as evidence for a what-where division of auditory processing caused by sequential interactions between the tones. They argued that the pitch follows the frequency presented to the dominant ear but is lateralized toward the higher frequency component. This model was examined in 4 experiments. Results indicate that the perceived pitch approximates the fundamental frequency and that the illusion does not depend on sequential interactions. The octave illusion may arise from an interaction between dichotic fusion and binaural diplacusis rather than from suppression as proposed by Deutsch.     

The spacing illusion: a spatial aperture problem?

A geometrical illusion in which the horizontal spacing between adjacent parallel lines in a row is underestimated when the lines are tilted away from vertical in a chevron configuration was investigated in two experiments. The perceived spacing was found to decrease as the tilt angle increased, consistent with the idea that separation judgements are influenced by the normal spacing between lines ie at right angles to the line orientation. It is proposed that this illusion reveals an analogue in spatial perception to the well-known aperture problem in motion perception. In establishing the separation of nearby or overlapping shapes in an image, the visual system cannot only rely upon the normal separation of contours belonging to each shape (as would be visible through small spatial apertures or receptive fields), since this varies with contour orientation. The system is therefore faced with a spatial aperture problem. The spacing illusion may arise because information usually available to solve the problem is absent in the illusion figure, or it may reflect a bias in favour of the orthogonal, which is adopted in the face of the ambiguity.     

The hollow-face illusion: object-specific knowledge, general assumptions or properties of the stimulus?

The hollow-face illusion, in which a mask appears as a convex face, is a powerful example of binocular depth inversion occurring with a real object under a wide range of viewing conditions. Explanations of the illusion are reviewed and six experiments reported. In experiment 1 the detrimental effect of figural inversion, evidence for the importance of familiarity, was found for other oriented objects. The inversion effect held for masks lit from the side (experiment 2). The illusion was stronger for a mask rotated by 90 degrees lit from its forehead than from its chin, suggesting that familiar patterns of shading enhance the illusion (experiment 2). There were no effects of light source visibility or any left/right asymmetry (experiment 3). In experiments 4-6 we used a 'virtual' hollow face, with illusion strength quantified by the proportion of noise texture needed to eliminate the illusion. Adding characteristic surface colour enhanced the illusion, consistent with the familiar face pigmentation outweighing additional bottom-up cues (experiment 4). There was no difference between perspective and orthographic projection. Photographic negation reduced, but did not eliminate, the illusion, suggesting shading is important but not essential (experiment 5). Absolute depth was not critical, although a shallower mask was given less extreme convexity ratings (experiment 6). We argue that the illusion arises owing to a convexity preference when the raw data have ambiguous interpretations. However, using a familiar object with typical orientation, shading, and pigmentation greatly enhances the effect.     

Wagon-wheel illusion under steady illumination: real or illusory?

Wheels turning in the movies sometimes appear to rotate backwards. This is called the wagon-wheel illusion (WWI). The mechanism of this illusion is based on the intermittent nature of light in films and other stroboscopic presentations, which renders them as a series of snapshots rather than a continuous visual data stream. However, there have been claims that this illusion is seen even in continuous light, which would suggest that the visual system itself may sample a continuous visual data stream. We examined the rate of this putative sampling and its variations across individuals while in different psychological states. We obtained two results: (i) WWI occurred in stroboscopic lights as expected, (ii) WWI was never reported by our subjects under continuous lights, such as sunlight and lamps with DC power source. Thus, WWI cannot be taken as evidence for discreteness of conscious visual perception.     

“Octave illusion” or “Deutsch’s illusion”?

The “Deutsch’s illusion” occurs in most people when a dichotic pair of tones spaced an octave apart is presented repeatedly in alternation, so that when the right ear receives the high tone, the left ear receives the low tone, and vice versa. The illusory percept consists typically in a single low tone heard at one ear alternating with a single high tone heard at the other ear. Here, we investigate whether the frequency interval between the tones and their duration play a role in the perception of the illusion. By testing 74 subjects we demonstrate that the illusion is not confined to tones spaced an octave apart but it is perceivable also with tones separated by a major seventh, a minor ninth, a major ninth, and a minor tenth. Regarding duration, the present results show that the illusion is stronger with tones lasting 500 than 200 ms. The present results suggest that the perceptual mechanisms at the basis of the illusion are not strictly linked to the frequency relationships between the dichotic tones.     

Horizontal-vertical illusion: continuous decrement or the deviant first guess?

Numerous studies have reported that repetitive or extensive inspection leads to short-term decrement of the horizontal-vertical illusion. The present experiment explored whether this decrement reflects a gradual decline, as previously assumed, or is better described as a singular drop-off beyond the initial evaluation. 111 student participants adjusted vertical or horizontal lines such that they appeared equally long with a perpendicular standard. There were 8 successive adjustment trials for each subject. The results suggest that a substantial component of the illusion depends on the first impression assessment. The earlier anatomical and cognitive theories of the horizontal-vertical illusion cannot incorporate this datum. However, recent findings suggest that a motor theory of illusion might accommodate the observed one-step decrement in the illusion.     

Curved movement paths and the Hering illusion: Positions or directions?

When trying to move in a straight line to a target, participants produce movement paths that are slightly (but systematically) curved. Is this because perceived space is curved, or because the direction to the target is systematically misjudged? We used a simple model to investigate whether continuous use of an incorrect judgement of the direction to the target could explain the curvature. The model predicted the asymmetries that were found experimentally when moving across a background of radiating lines (the Hering illusion). The magnitude of the curvature in participants' movements was correlated with their sensitivity to the illusion when judging a moving dot's path, but not with their sensitivity when judging the straightness of a line. We conclude that a misjudgement of direction causes participants to perceive a straight path of a moving dot as curved and to produce curved movement paths.     

The moon illusion: I. How high is the sky?

The most common explanations of the moon illusion assume that the moon is seen at a specific distance in the sky, which is perceived as a definite surface. A decrease in the apparent distance to the sky with increasing elevation presumably leads to a corresponding decrease in apparent size. In Experiment 1 observers (N = 24) gave magnitude estimates of the distance to the night sky at different elevations. The results did not support the flattened-dome hypothesis. In Experiment 2 observers (N = 20) gave magnitude estimates of the distance to the sky at points around a 360 degrees circle just above the horizon. The results were consistent with those of Experiment 1, and in addition, estimates were highly correlated with the physical distances of buildings at the horizon. In a third, control experiment, observers (N = 20) gave magnitude estimates of the distances of buildings at the horizon. A power function fit the relation between estimated and physical distance (exponent = 1.17) as well as the relation between estimates of the sky points above the buildings (Experiment 2) and estimates of building distances (exponent = .46). Taken together, the results disconfirm all theories that attribute the moon illusion to a "sky illusion" of the sort exemplified by the flattened-dome hypothesis.     

The Animus: Help or Hindrance?

The “masculine” side of the woman’s psyche is seen as carrying two kinds of energy: drive, aggressiveness, and self-assertion as well as objectivity, consciousness, and concern with meaning and spiritual values. The need for (and problems with) becoming aware of these basic energies are discussed, using many contemporary examples.     

The fundamental: Ungrounded or all-grounding?

Philosophical Studies - Fundamentality plays a pivotal role in discussions of ontology, supervenience, and possibility, and other key topics in metaphysics. However, there are two...     

The illusion of mental health: in the mind of which beholder?

We reference self-ratings and clinician ratings of childhood anxious symptoms to a third data source well delineated with regard to the pathophysiology of anxiety. A total of 36 children with anxiety disorders and other children were administered yohimbine, an alpha-sub-2-adrenoreceptor antagonist, in response to which anxiety-prone children have blunted output of growth hormone. We assessed neuroendocrine reactions. In general, participants who claimed anxiety that was unconfirmed by clinicians displayed anxiotypic neuroendocrine profiles, whereas those who denied anxiety detected by clinicians did not, suggesting self-report may have had the advantage over clinician ratings in some instances. Nuanced and contextualized conclusions in this area of work are needed. In response to the question "the illusion of mental health: in the mind of which beholder?," we answer "it depends on the sample and the syndrome under study."     

A new temporal illusion or the TOE once again?

Recently, Nakajima, ten Hoopen, and van der Wilk (1991) and Nakajima, ten Hoopen, Hilkhuysen, and Sasaki (1992) described what they believed to be a new illusion of auditory time perception. They reported that the perceived duration of a temporal interval was influenced by an immediately preceding or succeeding temporal interval The influence of a neighboring temporal interval on perceived duration is not a new illusion, however, but is another demonstration of the time-order error     

The number–weight illusion

Psychonomic Bulletin & Review - When objects are manually lifted to compare their weight, then smaller objects are judged to be heavier than larger objects of the same physical weights: the...     

The osteopathic distinction: Fact or fancy?

Since osteopathic medicine's inception its distinction has been proclaimed steadfastly in the osteopathic literature. The uniqueness has been claimed to reside in: (1) rigid adherence to A.T. Still's tenets; (2) osteopathic manipulative treatment (OMT); (3) claims of “holism”; (4) “osteopathic principles”, (5) esoteric definitions; and (6) other suggested differences. None of these claims can be successfully defended. An aspect of the osteopathic distinction may lie in the didactic of OMTper se. Certain experiences in medical school contribute to the “reconstruction” of the student's view of the patient. Touch, through OMT, may be a quality that affects this change and helps make the osteopathic physician different. When blended with traditional medical modalities thismay result in a unique medical perspective. The ideal approach for the osteopathic profession would be an honest evaluation of its function in society and its uniqueness in medicine. The profession may discover a uniqueness withtouch as an integral part.     

The verbal label: Mediator or classifier?

Three experiments on the role of verbal labels and perceptual cues in concept attainment are reported. Ss were kindergarten and second-grade upper-middle-class children. The results indicated that when Ss learned to associate two labels (or two perceptual cues) with each stimulus no positive transfer resulted, despite the fact that one of the labels (or cues) was relevant to solution. When one label only (or one perceptual cue) was associated with each stimulus, substantial positive transfer was observed. The effects of verbal labeling and perceptual cuing were identical.On the basis of these finding the authors reject the hypothesis that labels give rise to representational responses which act as mediators, and instead propose a new hypothesis, that labels and perceptual cues facilitate performance because they facilitate the division of the stimulus set into subsets which are correlated with the response systems the subjects are expected to learn.     

The laterality effect: myth or truth?

Tzelgov and colleagues [Tzelgov, J., Meyer, J., and Henik, A. (1992). Automatic and intentional processing of numerical information. Journal of Experimental Psychology: Learning, Memory and Cognition, 18, 166-179.], offered the existence of the laterality effect as a post-hoc explanation for their results. According to this effect, numbers are classified automatically as small/large versus a standard point under autonomous processing of numerical information. However, the genuinity of the laterality effect was never examined, or was confounded with the numerical distance effect. In the current study, I controlled the numerical distance effect and observed that the laterality effect does exist, and affects the processing of automatic numerical information. The current results suggest that the laterality effect should be taken into account when using paradigms that require automatic numerical processing such as Stroop-like or priming tasks.     

The near-death experience: Private or public?

This editorial contrasts the private, personal near-death experience with the public concept of the experience, and finds important messages for humanity that are common to both.