A simple but powerful theory of the moon illusion

Modification of Restle's theory (1970) explains the moon illusion and related phenomena on the basis of three principles: (1) The apparent sizes of objects are their perceived visual angles. (2) The apparent size of the moon is determined by the ratio of the angular extent of the moon relative to the extents subtended by objects composing the surrounding context, such as the sky and things on the ground. (3) The visual extents subtended by common objects of a constant physical size decrease systematically with increasing distance from the observer. Further development of this theory requires specification of both the components of the surrounding context and their relative importance in determining the apparent size and distance of the moon.     

The parallel-less Poggendorff: Virtual contours put the illusion down but not out

Four versions of Poggendorff displays were compared: (1) the conventional display of a transversal interrupted by parallel lines, (2) a transversals-only display, (3) a virtual-contour display where the parallels were suggested (but not drawn) via “good continuation” and “c1osure, ” and (4) the profile display, a degraded version of the virtual-contour display that retained many of its borders but did not suggest parallels. Each display was drawn with transversal tilted at 45 and 51 deg from vertical. All displays produced significant illusions at both tilts. By comparison with the illusion magnitudes of the conventional display, the effects for the other displays were small. The outcome supports the existence of two salient illusion-producing factors: the necessity for actual contours to form the subtended angle and assimilation of the transversal toward O’s horizontal.     

Area-specific attentional effect in the Delboeuf illusion

In the Delboeuf illusion, a circle judged initially has a weaker effect of size induction than a circle judged subsequently (the judgment-order effect). This effect has been attributed to differential allocation of visual attention (Hamada et al, 2002 Japanese Journal of Psychology 73 58 - 63, in Japanese). To establish the influence of attention, in experiment 1 we examined whether the effect occurred mandatorily once the outer circle was attended to, or whether it was necessary to direct attention specifically to the size of the area of the outer circle. Observers trisected the circumference of the outer circle thus attending to the outer circle in terms of its circumference, but ignoring its area. The illusion was stronger when the inner-circle area estimation was followed by the outer-circle area estimation than when the inner-circle area estimation was followed by the trisection task. In experiment 2 this result was replicated by using diameter judgment, instead of the size of the area. These findings indicate that mere allocation of attention to the outer circle contour is not sufficient to produce the judgment-order effect. Rather, attention must be specific to the task-relevant dimension, in this instance the visual area, to be effective.     

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.     

You don't know me, but I know you: the illusion of asymmetric insight

People, it is hypothesized, show an asymmetry in assessing their own interpersonal and intrapersonal knowledge relative to that of their peers. Six studies suggested that people perceive their knowledge of their peers to surpass their peers' knowledge of them. Several of the studies explored sources of this perceived asymmetry, especially the conviction that while observable behaviors (e.g., interpersonal revelations or idiosyncratic word completions) are more revealing of others than self, private thoughts and feelings are more revealing of self than others. Study 2 also found that college roommates believe they know themselves better than their peers know themselves. Study 6 showed that group members display a similar bias-they believe their groups know and understand relevant out-groups better than vice versa. The relevance of such illusions of asymmetric insight for interpersonal interaction and our understanding of "naive realism" is discussed.     

The solitaire illusion: An illusion of numerosity

A new illusion in which the apparent number of elements of two kinds is determined by their spatial arrangement is described. The illusion is such that one large cluster appears to contain more elements than several small clusters, clustering being determined by Gestalt principles. The illusion was found both in adults and in children of 8 years.     

The oblique line illusion: The poggendorff effect without parallels

The apparent misalignment of two oblique collinear lines was investigated in two experiments. In the first the effect with the lines at 45° to the median plane was compared with that for the same two lines separated by the conventional parallels of the Poggendorff figure. The illusion with the two lines was consistent and significant but about one-third the magnitude of that with the parallels. The two illusions were significantly correlated. In the second experiment the angle of the two oblique, collinear lines was varied in 15° steps. The misalignment illusion was maximal at 45° and smaller but significant at 60 and 75°. There was no significant effect at 15 and 30°.     

Emotional enhancement effect of memory: removing the influence of cognitive factors

According to the modulation hypothesis, arousal is the crucial factor in the emotional enhancement of memory (EEM). However, the multifactor theory of the EEM recently proposed that cognitive characteristics of emotional stimuli, e.g., relatedness and distinctiveness, also play an important role. The current study aimed to investigate the individual contribution of arousal to the neural correlates of the EEM by controlling for these additional cognitive factors. We observed the characteristic neuronal correlates of the EEM, in particular enhanced activity in the amygdala and hippocampus, which provides evidence for an arousal-driven EEM in the amygdala as proposed by the modulation hypothesis.     

The peripheral drift illusion: a motion illusion in the visual periphery

Circularly repeating patches containing sawtooth luminance gradients produce a sensation of motion when viewed in the periphery. Illusory motion is perceived in a dark-to-light direction, but only when one's gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.     

Spatial limits on the nonvisual self-touch illusion and the visual rubber hand illusion: Subjective experience of the illusion and proprioceptive drift

The nonvisual self-touch rubber hand paradigm elicits the compelling illusion that one is touching one’s own hand even though the two hands are not in contact. In four experiments, we investigated spatial limits of distance (15 cm, 30 cm, 45 cm, 60 cm) and alignment (0°, 90° anti-clockwise) on the nonvisual self-touch illusion and the well-known visual rubber hand illusion. Common procedures (synchronous and asynchronous stimulation administered for 60 s with the prosthetic hand at body midline) and common assessment methods were used. Subjective experience of the illusion was assessed by agreement ratings for statements on a questionnaire and time of illusion onset. The nonvisual self-touch illusion was diminished though never abolished by distance and alignment manipulations, whereas the visual rubber hand illusion was more robust against these manipulations. We assessed proprioceptive drift, and implications of a double dissociation between subjective experience of the illusion and proprioceptive drift are discussed.     

The effect of a moving dot transversal on the Poggendorff illusion

In attempting to derive the minimal component of the Poggendorff figure which would still produce an illusion, responses to three types of transversal were measured. One was the customary solid line type; a second type presented the two segments sequentially, alternating between them; and the third consisted of a moving dot which traveled the transversal path. Each transversal was shown with and without verticals, for a total of six conditions. Ten subjects in each condition adjusted the luminous transversal until the segments appeared to be collinear. Figures with verticals present showed a greater magnitude of illusion than those without, and discrepancies for moving dot transversals were greater than those for comparable solid line figures. Since alternating transversals were not significantly larger than solid line figures, it was concluded that the magnitude of the moving dot effect could not be attributed to temporal sequence. An eyemovement hypothesis was suggested instead.     

The effect of retinal location on the magnitude of the Poggendorff illusion

The effect of retinal locus on the magnitude of the Poggendorff illusion was investigated. A significant illusion was found to occur in the fovea and in undiminished magnitude at the peripheral locations horizontally displaced from the fovea. No significant illusion was induced at the vertically displaced positions. It is suggested that the results obtained at the positions displaced from the fovea may be attributable to the refracting surfaces of the cornea, and that these findings lend support to an account of the Poggendorff illusion which emphasizes the significant involvement of peripheral mechanisms.     

An illusion of movement complementary to the horizontal-vertical illusion

Blindfolded subjects moved a stylus held in the hand over a standard distance of 4.5 ins. in a given direction. They then attempted to move the same distance in a direction at right angles to the first. Eight combinations of movements were investigated. The results reveal an illusion such that the extent of movements to left or right across the body is underestimated, while the extent of movements towards or away from the body in the mid-line is overestimated. The illusion applies to speed as well as extent of movement. Movement up or down in a vertical plane is equivalent to movement towards or away from the body in a horizontal plane.

The interaction of this illusion with the well-known horizontal-vertical illusion of visual perception explains a failure to find any net illusory effect where lines visually displayed in different orientations were matched for length by unseen movements in similar orientations.

Whether the visual and movement illusions simply co-exist or whether they are functionally related is not yet clear.     

The orientation of a parallel-line texture between the verticals can modify the strength of the Poggendorff illusion.

In the present experiments, we attempted to evaluate the modification of the strength of the Poggendorff illusion as a function of the different orientation of a parallel-line texture filling the space between the vertical lines. In Experiment 1, the standard version of the Poggendorff configuration was tested against four different parallel-line textures oriented at 0 degrees, 45 degrees, 90 degrees, and 135 degrees with respect to the obliques. The results showed that the illusory effect was a linear function of the progressive discrepancy between the angle of the lines of the texture and that of the obliques. In Experiment 2, we tested the same textures used in Experiment 1 after the elimination of the two vertical lines. The data obtained approximated a linear function, as in the previous experiment, but the alignment errors were consistently lower. The statistical analysis performed on the data of all eight experimental conditions shows that both factors--texture and presence/absence of verticals--were significant, but most of the effect was due to the texture factor. The results may be interpreted through the "perceptual compromise hypothesis," originally proposed for the bisection forms of the Poggendorff illusion, but with important modifications. The data are also discussed in terms of their implications for other theories proposed for the Poggendorff illusion.