The floating-finger illusion.

Sharp, Werner L.

doi:10.1037/h0070164

Cited by 12 publications

(5 citation statements)

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“…Ebbinghaus illusions demonstrate object size perceived relative to surrounding objects (Roberts, Harris, & Yates, 2005). The floating frankfurter illusion (Sharp, 1928), when staring at two nearly touching fingers before the eyes, and diverging the eyes beyond them, reflects inappropriate binocular fusion.…”

Section: Visual Illusionsmentioning

confidence: 99%

The Eyes Wide Shut Illusion

Hochstein

2018

Perception

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The new "eyes wide shut" illusion uses a standard enlarging (shaving or makeup) mirror. Close one eye and look at the closed eye in the mirror; the eye should take up most of the mirror. Switch eyes to see the other closed eye. Switch back-and-forth a few times, then open both eyes. You see an open eye. Which eye is it? To find out, close one eye. Whichever you close, that's the eye you see. How can this be possible? The brain is fusing two images of the two eyes! The illusion depends on (a) binocular fusion: The brain combines two images to a single percept; (b) symmetry: Mirrors don't affect appearance of left-right symmetric objects and the eyes are sufficiently left-right symmetric for the brain to combine them. Why aren't the lingering asymmetries sufficient to prevent fusion? (c) Only vision with scrutiny affords conscious access to scene details. Consistent with reverse hierarchy theory, vision at a glance grants conscious perception of the gist of the scene, integrating images of nonperfectly symmetric eyes.

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Section: Visual Illusionsmentioning

confidence: 99%

The Eyes Wide Shut Illusion

Hochstein

2018

Perception

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“…What happens is that the double image includes a region of "overlap." The central region of overlap is the left portion of the rectangle due to the right eye's input and the right portion of the rectangle in the left eye's input (Schiffman, 1990, p. 358, Figure 16.22;Sharp, 1928). The overlap region is, ofcourse, narrower than either of the rectangles contributing to the overlap.…”

Section: Methodsmentioning

confidence: 99%

Misalignment effects in 3-D versions of Poggendorff displays

Liu

Kennedy

1995

Perception & Psychophysics

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Strong misalignment effects are found in three-dimensional (3-D)versions of Poggendorff displays viewed binocularly. The components of the standard 2-D Poggendorff figure-the parallels and the oblique segments-were presented in 3-Ddepth as a flat rectangular object with occluding edges and an oblique line situated behind the object. Three experiments investigated the misalignment effects under three different observation instructions: Subjects were told to look at the oblique (Experiment 1), at the rectangle (Experiment 2), or at the background (Experiment 3). Experiments 1 and 2 examined the effects on judgments of alignment of varying the distance in depth that separates the oblique from the rectangle. Experiment 3 examined the effects of varying the distance between the fixated background and the 3-DPoggendorff figure. Both standard and reversed misalignment effects were obtained. When the viewing condition produces crossed disparity for the oblique, perceived misalignment occurs in the usual Poggendorff direction, but it is reversed with uncrossed disparity. Moreover, the amount of misalignment is related to the amount of disparity, and it can be much stronger than is usual in the 2-D versions of the Poggendorff. The misalignment effects can be explained by binocular integration to produce a single cyclopean image.In the Poggendorff illusion (Figure 1), the oblique lines erroneously appear to be misaligned. What we show here is that misalignment effects also appear in solid (three-dimensional, or 3-D) binocular versions of Figure 1. We show how the effects depend on factors arising during binocular integration. There is a variety of contradictory reports on binocular versions of the Poggendorff in the literature, and we show how each of the varied reports can be obtained and explained by standard principles of stereopsis.While sometimes it has been considered to be due to depth perception, Poggendorff misalignment has only rarely been associated with binocular vision. Fisher and Lucas (1969), Schiffman (1990) report that pictures of real-life settings, such as an oblique tree behind an upright tree, create the same effect as the Poggendorff figure. However, the observations were undertaken only with flat pictures, and possible binocular versions, though noted by these authors, were not assessed. Pieron (1955) tried explicitly to observe the Poggendorff effect in a fully 3-D world. He observed that the effect failed there! He stated that if the two segments ofthe oblique line are made ofrope passing behind a column and serving to pull a bucket out of a well, the illusion disappears completely. Julesz (1971) examined several illusions in random-dot stereograms. In particular, he observed that when the Poggendorff rectangle is sepWe would like to thank P. Bennett for his comments on an early version of this paper. Correspondence should be addressed to C.

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“…Sharp (30) describes a rather novel tactual-visual illusion. The individual brings his two hands before his eyes, palms facing him, with the index fingers touching end to end.…”

Section: Illusionsmentioning

confidence: 99%

Cutaneous and kinaesthetic space.

Ewert¹

1929

Psychological Bulletin

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The floating-finger illusion.

Cited by 12 publications

References 0 publications

The Eyes Wide Shut Illusion

The Eyes Wide Shut Illusion

Misalignment effects in 3-D versions of Poggendorff displays

Cutaneous and kinaesthetic space.

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