Accidental viewpoint

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Street art illustrating the illusion of form-continuity from a particular viewpoint

An accidental viewpoint (i.e. eccentric or fixed viewpoint) is a singular position from which an image can be perceived, creating either an ambiguous image or an illusion. The image perceived at this angle is viewpoint-specific, meaning it cannot be perceived at any other position, known as generic or non-accidental viewpoints. These view-specific angles are involved in object recognition.[1] In its uses in art and other visual illusions, the accidental viewpoint creates the perception of depth often on a two-dimensional surface[2] with the assistance of monocular cues.

Object recognition

According to the recognition-by-components theory, object recognition is viewpoint-invariant. However, viewpoint specific angles are a necessity in object recognition when identifiable features cannot be viewed from all angles.[1] Object recognition is more accurate when identifying similarities between objects that are moving compared to objects that are static. In this case, viewing an object from an accidental viewpoint can result in altered perception in relation to mental prototypes.[3] When viewing an object from an accidental viewpoint scene consistency is more critical for object recognition than when viewing that object from a non-accidental viewpoint,[4] so in some cases viewing an object from its accidental viewpoint actually makes it harder to recognize the object, but we counteract that difficulty using contextual inference.

The Ambassadors, 1533, Hans Holbein the Younger
The Ambassador's Skull: detail when viewed from the accidental viewpoint (from The Ambassadors – Hans Holbein the Younger)

Controversy

2D symmetry was once thought to be able to facilitate 3D object recognition under accidental viewpoints. Some psychologists have proposed that the accidental viewpoints of 3D objects often involves the 2D symmetrical images that may not be perceived in the 3D objects.[5] However, researches showed that 2D symmetry will not help object matching in accidental viewpoints,[6] and others have argued that accidental viewpoints with 2D symmetry will even hinder 3D object matching and object recognition.[7] Results from face recognition study also agrees on the negative effect of symmetric face from accidental views.[8]

Art

Accidental viewpoint contributes to the successful perception of

monocular depth cues), Hans Holbein's The Ambassadors (1533) is no different in that sense, however, Holbein also includes an anamorphic image of a skull which has a completely different view point in order to accurately view the object. In the 17th century, perspective boxes (peep boxes, raree shows) became popular attractions. These took advantage of the accidental viewpoint by creating a scene that appeared to be three dimensional when viewed through a single hole in the box. A modern representation of anamorphic images that makes use of an accidental viewpoint can be found in illusionistic street art.[9]

Psychological illusion

View of one side of the interior, not through the intended viewpoint
Peepshow with Views of the Interior of a Dutch House – Samuel van Hoogstraten

Psychologists have exploited the assumption of the generic viewpoint by using an accidental viewpoint to trick the brain into perceiving a scene that is realistically impossible. One famous example of this is the

Gestalt principles such that a curved line can appear straight when viewed from an accidental viewpoint.[11] The accidental viewpoint it also used when creating possible versions of impossible object illusions.[2]

References

  1. ^
    PMID 12706220
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  2. ^
    doi:10.1016/j.cagd.2020.101826
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  3. S2CID 15584115
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  4. PMID 25522833
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  5. PMID 9718963
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  6. S2CID 35284032
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  7. PMID 7772550
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  8. S2CID 13115909
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  9. ^
    S2CID 150168579
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  10. S2CID 8462408
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  11. OCLC 1062308318
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