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Against better knowledge: The magical force of amodal volume completion.

Ekroll V, Sayim B, Wagemans J - Iperception (2013)

Bottom Line: In a popular magic routine known as "multiplying billiard balls", magicians fool their audience by using an empty shell that the audience believes to be a complete ball.Here, we present some observations suggesting that the spectators do not merely entertain the intellectual belief that the balls are all solid, but rather automatically and immediately perceive them as such.Our observations demonstrate the surprising potency and genuinely perceptual origin of amodal volume completion.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Tiensestraat 102 - box 3711, 3000 Leuven, Belgium; e-mail: vebjorn.ekroll@ppw.kuleuven.be.

ABSTRACT
In a popular magic routine known as "multiplying billiard balls", magicians fool their audience by using an empty shell that the audience believes to be a complete ball. Here, we present some observations suggesting that the spectators do not merely entertain the intellectual belief that the balls are all solid, but rather automatically and immediately perceive them as such. Our observations demonstrate the surprising potency and genuinely perceptual origin of amodal volume completion.

No MeSH data available.


Two views of the same semi-spherical shell. When it is lying on the table (a) it is perceived as a semi-sphere. When it is tilted off the table towards the observer (b), however, it looks like a complete ball.
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Figure 3: Two views of the same semi-spherical shell. When it is lying on the table (a) it is perceived as a semi-sphere. When it is tilted off the table towards the observer (b), however, it looks like a complete ball.

Mentions: Although the latter may seem self-evident and unproblematic, the visual stimulus is in fact compatible with an infinite number of different completions of the visible parts of the semi-spherical shell and the table (Gerbino & Zabai, 2003). For instance, it is also compatible with a full sphere resting in a semi-spherical indentation in the table. Based on the findings of Gerbino and Zabai (2003), one would actually expect the latter interpretation to be perceived. In a systematic investigation of the factors determining how the visual ambiguities associated with joined objects are resolved, they found that two factors were particularly effective. First, the smaller of the two objects tends to be perceived as penetrating the other. Second, the same tendency was found for the object that is above the other. In our case, both of these tendencies should favour the percept of a full sphere partially penetrating the table, but what we actually perceive is a semi-sphere on a completely planar surface. So, what are the differences between our situation (Figure 3[a]) and the stimuli investigated by Gerbino and Zabai (2003) that may potentially explain this discrepancy? First, most of their stimuli were uniformly coloured, while the table surface in our Figure 3(a) is textured. Thus, amodal completion of the texture elements (the small dots on the table cloth) may be a factor that favours the perception of an unbroken planar surface. Second, the object intersections studied by Gerbino and Zabai (2003) all had the property that if one of the two objects was completed in the most simple way, the other one would necessarily have a concave indentation. In our case, however, the percept actually observed involves two non-concave objects, namely a flat surface and a semi-sphere, while the converse solution would involve a cavity in the table surface. Thus, the discrepancy between our observation and the results of Gerbino and Zabai (2003) may be taken to suggest that (a) the visual system has a tendency to avoid concave completions, and (b) that this tendency may override those documented in Gerbino and Zabai's (2003) study. Although this issue is not the main point of the present note, it appears interesting and important enough to warrant further research.


Against better knowledge: The magical force of amodal volume completion.

Ekroll V, Sayim B, Wagemans J - Iperception (2013)

Two views of the same semi-spherical shell. When it is lying on the table (a) it is perceived as a semi-sphere. When it is tilted off the table towards the observer (b), however, it looks like a complete ball.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4129385&req=5

Figure 3: Two views of the same semi-spherical shell. When it is lying on the table (a) it is perceived as a semi-sphere. When it is tilted off the table towards the observer (b), however, it looks like a complete ball.
Mentions: Although the latter may seem self-evident and unproblematic, the visual stimulus is in fact compatible with an infinite number of different completions of the visible parts of the semi-spherical shell and the table (Gerbino & Zabai, 2003). For instance, it is also compatible with a full sphere resting in a semi-spherical indentation in the table. Based on the findings of Gerbino and Zabai (2003), one would actually expect the latter interpretation to be perceived. In a systematic investigation of the factors determining how the visual ambiguities associated with joined objects are resolved, they found that two factors were particularly effective. First, the smaller of the two objects tends to be perceived as penetrating the other. Second, the same tendency was found for the object that is above the other. In our case, both of these tendencies should favour the percept of a full sphere partially penetrating the table, but what we actually perceive is a semi-sphere on a completely planar surface. So, what are the differences between our situation (Figure 3[a]) and the stimuli investigated by Gerbino and Zabai (2003) that may potentially explain this discrepancy? First, most of their stimuli were uniformly coloured, while the table surface in our Figure 3(a) is textured. Thus, amodal completion of the texture elements (the small dots on the table cloth) may be a factor that favours the perception of an unbroken planar surface. Second, the object intersections studied by Gerbino and Zabai (2003) all had the property that if one of the two objects was completed in the most simple way, the other one would necessarily have a concave indentation. In our case, however, the percept actually observed involves two non-concave objects, namely a flat surface and a semi-sphere, while the converse solution would involve a cavity in the table surface. Thus, the discrepancy between our observation and the results of Gerbino and Zabai (2003) may be taken to suggest that (a) the visual system has a tendency to avoid concave completions, and (b) that this tendency may override those documented in Gerbino and Zabai's (2003) study. Although this issue is not the main point of the present note, it appears interesting and important enough to warrant further research.

Bottom Line: In a popular magic routine known as "multiplying billiard balls", magicians fool their audience by using an empty shell that the audience believes to be a complete ball.Here, we present some observations suggesting that the spectators do not merely entertain the intellectual belief that the balls are all solid, but rather automatically and immediately perceive them as such.Our observations demonstrate the surprising potency and genuinely perceptual origin of amodal volume completion.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Tiensestraat 102 - box 3711, 3000 Leuven, Belgium; e-mail: vebjorn.ekroll@ppw.kuleuven.be.

ABSTRACT
In a popular magic routine known as "multiplying billiard balls", magicians fool their audience by using an empty shell that the audience believes to be a complete ball. Here, we present some observations suggesting that the spectators do not merely entertain the intellectual belief that the balls are all solid, but rather automatically and immediately perceive them as such. Our observations demonstrate the surprising potency and genuinely perceptual origin of amodal volume completion.

No MeSH data available.