vrijdag 31 augustus 2012

Picasso in the mind’s eye of the beholder: Three-dimensional filling-in of a...

 
 

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Publication year: 2012
Source:Cognition
Jan Koenderink, Andrea van Doorn, Johan Wagemans
Cartoon-style line drawings contain very condensed information, after all most of the page stays blank. Yet, they constrain the contents of immediate visual awareness to an extraordinary extent. This is true even for drawings that are – though nominally "representational" – not even in central projection. Moreover, the strokes used in a drawing may stand for a bewildering variety of entities in the world. We studied Picasso drawings from the 1940s in which the artist famously combined multiple viewpoints. We find that the pictorial reliefs obtained from various observers agree to a large extent, and that the differences are of a very specific nature, typically involving variations in the mutual spatial attitudes of rigid body parts in figure studies. Although the purely planar layout of the drawings accounts for much of visual awareness, observers also use the sparse depth cues provided by the artist to evoke volumetric impressions. Observers also freely insert "template knowledge" about the structure of familiar generic objects.

Highlights

► Cartoon-style line drawings constrain the contents of immediate visual awareness. ► Observers perceive body parts of depicted human figures in idiosyncratic attitudes. ► Observers use sparse depth cues used by the artist to evoke volumetric impressions. ► Observers freely insert "template knowledge" about generic object structure.

 
 

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donderdag 16 augustus 2012

Grouping by closure influences subjective regularity and implicit preference...

 
 

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via i-Perception by Pion on 8/15/12

A reflection between a pair of contours is more rapidly detected than a translation, but this effect is stronger when the contours are closed to form a single object compared to when they are closed to form 2 objects with a gap between them. That is, grouping changes the relative salience of different regularities. We tested whether this manipulation would also change preference for reflection or translation. We measured preference for these patterns using the Implicit Association Test (IAT). On some trials, participants saw words that were either positive or negative and had to classify them as quickly as possible. On interleaved trials, they saw reflection or translation patterns and again had to classify them. Participants were faster when 1 button was used for reflection and positive words and another button was used for translation and negative words, compared to when the reverse response mapping was used (translation and positive vs. reflection and negative). This reaction time difference indicates an implicit preference for reflection over translation. However, the size of the implicit preference was significantly reduced in the Two-objects condition. We concluded that factors that affect perceptual sensitivity also systematically affect implicit preference formation.

 
 

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woensdag 8 augustus 2012

The integration of straight contours (snakes and ladders): the role of spati...

 
 

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via Vision Research on 8/8/12

Publication year: 2012
Source:Vision Research
Rosilari Bellacosa Marotti, Andrea Pavan, Clara Casco
In the present study we addressed the issue of whether the Gestalt principle of grouping by similarity (iso-orientation) subtends extraction of straight contours made up of disconnected, iso-oriented Gabor elements, whether collinear (snakes) or parallel (ladders). To prevent the use of the most obvious grouping principle of good continuation, which allows us to perceive the relation between local and global orientation along the contour, we manipulated the spatial arrangement of randomly oriented Gabors in the background: they were positioned on an ordered grid, and grouped on the basis of good continuation, or randomly positioned and not grouped. Grid-positioned backgrounds exert a suppressive contextual influence on detection of good continuation along the contour path. Results obtained in a two-interval forced choice task showed that the orderly-positioned background did not completely prevent detection of snakes and ladders. Detection of snakes was hampered at low spatial frequency whereas detection of ladders was improved by the randomly-positioned background at high spatial frequency. These contextual influences support the suggestion that both iso-orientation and good continuation rules are employed by the association field underlying the binding of straight contours. In addition, they are not compatible with integration of snakes and ladders elements within a single receptive field. In support of this suggestion we found that phase constancy within contour elements (as opposed to phase randomization) improved snake detectability at low spatial frequency, and, unexpectedly, impaired ladder detectability at high spatial frequency. This suggests that a low-level mechanism based on the balance between excitatory and inhibitory lateral interactions at a first stage may account for the detection of both straight contours.

Highlights

► In this study we examined the integration of straight snake and ladder contours. ► We used a randomly- and a grid-positioned background to test global context effects. ► We tested the effects of three spatial frequencies and of phase randomization. ► We found that snakes only are hampered by background manipulation at low frequencies. ► Phase randomization only impairs snake detection and only at low spatial frequencies.

 
 

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