vrijdag 25 november 2011

Gestalt perception and the decline of global precedence in older subjects

Gestalt perception and the decline of global precedence in older subjects

Markus R. Staudinger a,b, Gereon R. Fink a,c, Clare E. Mackay d,e and Silke Lux a,* 

Our visual world is hierarchically organized. Hierarchical processing is frequently inves- tigated using Navon figures (large letters made up of smaller ones). In young adults, many studies reported faster reaction times (RT) to target letters presented at the global level [i.e., global precedence (GP)]. Furthermore, an age-related decline of this GP has been reported. We tested whether deficits in perceptual grouping via Gestalt laws (Gestalt principles of Proximity and Continuity) might contribute to this decline. In a directed attention task with valid and invalid cues, 20 young (mean age 22) and 20 older (mean age 57) male subjects had to indicate whether a target letter appeared at the global or local level of a Navon figure. The number of local letters forming the global figure was modulated in 5 steps. As expected, during valid trials, young adults showed a GP that linearly increased with increasing numbers of local letters (i.e., GP enhancement). This suggests that GP is related to perceptual grouping via Gestalt laws. By contrast, the group of older subjects demonstrated no precedence effect in RT and a non-significant trend toward GP in error rates (ER). No GP enhancement with an increasing number of local elements was observed. Exploratory analysis revealed that individual insensitivity to the modulation of matrix density, as revealed by a lack of global RT acceleration, was restricted to subjects that showed an overall local precedence (LP). Because older subjects tended to more frequently display an insensitivity to matrix modulation and an LP, we conclude that deficient Gestalt detection as indicated by non-enhanced global RT might contribute to the RT-related decline of GP with age. 

doi:10.1016/j.cortex.2010.08.001 
cortex 47 (2011) 854-862    

  
----
Krista Overvliet, PhD.
 
Laboratory of  Experimental Psychology
University of Leuven
Tiensestraat 102, bus 3711
Room 00.74
3000 Leuven
Belgium
 
phone: +3216326146
skype: kristaovervliet
krista.overvliet@gmail.com
krista.overvliet@ppw.kuleuven.be
http://web.me.com/krista.overvliet

Gepost door op Geen opmerkingen:

woensdag 23 november 2011

The construction of perceptual grouping displays using GERT

 
 

Sent to you by Frouke via Google Reader:

 
 


Abstract  
To study perceptual grouping processes, vision scientists often use stimuli consisting of spatially separated local elements that, together, elicit the percept of a global structure. We developed a set of methods for constructing such displays and implemented them in an open-source MATLAB toolbox, GERT (Grouping Elements Rendering Toolbox). The main purpose of GERT is to embed a contour in a field of randomly positioned elements, while avoiding the introduction of a local density cue. However, GERT's modular implementation enables the user to create a far greater variety of perceptual grouping displays, using these same methods. A generic rendering engine grants access to a variety of element-drawing functions, including Gabors, Gaussians, letters, and polygons.

  • Content Type Journal Article
  • Pages 1-8
  • DOI 10.3758/s13428-011-0167-8
  • Authors
    • Maarten Demeyer, Laboratory of Experimental Psychology, University of Leuven (K.U. Leuven), Tiensestraat 102, bus 3711, 3000 Leuven, Belgium
    • Bart Machilsen, Laboratory of Experimental Psychology, University of Leuven (K.U. Leuven), Tiensestraat 102, bus 3711, 3000 Leuven, Belgium

 
 

Things you can do from here:

 
 
Gepost door op Geen opmerkingen:

dinsdag 8 november 2011

Bayesian Inference: From Spikes to Behaviour

Confirmed Speakers:

Michael Black, Max Planck Institute for Intelligent Systems, Tübingen, Germany
Daniel Braun, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
Opher Donchin, Ben Gurion University of Negev, Be'er Sheva, ISRAEL
Dominik Endres, Eberhard Karls University of Tübingen, Tübingen, Germany
Adrienne Fairhall, University of Washington, Illinois, USA
Moritz Grosse-Wentrup, Max Planck Institute for Intelligent Systems, Tübingen, Germany
Peter Földiak, University of St. Andrews, St. Andrews, UK
Konrad Körding, University of Chicago, Illinois, USA
Peter Latham, University College London, London, UK
Laurence Maloney, University of New York, New York, USA
Aude Oliva, Massachusetts Institute of Technology, Massachusetts, USA
Uta Noppeney, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
Jan Peters, TU Darmstadt, Darmstadt, Germany
Josh Tenenbaum, Massachusetts Institute of Technology, Massachusetts, USA


http://www.bccn-tuebingen.de/events/bernstein-symposium-series-2011/symposium-c.html 

Gepost door op Geen opmerkingen:

What the Brain Sees After the Eye Stops Looking

 
 

Aan u verzonden door Sander via Google Reader:

 
 


When we gaze at a shape and then the shape disappears, a strange thing happens: We see an afterimage in the complementary color. Now a Japanese study has observed for the first time an equally strange illusion: The afterimage appears in a "complementary" shape—circles as hexagons, and vice-versa.

"The finding suggests that the afterimage is formed in the brain, not in the eye," the author, Hiroyuki Ito of Kyushu University, wrote in an email. More specifically, the illusion is produced in the brain's shape-processing visual cortex, not the eye's light-receiving, message-sending retina. The findings appear in an upcoming issue of Psychological Science, a journal published by the Association for Psychological Science.

Ito conducted three experiments with 82, 92, and 44 participants respectively. In the first two, he showed participants yellow circles or hexagons – outlined or filled, static or rotating on a gray ground. In each, after they observed the images for 10 seconds, the images disappeared, leaving only the blank gray field. The observers were asked to indicate which of seven shapes, on a piece of paper, the afterimage most resembled.

In the third experiment, Ito split the visual field between the two eyes. In the left eye, participants saw rotating circles and hexagons, as well as rotating asterisk-like "stars"—shapes that were neither round nor angular. The right eye viewed static circles in all conditions.  When the circles, hexagons, and stars disappeared, the left field was black, which suppressed the formation of afterimages, and the right was white, which heightened it.

In Experiments 1 and 2, participants tended to see circles after hexagons and hexagons after circles. In the third, the right eye produced the most angular afterimages when circles had been projected in the left eye; the most rounded ones after the rotating hexagons; and after the "stars," images that were neither circular nor edged.

How did Ito infer that the brain, not the eye, was producing these afterimages? He eliminated the theory that the afterimage was a manifestation of "retinal bleaching"—when the photoreceptors on the retina become ineffective or fatigued through prolonged exposure to light.  Viewing static circles or hexagons produce circular or hexagonal bleached areas on the retina. However, the afterimage shapes were not in the bleached shapes.  A spinning circle or hexagon produces a circular trace of light on the retina, causing circular shape of retinal bleaching just as painting on the retina. However, spinning circles produced hexagonal afterimages and vice versa.

Retinal bleaching could not produce "an afterimage shape different from the [typical] retinal bleaching shape." Neither could the retina transfer information taken in by the left eye to produce an afterimage in the right eye.  "The only site that can happen is the brain."

The research adds to science's understanding of the role of the brain in vision. "People tend to think that afterimages are meaningless by-products arising from the physiological characteristics of the eye," wrote Ito. "But I think that the afterimages reflect brain activities and provide us the means to know those activities in a directly visible form."


 
 

Dingen die u vanaf hier kunt doen:

 
 
Gepost door op Geen opmerkingen:

vrijdag 28 oktober 2011

Fwd: CVNet - AVA Xmas Meeting abstract submission extension

Still time to submit an abstract for the AVA meeting! (York, UK)

__________________________________________________________________________


The AVA Christmas Meeting will be held at the University of York on 19
December 2011.

This year's organiser is Peter Thompson.

The conference website is at

http://www.theava.net/conf/index.php?conference=Meeting&schedConf=X2011

The original deadline for the submission of Abstracts was 1 November
2011. We have decided to extend the deadline to midnight on Sunday 6
November. Please submit abstracts via the AVA website and register for
the meeting at the same time.

WIth best wishes

Peter Thompson: Meeting Orgnaniser
Tom Troscianko: AVA Secretary

Gepost door op Geen opmerkingen:

woensdag 26 oktober 2011

Illusory Contours over Pathological Retinal Scotomas.

 
 

Aan u verzonden door Sander via Google Reader:

 
 


PLoS One. 2011; 6(10): e26154
De Stefani E, Pinello L, Campana G, Mazzarolo M, Lo Giudice G, Casco C

Our visual percepts are not fully determined by physical stimulus inputs. Thus, in visual illusions such as the Kanizsa figure, inducers presented at the corners allow one to perceive the bounding contours of the figure in the absence of luminance-defined borders. We examined the discrimination of the curvature of these illusory contours that pass across retinal scotomas caused by macular degeneration. In contrast with previous studies with normal-sighted subjects that showed no perception of these illusory contours in the region of physiological scotomas at the optic nerve head, we demonstrated perfect discrimination of the curvature of the illusory contours over the pathological retinal scotoma. The illusion occurred despite the large scar around the macular lesion, strongly reducing discrimination of whether the inducer openings were acute or obtuse and suggesting that the coarse information in the inducers (low spatial frequency) sufficed. The result that subjective contours can pass through the pathological retinal scotoma suggests that the visual cortex, despite the loss of bottom-up input, can use low-spatial frequency information from the inducers to form a neural representation of new complex geometrical shapes inside the scotoma.


 
 
 
 
Gepost door op Geen opmerkingen:

vrijdag 21 oktober 2011

Online social network size is reflected in human brain structure

My friend here is reinventing phrenology…

 

http://www.ncbi.nlm.nih.gov/pubmed/22012980

 

Proc Biol Sci. 2011 Oct 19. [Epub ahead of print]

 

Online social network size is reflected in human brain structure.

Kanai R, Bahrami B, Roylance R, Rees G.

UCL Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR, UK.

 

Abstract

The increasing ubiquity of web-based social networking services is a striking feature of modern human society. The degree to which individuals participate in these networks varies substantially for reasons that are unclear. Here, we show a biological basis for such variability by demonstrating that quantitative variation in the number of friends an individual declares on a web-based social networking service reliably predicted grey matter density in the right superior temporal sulcus, left middle temporal gyrus and entorhinal cortex. Such regions have been previously implicated in social perception and associative memory, respectively. We further show that variability in the size of such online friendship networks was significantly correlated with the size of more intimate real-world social groups. However, the brain regions we identified were specifically associated with online social network size, whereas the grey matter density of the amygdala was correlated both with online and real-world social network sizes. Taken together, our findings demonstrate that the size of an individual's online social network is closely linked to focal brain structure implicated in social cognition.

 

 

Ervin Poljac, PhD

Laboratory of Experimental Psychology

University of Leuven (K.U. Leuven)

Tiensestraat 102

B-3000 Leuven

Belgium

tel. +32-16-32.61.43 (office)

fax. +32-16-32.60.99

Email: Ervin.Poljac@psy.kuleuven.be

 

Gepost door op Geen opmerkingen:
Abonneren op: Posts (Atom)