copy of how the brain interprets complex visual scenes is an enduring mystery for researchers

8/4/2019 Copy of How the Brain Interprets Complex Visual Scenes is an Enduring Mystery for Researchers

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How the brain interprets complex visual scenes is an enduring mystery for researchers. Thisprocess occurs extremely rapidly - the "meaning" of a scene is interpreted within 1/20th of asecond, and, even though the information processed by the brain may be incomplete, theinterpretation is usually correct.Occasionally, however, visual stimuli are open to interpretation. This is the case withambiguous figures - images which can be interpreted in more than one way. When anambiguous image is viewed, a single image impinges upon the retina, but higher order

processing in the visual cortex leads to a number of different interpretations of that image.Only one of these interpretations is available to our conscious awareness at any one time.Repeated viewing of the image leads to perceptual reversal, whereby first one, and then theother, interpretation is perceived. For psychologists and neuroscientists, ambiguousfigures provide a means by which the functioning of the human visual system can beinvestigated.Salvador Dali's 1940 paintingSlave Market with the Disappearing Bust of Voltaire(top) isan example of an ambiguous figure. In this painting, the two nuns just left of centre can also

be perceived as the bust of the French writer and philosopher Voltaire. When looking at thepainting, our perception of the painting switches from one interpretation to the other.In a study published in 2002, Lizann Bonnar, then at the University of Glasgow, and hercolleagues, investigated the stimuli which drive perception of the visual scene depicted inDali's painting. Participants were presented with a cropped greyscale version of the painting,

consisting solely of the area containing the nuns. A "bubble" filter was used to enhance orobscure certain features of that part of the painting. They found that the participantsreported seeing the bust of Voltaire when the finer details of the painting were obscured, andreported seeing the nuns when large scale features were obscured.This experiment showed the importance of scale information in perception. The researchersspecifically manipulated the spatial resolution of the painting (that is, the periodicity with

which image intensity changes). Large scale features change little over a given distance, andtherefore have a low spatial resolution, while fine-grained features change much more overthe same distance, and so have a high spatial resolution.
http://www.perceptionweb.com/abstract.cgi?id=p3276http://www.perceptionweb.com/abstract.cgi?id=p3276http://www.perceptionweb.com/abstract.cgi?id=p3276


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In a second experiment, the participants were shown random noise patterns before thecropped greyscale painting. One group was shown a pattern with a high spatial resolution,the other a pattern with a low spatial resolution. Afterwards, the former reported seeing the

bust of Voltaire, while the latter reported seeing the nuns. This showed that previousexperience is an important factor in perception. The participants had selectively perceivedthe frequency channels presented to them before they viewed the image.

Aude Oliva, head of the Computational VisualCognition Laboratoryat the Massachusettes Institute of Technology, has been using a similarapproach to gain a better understanding of the processing of information in the visual cortex.For more than 10 years, Oliva and her colleagues have been creating and using hybridimagesthat consist of two superimposed images, both of which have been altered withspecialized filtering software.

Using these filters, sharp facial features, such as wrinkles and other blemishes, are removedfrom one image, and coarse features, such as the shape of the mouth or nose, are removedfrom the other. The two images are then superimposed; because features with a high spatialfrequency are visible only from up close, and those with low spatial frequencies are only

visible from further away, superimposition of the two produces a single image whoseperception changes as a function of viewing distance.Thus, the hybrid is a single image with two stable percepts; at a given distance, only one ofthe images is visible, and it is this image that dominates processing in the visual system; theother image is perceived as something lacking internal organization (noise).

Above is an example of the hybrid images created by Oliva's group. From up close, the imageis perceived as Albert Einstein, because only the sharp features are visible; but if you step afew metres away from the monitor, the blurred features become visible, and the image ofMarilyn Monroe emerges.

Oliva's group has been using this and similar images to investigate the role of differentfrequency channels for image recognition, and the time course over which this processoccurs. What they have found is that when participants are shown hybrid images fordurations of 30 milliseconds, they only recognized the low spatial resolution component ofthe image; when the images were displayed for 150 milliseconds, they only recognized thehigh spatial resolution component; In both cases, the participants were oblivious to the otherinterpretation of the image.Participants were also shown hybrid images consisting of sad and angry faces (high and lowspatial resolution, respectively) of superimposed male and female faces. When the images
http://cvcl.mit.edu/Aude.htmhttp://cvcl.mit.edu/Aude.htmhttp://cvcl.mit.edu/hybridimage.htmhttp://cvcl.mit.edu/hybridimage.htmhttp://cvcl.mit.edu/hybridimage.htmhttp://cvcl.mit.edu/Aude.htmhttp://cvcl.mit.edu/Aude.htmhttp://cvcl.mit.edu/hybridimage.htmhttp://cvcl.mit.edu/hybridimage.htm


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were displayed for 50 milliseconds, and the participants were asked to determine theemotion of the face they had seen, they always reported seeing an angry face; but when askedto determine the sex of the person in the image, they reported seeing a male as often as theyreported seeing a female, although the two faces had different spatial resolutions.Thus, selection of frequency bands during fast image recognition appears to be flexible - insome cases, the brain picks out characteristics with a low spatial resolution, while in others, it

discriminates those with a high resolution. It seems that the brain is adept at selecting thefrequncy band containing the most information relevant to a particular task. Again, theparticipants were unaware that the images they viewed contained information in the otherfrequency range.The work carried out by Oliva's group shows that the brain extracts large-scalefeatures slightly earlier than fine-grained features. Large scale features are processed within50 milliseconds, giving an overall impression of the visual scene. The processing of fine-grained details begins slightly later, at around 100 milliseconds. The fine- and coarse-grainedfeatures are extracted separately, and processed in parallel through different channels, insuccessively higher order areas of the visual cortex. In a process called perceptual grouping,the information from the channels is then seamlessly recombined at visual cortical areas ofthe highest order to produce a coherent, and usually unambiguous, image.


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Count the face


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Nature Sadness Illusion

Illusion of mans face with depressed looks.
http://www.illusionspoint.com/billboard-optical-illusions/nature-sadness-illusion-2/http://www.illusionspoint.com/billboard-optical-illusions/nature-sadness-illusion-2/


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Crying Illusion

Optical illusion of a mans face in rocks with crying looks
http://www.illusionspoint.com/billboard-optical-illusions/crying-illusion/http://www.illusionspoint.com/billboard-optical-illusions/crying-illusion/


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Count The Number Of Blocks

Illusionary picture of number of blocks shown


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Have you ever experienced that moment, when the drawing of theold witch transforms into a

young lady? Or stared at a Magic Eye picture of coloured dots to suddenly see abutterflyemerge?Or that moment in the film The Matrix when Neo sees the data that makes the world in zeros andones?
http://files.sharenator.com/illusion_Optical_illusions-s300x369-13681-580.jpghttp://files.sharenator.com/illusion_Optical_illusions-s300x369-13681-580.jpghttp://stereogrammes.org/d/26398-3/butterfly.pnghttp://stereogrammes.org/d/26398-3/butterfly.pnghttp://stereogrammes.org/d/26398-3/butterfly.pnghttp://hunternuttall.com/blog/wp-content/uploads/2010/06/matrix-code-agents.gifhttp://hunternuttall.com/blog/wp-content/uploads/2010/06/matrix-code-agents.gifhttp://files.sharenator.com/illusion_Optical_illusions-s300x369-13681-580.jpghttp://files.sharenator.com/illusion_Optical_illusions-s300x369-13681-580.jpghttp://stereogrammes.org/d/26398-3/butterfly.pnghttp://hunternuttall.com/blog/wp-content/uploads/2010/06/matrix-code-agents.gifhttp://hunternuttall.com/blog/wp-content/uploads/2010/06/matrix-code-agents.gif


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copy of how the brain interprets complex visual scenes is an enduring mystery for researchers

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