How human eye figures out twisted and looped letters
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Last Updated: Wednesday, July 03, 2013, 16:45
  
Washington: A team of neuroscientists have demonstrated how complex a visual task or any image consisting of simple and intricate elements, actually is to the brain.

The task of human eye figuring out letters that are twisted and looped in crazy directions task is actually so complex that no one has been able to write computer code that translates these distorted letters the same way that neural networks can, which is why this test, called a CAPTCHA, is used to distinguish a human response from computer bots that try to steal sensitive information.

The researchers published two studies within days of each other to demonstrate the complexity of the tasks.

The findings of the study by Salk Institute for Biological Studies neuroscientists Tatyana Sharpee and John Reynolds take two important steps forward in understanding vision.

Sharpee, an associate professor in the Computational Neurobiology Lab, said that understanding how the brain creates a visual image can help humans whose brains are malfunctioning in various different ways - like people who have lost the ability to see.

She said that one way of solving that problem is to figure out how the brain - not the eye, but the cortex - processes information about the world and if you have that code then you can directly stimulate neurons in the cortex and allow people to see.

In these studies, the researchers sought to figure out how a part of the visual cortex known as area V4 is able to distinguish between different visual stimuli even as the stimuli move around in space. V4 is responsible for an intermediate step in neural processing of images.

Reynolds, a professor in the Systems Neurobiology Laboratory, said that neurons in the visual system are sensitive to regions of space - they are like little windows into the world.

He said that in earlier stages of processing, these windows - known as receptive fields - are small and only have access to info within a restricted region of space.

Reynolds asserted that each of the neurons sends brain signals that encode he contents of a little region of space - they respond to tiny, simple elements of an object such as edge oriented in space, or a little patch of colour.

Both new studies investigated the issue of translation invariance - the ability of a neuron to recognize the same stimulus within its receptive field no matter where it is in space, where it happens to fall within the receptive field.

The Neuron paper looked at translation invariance by analyzing the response of 93 individual neurons in V4 to images of lines and shapes like curves, while the PNAS study looked at responses of V4 neurons to natural scenes full of complex contours.

The Salk researchers found that neurons that respond to more complicated shapes - like the curve in 5 or in a rock - demonstrated decreased translation invariance. "They need that complicated curve to be in a more restricted range for them to detect it and understand its meaning," Reynolds said. "Cells that prefer that complex shape don't yet have the capacity to recognize that shape everywhere."

The findings of the two studies have been published in Neuron and June 24 in the Proceedings of the National Academy of Sciences (PNAS).

ANI


First Published: Wednesday, July 03, 2013, 16:44


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