Like a slight person lifting a massive weight, it calls out for an explanation: How does it do so much with so little? Young, Shapley and Chariker are not the first to try and answer that question with a mathematical model. Mathematicians have a long, successful history of modeling changing phenomena, from the movement of billiard balls to the evolution of space-time.
LGN cells send the cortex a train of electrical impulses one-tenth of a volt in magnitude and one millisecond in duration, setting off a cascade of neuron interactions. Lai-Sang Young and Robert Shapley have devised a mathematical model that attempts to reproduce the processing abilities of the visual cortex.
Individual neurons receive signals from hundreds of other neurons simultaneously. Some of these signals encourage the neuron to fire. Others restrain it. As a neuron receives electrical pulses from these excitatory and inhibitory neurons, the voltage across its membrane fluctuates. The situation is even more complicated than that.
Those hundreds of neurons connected to your single neuron? Each of those is receiving signals from hundreds of other neurons. The visual cortex is a swirling play of feedback loop upon feedback loop. Earlier models of the visual cortex ignored this feature. In their initial paper , Young, Shapley and Chariker began to try and take these feedback loops seriously. Young, Shapley and Chariker demonstrated that their feedback-rich model was able to reproduce the orientation of edges in objects — from vertical to horizontal and everything in between — based on only slight changes in the weak LGN input coming into the model.
Vision is much more than edge detection, though, and the paper was just a start. A good model should replicate the same kinds of pulses when presented with the same stimuli.
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In , the three researchers published a second paper in which they demonstrated that the same model that can detect edges can also reproduce an overall pattern of pulse activity in the cortex known as the gamma rhythm. They have a third paper under review that explains how the visual cortex perceives changes in contrast. Currently Young, Shapley and Chariker are working on adding directional sensitivity into their model — which would explain how the visual cortex reconstructs the direction in which objects are moving across your visual field.
While their model is far from uncovering the full mystery of vision, it is a step in the right direction — the first model to try and decipher vision in a biologically plausible way. Get highlights of the most important news delivered to your email inbox.
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Foccacia bread is also synonymous with the city as is farinata, a flatbread made with chickpeas. Testaroli, a type of pasta from southern Liguria, is also popular, while vegetable quiche is eaten abundantly.
The Genovese also eat eggs, cheese and drink wine, with the added benefit of most of the ingredients they consume being produced locally or regionally. All three women were born in the city, albeit from different socioeconomic backgrounds.
Corsanego came from a bourgeois family that had the means to retreat to a mountain village in Piedmont during the second world war. She led a mostly privileged life and ate the best quality food.
Verdoia was born into a poor family, and Travi spent a period of her youth in a home run by nuns after her parents were left destitute. All three had one child. Verdoia is cared for by her daughter, who is in her 70s.
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Neither had parents or siblings who lived beyond All three eat a simple, fresh diet, which includes pasta and wine with every meal, as well as the typical Genoa staples of pesto sauce and focaccia. Over their lives they would deal with common ailments by letting them pass instead of taking medicine. Walking in the city is difficult to avoid, whether through the narrow alleyways of the centre or up and down the hills of neighbourhoods beyond. These are also fairly friendly, close-knit communities. It should instead be a good problem — living a long life should reflect that the quality of life and social system are good.
Friendship is another key, she said.