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quinta-feira, abril 05, 2007

Semana da Física Biológica - Física da Psicofísica




A. Uma visão esquemática do potencial de ação idealizado. Ilustra as suas várias fases à medida que ele percorre um único ponto da membrana plasmática. B. Registros reais de potenciais de ação são comumente distorcidos em comparação às visões esquemáticas devido a variações nas técnicas eletrofisiológicas de registro.

Figuras da Wikipédia para meu minicurso na Semana da Física Biológica em São José do Rio Preto (informações ainda não estão nesta página, mas acho que logo estarão). Vou falar do meu trabalho com o Mauro, ver aqui (atenção, copyrighters, não fui eu que coloquei na net isso!), aqui, aqui, aqui e aqui. Somos até citados aqui (não sei se isso é bom ou não):

Criticality of the Brain and Criticality of Art

Igor Yevin

Mechanical Engineering Institute, Russian Academy of Sciences

1. Criticality of the Brain

The ability of our brain to respond to small extrinsic or intrinsic perturbations points out that the brain as a complex system is operating close to instability, or criticality, because any system at the critical state has a very high sensitivity to tiny perturbations [Haken 1996]. Per Bak gives another reason why the brain should be critical: the input signal must be able to access everything that is stored in the brain. The brain cannot be in subcritical state. In this case input signal would be access to only a limited part of information. But the brain cannot be supercritical either: in this case any input would cause an explosive process in the brain, and connect the input with everything that is stored in the brain [Bak 1996]. Hence, the waking brain must operate strongly at the critical state, where a neural network reveals Weber-Fechner logarithmic law and Steves power law [Kinouchi 2006]. The critical point maximizes information transmission within a neural network.
(...)

D.Chek Ling Ngo and L.Seng Teo proposed an objective measure for quantitative evaluation screen layouts balance for computer graphic but this method does not fit for investigation of painting pictorial balance [Chek Ling Ngo D 2001].

[Paro o Mauro Copelli e Pedro Maldonado:] More promising for painting is empirical approach based on eyes-movements studies. As one gathered information from a picture, the eyes move in rapid jumps or succades followed by pauses of fixation. The average duration of fixation is typically between 200 and 300 milliseconds. The map of the location of fixations, called a scanpath, provides a graphic record of how information is selected and processed perceptually as a viewer looks at a picture.

One of the first eye-movement investigations of pictorial balance in painting was the work by Nodine in 1982 [Nodine 1982]. Nodine created a less-balanced version of each examined painting by cutting a copy of original apart and rearranging the pictorial elements. Comparison of fixation times of original versus altered version of paintings revealed that a change in the balance structure of the compositions produces a change in the pictorial weights (by changes in viewing time) of the key elements of the paintings.

As well known, balancing state may be stable or unstable. No doubt, R.Arnhiem considered compositional balance in painting as a stable state. Indeed, he wrote in his book "Art and Visual Perception": "It must be remembered that visually, just as physically, balance is the state of distribution in which everything has come into standstill…..In physics the principle of entropy, also known as the second law of thermodynamics, asserts that in any isolated system each state represents an irreversible decrease of active energy. The Universe tends toward a state of equilibrium, in which existing asymmetries of distribution will be eliminated” [Arnheim1964].
Of course, compositional balance in painting is always unstable, because adding or removal of any element in a canvas upsets this balance

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