Thursday, September 8, 2016

The macro- and micro- worlds in physics and perception

It is well established that there is a contradiction between gravitational physics and quantum mechanics. I shall refer to the former as macro-physics and to the latter as micro-physics. The laws of one do not apply to the laws of the other. The behaviour of particles in the micro-physical world is so unpredictable from the known laws that operate in the macro-physical world that Niels Bohr reputedly said, “Anyone who is not shocked by quantum mechanics has not really understood it”. Schrodinger – a pioneer in quantum mechanics - reputedly said, “I don’t like it and I wish I had had nothing to do with it”.

Ever since the early part of the last century, there have been many attempts to reconcile the two – among them string theory and quantum gravitation. These attempts has so far had no success, which is not to say that they will not be successful in the future.

There is an apparent contradiction in perception which, in some ways, parallels that in physics, although the similarity must not be exaggerated. It is, however, always interesting to draw parallels between remote fields, even if one does not illuminate the other.

As is common knowledge, in ordinary experience different visual attributes such as the colour, form and direction of motion of an object are perceived to be in precise spatial and temporal registration. Let us refer to this as macro-perception, or macro-vision.

One would be forgiven to assume from this common, daily, experience that, likewise, the very earliest visual experience, in what we can refer to as micro-vision – in the first 150 milliseconds after the appearance of a visual stimulus – its attributes of colour, form and motion will also be perceived as being in precise spatial and temporal registration.

But experiments show that this is not necessarily so. Apparently – dependent upon the task – subjects often perceive colours before perceiving the form (orientation) of the stimulus, and before perceiving its direction of motion. The difference in time between perceiving colour and direction of motion is about 80 milliseconds. This is a huge difference in neural terms, given that it takes about 0.5 to 1 milliseconds for the nervous impulse to travel from one nerve cell to the next. And, crucially, this temporal perceptual asynchrony could not have been (and was not) predicted from the apparently synchronous perception of different attributes in the macro-world of perception, just as the properties of the micro-physical world cannot be predicted from the laws governing the macro-physical world.

In general, physicists working in the macro-world are capable of developing their theories without paying much attention to the rules that operate in the micro-world; likewise, those working in micro-physics can ignore the rules that operate in the macro-world, which accounts for the enormous success of quantum mechanics.

Equally, neurobiologists concerned with macro-perception can (and have) generally ignored the rules that govern perception in the micro-world. This is well and good, except that it raises questions about the problem of what is known as “binding”, which refers to the bringing together of separately processed attributes (eg of colour, form and motion) to give us a coherent visual picture, with no trace of the asynchronous operations evident in the micro-world.

A similar dilemma faces physics. While it is possible for one arena of physics to ignore the other, this becomes a problem when things are projected backwards in time – billions of years ago – when the whole of the Universe was contained in a particle of infinite mass but of the size equivalent to a millionth of a millionth of that of an atom (or so physicists now believe). At such a small, micro-level, it is the rules governing the micro-world that must have been in operation. How these rules got transformed into the rules of the macro-world as the Universe began to expand after the “Big Bang” remains a puzzle.

Similarly, how the micro-perceptual, asynchronously operating world is transformed into the synchronous world of macro-perception remains a puzzle. An obvious explanation might be that the responses of cells are somehow ‘bound’ together to give us our unitary perception. But such a supposition brings numerous hurdles, among them that of the physiological mechanisms through which one group of cells in one area “waits” for another group of cells in a separate, specialized area, to terminate its task. This, so far, remains an unaddressed problem and no one has yet managed to clarify successfully how binding occurs.

Dragan Rangelov and I have suggested that the binding process that leads to the macro-world may lie in interactions beyond the perceptive cortex, but this is an idea that is entirely conjectural.

Remote though the worlds of physics and perception may seem, these parallels are worth drawing attention to.

©Semir Zeki

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