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

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.

A non-binding resolution to the binding problem?

Contributed jointly by Dragan Rangelov and myself

The binding problem is a specific example of a more general problem in brain studies, namely that of integration, that is to say of how the many, specialized, areas of the brain interact to provide the integration that is evident in our perceptions, thoughts and actions.

Binding has come to refer more to this problem within the confines of the visual brain. Here the binding problem becomes the problem of how the several, parallel, processing systems in the brain interact to give us our unitary perception of the visual world, in which different attributes such as form, colour and motion are seen in precise spatial and temporal registration.

The initial mistake is to suppose that we do see these attributes at precisely the same time. In fact, psychophysicalexperiments show that this is not true and that we see and become aware of some visual attributes such as colour before we see and become aware of others, such as motion.

This raises a question which has so far remained un-addressed, namely of whether there is some central station in the brain that “waits” for all the processing systems to complete their tasks before “binding” the results of their operations. There clearly is no such system because, over very brief time windows, we bind the colour that we see at time x to the motion that we had perceived 80 ms before. We therefore mis-bind in terms of the objective reality.

We discussed this issue some two years ago while at a meeting and thought that we should conduct some more experiments on this problem. Our approach was as follows: we presented subjects with lines of different orientation that could be in a number of colours. If colour is bound to orientation at perceptual or pre-perceptual stages, then the accuracy of reporting one attribute, say colour, should co-vary with the accuracy of reporting the other attribute (orientation), when the two are presented to subjects over very brief time windows.

If, however, the two attributes are not bound at the pre-perceptual or perceptual stage, then the accuracy of reporting one attribute (colour) should vary independently from the accuracy of reporting the other (orientation).

Our results, just published, showed that the accuracy of reporting the two attributes is independent, with the accuracy of reporting colour being always greater than the accuracy of reporting the orientation, probably reflecting the fact that colour is perceived before the orientation of lines by about 40 ms.

This suggests that these two attributes, at least, are not bound at either pre-perceptual or perceptual stages.

This result leads us to conclude that binding does not occur by physiological interaction between cells in the visual areas, but rather occurs at pos-perceptual stages, perhaps through the intervention of memory. We only experience attributes as being bound even though they are not bound physiologically, and only because they occur within the same, very brief memory time window.

Our results may provide, we think, an interesting resolution to the  binding problem, namely that there is no such problem to resolve at the perceptual level.

If binding occurs post-perceptually, then the search for how binding occurs shifts to a different arena.

Time will tell whether we are correct in our interpretation. 

We may of course be wrong, but we hope that our new view provides the ground for interesting new experiments and debates.