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Time Perception

Posted on: October 1, 2007

How do we directly perceive time? This is a philosophical question with a biological answer. The first critical debates about the nature of observation took place in ancient Greece between the followers of Plato and Aristotle. Platonic doctrine held that perception is passive. The world exists as a collection of imperfect copies of ideal forms. The task of the senses is to collect impressions of the forms from examples, and the work of the intellect in the brain is to deduce the ideals. He taught this scheme with the metaphor of the cave. Sunlight passing around the ideal objects cast shadows on the walls, which the senses imprinted onto the body for reasoning by the soul. Aristotelians held that perception is active. The observer acts into the world transitively by probing, cutting and burning, thus to acquire the forms of objects, then intransitively to comprehend the nature of the forms by logic and induction — abstraction and generalization. They held that the actively beating heart is the seat of comprehension, not the motionless brain that serves merely to cool the hot blood.

In modern times Descartes succeeded in mathematizing the Platonic view, but he failed rather badly in his attempt to biologize it. He conceived that the soul, residing in the body like a pilot in a boat, took charge of the machine by controlling the flow of nerve spirits from the brain through the nerves into the muscles, inflating them to make them contract. Physiologists in Italy and the Netherlands quickly showed that muscles do not increase in volume when they shorten in length, and that the ends of cut nerves do not give off bubbles of nerve spirit when they are stimulated. Kant (1781) then revolutionized Platonic doctrine by postulating that the ideal forms are not in the world but in the human mind, and that the world is only indirectly accessed through the impressions that objects make on the senses, from which the intellect constructs representations of the objects. These are all that the observer can know, and not the thing-in-itself.

 Cartesian-Kantian doctrine flourishes today in cognitivism, just as the dinosaur is said to survive in birds, because representationalism is at the heart of the logical machines that serve for many people as the instantiation of true intelligence and the early harbingers of the coming termination of the age of biological dominance. In this passive view, time is represented in our minds by the image of a straight line. The line is dotted with the steps of binary digits and measured by the basic cycle duration of a Central Processing Unit (CPU). The components in bodies and brains that correspond to the CPU are the biological clocks that imperfectly and unreliably give us the time of day or the season of the year, and that express their output in volleys of action potentials, which neurobiologists refer to as “units” when observing them with microelectrodes in awake brains.

 Aristotelian doctrine evolved independently and in parallel. It was resurrected from Arabic translations and transformed in the 13th century by St. Thomas Aquinas (1272), whose mission was to make it compatible with the Christian concept of free will. He did this by distinguishing between his conceptions of the human will versus the Aristotelian concept of intention as biological destiny, which he said humans shared with other animals. Unlike philosophy, which has been dominated by the Platonic passive view, medical science has been dominated by the Aristotelian-Thomist view of active perception, in which the deterministic Cartesian reflex is given its place in the machine, but the maintenance of the machine, according to surgeons, is by healing through first and second intention, and the use of the machine by the pilot is through exercise of the will. The pre-existing word “voluntary” was adapted for this purpose into English by Thomas Hobbes (1651) in the 17th century from the Thomist Latin “volere”, and it was firmly placed in the cerebrum by a then eminent neuroanatomist, who left his name on the circle of arteries at the base of the brain, Sir Thomas Willis (1664, 1683). The concept of volition has served as the core explanation of brains in 19th and 20th century textbooks on physiology and neurology, as well as in the doctrines of pragmatism and existentialism, even though people have long since forgotten where it came from. In accordance with this view we perceive time through our experiences of taking action into the space around us.

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