"THE MAGIC LOOM"
| "THE MAGIC LOOM" | |
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| Feedback Systems Yesterday brought one of those times when reality demonstrates theory. I had spent too long crouched over the computer's keyboard, so was pleased when a friend, Paula, telephoned me. She was acting as locus parentis to four refugee children from war-ravaged Bosnia. "Would I be prepared to join them for a beach picnic?" ""For sure!" The company of other people seemed a better alternative to watching lines of code tracking across the screen. We live in one of those seaside towns that saw its heydays in the Victorian era, flourished again in the post-war years of the 1950's, then gave up the ghost during the reign of Baroness Thatcher. Sited in a fold of the cliffs between the Kent countryside and the English Channel, its somnolence is only disturbed by the air traffic that uses the airfield a couple of miles inland. Although the town is directly under the flight path, its inhabitants have become habituated to the din of low-flying aeroplanes. How automatic it becomes for us to assume that what does not affect us will not harm others. We were crossing Harbour Street when the two military jets roared in from the sea and over the rooftops above our heads. The transition was instantaneous. One moment we had been a laughing group of people on the way to the picnic. The next moment Paula and I were left staring at each other as the three eldest children disappeared. One lad had scooped up his sister to throw them both into the doorway of a shop. The other lad just dropped flat onto the sidewalk to roll sideways underneath a parked car. Only little Stefano was left, clinging to me, stiff with terror. |
| It took several minutes of soothing reassurances before they were able to proceed. The warm sand and small waves delighted them but they were not happy on the beach. Too much open sky, too little shelter. It was with all-round sighs of relief that we departed in the direction of the nearest ice-cream parlour. I was glad that the coastguard station had not had occasion to fire the lifeboat maroons while we were there. The effect of the rockets exploding overhead would have been disastrous. What had happened was that deep in the children's middle brains the amygdala had snapped into automatic mode at the first perception of incoming planes. A million years ago that selfsame circuitry would have sent our forebears racing for cover at the first syllable of a carnivore's roar. It is but one of the brain's internal control and regulatory systems that retains its long heritage. It is one that we can learn to bring under conscious control. A literal translation of homeostasis is 'to remain the same'. The process relies on feeding back part of the input to a system to control its output. We would die if our body's homeostatic system was to fail for even a very short time. Our internal temperature would rise or fall according to the temperature around us; causing us to either freeze or overheat. We use mental feedback and feedforward systems in our daily lives without even being aware of their presence unless we are training for something that requires a new set of co-ordinated steps. They are the great tools for regulating change. |
| The players of any ball game are familiar with them, but, because a Frisbee can change its direction, altitude and velocity during flight, it provides a textbook demonstration of the principles involved. Watch an experienced player and you will see them fix their eyes on the Frisbee as their partner shapes up for a throw. All details are being fed into working memory. The release force, initial angle of takeoff and amount of spin are noted. To these are added any indications of breezes providing airlift at the throwers end, the height of surrounding bushes, and any gaps in them that will cause air eddies, patches of bare earth that may produce warm thermals that can lift the Frisbee by anything from a few inches to thirty feet. All of this is being plotted to calculate the disks final arrival point, which could be some distance from the receiver; so both the receiver and the disk are moving while the process is going on. The final intent is to arrive at the right place at the right time to pluck the disk from the air, possibly at the top of a high leap, without getting a fingernail ripped off. The full performance takes place while the disk is travelling a distance of about 80 yards at around 20 m.p.h. The number of mental calculations is phenomenal, and each new interpretation has to be translated into co-ordinated muscular reactions. This is an example of the brain's processing units using feedback plus feedforward. |
| A simple explanation of the principles involved is by way of a couple of examples of their use in engineering. During the Middle Ages, Europe was dependent upon its watermills and windmills to feed the population. When the rivers ran too high or the winds became too strong, the mills had to be closed down lest they be shaken to pieces by their own millstones. Although mainly ignorant of the brain's internal functions, the earliest engineers made great efforts to devise similar regulatory systems. With the Industrial Revolution, steam was harnessed to drive every conceivable machine.  It had a drawback. When the boiler was stoked, it developed a full head of steam, and the spinning wheels of the machines hurtled around. As the fires burned down, so the wheels turned slower, producing material of uneven quality. The diagrams show one of the many methods used to overcome the problem. The self-regulating system is composed of the spring-loaded piston [Diagram A]. Where it was found that a steam pressure of 98 pounds was best for turning the wheels,the spring could be made to withstand pressures of up to 100 pounds before being compressed. Normally, steam from the boiler would rise through the  inlet and pass through to the machinery. When the pressure rose beyond the optimum, It would force the piston back, overcoming the strength of the spring. [Diagram B] As the piston moved backwards,it would uncover the outlet safety valve and steam would be vented off. This would cause the internal pressure to drop below the set level. The spring would then reassert itself to push the piston forward, thus closing off the valve.Similar methods, using bi-metal bars instead of springs, are used to regulate our domestic hot water systems; while electronic versions are found in many appliances such as hi-fi sets. The human body uses numerous variations of feedback controls, the one most frequently observed being perspiration. We can survive within a very narrow band of internal temperatures, the optimum being 98.4 F. When external temperatures threaten us, our homeostatic controls take over. Pores open to discharge moisture over the skin. The heat causes this moisture to evaporate, and evaporation causes the surface temperature to drop. When a cloud covers the sun, temperature drops and the pores close to conserve internal heat. |
The mind also has its feedforward systems,  and it is these that we can learn to use to our advantage. Feedback is not always used to lower the reaction to a stimulus, many are designed to amplify the output; a weak input signal being magnified in increasing steps. It is the process by which an uneasy feeling can be raised to fear, to panic, to blind terror.The progression of steps through irritation to mindless rage is another example of how the primitive brain can overreact to a situation, swamping any attempts to rationalise events. A mechanical, amplified output system can be illustrated as follows: When the piston is forced back by pressure from Boiler A, it now permits the addition of the higher pressure from Boiler B. The output is now not only greatly magnified but the combined pressures keep the piston jammed back in the open position. It will stay like that until both boilers are exhausted. |