Close Up (Jul-Dec 1928)

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CLOSE UP The next reel shows the well-known experiments upon dogs. Food in a dog's mouth is naturally productive of saliva ; an unconditioned reflex. But from long continued association, the mere sight of the food will produce of itself saliva and therefore a conditioned reflex. It is easy to watch this in the film. An artificial opening is made " in the salivary duct from the paratid gland and a glass balloon is fixed to the opening connected by tubes with a recording instrument in another room. The dog is shown eating and the glass balloon fills with saliva. Further shots show it filling when the dog is merely shown food and before it reaches the mouth. Then another experiment was presented in which a metronome was started at a hundred beats and just after the hundred the dog was fed. After this had been repeated a number of limes the dog began to secrete saliva at the start of the metronome. But if a metronome of fifty beats a minute is started and no food is given and this is repeated a number of times, the dog produces less and less saliva at each repetition and a negative conditioned stimulus has arisen. Further experiments were shown with monkeys. A bell rings or at a certain metronome beat a blue plate is pushed within the monkey's reach with food. As soon as the monkey hears the accustomed sound, its ears prick and it climbs hurriedly down towards the expected morsel. But if another sequence of beats be used or a red plate the monkey remains on his perch, totally uninterested. Pavlov claims that these experiments are doing much to discover the nature of sleep, and even of neurasthenia, and that he is able to produce both in his dogs by giving them too 28