Based on the empirical evidence accumulated through thirty years of research, Pavlov was convinced of the idea of the four basic temperaments. He noted that these temperaments approximated closely to those differentiated in man by Hippocrates. Though various blends of basic temperamental patterns appeared in Pavlov's dogs, they could be distinguished as such instead of by creating new categories.
The first type corresponded with Hippocrates's "choleric" type which Pavlov called "strong excitatory." The second type: "sanguine" which Pavlov named "lively", applied to dogs of a more balanced temperament. The normal response to imposed stresses or conflict situations by these two types was increased excitement and more aggressive behavior, but that is where the similarity ended. The "strong excitatory", or choleric, type would turn so wild as to be completely out of hand as opposed to the "sanguine" type which continued to behave with purposeful and controlled reactions.
The phlegmatic type, Pavlov called "calm, imperturbable," and the melancholic was called "weak inhibitory" type. In these two types, imposed stresses and conflict situations were met with more passivity or "inhibition" rather than aggression. The "weak inhibitory" type, or melancholic, constitutional tendency was to meet anxieties and conflicts with passivity and avoidance of tension. Any strong experimental stress imposed on such a dog's nervous system resulted in the dog being reduced to a state of brain inhibition and "fear paralysis."
Pavlov found that the other three types, when faced with more stress than could be coped with by the usual means, would also eventually enter a state of brain inhibition similar to that state entered very quickly by the melancholic/weak inhibitory type. He regarded this as a protective mechanism normally employed by the brain as a last resort when pressed beyond endurance. The "weak inhibitory" type was an exception to the other three types: this type of dog went into a state of protective brain inhibition more rapidly and in response to lighter stresses. The important finding was, of course, that the four basic natures responded differently to different levels of stress both before, during, and after experiments, the most important datum being that the weak inhibitory type was particularly susceptible.
Regarding the weak inhibitory type, Pavlov observed that though the basic temperamental pattern is inherited, every dog has been conditioned since birth by varied environmental influences which can produce long-lasting inhibitory patterns of behavior under certain stresses. Therefore, the final pattern of behavior of any given dog will depend on both its own constitution as well as specific patterns of behavior induced by prior environmental stresses. [2]
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Among Pavlov's most important findings was what can happen to conditioned behavior when the brain of a dog is pushed to the "ultraboundary" limit by stresses and conflict beyond its habitual response capacity. He was able to bring about what he called a "rupture in higher nervous activity" by utilizing four main types of imposed stresses.
1) The first type of stress was simply an increase in the intensity of the signal to which the dog was initially conditioned. If this was gradually increased, at a certain point, when the signal was too strong for its system, the dog would begin to break down.
2) The second way of achieving the ultraboundary event was to increase the time between the giving of the signal and the arrival of food. If a dog was conditioned to receive food five seconds after the warning signal, and this period was then prolonged, signs of restlessness and abnormal behavior would become evident in the less stable dogs. Pavlov discovered that the dog's brains revolted against any abnormally long waiting period while under stress. Breakdown would occur when the dog had to either exert very strong, or very prolonged, inhibition. (Human beings also find protracted waiting while under stress to be debilitating: worse than the event that produces the anxiety.)
3) The third way of inducing a breakdown was to confuse the dogs by anomalies in the conditioning signal. If positive and negative signals were given one after the other, (yes, no, yes, no, etc), the hungry dog would become uncertain as to what would happen next and this disrupted the normal nerve stability. This is also true with human beings.
4) The fourth way of inducing a breakdown in a dog was to destabilize the dog's physical condition in some way, either by subjecting it to long periods of work, inducing gastro-intestinal disorders, fever, disturbing the glandular balance, surgery, etc.
If, in any case, the first three methods would fail to induce a breakdown in a particular dog, it could be achieved by utilizing the same stresses that had failed, but doing so only after initiating the fourth protocol: physical destabilization. Pavlov also discovered that, after physical destabilization, a breakdown might occur even in temperamentally stable dogs and also that any new behavior pattern occurring afterward might become a fixed element of the dog's personality even long after recovery from the debilitating experience.
In the weak inhibitory type of dog, new neurotic patterns implanted under such conditions could frequently be readily removed by little more than doses of sedatives. But in the calm and lively types - which often needed to be surgically castrated in order to physically debilitate them sufficiently to cause a breakdown - Pavlov discovered that the newly implanted pattern was quite often ineradicable after the dog had recovered its health. Pavlov thought that this was due to the natural toughness of the nervous systems in such types of dogs. The new behaviors were difficult to implant without temporarily induced debilitation and subsequently seemed to be as strong a part of the dog's "stubborn nature" as the old pattern.
As observed by Pavlov, tolerence of stimulation varies greatly between individuals. Highly sensitive persons may be overstimulated by the loud volumes in a movie theater or the background confusion of a large social gathering. Other individuals will find those same stimulations as ideal stimulation levels, or even understimulating.