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The effect of prior experience on a current learning task is of the utmost relevance to theories of learning. In special cases, prior experience may even prevent subsequent learning. These cases can generally be thought of as instances of the blocking phenomenon (e.g., Kamin, 1969; Wagner, Logan, Haberlandt, and Price, 1968). Specifically, if a stimulus A is paired with a reinforcer so that a response comes under the control of that stimulus, then when a novel stimulus B is simultaneously compounded with A and also paired with the reinforcer, stimulus B does not acquire control over the response, as measured by presentation of B alone in extinction. Stimulus A is said to "block" the establishment of stimulus control by B.

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Thesis (Ph.D.)--Boston University. / This study used the procedures of classical conditioning to investigate the possibility of producing asthmatic bronchospasm as a conditioned response. In order to carry out this study equipment was developed which permitted the experimental operations to be carried out while disguising the purpose of the experiment from the subjects. In the experiment, bronchospasm, induced by inhaled acetyl beta methacholine chloride, and shown to be highly similar to the condition of the lungs in asthma, was paired with auditory or visual stimuli. Similarly, Isuprel-induced relief of bronchospasm was paired with another exteroceptive stimulus in an attempt to condition the end of the attack. Subjects, on the average, received ten to fifteen conditioning trials depending on their cooperation and availability. Of four subjects who completed the necessary trials evidence for conditioning appeared in two. Magnitude of the conditioned responses is not great, producing, on the average, reduction of about 8% of the vital capacity in five minutes. Both of these subjects show conditioning to the experimental situation; one of the two, conditioning to the exteroceptive stimuli presented by the experimenter. The fact that conditioning did not automatically result from the experimental procedure and the complexity of the conditioning process apparent from detailed examination of the individual cases, led to discussion concerning the nature of conditioning, with special emphasis on the new area of interoceptive conditioning. The author takes the viewpoint that a central emotional-expectancy is an important aspect of conditioned visceral responses, and rejects connectionism between an external stimulus and a response. In addition, one peculiarity of the conditioning done in this experiment is noted. The unconditioned stimulus, rather than acting on the sensory nervous system, produces direct local change in the lungs. The resulting lack of representation of the UCS in the central nervous system is discussed in the reference to classical Pavlovian theory. The writer sees the application of interoceptive conditioning techniques as a fruitful method for further exploration of psychosomatic disorders. [TRUNCATED]

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Elevators serve a critical function in essential facilities such as hospitals and need to remain operational during and after earthquakes. However, they are still known to malfunction during earthquakes even after several design and sensing improvements required by the current code have been incorporated. Most of the damages were experienced or caused by the rail-counterweight system. Being the heaviest component of an elevator, the counterweight induced strong dynamic effects to the guiding system sometimes even collided and damaged the passenger car. A realistic analytical model of rail-counterweight system of an elevator that includes details of the supporting system is developed in this study. The nonlinearities caused by closing of the code specified clearances play an important role in determining the dynamic behavior of the system, and are thus included in this study. Also included are the acceleration inputs from different floor of building and the effect of different location of the counterweight along the guide rail. Parametric study is carried out to investigate the effect of different parameters on the seismic responses of the rail-counterweight system. In order to improve the seismic performance of the rail-counterweight system, several protective schemes are investigated. One simple approach is to increase the damping of the system using additional discrete viscous dampers. However, there is not much space available for installing the devices, and placement parallel to the spring at the roller guide assemblies is not quite effective due to contact between the restraining plate at the roller guide assemblies and the rail that makes the roller guides ineffective. Another method is to convert the top part of the weights into a tuned mass damper. This method can reduce the maximum stress in the rail if designed properly. The effectiveness of the passive tuned mass damper can be improved further by using it in an active mode by installing an actuator between the mass damper and the counterweight frame. The numerical results that confirm the effectiveness of such an active tuned mass damper are presented. As an alternative to the fully active control scheme, a semi-active control scheme using a magnetorheological damper device between the mass damper and the frame is also studied. This control approach is found to be as effective in reducing the seismic response as a fully active scheme. Since this MR damper can be operated using a simple battery, the external power requirements for implementation of this approach are quite minimal. / Ph. D.

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No description available.