Process in which the frequency or predictability of a behavioral response is increased through reinforcement (i.e., a stimulus or a reward for the desired response). Classical, or respondent, conditioning, which involves stimulus substitution, is based on the work of Ivan Pavlov, who conditioned dogs by ringing a bell each time the aroma of food was presented. Eventually the dogs salivated when the bell rang, even if no food odour was present; salivation was thus the conditioned response. In instrumental, or operant, conditioning, a spontaneous (operant) behaviour is either rewarded (reinforced) or punished. When rewarded, a behaviour increases in frequency; when punished, it decreases. Operant conditioning was studied in detail by B.F. Skinner.
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Control of temperature, humidity, purity, and motion of air in an enclosed space, independent of outside conditions. In a self-contained air-conditioning unit, air is heated in a boiler unit or cooled by being blown across a refrigerant-filled coil and then distributed to a controlled indoor environment. Central air-conditioning in a large building generally consists of a main plant located on the roof or mechanical floor and intermittently spaced air-handling units, or fans that deliver air through ducts to zones within the building. The air then returns to the central air-conditioning machinery through spaces called plenums to be recooled (or reheated) and recirculated. Alternate systems of cooling use chilled water, with water cooled by a refrigerant at a central location and circulated by pumps to units with fans that circulate air locally.
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Of people and animals: