The russian physiologist ivan pavlov discovered that
1) dogs would salivate to the sound of a bell due to habituation
2) dogs would salivate to the sounds of a bell due to reflexology
3) dogs would salivate to the sound of a bell due to a learned response called conditioning
4) dogs would salivate to the sounds of a bell due to their fear response

3) dogs would salivate to the sound of a bell due to a learned response called conditioning

Explanation:

Ivan Pavlov, was a Russian physiologist and psychologist. Pavlov's original observations were simple. If food or certain diluted acids are put in the muzzle of a hungry dog, it begins to secrete a flow of saliva from certain glands. This is the reflection of salivation, but that is not all. Pavlov observed that the animal also salivated when the food had not yet reached the snout: the food simply seen and touched provoked a similar response. In addition, the dog salivaba before the mere presence of the person who usually approached him food or any other stimulus that systematically announced. This led Pavlov to develop an experimental method to study the acquisition of new stimulus-response connections. Undoubtedly, those he had observed in his dogs could not be innate or connatural of this kind of animal, so he concluded that they should be learned (in their terms, conditional). The first step, when this experiment is carried out, is to familiarize the dog with the experimental situation that it will live, until it shows signs of alteration, especially when the harness is placed and left alone in an isolated room. A small opening or fissure is made in the dog's jaw, next to the duct of one of the salivary glands. Then, a tube (cannula) of glass is placed so that the saliva comes out of it at the moment when the salivary gland is activated. The saliva goes to a glass container with graduation marks, to facilitate its quantification.