The Little Albert experiment
That participant of the experiment was a child who, for the experiment, was called "Albert B" or just "Little Albert". When the child was nine months old, behaviorist John B. Watson and a graduate student named Rosalie Raynor exposed him to a series of different stimuli (a white rat, a monkey, a rabbit, masks, and burning newspapers) and observed his reactions. Initially, he showed no fear to any of the objects. The next time Albert was exposed to the rat, Watson paired it with a loud noise (hitting a metal pipe with a hammer). Of course, Albert began to cry. After many times of the rat being paired with the noise, Albert instantly began to cry upon seeing the white rat.
The result of this experiment was Little Albert crying upon seeing the white rat after many times of hearing a loud noise accompanied with the rat. The neutral stimulus was the rat, the unconditioned stimulus was the loud noise, the unconditioned response was fear, the conditioned stimulus was the rat, and the conditioned response was fear. By today's standards, this experiment could not be reproduced because it would be deemed unethical.
I chose this experiment because of how 'text book' it is. In my research I read that this is found in virtually every introduction to psychology course. I don't think that this experiment is especially bad, but it did use a small child who didn't really have any knowledge of what was going on. It could be argued, though, that this is better because it is a more natural response. I find this experiment to be an interesting display of a human beings ability to be conditioned to respond a certain way.