John B. Watson’s most famous record of experiments took place in 1920, testing whether classical conditioning could be used on children to produce an emotional response through neutral stimulus by misplacing distress from two different stimuli. Albert B., a healthy but allegedly rather emotionless infant, was presented with various stimuli, including dogs, rabbits, and rats, and with masks (without and with hair) and cotton wool. His responses were generally of interest but no fear.
Later, Albert was given a white rat again, but when he reached out to touch him, Watson or his assistant would make a loud noise, causing the child to cry in distress. After repeated exposure to this behavior, Watson introduced the rat without any noise, and Albert begin crying as soon as he spotted him. Eventually, Watson found out that the child reacted similarly towards all furry creatures, and even masks with cotton-wool beards by placing his distress on things that held similar features to the rat.