The Little Albert experiment, conducted by John Watson and his student Rosalie Rayner in 1920, is a landmark study in psychology that explored the principles of classical conditioning in humans. The primary objective was to determine whether fear could be conditioned in a human subject, building on previous research that had primarily focused on animals.

In the initial phase, known as the before conditioning phase, the unconditioned stimulus (UCS) was a loud noise produced by striking a steel bar with a hammer. This UCS elicited an unconditioned response (UCR) of fear in Albert, a 10-month-old boy, who would cry upon hearing the noise. The neutral stimulus (NS) in this phase was a white rat, which Albert showed no fear towards initially.

During the acquisition phase, Watson and Rayner paired the NS (the white rat) with the UCS (the loud noise). Each time Albert was presented with the rat, the loud noise would follow, leading to the UCR of fear. After several trials, Albert began to exhibit a conditioned response (CR) to the rat alone, indicating that the NS had transformed into a conditioned stimulus (CS). This demonstrated that the previously neutral rat could now elicit fear on its own.

Following the conditioning, researchers examined whether Albert's fear could generalize to other stimuli. They found that Albert exhibited fear responses not only to the white rat but also to similar objects, such as a fluffy white bunny and a Santa Claus beard. This phenomenon, known as stimulus generalization, illustrated that conditioned fears could extend beyond the original CS.

Additionally, the study investigated the persistence of the conditioned fear over time. It was observed that Albert's fear responses diminished in the days and weeks following the trials, suggesting that the fear was not deeply ingrained. This decrease in fear may be attributed to the artificial nature of the conditioning process, as opposed to a naturally occurring traumatic event that might have resulted in a more lasting fear response.

Despite its historical significance, the ethical implications of the Little Albert experiment cannot be overlooked. Modern ethical standards, enforced by Institutional Review Boards (IRBs), prioritize the physical and emotional safety of participants, making such experiments unacceptable today. However, it is believed that Albert's fear likely subsided after the experiment, as he had no ongoing reason to fear the previously neutral stimuli.

In summary, the Little Albert experiment remains a foundational study in psychology, demonstrating that classical conditioning can effectively explain emotional responses and complex behaviors in humans. Its findings have been supported by subsequent research, solidifying the relevance of classical conditioning in understanding human behavior.