Final answer:
The child's reaction of fear towards gentlemen with a white beard, after being conditioned to fear Santa Claus, is an example of stimulus generalization, a phenomenon where a conditioned response is triggered by stimuli similar to the conditioned stimulus.
Step-by-step explanation:
The phenomenon you described, where a child who has been conditioned to fear Santa Claus and then reacts with fear towards any gentlemen with a white beard, is known as stimulus generalization. This occurs when a conditioned response (CR) starts occurring in response to the presentation of new stimuli that are similar to the conditioned stimulus (CS). In the famous experiment with Little Albert conducted by Watson and Rayner, the infant developed a fear of a white rat after the rat was repeatedly paired with an aversive loud sound. Little Albert then began to show fear towards objects that resembled the white rat, such as furry things and a Santa Claus mask, indicating stimulus generalization. While the UCS (Unconditioned Stimulus) was the loud noise, the CS was the white rat, the UCR (Unconditioned Response) was the fear caused by the loud sound, and the CR was the fear toward the white rat and similar objects.