A girl arrives home from school to find a delicious cupcake sitting on the counter. As she eats it, a mouse scurries across the floor and triggers intense fear in her. Now, years later, the girl can't stand the taste of cupcakes. She has developed a taste aversion. Which is the unconditioned stimulus?

B) Mouse

Explanation:

The unconditioned stimulus is the one that evokes an automatic, natural or unconditional response from the person. It is one of the vital elements of classical conditioning which is an association of conditioned and unconditioned stimulus.

In this question, the mouse is the unconditioned stimulus as it evokes a sense of fear and panic into the girl naturally without any action. The reaction of the girl is quite automatic and no prior learned behavior exists here. Thus, the mouse exemplifies the unconditioned stimulus.