In the experiment with Little Albert, the unconditioned stimulus was _______.

A) the experimenter
B) the laboratory
C) the loud noise
D) the rat

The unconditioned stimulus in the Little Albert experiment was the loud noise that was created by striking a metal bar with a hammer behind Albert's head, which naturally elicited fear as an unconditioned response. The rat was the neutral stimulus that later became associated with the fear response through classical conditioning.