Pavlov's experiment.

[A_hma_d]

What observation led Pavlov to study classical conditioning?

[Scooby]

Pavlov was studying the role of salivation in digestion in dogs by measuring the amount and rate at which saliva was produced when the dogs ate. He noticed that the dogs began salivating not only in response to food, but also at the sight of the technician who fed them and the sound of a bell used so that he wouldn't forget to feed them, which led him to investigate classical conditioning 

[A_hma_d]

Thanks.
And also why is UCS is called neutral stimulus?

[Soul_Khan]

I think the conditioned stimuli (CS) which is associated with another stimuli e.g. when the bell was associated with the meat powder (UCS) is called a neutral response because at the start it produces no response but as you further condition it it produces a response (CR). The UCS is not neutral at all because it always produce a particular consistent response. In short when the CS is not fully conditioned yet it is a neutral stimulus, it ceases to be neutral when it produces a response after it becomes associated.

But feel free to disagree guys.

[Scooby]

Alright, so in Pavlov's experiment, the taste or smell of meat caused the dogs to start salivating. Therefore, the taste or smell of meat is the unconditioned stimulus, and the salivation due to the taste or smell of meat is the unconditioned response.

In classical conditioning, the unconditioned stimulus is associated with the neutral stimulus. In Pavlov's experiment, the neutral stimulus would have been the sound of the bell - it is neutral because it doesn't produce the unconditioned response.

Once an association has been formed between the two stimuli, the neutral stimulus becomes the conditioned stimulus, which again is the sound of the bell. The conditioned stimulus is able to produce the conditioned response - salivation due to the sound of the bell - even without the presence of meat