Abehavior change that is produced by differential reinforcement in which members of the current response class occur with greater frequency and unreinforced members occur with less frequency resulting in the emergence of a new response class is called

Response differentiation

Explanation:

Response differentiation was seen in the Skinner experiment conducted on rats in a Skinnerian box. When an animal has to be trained in the Skinner box and it is clear that it learns the nature of ope-rant conditioning which is called a response differentiation.

For instance, by changing the response requirement rat have to learn to depress the lever to get the food. It is very precious to learn to depress the lever.  

Thus here in the above statement, all process is related to the response differentiation.