Skinner designed a soundproof apparatus, often equipped with a lever or bar, with which he conducted his experiments in operant conditioning. this has been called a

Skinner box

Explanation: Skinner box is referred as the environment to conduct an experiment to observe the natural behavior of the element in a chamber. The Skinner box is also known as operant conditioning chamber. It is most commonly used for the experiments to be conducted with the animals in the operant conditioning chamber for the research purpose.

It is also soundproof tool and also refereed as the lever box as it contains lever .Thus the answer is Skinner box.

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