A Skinner box is used for

Concept — Operant conditioning is learning in which the frequency of a voluntary, emitted response is changed by the consequence that follows it: a reinforcing consequence raises the rate of that response and a punishing consequence lowers it. Studying it therefore demands a setting in which a single response can be emitted over and over, its consequence delivered immediately and automatically, and the resulting rate of responding recorded.

Application — The Skinner box, also called an operant conditioning chamber, is built to be exactly that setting. A typical chamber contains:

• a response device that the organism operates — a lever or bar for a rat, a lighted key or disc for a pigeon;

• an automatic dispenser that delivers a food pellet or a drop of water the moment the response is made;

• signal lights or a speaker that indicate when a consequence is available, and, in aversive studies, an electrified grid floor;

• a cumulative recorder that plots every response against time, yielding the rate-of-responding measure on which this form of learning is defined.

Because the chamber measures how often a freely emitted response occurs under a chosen consequence, Skinner used it to work out the schedules of reinforcement — fixed-ratio, variable-ratio, fixed-interval and variable-interval — and to demonstrate shaping through successive approximations.

Cross-check — The other categories of learning named in the question are investigated by quite different procedures:

• Verbal learning uses word lists, nonsense syllables and paired-associate or serial-recall tasks presented on a memory drum to a human learner.

• Motor learning uses skill apparatus such as the mirror-drawing board, the pursuit rotor and star-tracing tasks, scoring accuracy, errors and time on target across practice trials.

• Incidental learning is produced by an orienting cover task followed by an unannounced retention test, since what defines it is that the learner had no intention of learning.

• Classical conditioning, the other conditioning paradigm, uses Pavlov's harness-and-salivation arrangement, because there the response is elicited by a stimulus rather than emitted by the organism.

The apparatus therefore belongs to operant conditioning: a Skinner box is used to study how the consequences of an emitted response change the rate at which that response occurs.