Final answer:
To determine if a stimulus is a reinforcer for a person, the most scientific method is to conduct an experiment where the stimulus is presented after a behavior and changes in behavior are observed. This method is grounded in the principles of operant conditioning, as proposed by B. F. Skinner.
Step-by-step explanation:
To determine whether a particular stimulus is a reinforcer for a particular person, the most scientific and reliable method is to experiment by presenting the stimulus contingent upon a behavior and observe changes in behavior. This method, encapsulated in option C, is based on the principles of operant conditioning. If the presence of the stimulus increases the likelihood of the behavior occurring again, then it can be considered a reinforcer. This method of behavioral analysis allows for a clear understanding of the relationship between a behavior and its consequence.
This approach aligns with the work of the psychologist B. F. Skinner, who emphasized the importance of reinforcements and their consequences in the learning process. It is through this reinforcement that behaviors can be shaped and learned. In contrast, the other options such as observing emotional reactions (A), asking the person directly (B), or relying on general assumptions (D) might not accurately indicate whether a stimulus serves as a reinforcer because they do not involve a systematic study of behavior in relation to specific consequences.