What limitation did Skinner face regarding the generalization of his research?

Skinner's research primarily involved operant conditioning with animals, particularly rats and pigeons. A significant limitation he faced regarding the generalization of his findings is that the behavior of these animals could not be easily extrapolated to human behavior. The reasoning behind this is based on the complexity of human psychology, which includes cognitive processes, social influences, and emotional factors that were not present in Skinner's animal subjects. This variation in behavior between species raised questions about the extent to which his findings could apply to human learning and behavior in various contexts.

The other options highlight different aspects of the research environment or methodology but do not directly address the core issue of generalizability to humans. For example, although experiments may have been conducted in controlled environments, the unique responses of animals cannot adequately reflect the multifaceted nature of human behavior. Similarly, if rats showed unpredictable behavior under pressure or if results were not replicable, these issues pertain to the reliability and validity of the findings rather than the generalization to human behavior specifically.