Which research method was primarily used in the Pepperburg study?

The Pepperberg study primarily utilized a case study research method, which involves an in-depth investigation of a single subject or a small number of subjects over time. In this case, Dr. Irene Pepperberg focused on the African grey parrot named Alex to explore his cognitive abilities, particularly in the areas of language comprehension and communication. The case study approach allowed for detailed observation and analysis of Alex's behavior and interactions in various contexts, providing rich qualitative data about his learning processes and cognitive skills.

While longitudinal studies look at subjects over an extended period to observe changes, or experimental methods manipulate variables to establish cause-and-effect relationships, the case study offers a depth of understanding of a unique subject's complex behaviors and learning, which was essential in evaluating Alex's capabilities. Cross-sectional studies, on the other hand, compare different groups at a single point in time, which was not the method used in the Pepperberg study. Thus, the case study method was the most suitable choice for exploring the intricate details of Alex's cognitive behaviors.