How did studies of the African gray parrot Alex show that parrots can connect sounds with meaning?

Studies conducted by animal behaviorist and psychologist Irene Pepperberg with the African gray parrot named Alex were instrumental in proving that parrots can associate sounds with meaning, rather than simply mimicking human speech.1

Using positive behavioral reinforcement, Pepperberg trained Alex to interact with his environment through language. By the time of his death in 2007, Alex demonstrated significant cognitive abilities, including:1

• Categorization: He could correctly label objects based on five shapes and seven colors.1
• Quantitative Skills: He was able to use English to count up to six.1
• Differentiation: He could distinguish groups of objects by their color, material, and shape.1
• Communication: He used English to interact with other parrots in the lab, encouraging or chastising their efforts at labeling and categorization.1

These findings challenged long-held theories that birds were capable only of rote mimicry, demonstrating instead a level of comprehension and intelligence comparable in some respects to that of a three- or four-year-old human child.12