Student or Learner
One African grey parrot Alex is said to have the cognitive abilities of a five-year-old child. Alex can identify 50 different objects, seven colors, five shapes, quantities up to six, and the concepts of bigger, smaller, same and different. Also Alex is considered to make reasoned decisions. During an experiment, researchers gave Alex different-colored blocks in sets of two, three and six. When asked which color group had five blocks, Alex replied, “None.”And he answered the same in repeated tests. Obviously, he interpreted the concept of “none” as an absence of quantity all on his own.
What does the underlined sentence mean in this passage?
Please be aware that I'm neither a native English speaker nor a teacher.