Modern examples, such as Alex the African grey parrot, which could count up to six and knew sums and differences, are seen by some as special cases or the product of conditioning.

较近的例子，比如能数到6，懂得和与差的非洲灰鹦鹉alex，它只不过是特殊条件或训练的结果。

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For the past 30 years, Dr Pepperberg, who studies parrots at Brandeis University in Massachusetts, has been producing research papers on the cognitive abilities of her African Grey, Alex, who died in September 2007 and who was the subject of an Economist obituary.

ECONOMIST: Alex the African Grey