Number comprehension by a grey parrot (Psittacus erithacus), including a zero-like concept.

  title={Number comprehension by a grey parrot (Psittacus erithacus), including a zero-like concept.},
  author={Irene M. Pepperberg and Jesse D Gordon},
  journal={Journal of comparative psychology},
  volume={119 2},
A Grey parrot (Psittacus erithacus) that was able to quantify 6 item sets (including subsets of heterogeneous groups, e.g., blue blocks within groupings of blue and green blocks and balls) using English labels (I. M. Pepperberg, 1994a) was tested on comprehension of these labels, which is crucial for numerical competence (K. C. Fuson, 1988; see also record 1987-98811-000). He was, without training, asked "What color/object [number]?" for collections of various simultaneously presented… 

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