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Grey parrot numerical competence: a review

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Abstract

The extent to which humans and nonhumans share numerical competency is a matter of debate. Some researchers argue that nonhumans, lacking human language, possess only a simple understanding of small quantities, generally less than four. Animals that have, however, received some training in human communication systems might demonstrate abilities intermediate between those of untrained nonhumans and humans. Here I review data for a Grey parrot (Psittacus erithacus) that has been shown to quantify sets of up to and including six items (including heterogeneous subsets) using vocal English labels, to comprehend these labels fully, and to have a zero-like concept. Recent research demonstrates that he can also sum small quantities. His success shows that he understands number symbols as abstract representations of real-world collections, and that his sense of number compares favorably to that of chimpanzees and young human children.

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Notes

  1. Note that the estimation of larger versus smaller in the salamander study might have arisen from the amount of movement rather than of number.

  2. This percentage represented 106 matches of 108 vocalizations. As an additional control, the principal investigator made two transcriptions of a student, new to the lab, as he responded to the same type of questions as Alex. The first transcription was live; the second, made several days later, was of a tape from which all questions had been edited. The two transcriptions of the student's vocalizations matched to within 95.8% (68 of 71 vocalizations).

  3. If we indeed factored this possibility of error into our calculations, I would have to use much higher chance values for all the experiments. As noted, I always used the more conservative value of chance.

  4. On one trial during a comprehension study, Alex was asked “What object is purple?” when no purple object was present in an attempt to determine if he would use “none”; he requested a grape (Pepperberg 1990). Although the likelihood of his requesting that particular item was small (1/11 even if we restrict chance to foods he could label at the time rather than his entire repertoire), the request could simply have been one of his frequent requests for treats during sessions. We did not pursue this line of inquiry further.

  5. Alex's “none” is unlikely to be related to a child's “allgone”: He did not use the term after eating all the jelly beans or after tossing all the blocks to the floor, which is the common response of children.

  6. Other studies have used smaller quantities (e.g. 0–4, which are within what is generally accepted as the subitizing range), and will not be discussed because tasks involving these small quantities can be solved by perceptual mechanisms (see discussion in Beran 2004). Experiments with Alex specifically involved quantities >4 so as to test his capacities beyond the subitizing range.

  7. An example might help here: Let us assume that a bird can sing a song and can make a one-to-one correspondence between the notes in the song and various objects as they are placed in each pile \(\ldots\) and it gets a reward for choosing the pile with more “stuff”. So it might, for a given trial, sing “The itsy bitsy spider went up the water spout, down \(\ldots\)” for one pile and \(\ldots\)“The itsy bitsy spider went up the water spout, down came \(\ldots\)” for the other, and choose the pile associated with the longer song; in an “addition” study, it then adds one or two notes to the appropriate song depending on what is added to which set \(\ldots\) but has not a clue as to how many things are in each pile, merely still a sense of more versus less.

  8. Alexandrian Greeks, for example, used zero to denote the absence of quantity, but it did not function for them as a number (Kline, 1972).

  9. Some researchers are truly wedded to the accumulator model and others to object files, and considerable controversy exists as to which should prevail. At some point, every researcher must weigh the data on both sides and decide which are more convincing; I agree with Mix et al.

  10. A reviewer has suggested that Alex is using an accumulator that, over the course of the many years that he has been exposed to numbers, has been sharpened such that errors at discriminating neighboring numerosities have been reduced. Such would, of course, also be true for humans, and would be impossible to distinguish from counting for both humans and animals. I leave it to the readers of this paper to evaluate this possibility.

  11. Note definition of counting in the Introduction; Alex does not vocally tag items, which is why his behavior can only be considered “like” human counting.

  12. Note that Coull and Nobre (1998) suggest that the left IPS is more active in temporal attention and the right IPS in spatial attention, but Fias et al. (2003) find more activity in the left IPS for representation of symbolic and nonsymbolic magnitude. All cited studies do, however, implicate the IPS in numerical tasks.

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  1. Department of Psychology, Brandeis University, Waltham, MA, 02454, USA

    Irene M. Pepperberg

  2. Department of Psychology, Harvard University, William James Hall, Vision Science Center, 33 Kirkland Street, Cambridge, MA, 02138, USA

    Irene M. Pepperberg

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This contribution is part of the special issue “Animal Logics” (Watanabe and Huber 2006).

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Pepperberg, I.M. Grey parrot numerical competence: a review. Anim Cogn 9, 377–391 (2006). https://doi.org/10.1007/s10071-006-0034-7

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