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Alex Understands Concept of Zero

By Betsy Lindsay

For the past 28 years, Dr. Irene Pepperberg has been doing research on cognition and communication in African grey parrots. She has shown that, far from being mindless mimics, greys can be taught to understand human speech and use it in meaningful ways. Alex, her oldest research subject, now 29 years old, has recently demonstrated that he understands the meaning of his labels for numbers and that he may even have a concept of zero. These findings were published in the May, 2005, issue of Journal of Comparative Psychology . The results of the study indicate that Alex's ability to understand numbers is comparable to, or may even surpass, that of chimpanzees and very young children.

Comprehension of Number Labels

The purpose of the study was to provide evidence that Alex could understand his number labels fully, rather than merely produce them. Alex, who had received no previous training on the task, was presented with various collections of objects on a tray. He was shown either three different sets of 1 to 6 of the same objects but of different colors (for example: 2 red blocks, 4 yellow blocks and 5 green blocks). Or he was shown three sets of different objects, each set being a different color and number (for example: 1 blue block, 5 yellow pompons and 3 orange keys). The blocks were scattered randomly on the tray, and Alex was asked the question, “What color X?” where X is a number from 1 to 6. Alex gave the correct answer in an impressive 58/66 trials--87.9% accuracy. The results show that Alex understands what his number labels represent. It also shows that he does better at such tasks than children up to 3-years-old, who, for example, may point to each of a set of three objects and say, “1, 2 , 3”, but not fully understand that three objects are present.

A “Zero-Like” Concept

On one of the trials in the above experiment, Alex was presented with a set of two, three and six objects and asked “What color 3?” He answered “five.” When questioned twice more, he replied “five” both times. The experimenter then asked, “OK, Alex, tell me, what color 5?” He immediately answered, “None.” This was the correct answer, since there was no group of five objects on the tray. Alex had apparently used “none” to indicate the absence of a quantity, although he had never been taught to do so. He had previously used “none” to indicate that no category (color, shape, or material) was the same or different when he was asked about the similarity or difference between two objects. For example, when shown two identical objects and asked “What's same?” Alex would say “none”. Alex then spontaneously transferred his response to the question “What color bigger?” When first shown two differently-colored objects of identical size and asked, “What color bigger?” he said, “What's same?” When queried again, he answered “None”. Now he had used it to indicate an absence of a quantity.

In order to be sure that Alex's new use of “none” was not a fluke, the experimenters gave Alex the opportunity to respond “none” in future trials. On these “none” trials, Alex's accuracy was 5/6--83.3%. As Dr. Pepperberg had not trained Alex to use the term “zero”, his use of “none” was impressive for several reasons. Since the use of zero by humans is more recent than the use of other numbers, the use of a zero-like concept by a parrot, whose walnut-sized brain is so small and so different from ours, is quite an accomplishment. Also, the idea of none , even though Alex had previously used it to indicate an absence of similarity or difference, is abstract and relies on the violation of the expectation that something will be present. Therefore, Alex's ability, without training, to transfer “none” to the domain of absence of quantity was unexpected. Finally, and perhaps most importantly, Alex's use of “none” was impressive because it was his own idea to do so. Dr. Pepperberg believes that Alex has a “zero-like” concept, though it may be somewhat different from that of humans.

Future Research

Dr. Pepperberg still does not know whether Alex can count in the same way that humans do. True counting is complex and requires (1) producing a standard series number tags, such as 1, 2, 3, etc; (2) giving each item to be counted its own unique number tag; (3) remembering which items have already been counted; and (4) knowing that the last number tag indicates the total number of items. For quantities of four or less, Alex may be subitizing. That is, he may perceive the number of objects at a glance, as we do when we count the number of spots on dice. Future research will be needed to determine whether Alex is counting quantities larger than four or if he is using some other cognitive strategy. Dr. Pepperberg is also studying whether Alex can add and subtract small quantities.

This article was published in Issue 012 of Nature's Corner® Magazine. All rights reserved. No part of this article may be reproduced in any form without the permission of the author.

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