July 15, 2005 — An African gray parrot named Alex may understand the concept of zero, something which eluded mathematicians for centuries, according to a study described in a recent press release by Brandeis University.

The 28-year-old parrot spontaneously began using the word "none" when presented with an absence of objects during numerical tests, according to researchers Irene Pepperberg and Jesse Gordon, who described their findings in the May issue of The Journal of Comparative Psychology.

Alex possesses a "zero-like concept," said the researchers in the release. The pair are subjecting Alex to further tests to determine whether he truly understands the arithmetical concept of zero.

The concept of zero didn't come into widespread use in Western civilization until the 1600s, though it was being used in India a millennium earlier, said the release.

Zero and none are "not identical," said Pepperberg in the release. According to Merriam-Webster's dictionary, "zero" is an "arithmetical symbol...denoting the absence of all magnitude or quantity," while "none" means "not one" or "nothing."

Several years ago, Alex was taught that "none" means "lack of information." The researchers believe he may have spontaneously expanded this definition to describe something more akin to arithmetical zero.

According to the release, the big moment occurred while Alex was being tested for the ability to understand small numbers. In a typical test, the parrot was presented with three different sets of objects, each of a different quantity and color, and then asked to name the color of one of the sets.

When the tests first began, Alex was a whiz, despite his lack of training. But over time, his near-perfect performance dropped off. He would often not answer questions or, according to researchers, delight in deliberately giving incorrect responses.

One day, Alex was presented with sets of two, three and six objects. The researcher asked Alex, "what color three?" The bird responded "five," which made no sense. After several attempts to get the bird to concentrate, the exasperated researcher gave in and said, "OK, Alex, tell me: what color five?" to which Alex responded, "none."

"We cannot determine what cognitive process led to this behavior," the researchers said in the release. "We suggest only that his action, occurring soon after a period of noncompliance, resulted from a lack of interest in the given task and was a possible attempt to make the procedure more challenging."

Whether Alex meant, "I lack the information to respond to your question" or "there are no sets of five objects" is yet to be determined.

If further tests show that Alex truly understands arithmetical zero, he would be the first non-primate to grasp the concept, and the first animal to do so without training, according to the release.