Abstract

Trained to a smaller number of elements versus a larger one and then tested faced with the larger number and twice the smaller one, one set on the left and the other on the right of the larger number, the ants essentially reacted to the smaller number located on the left of the larger one. Trained to a larger number of elements versus a smaller one and then tested faced with the smaller number and twice the larger one, one set on the left and the other on the right of the smaller number, the ants went preferentially to the larger number located on the right of the smaller one. They similarly reacted when trained to zero versus 2 elements (mostly reacting to the zero element located on the left of the 2 elements), and when trained to 2 elements versus zero element (going essentially to the 2 elements located on the right of the zero element). Thus, the ants responded mostly to the left smaller and the right larger number of elements, and this only when a larger and a smaller respectively number of element was set in the middle. In the absence of the latter, the ants went equally to the left and the right numbers of elements. The ants arrange thus mentally the numbers (amounts) on a scale, a number line, locating the smaller quantities on the left and the larger ones on the right, as do humans and the vertebrates which have already been studied as for this numerosity characteristic. Also, the ants’ accuracy of response decreases with increasing numbers of elements.

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