PIGEONS SERIAL ORDERING OF NUMEROSITY WITH VISUAL ARRAYS

Pigeons were trained in a conditional discrimination paradigm to diffe rentiate successively presented visual arrays according to the relativ e number of their elements. Transfer tests with novel stimuli demonstr ated that they discriminated the categories of ''many'' (6 or 7) from ''few'' (1 or 2) items. In further tests, other new stimuli were intro duced that consisted not only of these training numerosities, but also of the intervening ones (3, 4, and 5). Variations in the birds' discr imination performance corresponded to the order of stimuli on a numero sity dimension. This serial ordering was maintained when other factors such as brightness, size, shape, area, and contour of the elements we re systematically controlled across tests. Smaller numerosities were s omewhat better discriminated than those at the higher end of this test range.