Rats were trained in a triangular-shaped pool to find a hidden platform, whose location was defined in terms of two sources of information, a landmark outside the pool and a particular corner of the pool. Subsequent test trials without the platform pitted these two sources of information against one another. In Experiment 1 this test revealed a…

We investigated how within-stimulus heterogeneity affects the ability of rhesus monkeys to order pairs of the numerosities 1 through 9. Two rhesus monkeys were tested in a touch screen task where the variability of elements within each visual array was systematically varied by allowing elements to vary in color, size, shape, or any combination of…

Pigeons learned discrimination rapidly and responded differentially to pictures seen for the first time. The essential feature of a natural discrimination--which is the ability to cope with natural ranges of variation--was approached and earlier experimental results were extended using other classes of stimuli. (Author/RK)