RELATIVE NUMEROSITY AS A DIMENSION OF STIMULUS-CONTROL - THE PEAK SHIFT

Pigeons were trained to discriminate between arrays containing equal n umbers of two different elements as S+, and arrays which contained mor e elements of one kind than the other as S-. They were then tested wit h the full range of the proportions of the two elements. This resulted in behavioral contrast and peak shift, as the pigeons responded more to arrays containing more positive than negative elements than they di d to the positive training arrays. These findings were obtained with e lements that differed in color (blue vs. red dots) and with elements t hat differed in orientation (horizontal vs. vertical rectangles). The results indicate that the stimulus control exerted by the derived dime nsion of relative numerosity involves the same processes as the fundam ental dimensions that characterize simple stimulus elements.