Same-different texture discrimination in pigeons: testing competing models of discrimination and stimulus integration.

The choice behavior of 6 pigeons performing a mulltidimensional same-different texture discrimination was examined. On each trial, they had to choose among 2 choice hoppers depending on whether a color, shape, or redundant (color and shape) target signal was present or not in a textured stimulus. Receiver operating characteristic (ROC) curves were produced by variations in the priori signal presentation probabilities across conditions. Quantitative analyses of these ROC curves were used to evaluate different competing theories of discrimination (signal detection vs. high-threshold-default response models) and information integration (independent observations, additive integration, unidimensional models). The results suggested the structure of the pigeons' choice behavior in this same-different discrimination was best described by an unequal variance signal detection model involving a unidimensional evidence variable (e.g., degree of difference).