Illustration of the final parameters for the
best-fitting signal detection account of the present experiment

The results of this experiment merit several conclusions. First, the weight of evidence more strongly favors a signal detection account of the pigeons= choice behavior in this task than does the HTT/default response account. Interpreted within this signal detection framework, we also established that the variance of the distribution of strength of evidence associated with the Different displays was substantially greater than that of the Same displays (s5_Same < s5_Different). Further, the variance estimates associated with color, shape, and redundant signal distributions were, within the limits of measurement error, probably equivalent (s5_color = s5_redundant _ s5_shape). Finally, the results suggest that performance with redundant displays was equal to the additive combination of discriminative performance on color and shape trials (d'_redundant = d' _color + d' _shape). Together, these observations best fit the predictions of a unidimensional decision model -- one suggesting that these birds were making their discriminations based on the extraction of a single type of information from the different types of textured stimuli.

The figure below visually depicts these conclusions and their structural implications for the decision space used by the pigeons.