This volume is based on the 10th annual Harvard Symposium for the Quantitative Analysis of Behavior. The first Harvard Symposium was devoted to signal-detection analyses of reinforcement and choice behavior. The present volume reprises the original signal- detection theme, incorporating additional insights based on experimental and theoretical analyses undertaken during the years separating the two conferences. This collection illustrates how signal-detection theory, first advanced to account for performance in threshold-level sensory discrimination, has broadened to encompass a variety of...