Figure 5.  Results of a generalization test for birds that were trained to discriminate between two sound intensities. The proportions of responses to the high intensity key, R2, are shown as a function of sound intensity. The solid dots are the proportions for the stimuli used in training. The open dots are the proportions for the generalization test stimuli. The smooth curves fitted to the data are based on our signal detection analysis of these data (see Heinemann et al., 1969).