Range effects using instrumental choice procedures

Pigeons were trained to discriminate visual flicker-rate stimuli using two types of instrumental choice procedures. One experiment used a free-operant concurrent schedule with multiple schedule components. Two additional experiments used a two-alternative, discrete-trial procedure. In all experiments, the range of training stimuli was manipulated across conditions. Results from all three experiments showed typical range effects on discrimination performance. That is, performance declined with increases in the overall range of variation of training stimuli. These range effects occurred with either continuous response rate measures or discrete choice measures. Moreover, range effects appeared with relatively high or low levels of overall discrimination accuracy and with either symmetrical or asymmetrical extensions of stimulus range. The results of these experiments suggest that increasing stimulus range influences both perceptual sensitivity and bias to response alternatives.