Two types of bias in psychophysical detection and recognition procedures: nonparametric indices and effects of drugs.

In many conditional discrimination procedures, subjects are required to emit one of two responses in the presence of one stimulus and the other response in its absence. The two responses that occur may be formally differentiated, for example by their positions in the experimental space, and functionally differentiated, by the discriminative stimuli that control their occurrence. For example, the stimuli displayed on two response keys, such as color, may be discriminative stimuli for the particular key on which responses are reinforced. The behavior that occurs under these procedures can be analyzed according to signal detection methods for the control by the stimuli, or sensitivity, and the tendency to make one of the two responses, or bias. The present report describes a procedure that allows the independent assessment of position bias and bias towards the stimulus displayed on the response key and presents nonparametric formulae for their computation. Finally, some representative drug effects are shown indicating that certain drugs may selectively affect the two types of bias.