stimulus–organism–response psychology: an extension of the S–R psychology of behaviorists incorporating the notion of Robert S. Woodworth that factors within the organism help determine what stimuli the organism is sensitive to and which responses may occur. The O factors could be biological or psychological. S–O–R psychology has been extended beyond classical conditioning and instrumental conditioning to encompass areas such as marketing and consumer behavior. For example, an individual’s emotional state when shopping may influence how many products he or she purchases and the particular types or brands.