The evolution of a model: A review of Thurstonian and conditional stimulus effects on difference testing

The application of Thurstonian modeling to difference tests is reviewed and explained non-mathematically. How experimental variables can affect the variance of perceptual distributions and reduce discriminability (d′ values) is described. The tendency of triangle and 3-AFC tests with one stronger stimulus and two weaker stimuli to be more sensitive than triads with one weaker and two stronger stimuli, is explained using the idea of conditional stimuli. From this, the development of sequential sensitivity analysis and the four distribution Thurstonian model is described. These ideas are then developed further to produce a potential eight distribution conditional stimulus model, to account for the effects of various interstimulus rinses and cognitive contrast. Also, the physical and physiological properties of the salt taste detection system, used in the development of these models, are outlined.