Obituary: Jan E.R. Frijters (1947-2022

Abstract

Jan Frijters was born in Eindhoven, the Netherlands in 1947. From 1967 to 1972 he studied psychology in Utrecht, where Ep Köster’s classes in psychophysics and perception motivated him to continue working in the field. The work Jan performed at the Spelderholt, an agricultural poultry institute, became the basis for his PhD thesis “Psychophysical and Psychometrical Models for the Triangular Method,” which he defended in Utrecht in 1980, again with Ep Köster.

Jan was intrigued by the question of how we could measure the sensations that people perceive, these internal representations that are private and cannot be observed from the outside. He built his research on classical psychophysical methods, starting with Thurstonian modeling and Signal Detection Theory. In one of his classic papers with the elusive title “The Paradox of Discriminatory Nondiscriminators Resolved,” he describes how the differences in the number of correct responses between the triangular test and the 3-alternative forced choice (3-AFC) test can be explained by task differences. While the triangular test asks to pick the deviant sample, the 3-AFC procedure asks to pick the least or most intense of 3 samples. In either case, a statistical argument would suggest that P(correct) = 0.33. However, the 3-AFC task is easier because participants already know whether the target sample is more or less intense than the others. The descriptions of the cognitive decision rules underlying simple psychophysical tasks, calculating the expected response distributions, and their use in interpreting the outcomes of sensory tests have found application in sensory testing labs around the world and have formed the basis for standardized ISO testing protocols.