The International Society for Psychophysics

Stephen Link
University of California, San Diego

Douglas Vickers, age 64, died suddenly at his home in Adelaide, Australia, on October 31, 2004. He is survived by his wife Yvonne, children Marc and Anne, and six grandchildren. His impressive career as a theoretical psychologist, experimental scientist, and mentor to famous students spanned forty years. Held in the greatest esteem, his students refer to him as a teacher of unfailing sincerity who was generous and warm in his dealings with others.

Vickers’ graduated from Edinburgh University in 1961, and continued to an Honours BA Degree from Cambridge University where he placed first in of the Natural Sciences Tripos (Part 2). In 1967 he received his Ph.D. supervised by Alan Welford. In 1994 Cambridge honored him with its Sc.D. In 2000-2002 Douglas Vickers served as President of the International Society for Psychophysics.

Douglas’ scientific career began in earnest with the famous Shallice and Vickers (1964) paper “Theories and experiments on discrimination time” in volume 7 of Ergonomics. This important review of psychophysical models provided an English approach to a topic of deepening interest in Europe and the United States. His Ph.D. thesis “Visual discrimination and the perception of visual depth” (1967) continued his exploration of perceptual phenomena investigated by psychophysical means. Professor Malcom Jeeves, Head of the Psychology Department at Adelaide University, offered him a Position as Lecturer and Doug immigrated to Australia.

At the time Alan Welford championed investigations of models of the time taken to perform judgment tasks. In 1970 Vickers added new ideas to the ongoing scientific adventure in the paper “Evidence for an accumulator model of psychophysical discrimination.” The theory can be imagined as a stochastic development of Fechner’s theory of sensory representation and Thurstone’s idea of comparative difference. The simplicity of the theory is its charm: two stimuli, a single distribution of sensory differences (a la Thurstone), two accumulators, and two response outcomes. The beauty of the theory is the vast number of predictions made about response probability and response time. In a way, the two accumulators race to be the first to generate a response.

The 1976 meeting of Attention and Performance VII, offered Douglas an opportunity for an important advance in the accumulator theory. The title of the paper, “An adaptive model for simple judgment,” does not prepare one for the major extensions suggested and empirically evaluated. The two accumulator model is described and then a three category model is described to account for judgments of sameness and difference. The manner in which parameters of the theory adapt to experimental conditions is discussed. Then, in a stunning contribution to psychophysical theory, Vickers provided further theoretical investigations and elaborations that accounted for the third important measurement variable, response confidence. In his book “Decision Processes in Visual Perception” (1979) Vickers provided a broad survey and theoretical investigation of simple decision processes, confidence and adaptation, and complex decision processes. This monograph followed up Vickers’ previous paper (“Where Angell feared to tread: response time and frequency in three- category discrimination”, 1975) by proposing a theory of equal judgments that yielded a convincing account of much experimental data. With references to 538 important experimental and theoretical papers, this masterful treatment of decision processes merits the attention of modem scholars, and is one of the most important psychophysical publications in the 20th century.

Decades of investigations into the underlying mechanisms of human perception and cognition followed this propitious beginning. The following jointly-authored articles provide an impression of the many different ideas and applications of Douglas’ contributions: “Effects of alternating set for speed or accuracy on response time, accuracy and confidence in a unidimensional discrimination task” in 1982, “The accumulator model of two-choice discrimination in 1988, “Interoperative patient controlled sedation” in 1991, “Intelligence and visual and auditory discrimination” (1995), “Towards a dynamic constructionist model of memory,” (1996) “Memory capacity and intelligence,” ( 1997), “Never cross the path of a traveling salesman,” (1998), “Human performance on visually presented traveling salesman problems,” (2001 ), “Towards a generative transformational approach to visual perception,” (2001), “Decision making and memory,” (2001), and “The perception of minimal structures,” in 2003 – just a sampling of his wide-ranging scientific interests.

Douglas gave members of the International Society for Psychophysics (ISP) new ideas on a regular basis. His publications at the ISP meetings began in 1989 with “Stopping rules in discrimination models,” and continued with “Individual differences in the rate of accrual of information, the FAST (frequency accrual speed test) index,” (1990), “Confidence and memory in simple judgments,” (1999), “Decision making and memory: Predicting accuracy, response time and confidence on individual trials,” (2000), “Where does the balance of evidence lie with respect to confidence?” (2001), and “Confidence and time in three-category judgments” (2003).

He was the organizer of many scientific sessions including “Human Decision and Choice” at the Twelfth Annual Conference of the Australian Psychological Society (1977), “Decision and Control Mechanisms in Perception and Memory” at the XXIV International Congress of Psychology (1988), “Theoretical Modeling in Psychophysics ” at the Sixteenth Annual Meeting of the International Society for Psychophysics (2000), and “Confidence and Psychophysical Judgments” at the Nineteenth Annual Meeting of the International Society for Psychophysics (2003). He was a member of the Organizing Committee of the 29th Experimental Psychology Conference in Adelaide, Australia, (2002) and Organizer for the Twenty-First Annual Meeting of the International Society for Psychophysics to be held in Adelaide, Australia in 2005.

Beyond these major events Doug also provided the field with his capabilities as reviewer of journal submissions, grant” applications, manuscripts, conference submissions and professional appointments. He was a founding member of Non-linear dynamics, Psychology and Life Sciences and Editor, with P. L. Smith, of Proceedings of the XXIV International Congress of Psychology (Volume 2) entitled Human Information Processing: Measures, Mechanisms and Models. He reviewed articles for such major journals as Psychological Review, Journal of Mathematical Psychology, Acta Psychologica, Perception, Journal of Experimental Psychology: Human Perception and Performance, Psychonomic Bulletin & Review, Perception & Psychophysics, Memory & Cognition, Australian Journal of Psychology, Perceptual and Motor Skills, Personality and Individual Differences, and Nonlinear Dynamics, Psychology and Life Sciences.

I believe that, in appreciation of this remarkable life, we should celebrate Doug’s career – a career peopled by famous teachers, outstanding contributions to our science, memorable lectures, insight, wit, intelligence, esteem, and international recognition. We can celebrate his many contributions through our fond memories of a charming colleague, an excellent scientist, and, to so many, a very good friend.