Quantitative sensory assessment in toxicology and occupational medicine: applications, theory, and critical appraisal

Sensory systems are affected by a number of chemicals. Their functions can be quantitatively assessed with psychophysical methods. Psychophysics is the scientific study of the relationship between the physical dimension(s) of a stimulus and the behavioral response it generates. First, the unique contribution of psychophysics to toxicology is illustrated with a few examples taken from the fields of audition, vision, and somatosensory sensitivity. Then, a brief survey of the evolution of psychophysics is presented and followed by a review of its basic scientific foundations. Psychophysical evaluation is accomplished by delivering quantified stimuli in a prespecified order and by requesting a standardized response from the subject. Psychophysical methods specify the sequence of presentation of stimuli, and include the method of limits, the method of constant stimuli, as well as the adjustment and tracking methods. The response paradigms specify the standardized response the subject has to make to stimuli presented according to a specific format. The three major response paradigms are the yes-no, forced-choice, and rating paradigms. Sensory processes can be studied in humans as well as in animals by several techniques, such as classical conditioning, operant behavior, and reflex modulation. A critical review of the application of psychophysical methods and response paradigms is developed. Several examples illustrate the potential confusion brought about by unorthodox use of psychophysical terminology and methodology. Finally, a few suggestions are given for the evaluation of sensory processes in humans.