Psychophysical testing in human populations exposed to neurotoxicants

Sensory organs can be studied from different points of view: biochemical, morphological, electrophysiological, clinical, and psychophysical. In this paper, the psychophysical and electrophysiological approaches are discussed and compared. Even though close parallels have been drawn between these two methodologies, discrepancies clearly indicate that they do not measure the same phenomenon. Vibration sensitivity is used to illustrate the role sensory assessment plays in neurotoxicology. Several psychophysical techniques are described to measure this sensory modality. Emphasis is placed on the need to quantitatively define stimulus parameters. The validity of vibration sensitivity as an indicator of sensory peripheral nerve dysfunction is established through a review of diseases, physical agents, pharmaceuticals, and other neurotoxicants known to alter the morphology and/or the physiology of the peripheral nervous system or sense organs. A series of factors or conditions affecting vibration detection thresholds, such as age, laterality, gender, temperature and others, are examined. Finally, a review of the psychophysical methods and procedures illustrates the advantages of the forced-choice paradigm and the tracking technique over other procedures and methods of stimulus presentation. The importance of psychophysical assessment of sensory functions in neurotoxicology is emphasized.