Psychometric functions for efficient and effective psychophysical testing of sensory function.

An efficient test for sensory function has been reported using random order pairs of real and sham stimuli. The constant magnitude of the real stimulus is chosen such that the first error in a patient's forced-choice report on the order of real and sham stimulation, immediately indicates abnormal sensory function. This magnitude just exceeds a critical large percentile of the psychometric function (i.e. the relationship between percentage of detection and stimulus magnitude in healthy subjects). The aim was to determine psychometric functions for one tongue site and six facial sites for adjusting three variants of the real/sham stimulus method (i.e. for light touch, cold sensation and for two-point discrimination). All 150 healthy subjects participated in testing for light touch sensation, 100 subjects additionally participated in testing two-point discrimination and 50 subjects participated additionally in testing cold sensation. The stimulus magnitude was varied using a staircase-limits procedure. Following curve fitting with a Boltzmann function, 90th, 95th or 99th percentiles of the psychometric functions were determined. A set of at least two real/sham tests, one testing the function of large nerve fibres and one for small fibres, allows quick assessment of a patient's disturbed sensory function including its fibre pathology.