Two Measures of Tactile Acuity in CRPS Type I Patients

tactile acuity as measured by 2-point-discrimination

Thresholds on the tip of the index finger of boths hands are assessed using the method of constant stimuli. One single needle and seven pairs of needles with different spacings are tested in randomized order. After each presentation, the subject has to report the sensation of one or two needles by answering immediately "one" or "two." Each distance is presented eight times resulting in 64 single decisions. The summed responses are plotted against distance as a psychometric function for absolute threshold and get fitted by a binary logistic regression. Thresholds are taken from the fit at the distance at which 50% correct answers are given

Time frame: unique measurement of maximal one hour duration

tactile acuity as measured by the Grating Orientation Task (GOT)

Stimuli are taken from a set of dome-shaped plastic gratings with equal groove and ridge widths. Gratings are applied to the immobilized distal fingerpad of the index finger of boths hand with the ridges oriented either along or across the long axis of the finger in randomized sequences of the two alternatives. Subjects have to report the orientation of the gratings as "along" or "across". The largest groove widths in the set is 6mm, the minimal width is 0.5mm. Thresholds were taken from the groove width at which the performance was 75% correct. Unless the performance is exactly 75% for a particular grating, interpolation between gratings spanning the 75% correct responses ared used

Time frame: unique measurement of maximal half an hour duration