Measurement of Socket Discomfort -- Part II: Signal Detection

Document Type



The purpose of the study was to demonstrate how the psychophysical theory of signal detection (SDT) can be applied to the process of fitting sockets and used to model the ability of patients to make judgments concerning the expectation of discomfort problems when uncertainty exists. For experimental purposes, a signal was defined as the ability of a patient to detect aspects of socket geometry that could lead to discomfort or tissue breakdown after initial fitting. An experiment was designed that consisted of varying the check socket geometries for three transtibial amputees by inserting 1.6-mm and 2.6-mm thick wafers at the distal tibia and fibula head and asking the subjects to report the degree of certainty they had regarding the discomfort the socket might produce after a day of use. In addition, psychophysical category ratio scales were used to measure the magnitudes of the pressure, discomfort, and pain perceived by the subjects for each experimental condition. Two of the subjects were experienced prosthesis users, and the third was an inexperienced individual in the process of being fitted for a first temporary prosthesis. One experienced subject indicated with maximum certainty that any alteration which reduced relief at the distal tibia and fibula head by even 0.6 mm, the thinnest insert in the experiment (a pressure-sensing element), would produce intolerable discomfort. However, the other two subjects provided good experimental data representing a range of uncertainties, and receiver operating characteristic (ROC) curves were fitted to their responses. The curves for the inexperienced subject for the weakest signals presented (1.6-mm thickness) indicated performance no better than pure guessing, but performance improved for the thicker wafers (2.6-mm thickness). The ROC curves for the remaining experienced subject indicated much less uncertainty with the thinnest wafer and nearly perfect signal detection for the thicker wafer. Possible explanations for these results are presented. The paper also discusses how the probabilities associated with the four possible outcomes of the judgment task—hit, miss, correct rejection, and false alarm—are dependent on the relative costs and benefits of the outcomes.


Biomedical Devices and Instrumentation | Civil and Environmental Engineering | Civil Engineering | Engineering | Orthotics and Prosthetics


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