Determination of the just noticeable difference (JND) in trunk posture perception

The purpose of this study was to assess the ability of subjects to detect a visual difference between trunk postures. Three groups of participants, ranging from novices to experts, were required to make perceptual discriminations between two trunk postures from a series of image pairs on a computer screen. Images were presented for flexion and lateral bending motions from three different reference postures in both ascending and descending directions. Overall, direction played the largest role, interacting with all other variables. Subjects were most sensitive to changes in the ascending direction, where differences were detected at an average of 2°. In the descending direction, subjects detected differences at an average of 7° between postures. These data have implications for the usability and design of posture matching-based biomechanical software interfaces and the accuracy of peak and cumulative load estimates from models that utilize such interfaces to acquire segment posture inputs.