Case study on repeatability of a threshold-based calibration method for electrocutaneous feedback systems
Start date: 10 April 2012
Electrocutaneous feedback systems have the potential to be used in cases where people have impairment in the sensory modality. We developed a device that uses electrocutaneous feedback to redirect sensation from the feet to the upper limb for people with sensation loss in their extremities caused by diabetes or other diseases. To install the device electrodes have to be placed in the area of the upper leg. In order to adapt the device to the wearer’s requirements in terms of sensory thresholds a calibration method was designed and implemented to define the sensory thresholds. The calibration procedure increases the pulse width, starting from 0, by adding 4 µs every 0.3 seconds to increase the pulse width. Once the pulse width has reached a level where it starts to feel uncomfortable the user of the device confirms the maximum threshold by pressing a button. The pulse then decreases until the user presses the button again. To test the repeatability of the calibration method a case study on one subject was performed. The test person had to confirm the maximum and minimum threshold 10 times following the calibration procedure. Then the results were analyzed. The standard deviation of 5 µs for the maximum pulse width and 17.6 µs for the minimum pulse width demonstrated that the repeatability of the calibration method is significantly good considering the fact that the step width of the increase was 4 µs per 0.3 seconds. No correlation could be found between the trial number and the maximum and minimum pulse width. The calibration method was found to be adequate to define the range of comfortable sensation and can be used for other electrocutaneous feedback system in situations where the interval of stimulation has to be in a certain range.