The overall goal of this experimental protocol is to evaluate how quickly and accurately an individual can respond to specific types of vibrotactile stimuli. This method could help answer key questions in the rehabilitation engineering field such as what type of sensory information can be communicated through vibrotactile feedback and what is the best way to represent sensory information through vibrotactile signals. The main advantage of this technique is that it is very flexible for different bio feedback applications and can be easily adapted for use with a variety of bio sensors such as pressure sensors for measuring reaction force, or goniometers for measuring joint angles.
Though this method provides insight into how people respond to vibrations apply to specific areas of the thigh, it can also be extended to other areas of the body. By testing different tactile configurations, we can better understand what types of information can be communicated through bio feedback. Demonstrating this procedure will be Sam Shi a graduate student in our lab.
Begin the motor calibration by connecting the large microcontroller board to the computer using a USB port. Within the original microcontroller software, click the upload icon denoted by the circled right arrow to upload the custom script motor_test. ino to the board using the USB connection.
Then connect the Z axis output of the triaxis accelerometer to one of the analog input ports of the smaller microcontroller board. Connect the positive and ground leads from the accelerometer to the thigh bolt and ground ports of the microcontroller board respectively. Next mount the accelerometer to the vibrating motor ensuring that its z axis is orthogonal to the flat surface of the motor and then place the motor on a hard surface.
Open the motor_calibration. vi file in the data question software and connect the smaller microcontroller for the accelerometer to the computer through a USB port. Then using the fields provided, specify the serial port for the microcontroller input as well as the sampling rate of 500 hertz and 1000 samples to collect.
Using the fast 48 transform display on the motor_calibration. vi interface identify the largest peak and record the corresponding vibration frequency value. Repeat all of the steps thus far as well as manually record the pulse with modulated or PWM frequency relationship for each motor.
Next open the experiment1. vi file for each motor. Right click on the dropdown frequency menu and select property.
Under the edit items tab, use the table to enter the desired frequencies and corresponding PWM levels. Select okay to exit. Finally, after all motors have been calibrated use double sided tape to mount each one to the thigh.
Specifically place one motor on each of the anterior, posterior, medial, and lateral surfaces of the thigh approximately midway between the greater trochanter and lateral femoral condyle. To begin the first experiment, connect the push button directly to one of the computer's USB ports using a serial to USB connector and ensure that all required drivers are installed. Open the experiment1.
vi interface and select the file to record the results. Next, use the dropdown menus in the software interface to select the push button input ports and motor frequencies. Start the program.
When the participant feels a vibration, have them press the push button with the leg where the feedback is applied. After the button has been pressed, confirm the response in the data acquisition software interface by noting that the clock has stopped counting. Finally select the new set of frequencies from the dropdown menus to reset the motors for the next trial.
Begin the second experiment by connecting a second push button to another USB port using a serial USB connector. Then open the experiment2. vi data acquisition interface.
In order to examine frequency sensitivity at different portions of the leg place a single motor on the thigh midway between the greater trochanter and the lateral femoral condyle on each of the anterior, posterior, lateral, and medial surfaces. Next click on the motor icons in the software interface to select specific motors to be activated as well as the desired sequence of frequencies. To test user sensitivity, to frequencies at 140 hertz, 180 hertz and 220 hertz start by selecting a single combination.
For example 180 hertz followed by 140 hertz. Input the wait time and motor time. Then start the program.
To test other frequency combinations, select a new test of frequencies such as 220 hertz, followed by 180 hertz and rerun the program. Finally have the participant press one of the two push buttons to choose whether the second perceived frequency was higher or lower than the first and observe the responses that are automatically recorded by the program. The results of the fast 48 transform of the acceleration data are shown here for a single motor undergoing calibration.
Four trails were conducted to identify the PWM level corresponding to the 180 hertz vibration. When comparing able bodied individuals with three individuals with transfemoral amputations reaction times for the able bodied individuals significantly decreased as frequency went from 140 hertz to 220 hertz. While those for the individuals with amputations did not.
Once mastered, this protocol can be completed in 30 minutes to an hour depending on the number of frequency location combinations tested. While attempting this procedure, it is important to ensure that the trackers maintain good contact with the thigh throughout the experiments. Care should be taken to confirm that the trackers are secure before each trial.
While the protocol described here uses push buttons to record the user response, the method can be extended to other response mechanisms that are more physiologically relevant such as bending the knee. After its development, this method paved the way for researchers in the field or rehabilitation engineering to explore different strategies for communicating sensory information from a variety of sources through vibrotactile feedback in able bodied individuals as well as those with lower limb amputations. After watching this video, you should have a good understanding of how to evaluate the speed and accuracy of user responses to different combinations of vibrotactile stimulation frequency and location.
