Name: a method for evaluating timeliness and accuracy of volitional motor responses to vibrotactile stimuli
Uploaded: 2016-08-02T14:00:00
Description: Watch this Scientific Journal Video about A Method for Evaluating Timeliness and Accuracy of Volitional Motor Responses to Vibrotactile Stimuli at JoVE.com

This protocol was developed for research supported by the Natural Sciences and Engineering Research Council of Canada (grant RGPIN 401963).

The following protocol was approved by the Research Ethics Board at Holland Bloorview Kids Rehabilitation Hospital.
1. Motor Calibration
<ol>
	<li>Connect the microcontroller board to the computer using an USB port.</li>
	<li>Using the original microcontroller software, upload the custom script, &#34;Motor_and_AccelerometerTest.ino&#34; to the board using the USB connection by clicking the &#34;Upload&#34; icon, denoted by the circled right arrow.
	<ol>
		<li>Ensure that the vibration level is set to zer...

<ol>
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The purpose of this protocol is to provide the framework for evaluating stimulation parameters in vibrotactile ASF applications. Specifically, it examines the effects of vibration frequency, amplitude, location, and sequence on user sensorimotor response. This framework can be built upon and expanded to incorporate additional or alternative types of user response that may be more clinically relevant, such as bending a joint or shifting weight from one leg to another. These types of changes would require slightly differen...

Artificial sensory feedback (ASF) can be defined as the practice of providing real-time biological information to individuals, often compensating for compromised proprioception or other sensory mechanism. ASF has been long used in the realm of rehabilitation of injured or disabled persons to assist in recovering of aspects of physical function and movement1-3, allowing individuals to control physical processes that once were an involuntary response of the autonomic nervous system4. A subcategory of ASF, biomechanical biofeedback, uses external sensors to measure parameters relating to balance or gait kinematics, and communicate this information to the individual through some sort of applied stimulus. An increasingly popular approach to biomechanical feedback employs small vibrating motors, or tactors, placed at different parts of the body to provide spatial as well as temporal feedback. Previous literature has showed promising results supporting the use of vibrotactile feedback in applications to individuals with lower-limb amputations, vestibular impairments, and aging-related loss of balance5-9.
A thorough understanding of the mechanisms controlling an individual&#39;s perception and response to specific stimuli is necessary for informing effective implementation of ASF systems for different applications. For vibrotactile feedback, chief among these mechanisms are proprioception and the sensorimotor response, specifically the user sensitivity to the applied vibrations and the time required to execute the desired reaction. Any sensory information communicated through vibration stimuli must be encoded as specific combinations of vibration frequency, amplitude, location, and sequence. Therefore, design of vibrotactile ASF systems should select combinations of parameters to maximize user&#39;s perception and interpretation of the stimuli, as well as the timeliness and accuracy of the resulting motor response. The goal of this protocol is to provide a platform from which to evaluate response times and response accuracy to various vibrational stimuli to inform the design of ASF systems for use with different sensory-impaired populations.
The methods described here builds on prior research exploring human perception of tactile and vibrotactile feedback3,5,6, and was developed for use in two previous studies10,11. The latter two studies employed this protocol to examine the effects of vibration frequency and location on the accuracy and timeliness of user responses in lower-limb amputees, showing that both parameters significantly affect the outcome measures, and that a high degree of response accuracy can be achieved. These results can be used to inform the ideal placement of tactors in future studies and clinical applications of vibrotactile ASF systems. Other recent work by Crea et al.12 examined user sensitivity to changes in vibration patterns applied to the thigh during walking, using verbal responses to signify perceived changes to the vibration patterns, rather than a motor response. While these verbal responses can be used to measure detection accuracy, they do not account for errors and delays that may be present in the motor control process.
The primary setup for the following experiments consists of a number of vibrating motors connected to pulse-width-modulated output pins of a microcontroller board. The board is, in turn, controlled through a Universal Serial Bus (USB) connection to a computer running commercially available system design software. The motors require an additional amplifying circuit to ensure sufficient voltage and current is supplied over a wide range of vibration frequencies. An example amplifier circuit is shown in Figure 1. The bipolar junction transistor (BJR) in the figure can be replaced with smaller metal-oxide-semiconductor field-effect transistor (MOSFET) for more efficient operation and smaller size. Similarly, the entire amplifying circuit can be replaced by an off-the-shelf haptic motor driver to provide additional control and reduced size. Each motor requires its own circuit, and using the equipment listed in this paper, up to ten motors can be controlled by a single microcontroller board.
<img alt="Figure 1" src="/files/ftp_upload/54223/54223fig1.jpg" /> 
Figure 1. Motor Wiring. (A) The amplification circuit for a single vibration motor is shown. Each motor requires a separate circuit and must be connected to a unique PWM output port on the microcontroller. The VDD here represents the 3.3 V power supplied by the microcontroller board, and the resistor R2 serves as a pull-down resister to ensure the transistor switch remains open when zero voltage is applied. (B) An example of the physical wiring of two motors. Although eight individual amplification circuits are shown, only two are connected to vibration motors. In this protocol R1 = 4.7 k&#937; and R2 = 100 k&#937;. <a href="https://www.jove.com/files/ftp_upload/54223/54223fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="0" cellpadding="0" cellspacing="0" width="849">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Vibrating Pager Motors</td>
			<td style="width:107px;">Precision Microdrives</td>
			<td style="width:119px;">Model 310-101</td>
			<td style="width:407px;">Coin eccentric rotating mass motors.&#160; As many as necessary to test all locations and interactions of interest</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Tri-axis Accelerometer</td>
			<td style="width:107px;">Dimension Engineering</td>
			<td style="width:119px;">ADXL 335</td>
			<td style="width:407px;">Advanced analog accelerometer. 500Hz bandwidth, 3.5-15V input.&#160; Designed for motion, tilt, and slope measurement, as well as vibration and shock sensing</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Arduino Uno</td>
			<td style="width:107px;">Arduino</td>
			<td style="width:119px;">DEV-11021</td>
			<td style="width:407px;">Microcontroller board for communicating with the tri-axis accelerometer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Arduion Mega 2560</td>
			<td style="width:107px;">Arduino</td>
			<td style="width:119px;">DEV-11061</td>
			<td style="width:407px;">Microcontroller board for interfacing with the vibration motors.&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">LabVIEW</td>
			<td style="width:107px;">National Instruments</td>
			<td style="width:119px;"></td>
			<td style="width:407px;">Data acquisition software used to control motors and display accelerometer signals</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Arduino IDE Software</td>
			<td style="width:107px;">Arduino</td>
			<td style="width:119px;">v. 1.6.5</td>
			<td style="width:407px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Push-Button</td>
			<td style="width:107px;">Bridges</td>
			<td style="width:119px;">Buddy Button</td>
			<td style="width:407px;">Wired switch featuring a 2.5in/6.35cm activation surface that provides an auditory click and tactile feedback.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optional:</td>
			<td style="width:107px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dedicated haptic motor driver</td>
			<td style="width:107px;">Texas Instruments</td>
			<td>DRV2605L</td>
			<td style="width:407px;">Can be used to replace the entire amplification circuit described in Step 1.</td>
		</tr>
		<tr height="105">
			<td height="105" style="height:105px;width:216px;">Flexible wearable goniometer</td>
			<td style="width:107px;">Biometrics Ltd.</td>
			<td style="width:119px;">SG110</td>
			<td style="width:407px;">Twin axis flexible goniometers to measure angles in up to two planes of movement that can be used in lieu of the push button to measure joint movement in response to stimuli. 
			www.biometricsltd.com/gonio.htm</td>
		</tr>
	</tbody>
</table>

a method for evaluating timeliness and accuracy of volitional motor responses to vibrotactile stimuli

Artificial sensory feedback (ASF) systems can be used to compensate for lost proprioception in individuals with lower-limb impairments. Effective design of these ASF systems requires an in-depth understanding of how the parameters of specific feedback mechanism affect user perception and reaction to stimuli. This article presents a method for applying vibrotactile stimuli to human participants and measuring their response. Rotating mass vibratory motors are placed at pre-defined locations on the participant's thigh, and controlled through custom hardware and software. The speed and accuracy of participants' volitional responses to vibrotactile stimuli are measured for researcher-specified combinations of motor placement and vibration frequency. While the protocol described here uses push-buttons to collect a simple binary response to the vibrotactile stimuli, the technique can be extended to other response mechanisms using inertial measurement units or pressure sensors to measure joint angle and weight bearing ratios, respectively. Similarly, the application of vibrotactile stimuli can be explored for body segments other than the thigh.

Figure 4 illustrates the calibration curves identifying the PWM value for a 180 Hz vibration frequency of a single motor. Starting at a 50% duty cycle, the PWM values are iterated until the primary frequency spike occurs at 180 Hz. Successful calibration trials should show a clear spike at the primary vibration frequency. Poor fixation of the accelerometer to the motor, or of the motor to a support surface may result in a more diffuse FFT without a clear spike. In this situation, the calibration trial sh...

Watch this Scientific Journal Video about A Method for Evaluating Timeliness and Accuracy of Volitional Motor Responses to Vibrotactile Stimuli at JoVE.com

A Method for Evaluating Timeliness and Accuracy of Volitional Motor Responses to Vibrotactile Stimuli

This article describes a technique for applying vibrotactile stimuli to the thigh of a human participant, and measuring the accuracy and reaction time of the participant&#39;s volitional response for various combinations of stimulation location and frequency.

Artificial sensory feedback (ASF) systems can be used to compensate for lost proprioception in individuals with lower-limb impairments.  Effective design ...

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.

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