Vibrotactile Stimulation System Research Articles

Vibrotactile piezoelectric stimulation system with precise and versatile timing control for somatosensory research

BackgroundTactile stimulations systems are useful for studying the somatosensory system in children because they are innocuous and safe. Stimulators based on piezoelectric actuator are useful, but there is still a need for such systems capable of providing accurate and versatile control of timing and pattern of activation. New methodWe have implemented a vibrotactile stimulating system useful for behavioral and electroencephalography (EEG) and magnetoencephalography (MEG) research. Our design goal was to create a system capable of providing up to five independently controlled mechanical stimulations with precise timing. We developed a Graphic User Interface (GUI) in LabVIEW, which controls a commercially available piezoelectric braille stimulator using an Arduino based controller. We made a customized braille stimulator based on the Metec Braille device. ResultsOur system can control up to five tactile stimulators with independent timing control and negligible errors. Although it can be directly used for behavioral and EEG research, the piezoelectric stimulators in our system generate stimulus artifacts that interfere with MEG recordings. A moving averaging subtraction algorithm we developed can remove the artifact. The stimulator can be used to measure somatic evoked magnetic fields from the somatosensory cortex of a child without the artifact. Comparison to existing methodsOur system provides an accurate independent control of one or more piezoelectric actuators using a GUI-based easy-to-control programming approach based on recent advances in embedded systems and software. Versatility and precise stimulation timing distinguish our system compared to existing somatic stimulators. ConclusionsOur system may be useful for somatic research.

Validation of a Vibrotactile Stimulation System Using the Wii Remote for Studies of Tactile Sensitivity

Background: Vibrotactile stimuli are widely used to study the functional characteristics of the haptic sense. Although many vibrotactile stimulators are commercially available, most are expensive. Objective: We developed a low-cost vibrotactile stimulation system using a Nintendo Wii Remote and a personal computer. In the present study, we examined the validity and accuracy of this vibrotactile stimulation system. Method: In the first experiment, we measured the linearity of vibration amplitude and changes in peak vibration frequency generated by the Wii Remote as a function of activation intensity. In the second experiment, the effect of vibrotactile stimuli applied to the dorsal surface of hand on two-point discrimination threshold at the index finger was examined in twelve participants. Results: The peak vibration frequency was about 150 Hz irrespective of vibration intensity, which would effectively activate fast adapting type II (FAII) cutaneous mechanical receptors. The two-point discrimination threshold measured at the third pad of the index finger decreased significantly when a near-threshold vibrotactile stimulus was applied to the dorsal hand, a response termed stochastic resonance (SR). These SR results are consistent with findings in the other sensory systems, such as auditory, visual, and somatosensory systems. Conclusion: This newly developed stimulation system produces controllable vibrotactile stimuli useful for study of the haptic sense.

Combining Vibrotactile Feedback with Volitional Myoelectric Control for Robotic Transtibial Prostheses.

In recent years, the development of myoelectric control for robotic lower-limb prostheses makes it possible for amputee users to volitionally control prosthetic joints. However, the human-centered control loop is not closed due to the lack of sufficient feedback of prosthetic joint movement, and it may result in poor control performance. In this research, we propose a vibrotactile stimulation system to provide the feedback of ankle joint position, and validate the necessity of combining it with volitional myoelectric control to achieve improved control performance. The stimulation system is wearable and consists of six vibrators. Three of the vibrators are placed on the anterior side of the thigh and the other three on the posterior side of the thigh. To explore the potential of applying the proposed vibrotactile feedback system for prosthetic ankle control, eight able-bodied subjects and two transtibial amputee subjects (TT1 and TT2) were recruited in this research, and several experiments were designed to investigate subjects’ sensitivities to discrete and continuous vibration stimulations applied on the thigh. Then, we proposed a stimulation controller to produce different stimulation patterns according to current ankle angle. Amputee subjects were asked to control a virtual ankle displayed on the computer screen to reach different target ankle angles with a myoelectric controller, and control performances under different feedback conditions were compared. Experimental results indicated that subjects were more sensitive to stimulation position changes (identification accuracies were 96.39 ± 0.86, 91.11, and 93.89% for able-bodied subjects, TT1, and TT2, respectively) than stimulation amplitude changes (identification accuracies were 89.89 ± 2.40, 87.04, and 85.19% for able-bodied subjects, TT1, and TT2, respectively). Response times of able-bodied subjects, TT1, and TT2 to stimulation pattern changes were 0.47 ± 0.02 s, 0.53 s, and 0.48 s, respectively. Furthermore, for both TT1 and TT2, the absolute error of virtual ankle control reduced by about 50% with the addition of vibrotactile feedback. These results suggest that it is promising to apply the vibrotactile feedback system for the control of robotic transtibial prostheses.

A microfabricated strain gauge array on polymer substrate for tactile neuroprostheses in rats

In this study, we present the design, microfabrication and characterization of a tactile sensor system which can be used for sensory neuroprostheses in rats. The sensor system consists of an array of 2 × 7 cells, each of which has a series combination of four strain gauges. Each group of four strain gauges is placed around a square membrane with a size of 2.5 × 2.5 mm2. Unlike most common tactile sensors based on silicon substrates, we used 3D-printed polylactic acid as a substrate, because it is not brittle, and under local extremes, it would prevent the catastrophic failure of all cells. The strain gauges were fabricated by depositing and patterning a 50 nm thick aluminum (Al) film on a polyimide sheet with a thickness of 0.125 mm. Polydimethylsiloxane (PDMS) elastomer was bonded on the top surface of the PI membrane. The PDMS layer was prepared in two different thicknesses, 1.2 and 1.7 mm, to investigate its effect on the static response of the sensor. The sensitivity and the maximum allowable force, corresponding to the maximum deformation of 0.9 mm at the center of each cell, changed based on the thickness of the PDMS layer. Sensor cells operated linearly up to 3 N with an average sensitivity of 200 mΩ N−1 (0.7 Ω mm−1) for 1.2 mm thick PDMS. These values changed to 4 N and 70 mΩ N−1 (0.3 Ω mm−1), respectively, for 1.7 mm thick PDMS. The nonlinearity was less than 3%. The cells had low cross-talk (~5 mΩ N−1 and 0.02 Ω mm−1) relative to the average sensitivity. Additionally, the dynamic response of the sensor was characterized at several frequencies by using a vibrotactile stimulation system previously designed for psychophysics experiments. The sensor was also tested inside the rat conditioning chamber to demonstrate the relevant signals in a tactile neuroprosthesis.

Contact force‐ and amplitude‐controllable vibrating probe for somatosensory mapping of plantar afferences with fMRI

To study cerebral responses evoked from mechanoreceptors in the human foot sole using a computer-controlled vibrotactile stimulation system. The stimulation system consisted of two stationary moving magnet actuators with indentors to gently contact and vibrate the foot sole during functional MRI (fMRI) experiments. To allow independent settings of contact force (0-20 N) and intensity of vibration (frequency range=20-100 Hz) the actuators were controlled by a digital servo loop. For fMRI experiments with complex stimulus protocols, both vibrating probes were further operated under supervisory control. The MR compatibility of this electromagnetic system was tested in a 1.5T scanner with an actively shielded magnet (Siemens Magnetom Sonata). Blood oxygenation level-dependent (BOLD) responses were detected in the contralateral left pre- and postcentral gyrus, bilaterally within the secondary somatosensory cortex, bilaterally within the supplementary motor cortex, and bilaterally within the anterior cingular gyrus. This stimulation device provides a new tool for identifying cerebral structures that convey sensory information from the foot region, which is of promising diagnostic value, particularly for assessing sensorimotor deficits resulting from brain lesions.

Vibrotactile Stimulation System to Treat Apnea of Prematurity

We modified a system that uses vibrotactile stimulation (VTS) to treat apnea (a cessation of respiration) in neonates in order to make the system more portable and easier to use by clinicians and nurses. The biomedical engineering department at Hartford Hospital (Hartford, CT) together with the Neonatology Division at the Connecticut Children's Medical Center (CCMC) (Hartford, CT) has been involved in developing the VTS system. Clinical trails were conducted in the neonatal intensive care unit of CCMC, and further preliminary data were collected. The main components of the system are a Tacaid vibrotactile stimulator (Audiological Engineering, Somerville, MA), a neonatal physiological monitor (Model 511; CAS Medical Inc, Branford, CT), a laptop computer running Windows 95 by Microsoft, National Instruments' data acquisition cards DAQCard-1200 and DAQCard-5102, and a software application developed by Premise Development Corporation, Hartford, CT. Heart rate, oxygen saturation, pulse, thoracic impedance, nasal airflow, and electrocardiogram are recorded from the monitor to the laptop. Whenever an apneic spell is detected, the nurse has the option of triggering a 3-second, 10-V, 250-Hz square-wave pulse to the transducer. The vibrotactile transducer is placed noninvasively with tape on the infant's thorax. This stimulus should arouse the infant and end the apneic event. To facilitate clinical study, the system provides voice and visual prompts for the clinician and nurses. Preliminary data continue to support both the safety and efficacy of the VTS.