Herman R. Weed

Effect of Tactile Stimulation Pulse Characteristics on Sensation Threshold and Power Consumption

The psychophysical responses of human subjects to vibratory tactile stimulation of the skin were investigated experimentally. The parameters, of the waveform important to the minimization of power consumed by the tactile array of electromechanical vibrators and the maximization of the skin sensitivity to the stimulus were explored to develop optimum stimulation. Parameters investigated included the amplitude, frequency, and duty cycle of the current waveform used to drive the vibrators as well as the number of pulses per stimulating burst and the recovery time between bursts. Graphical techniques were used to determine, the optimal combination of the parameters which gave a stimulus that excited the skin to above tactile threshold while maintaining at a relative minimum the power required for the stimulus. The optimal stimulation waveform contains a burst of 10 rectangular pulses of 4% duty cycle separated by a period of nonstimulation of 2 s. Such a waveform can elicit a sensitivity of 29.4 mA−1 consuming only 55 μW of power.

Optimization Of The Relationship Between Pulse Width, Pulse Frequency And Sensation Thresholds For Vibrotactile Information Transfer

The paper presents results of determining sensation thresholds to vibration waveforms in the range of pulse frequencies 25 to 800 Hz and Pulse widths 0.2 to 39.9 ms in which the mechanoreceptors are most sensitive to stimulation (1,2). The psychophysical response to vibrotactile stimulation was measured on three subjects employing a miniature audio-transducer and an excitatory waveform composed of a stimulatory period of rectangular pulses with varying pulse width followed by a recovery time. The results showed that the sensitivity for very short pulses is not good. As the pulse widens, it reaches a region where the sensitivity does not increase with pulse width. At the other extreme, when the pulse width becomes almost as wide as the period of the waveform, the sensitivity decreases again. The results show that duty cycle is not an appropriate parameter to characterize the sensitivity to mechanical stimulation because the response is not dependent on a particular ratio between the on/off period of the waveform but on a minimum pulse width. These results make it possible to determine a combination of pulse width and frequency which maximizes sensitivity while minimizing power delivered by the waveform.

Lower extremity functional electrical stimulation in a cerebral palsy subject

A study of the effects of a program of functional electrical stimulation on the ambulation of a subject with spastic diplegic cerebral palsy is reviewed. Knee joint motion, ankle joint motion, and knee joint torque were measured. Improvements in range of motion, distance, velocity, and torque were documented in this subject. Spasticity reduction and posture improvement were also observed.<<ETX>>

Analysis and Modeling of Body Water Regulation

Abstract Introduction of the concept of central nervous system control in visceral functions to regulate the necessary internal environment of higher animals is followed by the development of the specific system for fluid control as it regulates both total volume and distribution. The total fluid is considered to be in one of three general locations: intravascular and interstitial (together extracellular) and the intracellular. The relative volume control mechanism between the intravascular and interstitial compartments is set up around the two opposing forces of hydro-dynamic pressure and colloid osmotic pressure as they vary over the length of the capillaries. Basic equations and block diagrams are developed to demonstrate the relationship of these variables together with the vascular and osmotic receptors which control the feedback links to stimulate the necessary change in reabsorption of the renal tubules. The overall model is developed showing the interrelationship of the major factors in water control and various simplifications and portions of the system are analyzed using nonlinear control system techniques.

Parameter optimization and system miniaturization for vibrotactile information transfer

of these computed values for Lp with the actual Lp values defined in the model allows for an evaluation of the accuracy of each method. The results demonstrate that the distensibility of the capillary wall, blood viscosity, the particular Lp distribution along the capillary, the hematocrit, and the instant in time after occlusion when Lp is computed can introduce large errors into the computation of Lp when rendered by any single capillary micro-occlusion method. To remove the unfavorable effects which these factors have upon the computed magnitude of Lp, a non-occlusive method was developed. Results rendered by the model suggest that the non-occlusive method may yield more accurate values for Lp than either the Landis or Lee methods.

Investigation of significant interface parameters involved in the electromechanical transfer of tactile information

The authors describe work toward the implementation of a tactile vision information system (TVIS). The prototype system consists of a video camera for image acquisition, a microcomputer for image processing, and a 16*16 vibro-tactile array for image transfer to the skin. The characteristics of the TVIS are discussed and proposed modifications are analyzed to determine the optimum configuration. The mechanical impedance of both vibrator and selected skin sites are discussed and related to the image-transfer process. This is combined with the published properties of the tactile sensors to determine the overall transfer function of electromechanical-physiological interface.<<ETX>>

Microcontrolled system to transform visual images into vibrational images

Details are presented of a system configuration to convert a prestored 256-element image into a vibrational image. The purpose of the system is to interface with the human tactile sensory system to transfer visual information. A vibratory array is driven by pulses with amplitudes proportional to the amount of light in the corresponding spatial position of the image, using fours gray levels. The array is scanned ten times in 4 ms, giving the sensation of continuous stimulation. A recovery time of 1 s is allowed every ten pulses (one burst) to minimize adaptation. Parameters such as number of pulses per burst, duty cycle, pulse shape and modality of scanning are programmable. The flexibility of the system makes it possible to study the best combination of parameters to transfer maximum information using relatively low power.<<ETX>>

Transfer function of electromechanical-tactile stimulation

The overall transfer function for a tactile vision information system (TVIS) used as an aid to the visually impaired is described. Included in this transfer function are the electromechanical vibrators, the skin interface, and the tactile skin sensors. In previous work, individual components have been analyzed, but no attempt has been made to evaluate the process in its entirety. Each transfer function is also analyzed in detail to describe the input-output relationships important in the effective transfer of optical information in a TVIS. The overall transfer function is developed and its equation is given. Here, a theoretically derived stimulation waveform was used for the vibrator driving current. Under computer simulation, this waveform reduces the vibrator noise levels to less than 70 dB(C) while requiring only 3 mW of power for each vibrator to elicit tactile sensation.<<ETX>>

Sensation thresholds for vibrotactile information transfer

The authors present results of determining sensation thresholds to vibration waveforms in a range of frequencies and duty cycles for vibrotactile information transfer applied to the visually handicapped. The stimulation waveform is composed of an excitatory part, i.e. a burst of rectangular pulses, and a recovery time, i.e. a period of no stimulation, to minimize adaptation. Several subjects were tested, all giving similar threshold curves. The results make it possible to determine a combination of parameters that permits optimization of sensation with minimization of power delivered.<<ETX>>

Optimization of Man-Machine Interface for Real-Time Visual Information Transfer to the Visually Handicapped

Abstract The research is directed at investigation of the parameters involved in optimization of the man-machine interface for transmission, recognition and individual control of real-time visual information access for the visually handicapped. Three overlapping areas are considered -- the visual information access with the concept of controlled feedback for distance, depth of field, focus and angle of observation; the basic parameters of physiological neural integration combined with the electro-mechanical interface of vibrator-matrix-to-skin information exchange and recognition; and the detail of micro miniature circuit design to provide the optimum signal processing and transducer excitation. The theoretical solutions are implemented in a prototype capability used experimentally to validate the system operation and to identify critical parameter values. The boundary values of non-invassive acceptance, neural X-Y correlation and recognition, and skin sensitivity versus pain thresholds resulted in the selection of a vibrotactile array as the man-machine interface, each of the miniature vibrators being individually driven at four levels of excitation with controlled presentation parameters of random, sweep, and trace, and with possible selection of mode by the operator. The paper presents the theory and experimental results of threshold and recognition sensitivity versus the control parameters of pulse shape, repetition frequency, duty cycle, pulses per burst, and recovery period for skin adaptation versus driving power and noise level. The visual information access was optimized using a light-sensitive RAM with a 128x256 matrix array, reduced to fit the tactile unit, coupled to a focusing lens with eventual capability to control depth of focus and visual field angle. Signal processing and vibrator drive requirements involve the theoretical design and optimization of microprocessor circuits capable of providing the necessary control of the critical parameters of wave shape, randomization of vibrator excitation, sweep, trace, or random presentation together with four levels of amplitude representing four gray levels of light. Vibrator noise is reduced to 70dBC or less by special excitation pulse wave shaping and storing of the pulse in memory. The paper presents details of the three system areas, their experimental validation on both sighted and blind subjects, with possible feedback optimization capabilities available to the operator.