John Lyman

Electrotactile two-point discrimination as a function of frequency, body site, laterality, and stimulation codes.

The feasibility of frequency modulated two-point discrimination as a design concept for electrocutaneous sensory substitution display has been studied. Three stimulation techniques were tested on human subjects: spatial stimulus, temporal stimulus, and frequency on frequency stimulus. The frequency on frequency technique yielded the lowest threshold when compared to the temporal and spatial techniques. In addition, some of the characteristic behavior of cutaneous sensation is discussed relating two-point discrimination with frequency, body sites, and stimulation codes. Implications of the results for clinical applications are reviewed.

Comparison of codes for sensory feedback using electrocutaneous tracking

Ten electrocutaneous codes suitable for sensory feedback were systematically compared using a random tracking task. The representative sample of codes used single and multiple electrode displays, bipolar and monopolar electrocutaneous stimuli, and frequency, intensity, and spatial modulation. The experimental results from 2 preliminary studies using 4 subjects each, and a full scale study, using 21 subjects, suggested that electrocutaneous tracking was a reliable and sensitive indicator of a codes intrinsic effectiveness for transmitting information cutaneously. In addition, multiple electrode codes using spatial modulation were clearly and significantly superior to any single electrode codes examined. Single electrode codes using frequency modulation were superior to intensity modulation codes whether the pulse stimulus used was monopolar or bipolar. Although subjects rated bipolar stimulation as being slightly more comfortable than monopolar stimulation, they performed better when using monopolar stimulation. Furthermore, sensory adaptation to the monopolar stimulus was considerably less than to the bipolar stimulus. The most effective multiple electrode code was Seven Electrodes in a Linear Array on the Abdomen. The most effective single electrode code was the Low Pulse Rate Modulation Code, wherein the sensory information was embedded in pulse rates between 1 and 15 per second.

A Computer-Based Learning System for Remote Manipulator Control

A concept of adaptive aiding for performance improvement in remote handling is described. The concept incorporates an autonomous control subsystem (ACS) that is able to supplement the operators control function. The behavior of the ACS is established through a process of learning by observing the operators control function in relation to the environment and manipulator output. The computer-based system establishes a decision-making policy which is based on conditional probability. Initially, the output device is totally controlled by the operator, while the computer system acts as a passive observer. As the operation continues, the computer system gradually assumes the role of active controller, reducing the operators function to that of an action initiator and inhibitor. A pilot experiment indicates the feasibility of the concept; with a relatively short training period, the ACS was able to assume the bulk of the decision-making load and guide a three-dimensional manipulator satisfactorily through a series of manipulative tasks.

Electrocutaneous Pulse Rate and Pulse Width Psychometric Functions for Sensory Communications

Psychometric functions of pulse rate (PR) and pulse width (PW) from electrocutaneous stimuli were determined using the method of comparative judgments. The study revealed that changes in PR were more easily detected than changes in PW, as measured by the percent of just noticeable difference (jnd). The PR jnd data from test subjects indicated that maximum frequency discrimination occurred near 20 pulses per second. Using the PR and PW psychometric curves, compensatory transfer functions can be determined which will improve the efficacy of sensory communication systems based on electrocutaneous stimulation.

Electrotactile two point discrimination as a function of frequency, pulse width and pulse time delay

The feasibility of frequency modulated two-point discrimination as a design concept for electrocutaneous sensory substitution displays has been investigated further. Two new parameters have been tested on human subjects for their effect on the two-point threshold: pulse width and pulse time delay (phase shift). The pulse width study has shown that 100-μsec pulses resulted in the lowest threshold for spatial stimulation while 10-μsec pulses yielded the lowest threshold for temporal stimulation. It was also shown that pulse phase shifts of 0 to 180° result in different threshold values. Phase shifts of 0 to 135° showed slight threshold improvement. The 180° phase shift yielded substantial improvement.

System integration of pattern recognition, adaptive aided, upper limb prostheses

Abstract An integrated externally energized artificial arm which combines computer control techniques and sensory feedback is presented. The arm, which is intended for above elbow amputees, contains the functions of prehension, wrist rotation, elbow flexion and extension and humeral rotation. The paper outlines the nature of control problems in artificial limbs and reviews techniques for their solutions. A detailed description of the system involving myoelectric pattern control, adaptive computer aiding and electrocutaneous feedback is included with a discussion of the integration and interfaces of these factors.

Artificial sensory communications via the tactile sense: space and frequency optimal displays.

The electrotactile two point discrimination threshold (TPDT) was considered as a design concept for multichannel artifical sensory communication displays. Data relating two point discrimination threshold with frequency for three stimulation codes were used for the analysis and specifications of three classes of optimal displays: space optimal, frequency optimal, and space-frequency optimal. A table was constructed showing alternative display configurations for various applications, and a design procedure for optimizing each class of display was developed. Possible applications of each display class for various sensory augmentation requirements in rehabilitation of handicapped persons for tactile, kinesthetic, visual, and auditory categories have been identified.

Motivational factors in vigilance: effects of instructions on performance in a complex vigilance task.

Pre-task instructions have been a neglected source of motivation in vigilance. In the present study, 32 Ss monitored a complex visual vigilance display for 40 min. with a signal rate of 60/hr. 16 Ss were told that such tasks are usually challenging (positive set) and 16 were told such tasks are usually monotonous (negative set). Performance was significantly better throughout the session by Ss with the positive set and decrements did not occur with either group. The results indicate the importance of motivational factors in vigilance. Implications for vigilance research are discussed.

Model-based estimation and prediction of task-imposed mental workload

Mental workload has been an area of intensive research for better than a decade. One specific area of interest in aircrew related workload research is concerned with the development of quantitative indices of workload in aircraft piloting tasks. This paper presents a model-based approach for quantifying mental workload in operational terms. The suggested modelling framework is based on an interpreted Petri net characterization of a task in which “places” are equated to specific task-related activities and “transitions” are viewed as internal or external forcing events. It is shown that within this framework quantitative assessments can be made of both cumulative and instantaneous workload associated with the performance of a task and its individual component subtasks. It is suggested that insights gained from analyzing task-specific workload within this modelling paradigm can suggest plausible explanations for reconciling discrepancies between subjectively elicited workload estimates and behavioral/performance measures.

American and Japanese Control-Display Stereotypes: Possible Implications for Design of Space Station Systems

This study examined the stimulus-response stereotypes of American (United States citizens) and Japanese (Japanese citizens) subjects on the issue of control-display arrangements. Three questions were investigated. First, do Japanese and Americans operators adhere to the same compatibility principles, e.g., clockwise-for-increase, for certain configurations? Second, do the operators show similar or different responses to certain configurations? Third, are there arrangements in which both populations show strong or weak stimulus-response stereotypes? A paper and pencil test that contained 24 different control-display configurations was administered to 58 American subjects and 58 Japanese subjects, all of whom were right-handed. Out of the 24 configurations, only one elicited similar and statistically significant response stereotypes from American and Japanese subjects. The arrangement that did so emphasized that three compatibility principles (clockwise-for-increase, nearness of control-cursor relation, and scale-side) be in agreement with each other. The results provide initial, albeit speculative, guidelines for the design of control-display systems in NASAs international space station. Since multicultural crews will inhabit the space station for long duration missions, control-display designs which elicit common, consistent, and extremely strong control-movement stereotypes from different cultural populations is a necessity.