Velocity of mammalian skeletal muscle contraction as a function of fiber type, activation, initial length and temperature.

Multiple stepwise regression analyses techniques were applied to develop modifications of the Hill force-velocity equation. Specifically, predictive models of the Hill a coefficient, the Hill b coefficient, and isometric strength P0 were developed for the following set of variables: the fraction of slow-twitch fibers (X), the recruitment magnitude (A), the initial muscle length (L), and the muscle temperature (T). Results indicate that the Hill a and Hill b coefficients and isometric strength P0 can be predicted with a high degree of accuracy. The utility of the equation is that it would allow development of a computer program to control the velocity of contraction of muscles with differing fiber compositions and lengths such as are found in the leg.

Walking while using a sensory tactile feedback system: potential use with a functional electrical stimulation orthosis.

A major limitation in the utilization of a functional electrical stimulation (FES) orthosis for routine, daily standing and walking of the spinal-cord-injured person is that visual monitoring is required to maintain balance and the walking pace. For standing and walking to be continuous and automatic with such an orthosis, a closed-loop sensory feedback system is proposed and evaluated; it provides vibrotactile feedback as a substitute to one's own visual sensation. Eight blindfolded experimental subjects were utilized as 'imitators' to interpret the footfalls of a second person (the pace setter). The experimental objective was to test the hypothesis that sufficient information could be transferred by way of the sensory (tactile) feedback system to the 'imitator' and to determine effectively foot position and anticipate the next step of the pacesetter. Quantitative analysis evaluated the effect of three different levels of training, under two different levels of cognitive load. The results disclosed a significant improvement in subject performance at the higher training levels compared with the 'no training' level (P = 0.01). Neither the cognitive load nor the interaction of training and cognitive load altered significantly the effect of training on subject performance. The experimental hypothesis is therefore satisfied that sufficient information was indeed transferred using the apparatus described. Such information (when utilized in conjunction with a thorough training programme) could be used in a practical sense by a paraplegic individual to interpret his own foot steps. Through continued use and training, it is likely that this information could become subconscious and automatic.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction of chromostereopsis and stereopsis in stereoscopic CRT displays.

To give operators of high-speed, highly-manoeuvrable vehicles the ability to keep pace with their increasingly dynamic environment, stereoscopic 3-D displays may soon replace conventional 2-D displays. Important to the development of stereoscopic 3-D displays is the interaction of perceived depth created by hues (chromostereopsis) and perceived depth created by presenting different images of a single object to the left and right eye of the observer (stereopsis). The purpose of this research is to evaluate the interaction of chromostereopsis and stereopsis on a stereoscopic CRT by determining the level of accuracy with which subjects can properly interpret the relative depth differences of adjacent symbols containing six levels of hue and seven levels of stereoscopic disparity. This research demonstrated that hue, disparity, and the interaction of hue and disparity significantly influenced one's perception of depth on a stereoscopic monitor. The results suggest that caution should be exercised by the stereoscopic 3-D display format designer when choosing hues to represent images located in close proximity on a stereoscopic display. Due to the chromostereoscopic effect on the perception of depth, hues on extreme ends of the colour spectrum should not be used in situations where less than 3.39 arc minutes of disparity difference is being portrayed on a stereoscopic display, unless the hues are consistently being used to alter the depth presented by stereoscopic disparity, or the chromostereoscopic depth resulting from certain hues is consistently nullified by altering disparity levels accordingly.