| Volume 26 Issue 11-12 - Publication Date: 1 November- December June 2007 |
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| Perception of Delayed Stiffness |
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| YA. Pressman, Sensory Motor Performance Program
Rehabilitation Institute of Chicago
Chicago IL and Department of Biomedical Engineering
Ben-Gurion University of the Negev, Beer-Sheva, Israel L. J. Welty, Department of Preventive Medicine, Northwestern
University Feinberg School of Medicine, Chicago IL A. Karniel, Department of Biomedical Engineering
Ben-Gurion University of the Negev, Beer-Sheva, Israel and F. A. Mussa-Ivaldi Sensory Motor Performance Program
Rehabilitation Institute of Chicago and
Department of Physiology, Northwestern University
Feinberg School of Medicine, Chicago IL |
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| Advanced technology has recently provided truly immersive virtual
environments with teleoperated robotic devices. In order to control
movements from a distance, the human sensorimotor system has to
overcome the effects of delay. Currently, little is known about the
mechanisms that underlie haptic estimation in delayed environments.
The aim of this research is to explore the effect of a delay on perception
of surfaces stiffness. A forced choice paradigm was used in
which subjects were asked to identify the stiffer of two virtual springlike
surfaces based on manipulation without visual feedback. Virtual
surfaces were obtained by generating an elastic force proportional
to the penetration of the handle of a manipulandum inside a virtual
boundary. The elastic force was either an instantaneous function of
the displacement, delayed at 30 or 60 milliseconds after the displacement
or led the displacement (by means of Kalman predictor) by 50
milliseconds. It was assumed that, to estimate stiffness, the brain relates
the experienced interaction forces with the amount of penetration. The results of the experiment indicate a systematic dependence
of the estimated stiffness upon the delay between position and force.
When the force lagged the penetration, surfaces were perceived as
stiffer. Conversely, when the force led the penetration, surfaces were
perceived as softer. The perceptual findings were compared with different
regression models. This allowed some candidate models to be
discarded. To further refine the analysis, a second experiment was
carried out in which the delay was introduced only during part of the
hand/surface interaction, either while the hand was moving into the
spring-like surface or when it was moving out of it. Findings are consistent
with stiffness estimates based on dividing the maximum force
by the perceived amount of penetration. Findings are not consistent
with an estimate of compliance based on the maximum position or local
stiffness on the way out nor with linear estimates of stiffness based
on the entire force/motion history. |
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