Differential thresholds for limb movement measured using adaptive techniques

Abstract

Differential thresholds for limb movement were measured in 10 subjects, using the transformed up-down procedure. Subjects were required to indicate which of two random displacement perturbations delivered to their forearms had the larger standard deviation (Sm. The SD of the reference signal was fixed for each experimental condition at one of seven values ranging from 0.05 to 3.2 mm. The SD of the other signal varied depending on the subject's response. Using this procedure, the differential threshold for limb movement was calculated to be 8%, which is very similar to the thresholds estimated previously for changes in limb position (9%) and force (7%). The sensitivity of the human proprioceptive system to changes in limb displacement was much greater than anticipated, with subjects being able to resolve a 5-l'm difference between two perturbations delivered to their arms.

Passive and Active Discrimination of Natural Frequency of Virtual Dynamic Systems

“…The reported WF for stiffness is about 23% [15], [16] and that for inertia is about 21% [11]. These WFs are relatively larger than the reported WFs for force and displacements, which are in the 6%-8% range [12], [13], [29], [30]. Since humans possess no inertia-specific or stiffness-specific "sensors" in the peripheral sensory organs, the reported data is evidence of a loss of sensory resolution when force and displacement cues are combined.…”

Haptic Interfaces

“…Early kinesthetic studies by Clark and colleague and Jones and Hunter (Clark & Horch, 1986;Clark, 1992;Jones & Hunter, 1992) investigated human perception of limb positions and concluded that humans are capable of detecting joint rotations of a fraction of a degree performed over a second of time interval. Jones and Hunter (1992) also reported the differential threshold for limb movement as 8 percent.…”

Are there critical bands in kinesthesia?

“…o down method was used to calculate thresholds (see, e.g., Jones et al, 1992). As it was implemented, the latter procedure sought a stimulus level that corresponded to 71% correct performance.…”

“…The subjects were required to indicate which ofthe two low-pass filtered (with a cutoffat 15 Hz) signals had the larger amplitude (defined in terms of the root-mean square [RMS] deviation). It was found that subjects could reliably discriminate an 8% difference in the RMS deviation amplitude of two random displacements and, at the smallest amplitude, were able to resolve a 5-J.lm difference between the two perturbations (Jones et al, 1992). The latter accomplishment probably reflects the perception of skin indentation and not movement of the forearm.…”

“…Differential thresholds have been measured in one study in which Gaussian white-noise displacement perturbations were applied simultaneously to the arms (Jones, Hunter, & Irwin, 1992). The subjects were required to indicate which ofthe two low-pass filtered (with a cutoffat 15 Hz) signals had the larger amplitude (defined in terms of the root-mean square [RMS] deviation).…”