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A Dissertation Submitted to the Graduate School in Partial Fulfillment of the Requirements for the degree Doctor of Philosophy in the Field of Mechanical Engineering
In the first experiment, subjects performed a simple positioning task in an environment of non-uniform damping. Damping levels in the target and background regions were systematically varied, and movement times were recorded as a measure of task performance. The most striking result of the experiment was that when the targets were not visible to subjects, performance was very closely correlated with the absolute magnitude of the difference in damping between the target and background damping (i.e. target damping minus the background damping). Performance did not vary with the level of background damping.
In the second experiment, subjects performed a detection task in environments with haptic features generated using position-dependent stiffness. The single most important parameter for feature detectability was shown to be the amplitude of the change in force generated as the feature was traversed. The rate at which the force changed when the feature was traversed (i.e. the feature stiffness) was also shown to be important when detecting features under conditions of large background forces. Large background forces, and especially large background forces that varied with position, were shown to make the detection of features characterized by gradual changes in force more difficult. The same background forces had no effect on detection of features characterized by rapid changes in force.
The results of the two experiments suggest that frequency differences, as well as amplitude differences in resistance force can be used to make foreground-background distinctions, and that one kind of difference can be substituted for the other.
