Design of virtual environment for discrimination tasks to determine the psychometric function

Abstract

In this thesis, we used the Gazebo simulation software to develop a virtual environment for interactions of objects to perform psychophysical tasks to distinguish between objects at differing stiffnesses. The virtual environment is composed of a probing device, a cube, and a slider. The probing device is used to touch the cube which moves on the slider. The environment includes objects of different stiffnesses, and the user attempts to discriminate between these objects. To simulate the effect of deformation in the cube, we modeled the cube as a mass-spring-damper system, so the object generates a force proportional to the distance it is pushed by force generated from the probe contacting the cube. The virtual environment was tested by recording the step response of each cube with different k constants. The cube deformed according to the model. Six users were asked to perform psychophysical trials on the virtual environment for stiffness discrimination. Six identical cubes with different stiffnesses were used, where the stiffest cube was used as the reference. The subjects were asked to discriminate between each cube and the reference object. Then we plotted the psychometric curve and determined the discrimination threshold from the data produced. The experiment was done in three phases with twenty trials in each phase. In the first phase, the user would see the virtual environment and also listen to the auditory signal. In the second phase, the user was blindfolded and only received the audio signal. In the third phase, the auditory signal of the virtual environment was muted, and the user only received the visual signal, which was the distance the cube moved. The psychophysical trials show that the virtual environment can be used to determine the psychometric curve and discrimination threshold of the user’s ability to discriminate between objects of different stiffnesses.|Keywords : Psychophysics, Psychometric Function, Virtual Environment, Stimulus, Discrimination Threshold.