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Since tactile sensing is dominated by the nonlinear contact problem between object and finger surfaces and is recognized in nonlinear brain systems, it is closely related to complex systems science. We consider two phenomena caused by complex systems related to tactile sensing: Stochastic Resonance (SR) and the velvet hand illusion (VHI). Elucidation of these mechanisms provides important hints to develop robotic tactile sensors and tactile displays. The SR can enhance sensitivity by superimposing proper noise upon undetectable weak signals to detect that signal. In the research on SR, we perform a series of psychophysical experiments to accumulate the basic data on the SR of human tactile sensations. Experimental results of SR show that a subtle stimulus of 3 μm in amplitude with appropriate noise is easily perceived with a difference threshold of 1 μm, if appropriate noise is applied to the stimulus. In the VHI, a person rubs his/her hands together on either side of wires strung through a frame, producing the sensation of rubbing a very smooth and soft surface like velvet. We investigate the relationship between wire distance and intensity of illusionary sensation using a series of psychophysical experiments under active and passive touch. According to the experiments, the strength of VHI depends on the distance between two adjacent wires, and VHI caused by passive touch is considerably stronger than that caused by active touch.