Abdullah Chami

Experiments on Stochastic Resonance Toward Human Mimetic Tactile Data Processing

In the present research, human tactile stochastic resonance (SR) capable of enhancing sensitivity by superimposing proper noise upon undetectable weak signals is utilized to enhance the tactile processing method for social robotics. We develop an experimental apparatus composed of a piezoelectric actuator and its controller, and generate a step several microns high mixed with noise to perform a series of psychophysical experiments. Since psychophysical experiments are conducted based on the Parameter Estimation by Sequential Testing (PEST) method, we produce a PEST program that generates a stimuli sequence based on PEST. The experimental result shows that variation in the difference threshold (Difference Limen; DL) has a local minimum point in the relationship between DL and noise. Therefore, the tactile sensation’s just noticeable difference (JND) is decreased by appropriate external noise. Since JND denotes the scale divisions of sensation in the human mind, the present result shows that precise tactile sensations are enhanced by the appropriate external noise. Finally, we introduce a neural network model composed of nonlinear neurons with the bi-stable equilibrium condition to explain this result. Although original sensor data do not represent the morphology of the fine texture, the neural network model extracts the morphology and distinguishes the wave amplitude of the fine texture.

Investigation on influence of tangential stimulation on velvet hand illusion using psychophysical experiment

In the velvet hand illusion (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 focus on VHI to determine the specifications of an actuator for a tactile display enhanced by VHI. 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 using Thurstones Paired Comparison, 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. This result suggests that VHI is controlled by mechanical external stimulation using tactile displays. We think the mechanism of VHI is as follows: although the area bounded by two wires moves relative to the hands, tangential force does not occur on the hand surface except for wire-passing portion, causing operators to experience the illusion of touching a smooth virtual film with a zero coefficient of friction. Since VHI becomes weaker with a small distance between two adjacent wires, excessive tangential stimulation prevents the occurrence of VHI. Therefore, VHI control requires two actuations: one is for normal actuation on the operators finger surface to generate a touch feeling; the other is appropriate tangential actuation to generate a moving-edge feeling on the operators finger surface.

Psychophysical experiment on tactile stochastic resonance toward mathematical model

In the information processing done by biological organisms, stochastic resonance (SR) can enhance sensitivity by superimposing proper noise upon undetectable weak signals to detect that signal. In tactile sensing, since noise inevitably becomes mixed by contact with an object and a sensors movement on it, sensing accuracy can be increased by SR. In the present research, we perform a series of psychophysical experiments to accumulate the basic data on the SR of human tactile sensations. We developed an experimental apparatus composed of a piezoelectric actuator and a controller for it and generated a step several microns high mixed with noise. Since psychophysical experiments are conducted based on Parameter Estimation by Sequential Testing (PEST) method, we produce a computer program that generates stimuli sequence based on PEST. Experimental results show that a subtle stimulus of 3 µm in amplitude with appropriate noise is easily perceived with a difference threshold of about 1 µm if appropriate noise is applied to the stimulus.

A basic study on tactile displays using velvet hand illusion

To enhance artificial tactile sensation generated by a tactile display, we focus on the velvet hand illusion (VHI), in which 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. To determine the specifications of an actuator for a tactile display enhanced by VHI, we investigate the relationship between wire distance and intensity of illusionary sensation using a series of psychophysical experiments. According to the experimental results, the strength of VHI depends on the distance between two adjacent wires and saturates at around 55 mm. In VHI, although the area bounded by two wires moves relative to the hands, tangential force does not occur on either hand, causing operators to experience the illusion of touching a smooth virtual film with a zero coefficient of friction. Since the strength of VHI becomes small for a small distance between two adjacent wires, excessive tangential stimulation prevents the occurrence of VHI. Therefore, VHI control requires two actuations: one is for normal actuation on the operators finger surface to generate a touch feeling; the other is appropriate tangential actuation to generate a moving-edge feeling on the operators finger surface.

An Investigation of the Reason of Velvet Hand Illusion Perception Using FEM Analysis

We try to reveal the reason behind a haptic illusion called Velvet Hand Illusion (VHI) by mean of FEM analysis. In 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 focus on VHI to determine the specifications of an actuator for a tactile display enhanced by VHI. A simulated fingertip is modeled under the same contact condition that an actual finger is believed to undergo when under VHI. We collected the simulated responses of a number of SAI afferents (responsible for edges) for the purpose of relating them to the mechanism of the illusion. Even with a simple model which treats only one finger we notice a considerable difference between the responses of a number of SAI receptors, compared with that of a fingertip touching wires without the effect of the opposing finger. This study could help in the design of a haptic display which utilizes the illusion and make the person feels the same feeling using the proposed display