Spatial Summation of Electro-Tactile Displays at Subthreshold

Abstract: Electrotactile displays reproduce tactile properties of an object such as texture and shape to provide feedback in human-machine interactions. Electrotactile perception threshold (EPT) is a critical psychophysical parameter in designing a safe display as prolonged usage causes skin irritation. This study's main objective was to reduce EPT with background thermal stimulation (BTS) and analyze the qualitative and quantitative aspects of EPT with and without BTS. A psychophysical experiment was conducted to measure EPT with and without BTS (+7 °C)) over a wide range of stimulus frequencies of EPT from 20 Hz to 640 Hz. Findings from these experiments showed a reduction in the EPT (∆EPT), which was 13% to 17% (with an average of 15%). Reduced EPT may provide safer and comfortable electrotactile displays for prolonged usage.

Abstract: Electrotactile Perception Threshold (EPT) is critical for designing electrotactile displays, which is the minimum amplitude of an electrical stimulus that can be perceived. A significant concern in electrotactile displays is skin irritation and burns due to prolonged electrical stimulus with high amplitude. This study aims to propose a method for reducing the EPT using a background stimulation with a vibrotactile display at subthreshold: 90% of the Vibration Perception Threshold (VPT) at 235 Hz. A psychophysical experiment was conducted to measure EPT at the middle of the left forearm with and without the vibrotactile display using the staircase method. A reduction of 3 to 5% in EPT was observed, which can be further enhanced with varying study parameters. In addition, the comfort and safety aspects of the user’s assessment have been analyzed. Electrotactile stimulations have a higher Steven’s power exponent (1.51). Hence a reduced threshold (although it’s only 3 to 5%) would be perceptually significant and advantageous for sensory substitution and rehabilitation (vision, auditory, and gustatory).

Abstract: Although information from sense organs is used by all animals, only man can verbally report his sensory experience. A brief consideration of these experiences may be useful in providing insight into cutaneous sensory mechanisms. Nonnoxious deformation of the human skin with a stimulator having a small surface area (2–3 mm2) evokes sensations usually referred to as “touch”. If the stimulator remains stationary, the sensation fades. Movement of the stimulator perpendicular to the skin produces changes in the sensory process which allow even rapidly repeated stimuli (e.g. 500 Hz) to be distinguished from stationary ones. When larger stimulators are used, some appreciation of texture can be obtained, and this is enhanced by movement of the stimulating surface across the skin. A smooth stimulator or an insect moving slowly and gently over the skin evokes distinctive sensations usually referred to as “tickle”. A sharp object such as a pin lightly pressed against certain points in the skin leads to an unpleasant experience which differs from touch but is equivocally painful; when the pin is pressed against the skin more firmly it usually elicits pain. Thus, sensations induced by mechanical events can be diverse. Moreover, common experience indicates that they may occur with greater or lesser intensity. On the other hand, neurophysiological experiments defining the properties of cutaneous sense organs have most often been done on animals other than man.

Abstract: We studied a detailed somatosensory representation map of the human primary somatosensory cortex using magnetoencephalography. Somatosensory-evoked magnetic fields following tactile stimulation of multiple points in the right hemibody (including the tongue, lips, fingers, arm, trunk, leg, and foot) were analyzed in five normal subjects. We were able to estimate equivalent current dipoles (ECDs) following stimulation of the tongue, lips, fingers, palm, forearm, elbow, upper arm, and toes in most subjects and those following the stimulation of the chest, ankle, and thigh in one subject. The ECDs were located in the postcentral gyrus and generally arranged in order along the central sulcus, which is compatible with the somatosensory "homunculus." Linear distances, averaged in five subjects, from the receptive area of the thumb to that of the tongue, little finger, forearm, upper arm, and toes were estimated to be 2.42 +/- 0.28, 1.25 +/- 0.28, 2.21 +/- 0.72, 2.75 +/- 0.63, and 5.29 +/- 0.48 cm, respectively. The moment of each ECD, which suggested the size of the cortical areas responsive to the stimulation, was also compatible with the bizarre proportion of the homunculus with a large tongue, lips, and fingers. According to these results, we were able to reproduce a large part of the somatosensory homunculus quantitatively on an individual brain MRI.

Abstract: Thresholds were measured for the detection of vibratory stimuli of variable frequency and duration applied to the index fingertip and thenar eminence through contactors of different sizes. The effects of stimulus frequency could be accounted for by the frequency characteristics of the Pacinian (P), non-Pacinian (NP) I, and NP III channels previously determined for the thenar eminence (Bolanowski et al., J Acoust Soc Am 84 : 1680-1694, 1988; Gescheider et al., Somatosens Mot Res 18: 191- 201, 2001). The effect of changing stimulus duration was also essentially identical for both sites, demonstrating the same amount of temporal summation in the P channel. Although the effect of changing stimulus frequency and changing stimulus duration did not differ for the two sites, the effect of varying the size of the stimulus was significantly greater for the thenar eminence than for the fingertip. The attenuated amount of spatial summation on the fingertip was interpreted as an indication that the mechanism of spatia...

Abstract: The four information-processing channels of glabrous skin have distinct tuning characteristics which appear to be determined in the periphery at the level of sensory receptors and their afferent nerve fibers. The four-channel model [J Acoust Soc Am 84 (1988) 1680] has been updated to include measurement over a wider frequency range of tuning of the P and NP I channels, psychophysically determined by forward-masking and adaptation tuning curve methods. In addition to differences in their tuning, the P and NP channels differ in the following ways: (1) the P channel, but not NP channels, has been found to be capable of temporal summation, which operates by neural integration; (2) the capacity for spatial summation is also an exclusive property of the P channel; (3) sensitivity declines with age at a greater rate in the P channel than in the NP channels; (4) the masking or adaptation of a channel has no effect on the sensitivity of the other channels, although the channels interact in the summation of the perceived magnitudes of stimuli presented to separate channels.