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Vibrotactile Threshold Measurements at the Wrist Using Parallel Vibration Actuators

This article presents an investigation into the perceptual vibrotactile thresholds for a range of frequencies on both the inside and outside areas of the wrist when exciting the skin with parallel vibrations, realized using the L5 actuator made by Lofelt GmbH. The vibrotactile threshold of 30 participants was measured using a modified audiometry test for the frequency range of 25–1,000 Hz. The average threshold across the respective frequencies was then ultimately determined from acceleration minima. The results show that maximum sensitivity lies in the range of 100–275 Hz (peaking at 200 Hz) for the inside and 75–250 Hz (peaking at 125 Hz) for the outside of the wrist and that thresholds are overall higher for the hairy skin on the outside of the wrist than for the glabrous skin on the inside. The results also show that the vibrotactile thresholds varied highly between individuals. Hence, personalized threshold measurements at the actuator locations will be required to fine-tune a device for the user. This study is a part of an ongoing research and development project where the aim is to develop a tactile display device and a music encoding scheme with the purpose of augmenting the musical enjoyment of cochlear implant recipients. These results, along with results from planned follow-up experiments, will be used to determine the appropriate frequency range and to cast light on the dynamic range on offer for the tactile device.