  The use of vibrotactile feedback is of growing interest in the field of
prosthetics, but few devices fully integrate this technology in the prosthesis
to transmit high-frequency contact information (such as surface roughness and
first contact) arising from the interaction of the prosthetic device with
external items. This study describes a wearable vibrotactile system for
high-frequency tactile information embedded in the prosthetic socket. The
device consists of two compact planar vibrotactile actuators in direct contact
with the user's skin to transmit tactile cues. These stimuli are directly
related to the acceleration profiles recorded with two IMUS placed on the
distal phalanx of a soft under-actuated robotic prosthesis (SoftHand Pro). We
characterized the system from a psychophysical point of view with fifteen
able-bodied participants by computing participants' Just Noticeable Difference
(JND) related to the discrimination of vibrotactile cues delivered on the index
finger, which are associated with the exploration of different sandpapers.
Moreover, we performed a pilot experiment with one SoftHand Pro prosthesis user
by designing a task, i.e. Active Texture Identification, to investigate if our
feedback could enhance users' roughness discrimination. Results indicate that
the device can effectively convey contact and texture cues, which users can
readily detect and distinguish.
