During the exploration of surfaces with the bare finger, vibratory signals arise and
propagate through the finger and hand. While research into mechanical and neural response
characteristics has demonstrated that these signals carry rich information about touched
objects and their properties, only little is known about the role these propagation waves
play in human perception and to which extent the somatosensory system is able to collect
information from afferents at more proximal locations than the skin-object surface. Using
ring-block anaesthesia (lidocaine) we will temporarily inhibit haptic feedback sensations of
healthy participants' index finger during interactions with 3D-printed surface probes that
are systematically varied in two important material dimensions, namely their roughness and
hardness (elasticity), while the participants carry out a well-established psychophysical
discrimination task. The results will then be compared to a control condition without
anaesthesia. An accelerometer sensor, placed on the dorsal side of the hand, will serve to
simultaneously record the propagating tactile waves. Given their role in material perception,
thermal cues will be monitored during the experiment with a thermometer and the hydration
level of the fingertip skin will be measured regularly using a corneometer. This research
will allow us to understand the role of propagation waves in material perception. It seeks to
uncover some of the perceptual mechanisms that remain intact during surface discrimination of
textured, compliant surfaces, while local information is temporarily inhibited. The results
will have implications for how we provide feedback about material properties for sensorimotor
control to this living with prosthetic limbs. It is hypothesised that propagation waves that
arise during these haptic interactions contain behaviourally relevant information used for
the discrimination of surface properties.