  Brushed stimuli are perceived as pleasant when stroked lightly on the skin
surface of a touch receiver at certain velocities. While the relationship
between brush velocity and pleasantness has been widely replicated, we do not
understand how resultant skin movements - e.g., lateral stretch, stick-slip,
normal indentation - drive us to form such judgments. In a series of
psychophysical experiments, this work modulates skin movements by varying
stimulus stiffness and employing various treatments. The stimuli include
brushes of three levels of stiffness and an ungloved human finger. The skin's
friction is modulated via non-hazardous chemicals and washing protocols, and
the skin's thickness and lateral movement are modulated by thin sheets of
adhesive film. The stimuli are hand-brushed at controlled forces and
velocities. Human participants report perceived pleasantness per trial using
ratio scaling. The results indicate that a brush's stiffness influenced
pleasantness more than any skin treatment. Surprisingly, varying the skin's
friction did not affect pleasantness. However, the application of a thin
elastic film modulated pleasantness. Such barriers, though elastic and only 40
microns thick, inhibit the skin's tangential movement and disperse normal
force. The finding that thin films modulate affective interactions has
implications for wearable sensors and actuation devices.
