  Palm-based tactile displays have the potential to evolve from single motor
interfaces (e.g., smartphones) to high-resolution tactile displays (e.g.,
back-of-device haptic interfaces) enabling richer multi-modal experiences with
more information. However, we lack a systematic understanding of vibrotactile
perception on the palm and the influence of various factors on the core design
decisions of tactile displays (number of actuators, resolution, and intensity).
In a first experiment (N=16), we investigated the effect of these factors on
the users' ability to localize stationary sensations. In a second experiment
(N=20), we explored the influence of resolution on recognition rate for moving
tactile sensations.Findings show that for stationary sensations a 9 actuator
display offers a good trade-off and a $3\times3$ resolution can be accurately
localized. For moving sensations, a $2\times4$ resolution led to the highest
recognition accuracy, while $5\times10$ enables higher resolution output with a
reasonable accuracy.
