  Even before the Covid-19 pandemic, beneficial use cases for hygienic,
touchless human-machine interaction have been explored. Gaze input, i.e.,
information input via eye-movements of users, represents a promising method for
contact-free interaction in human-machine systems. In this paper, we present
the GazeVending interface (GaVe), which lets users control actions on a display
with their eyes. The interface works on a regular webcam, available on most of
today's laptops, and only requires a one-point calibration before use. GaVe is
designed in a hierarchical structure, presenting broad item cluster to users
first and subsequently guiding them through another selection round, which
allows the presentation of a large number of items. Cluster/item selection in
GaVe is based on the dwell time of fixations, i.e., the time duration that
users look at a given Cluster/item. A user study (N=22) was conducted to test
optimal dwell time thresholds and comfortable human-to-display distances.
Users' perception of the system, as well as error rates and task completion
time were registered. We found that all participants were able to use the
system with a short time training, and showed good performance during system
usage, selecting a target item within a group of 12 items in 6.76 seconds on
average. Participants were able to quickly understand and know how to interact
with the interface. We provide design guidelines for GaVe and discuss the
potentials of the system.
