  Auditory, haptic, and visual stimuli provide alerts, notifications, and
information for a wide variety of applications ranging from virtual reality to
wearable and hand-held devices. Response times to these stimuli have been used
to assess motor control and design human-computer interaction systems. In this
study, we investigate human response times to 26 combinations of auditory,
haptic, and visual stimuli at three levels (high, low, and off). We developed
an iOS app that presents these stimuli in random intervals and records response
times on an iPhone 11. We conducted a user study with 20 participants and found
that response time decreased with more types and higher levels of stimuli. The
low visual condition had the slowest mean response time (mean +/- standard
deviation, 528 +/- 105 ms) and the condition with high levels of audio, haptic,
and visual stimuli had the fastest mean response time (320 +/- 43 ms). This
work quantifies response times to multi-modal stimuli, identifies interactions
between different stimuli types and levels, and introduces an app-based method
that can be widely distributed to measure response time. Understanding
preferences and response times for stimuli can provide insight into designing
devices for human-machine interaction.
