  Variable frame timing (VFT), or changes in the time intervals between
discrete frame images displayed to users, deviates from our traditional
conceptualization of frame rate in which all frame times are equal. With the
advent of variable refresh rate (VRR) monitor technologies, gamers experience
VFT at the display. VRR, coupled with increased display refresh rates and
high-end hardware, enables smoother variation of frame presentation sequences.
We assess the effects of VFT on the perception of smoothness (experiment 1) and
performance (experiment 2) in first-person shooter (FPS) gameplay by
introducing frequent but relatively small (4-12 ms) variations in frame time
around typical refresh rates (30-240 Hz). Our results indicate that VFT impacts
the perception of smoothness. However, the results from experiment 2 do not
indicate differences in FPS task performance (i.e., completion time) between
variable and constant frame time sequences ranked equally smooth in experiment
1.
