mt_variable_labels: Labels for mousetrap variables.
Description
A named character vector specifying the names of the variables that mousetrap
uses for labeling the mouse-tracking variables. The default values are
xpos for x-positions, ypos for y-positions, timestamps
for timestamps, dist for distance traveled, vel for velocity,
and acc for acceleration. These labels will be used for labeling the
respective dimensions in the trajectory array (see mt_example).