/usr/share/psychtoolbox-3/PsychPriority/ is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/psychtoolbox-3/PsychPriority/Contents.m
/usr/share/psychtoolbox-3/PsychPriority/GetProcessDescriptorFromCommandName.m
/usr/share/psychtoolbox-3/PsychPriority/GetProcessList.m
/usr/share/psychtoolbox-3/PsychPriority/GetRawProcessList.m
/usr/share/psychtoolbox-3/PsychPriority/MachGetPriorityFlavor.m
/usr/share/psychtoolbox-3/PsychPriority/MachGetPriorityMex.m
/usr/share/psychtoolbox-3/PsychPriority/MachSetPriorityMex.m
/usr/share/psychtoolbox-3/PsychPriority/MachSetStandardPriority.m
/usr/share/psychtoolbox-3/PsychPriority/MachSetTimeConstraintPriority.m
/usr/share/psychtoolbox-3/PsychPriority/MaxPriority.m
/usr/share/psychtoolbox-3/PsychPriority/Priority.m
/usr/share/psychtoolbox-3/PsychPriority/Rush.m