/usr/share/psychtoolbox-3/PsychHardware/PsychHID.mex is in octave-psychtoolbox-3 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/psychtoolbox-3/PsychHardware/../../../lib/psychtoolbox-3/PsychHardware/PsychHID.mex