/usr/share/psychtoolbox-3/PsychBasic/moalcore.mex is in octave-psychtoolbox-3 3.0.14.20170103+git6-g605ff5c.dfsg1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/psychtoolbox-3/PsychBasic/../../../lib/psychtoolbox-3/PsychBasic/moalcore.mex