/usr/share/psychtoolbox-3/PsychBasic/GetSecs.mex is in octave-psychtoolbox-3 3.0.12.20160126.dfsg1-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/psychtoolbox-3/PsychBasic/../../../lib/psychtoolbox-3/PsychBasic/GetSecs.mex