/usr/share/psychtoolbox-3/Quest/ is in psychtoolbox-3-common 3.0.9+svn2579.dfsg1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/psychtoolbox-3/Quest/Contents.m
/usr/share/psychtoolbox-3/Quest/QuestBetaAnalysis.m
/usr/share/psychtoolbox-3/Quest/QuestCreate.m
/usr/share/psychtoolbox-3/Quest/QuestDemo.m
/usr/share/psychtoolbox-3/Quest/QuestMean.m
/usr/share/psychtoolbox-3/Quest/QuestMode.m
/usr/share/psychtoolbox-3/Quest/QuestP.m
/usr/share/psychtoolbox-3/Quest/QuestPdf.m
/usr/share/psychtoolbox-3/Quest/QuestQuantile.m
/usr/share/psychtoolbox-3/Quest/QuestRecompute.m
/usr/share/psychtoolbox-3/Quest/QuestSd.m
/usr/share/psychtoolbox-3/Quest/QuestSimulate.m
/usr/share/psychtoolbox-3/Quest/QuestTrials.m
/usr/share/psychtoolbox-3/Quest/QuestUpdate.m