  A synopsis of the various photoinduced changes of rheological, mechanical and
elastic properties is presented in the first part of the article. After a
critical appraisal of a large body of experimental data it suggested that the
photoviscous effect, that is, the athermal decrease of viscosity of a
non-crystalline chalcogenide upon illumination is the key for a plethora of
photoinduced effects reported so far in the literature under different names.
Morphic effects (shape or surface morphology) may ap-pear either in the
presence or absence of external mechanical stimuli leading to the fabrication
of a variety of technologically important photoprocessed structures. A few
representative examples of photoplastic effects are described, in the second
part of the paper, in some detail based on information provided by in situ
Raman scattering and nanoindentation experiments.
