Coma vigile, also referred to as "waking coma" or "akinetic mutism": "A state of speechlessness with an intact speech organ' as a result of a general inhibition of the motoric functions, including facial expression, gestures, speech. Speaking as well as movement do not occur spontaneously and, upon request, only delayed and slowly (...). Consciousness is retained completely, possibly there is amnesia."
(Lexikon der Medizin, Urban & Schwarzenberg)
"Coma vigil is an imprecise term that has been applied to a number of situations. In one type, the unfortunate victim has a lesion that disconnects the cerebral hemispheres from all areas below the level of the oculomotor nucleus in the brain stem. Hence the eyes can open but no other movement is possible. If the patient "hears" or receives any information, it is not possible to signal a response except by blinking (i.e. the patient is "locked in" but conscious). In the true coma vigil, the lesion is thought to be higher in the diencephalon, in the upper reaches of the seat of consciousness. Once again, the eyes are open but the patient is unconscious, does not receive most information and although appearing "alert" actually does not process any data, does not "think"."
Michael Salcman, M.D.
(...) The patients retain consciousness, but are not able to communicate (de-efferent state), which can be verified via electrophysiological methods. In some cases residual functions of the optico-motoricity are still present, e.g. vertical movements of the eyeballs, which can be enlisted in elaborating a code toward communicating with the outside world.
(Handbuch der Intensivmedizin, Georg Thieme Verlag)