It wasn’t brutal, but it was extremely effective. Under either circumstance, the long term results of sensory deprivation were the same. An ego without a sensory input to the world becomes disoriented and drifts without the anchor of social intercourse. The individuals who were subjected to long term deprivation of their sensorium, whether they were test subjects or prisoners, descended into a passive insanity from which there was no escape.
While he lacked any control whatsoever over his body, his last remaining sensory inputs meant he could at least be a passive observer.