Well, not anymore.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116730/
"[T]he relationship between sensory deprivation and brainwashing was made public when then director of the National Institute of Mental Health Robert Felix testified before the US Senate about recent isolation studies being pursued at McGill and the NIMH. Felix began by explaining that these experiments would improve medicine’s understanding of the effects of isolation on bedridden or catatonic patients. But when asked whether this could be a form of brainwashing, he replied, ‘Yes, ma’am, it is.’ He went on to explain how, when stimulation is cut off so far as possible the mind becomes completely disoriented and disorganised. Once in this state, the isolated subject is open to new information and may change his beliefs. ‘Slowly, or sometimes not so slowly, he begins to incorporate this [information] into his thinking and it becomes like actual logical thinking because this is the only feed-in he gets.’ He continues, ‘I don’t care what their background is or how they have been indoctrinated. I am sure you can break anybody with this’
"The day after the senate hearing an article entitled ‘Tank Test Linked to Brainwashing’ (1956) appeared in the New York Times and was subsequently picked up by other local and national papers. In Anglophone popular culture, an image took hold of SD as a semi-secretive, clinical, technological and reliable way of altering subjectivity. It featured in television shows such as CBC’s Twighlight Zone (1959), as a live experiment on the BBC’s ‘A Question of Science’ (1957) and the 1963 film The Mind Benders in which a group of Oxford scientists get caught up in a communist espionage plot."
I've tried btw to find any other reference to this testimony to US Senate by Robert Felix, "the director of the National Institute of Mental Health", but it always circles back to this singular Williams article. The mentioned NYTimes article also does not show up for me. (Maybe you have better search foo..) Note John Lilly's paper on the topic apparently remains "classified". Note subsequent matter associated with Lilly and sensory deprivation completely flipped the story about SD: Felix testified that the mind became 'disorganized' and 'receptive' whereas Lilly lore (see Altered States) completely flipped that and took it to a woo woo level certain to keep sensible people away from the topic. /g