Well, far from comatose, we do have examples of people like Hellen Keller, who managed to become a wonderful writer while being deaf-mute. — Manuel

Well Keller only lost both her sight and hearing after an illness at age two. So she had that much normal exposure to the world in terms of her social and biological development. And through a supportive family, she developed a reasonable system of sign language, such as miming putting on glasses to signify her father, or a tying up of her hair to signify her mother. As well as shakes of the head to mean yes and no, pushes and pulls to mean come or go. A "vocabulary" of about 60 signs to navigate her safe home world.

Then she had a carer who took her at six and taught her a laborious system of spelling out words through tapping out an alphabet on her fingers. From here, Keller – having had vital exposure to human speech in her first few years – learnt to talk herself. And talk of all the things she could now learn from now having added not just braille, but the ability to decode chalk writing on blackboards by touch, and spoken words from touching a person's moving lips.

But when she gave her public talks, many found her bookish and limited. Maxim Gorky, perhaps unkindly, called her affected and spoilt. Someone speaking of God's disapproval of revolution in a stilted and learnt way rather than with any worldly wisdom.

I know all this from researching these kinds of "parables" and what they reveal about the socially-constructed and language-scaffolded nature of the human mind. They illustrate exactly how language – as semiosis – plays a central role in structuring what we "phenomenologically experience".

Alexander Meshcheryakov wrote a book, Awakening to Life, about his own work teaching finger-spelling to people born deaf and blind and so really lacking any normal level of exposure to either the sensory world and the socio-linguistic world. They grew up in institutions where their experience was about limited to their internal spasms of hunger or cold, and the rough touch of the hands cleaning and feeding them. Years of training could get them to the level of dressing themselves, feeding themselves, using the toilet. But nothing much beyond as any grammatical structure must be connected to some matching semantic world of lived experience.

So consciousness is not an innate or singular property, but a learnt and developmental process. And in humans, we develop the set of neurobiological habits we would share with any large brained animal. Then we add a socially-constructed realm of language-scaffolded ideas and intellectual habits on top.

All this was already obvious to a Victorian neurologist like John Hughlings Jackson – the father of British neurology – who had already worked out that the brain is structured hierarchically and topographically. A structure that could model an organism's reality by both breaking it apart and putting it back together at the same time.

When asked about what made the human brain different from an animal's, he said it wasn't merely speech but the fact that speech was an ability to "propositionalise" or make meaningful claims. About anything and everything. "The unit of speech is a proposition," he declared. "We speak not only to tell other people what to think, but to tell ourselves what we think. Speech is part of thought."

Curious that so much that seemed clear enough to Victorian science then got forgotten and all muddled up again.

It's more so, what would a human be like, if they never developed senses….. — Manuel

Dunno. Maybe the autonomic system would still work, but the cognitive system wouldn’t for lack of direct sensory input, and the aestetic part wouldn’t work for lack of feelings about things of sense, so it looks like none of what is called a priori, like your “pure thought”, would be available. But hey….probably wouldn’t be dead.

I'd wonder if there's "something that it's like" to be that, from a phenomenological perspective, "pure thought", absent language. — Manuel

Again, don’t know, but given the otherwise fully equipped human, I’m convinced all thought is absent language.

…outside of language, we don't know what non-linguistic thought is. — Manuel

You mean outside the language we use to speculate on what non-linguistic thought is. I agree we don’t know what non-linguistic thought is, only because we don’t know what thought is regardless of its modifiers. Just as I’m convinced thought is absent language, so too am I convinced at least empirical thought is in the form of images which reflect the state of my knowledge. Even so, I haven't been able to pin down a describable form of pure thought, as it is called by the metaphysicians, a priori.