It may be that both of these factors are happening, since if Artyom stays for too long in a room with the blind ones, some sort of radiation 'blowout' will occur. Though it is assumed that Artyom's hallucinations in the Institute are caused by extreme radiation exposure, it is possible that he is being psychically attacked by the blind ones. This suggests a very high level of intelligence, comparable to the Librarians or even the Dark Ones. They are also able to do so with humans, since Artyom is able to understand them. The blind ones have also developed an ability to telepathically communicate with each other. They are the only surface mutants found in Novosibirsk, presumably because they are the only ones able to withstand the radiation levels. Blind ones are extremely strong and durable, able to kill any human or similar sized creature in seconds.
Their lack of eyes means that they primarily rely on sound and smell to locate their prey.
The blind ones closely resemble pre-war gorillas, except for their complete lack of eyes and their tendency to walk on two legs.
