Once the senses that a person relied on heavily were cut off, they had to rely on their other senses even more, and they would not be able to gain as much information to process whatever situation they were in.
That would be made even more difficult for any person in that type of situation when they would have to make up for their lack of sight or other senses with their imagination.
If they were left to their imagination, then it was possible that they would let their imagination negatively run wild, causing them to become even more fearful and like things were hopeless.
Those types of tactics were usually used to control the captive, and they could even be used for other purposes, like a form of torture to get information out of them.
If they had their senses cut off for a prolonged period of time, there would be some people who would not be able to cope so well.
