Human-computer interfaces usually are visual interfaces. There is some sort of screen to read with your eyes, and you've gto some ways to respond to the things you see on the screen. The backward channel is usually mechanical, a keyboard, a mouse, some sort of pen. Blind people would be able to use the feedback channel, but they can't read visual displays, so the loop is broken for them. Today I was reminded of a nice development - a sort of tablet-shaped reader or display which uses micro bubbles to produce braille letters and more generic shapes, which blind people can feel and understand by using their fingers: http://www.industrytap.com/worlds-first-braille-tablet-blind/32369 I'm happy to see such development. Given how ubiquitous smartphones and tablets have become in modern society, it's really a good thing that blind people get some support too, to help them participate in the virtual reality as well.
