Taking the chair example - the robot will not know what all chairs look like, but will maybe have a few examples. Every time a new example of that category is encountered, it must be able to add it to those already stored. I find hard to understand. A form of the symbol grounding problem will always be apparent. Vision shouldn't be necessary, but certainly some sensory interaction with the world is required.
Humans born blind are still able to learn.
Even without sight and hearing, humans have tactile sensory interaction with the world and this is an important sense to have. Babies and young children like to touch and play with things, and I believe this is an important part of learning. As humans learn, by interpretation of the world through any senses available, that interpretation is the manipulation of symbols, presented to the system, by the sensors. Indeed, to get around the symbol grounding problem, the robot cannot be told about the world by a supervisor, but has to make inferences for itself. Learning can indeed not be solely unsupervised.