Everyone has basic mental access to the Collective. The Collective is a database of the things that are the same for everyone, or mostly everyone.
The blind, or the color-blind, may have a messed up connection to the Collective in the visual node, but may have an overload in the hearing or smell nodes. Thus, hearing of smelling things more vividly or from farther away while having less capably, or glitched, sight.
Different areas of the brain rely on different nodes of the Collective to supply them with data. People with hallucinations may have some crossed wires that cause data to show up where it shouldn't. People with a 6th Sense may hear something and accidentally receive visual data with the sound data, being able to see what made the sound.
I like the reality-defining wiki comment, but I have a question. Is this starting to sound too much like an expansion of The Matrix to anyone? I've got a bad feeling about this... Thought and comments are still welcome, thank you.