Humans become conscious of a thing (like what they are seeing) when there is a meta representation of it in the higher-order parts of the brain. This is kind of like the “symballs” analogy from I Am a Strange Loop.
Global workspace theory
Information enters consciousness when it is accessed and broadcast in a “workspace”, moving information from local processing units to the brain-wide workspace.
Integrated information theory
Concsciousness arises from the integration of information in a system where the greater degree of integration (more connections) the higher the level of consciousness.
See also: Consciousness is categories but as Douglas Hofstadter would argue, it is conscious or it is not, there is no unit of consciousness
Recurrent processing theory
There needs to be a loop of information flow from higher-order cognitive areas to lower sensory processing areas in both directions—top-down and bottom-up.