Why are you limited to how much visual information you are able to process at any one given moment?
The thalamus, which directs information to the brain, can only filter so much information at any one moment in time.
The occipital lobe is smaller than the other cerebral lobes, so it can't process as much information.
The neurons in your visual cortex are wired in an inhibitory way.
The hypothalamus sets up an opponent process so that certain incoming visual information "blocks" other incoming visual information.