The messages we do not shadow are not remembered e.g. Moray found repetitions are not noticed, if the test is made within delays over say 5-7 words. If the delays are less than 5 words, or 5 units if they are syllables, recall is evident. The temporal lobe has cells relevant to selective attention. If that rectangle is a signal for rewards, likely it will be attended-to, and the cell will repond more strongly. This suggests some inhibition becomes involved.
Divided attention is reletively inefficient.
Binocular rivalry results if two very different signals are presented to the two eyes. Dichotic listeners fail to pick up target words is deviding attention. Typists can sight-type and shadow very well. Saccades are influenced by the structure of the scene, and by our purpose. Novel objects found in search of scenes hold our fixation longer.