Before reaching our eyes, light has to pas through an exterior-gateway that blocks parts of our visual field. The orbital bone isn't only there to protect our eyes from being physically hurt but it also defines the amount of imagery our brain has to process and it also creates an alignment with what we see (1.5.a Different alignment gives a different view ).

The level of transparency can be represented by what's called in Adobe's Photoshop and other image editing programs a "Masking Alpha Channel", this refers to a image composition layer that exists out of 3 possible values: black, white or gray; what's white is viewable what 's black is blocked, and what is gray is in-between.

Eyes have an unlimited view, but not in width and height, they are partly blocked by facial masking and aligning areas. On the image to the right we can see the nasal-intersection blocking a part of the visual field,  when we look sideways, the blocking increases automatically for one eye. These limitations create an alignment and hold-on.

Seeing is letting a stream of images project into our eyes, light passes the lens on to the back of our eye where it is captured by the Retina, a light-sensitive tissue, it converts patterns of light into electrical discharges known as action potentials. Most of these signals are send along the axons of Retinal Ganglion cells to the LGN a relay nucleus, a big part of the output of the LGN is relayed directly to the Primary Visual Cortex (V1) at the back of our brain and on to surrounding visual association areas.

Viewing with two eyes creates one Binocular field where both Visual fields are overlapping (central) and two Mococular view fields (peripheral). The facial masking alpha-areas narrow our Visual Fields and define the Binocular field, each part of our visual field is represented in the Primary Visual Cortex (V1),

Result: Different volumes of alpha give different input to the V1 region (see topic: 5.3 Alpha in Primary Visual Cortex (V1)) and in combination with movement of the eyes while tracking an object, the influence of alpha play's an important role (see topic: 1.2 Eye Movement & The Masking Alpha Channel )

[ Next: 1.2 Eye Movement & Facial Masking elements ]