Depth Perception

It’s already April, and at Experience Writing that means it’s time for NaPoWriMo (National /Global Poetry Writing Month) and the A-Z Challenge. Continuing this year’s theme, I’m writing about the A to Z of Depth.

Stereopsis

Binocular depth perception is also called stereopsis. Stereopsis is the process in which we perceive depth due to the merging of two different image inputs from our two eyes. The area in the field of vision where stereopsis is maintained is called Panum’s fusional area, fusion being the neural process of combining the two images into one.

When the two images cannot merge because they are too different, one image is suppressed, so only one is seen at a time for a few moments each. This is called Binocular rivalry. When the eyes are misaligned like for people who are crosseyed, binocular rivalry can lead to one eye being permanently suppressed which stops stereopsis leaving the person stereoblind.

Monocular Depth Cues

People who are stereoblind and people who have lost an eye can still perceive depth due to many monocular depth cues working together. Monocular depth cues consist of:

• relative size – as objects we are familiar with look smaller, we perceive them as farther away. When they get larger or closer to the size we are familiar with we perceive them as closer.
• interposition – when objects overlap, we perceive the overlapped object as further away.
• linear perspective – parallel lines converge to a point with increasing distance.
• aerial perspective – Because of the scattering of blue light in the atmosphere, creating a “wall” of blue light, distant objects appear more blue
• light and shade – because our visual systems assume light comes from above, light and shadow provide dimension cues and depth information.
• monocular movement parallax – when we move our heads side to side, objects move at different relative speeds. Closer objects move against the direction of head movement and farther objects move with the direction of head movement.

In Fixing My Gaze_{(assoc. link)} Susan R. Barry shares her experience being born stereoblind and later training her brain to see in three dimensions. As an infant she was crosseyed, so her growing brain compensated for her double vision by relaying information from only one eye. She had many surgeries to correct her vision, but remained stereoblind. Her whole life she believed she saw in three dimensions until in college it was brought to her attention that she didn’t see like her classmates. In an NPR interview Susan said, “When I didn’t see in stereo, space was very contracted and compacted. So, for example, if I looked at a tree, the leaves or the branches would appear to overlap one in front of another. But I didn’t actually see the pockets of space between the individual leaves or branches.” In her fifties, as a neuroscientist, she went through vision therapy and saw in three dimensions for the first time.

Dr. Dennis M. Levi at U.C. Berkeley is at the forefront of stereopsis recovery. He is using virtual reality in his efforts to retrain the brain to see in 3-D which you can read more about in his article “Applications and implications for extended reality to improve binocular vision and stereopsis.”

Today’s Poem

Song of the Psychopath

Driving under the streetlamps
he sings along with the radio
smiling, head bobbing
from shoulder to shoulder
the summer sun’s calling my name
I hear you now

He turns the wheel
coaxes the car through a gate
sings over muffled yells
and kicking from the trunk
Tires crunch gravel
as he brakes to a stop
He shuts off the engine
but the song still plays
everybody sings
so happy today

Sometimes sunny days torture
those not feeling well
guilting them for not going outside
calling and calling to work or to play
to be burned by the taunting
flame-ball in the sky

He sings as he douses
the car in gasoline
I gotta get out
get me some of those rays
He whistles as he walks away
and the car becomes a ball of flame.

This poem was inspired by today’s prompts at NaPoWriMo and Writer’s Digest’s April Poem a Day (PAD) Challenge. It was also inspired by a scene in the last episode of the show Castle which is available on Amazon Prime video.

Thank you so much for coming by and reading my post. Any thoughts or questions about Depth Perception? Come back tomorrow for more depth exploration and poetry.