4.17 Depth Perception and the Dorsal Stream

Depth Perception: The ability to determine the distance of objects from oneself.

Binocular Cues: Depth cues that utilize both eyes.
- Definition: "Bi" means two, indicating the use of both eyes simultaneously to perceive depth.
Monocular Cues: Depth cues that can be utilized with only one eye.
- Definition: "Mono" means one, denoting the reliance on a single eye for depth perception.

Convergence
- Definition: The inward turning movement of both eyes when focusing on a near object.
- Example: Bringing a pencil closer to one’s nose requires the eyes to converge.
- Brain Signal: The muscle activation pattern from the convergence provides a signal to the brain indicating that the object is close.
- Relaxed Eyes Signal: When the eye muscles are relaxed and the eyes are straight, it indicates the object is further away.
Retinal Disparity
- Definition: The comparison made by the brain of the slightly different images received from each eye.
- Example: The phenomenon when one sticks out their thumb and closes one eye alternately, observing the thumb's apparent movement due to the different perspectives from each eye.
- Stereopsis: The resulting perception of depth from this comparative analysis creates our three-dimensional understanding of objects.
- Alien Hypothetical: An analogy involving an alien with a banana-shaped head and multiple eyes, illustrating how each eye provides a different perspective and contributes to depth perception.

Strabismus: Commonly referred to as lazy eye, occurs when the eyes are not properly coordinated and unable to create overlapping images for depth perception.
- Depth Perception Impact: Without proper eye coordination, individuals cannot achieve the necessary overlap required to compare the two images effectively.

Background: A famous case of a woman named Stereo Sue who had strabismus for most of her life.
- Visual Experience: She perceived reflections in the mirror as flat images resembling paintings rather than having depth (the three-dimensionality that others perceive).
Intervention: Through intervention with a scientist, her eye coordination was improved, enabling her to perceive depth.
Neuroplasticity: This case exemplifies neuroplasticity, the brain's capacity to reorganize and adapt based on experiences. After training, her brain rewired itself to process depth perception effectively.

Overall Importance: Understanding depth perception, including its cues and the implications of its disruption, is vital in the fields of psychology and neuroscience, highlighting the brain's adaptability through neuroplasticity.