In-Depth Notes on Vision from Biological Psychology Chapter 5

Vision Overview

• Biological Psychology focuses on the processes involved in vision based on brain activity rather than simply optical input from the eyes.

General Principles of Perception

• Each sense possesses specialized receptors tuned to specific energy types.
• Law of Specific Nerve Energies: Each nerve's activity encodes a specific type of information.
  • Example: Neuron impulses indicate light in one case, sound in another.

Anatomy of the Eye

• Light Pathway:
  • Light enters through the pupil (the central opening in the iris)
  • It is focused by the lens and cornea onto the retina, lined with visual receptors.
  • Light from the left side of the world strikes the right side of the retina and visa versa, and similarly for above and below.

Retina Pathways

• Bipolar Cells:
  • Receive messages from visual receptors and convey them to ganglion cells.
• Ganglion Cells:
  • Their axons converge to form the optic nerve, which transmits signals to the brain.
• Amacrine Cells:
  • Integrate information from bipolar cells and modulate responses in other cells.

The Fovea

• The fovea is the central part of the retina, crucial for sharp and detailed vision.
  • It is densely packed with cones and has minimal blood vessels or ganglion cell axons.
  • Each foveal cone attaches to a single bipolar cell, which connects to a single ganglion cell, enhancing visual acuity.

Peripheral Vision

• Characterized by a larger convergence of rods into bipolar and ganglion cells, resulting in less detail.
  • Better suited for detecting faint light, particularly in low-light conditions.

Rods vs. Cones

• Rods:
  • 120 million in the retina, operate well in dim light, high sensitivity but low detail.
• Cones:
  • 6 million concentrated in the fovea, responsible for color vision in bright light.
  • Although fewer, cones contribute to about 90% of the brain's visual input.

Photopigments

• Chemicals in rods and cones, change in structure when exposed to light.
  • Consists of 11-cis-retinal bound to opsins.
  • Light catalyzes the conversion of 11-cis-retinal to all-trans-retinal, triggering biological processes within the cells.

Color Vision

• Humans perceive wavelengths of light between 400 and 700 nm.
• Trichromatic Theory: Color perception arises from the activity of three types of cones sensitive to short (blue), medium (green), and long (red) wavelengths.
• Opponent-Process Theory: Color perception is based on opposing pairs (red-green, blue-yellow, black-white).

Color Vision Deficiencies

• Can result from genetic factors affecting cones, most prevalent being red-green deficiency linked to X chromosome abnormalities.

Visual Processing Pathways

• Visual signals travel via the optic nerve to the lateral geniculate nucleus (LGN) in the thalamus before reaching the primary visual cortex (V1).
• Dorsal Pathway ("Where" Path): Involved in spatial awareness and movement guidance.
• Ventral Pathway ("What" Path): Essential for object recognition and identification.

Receptive Fields

• Cells in the visual system respond to specific visual properties of stimuli (e.g., movement or light intensity).
  • Includes simple, complex, and end-stopped cells.

Visual Cortex Processing

• Visual information undergoes further analysis in the cortex with various cell types detecting features such as edges, motion, and complex shapes.
  • Sensitivity can decrease with prolonged exposure to static visual stimuli.

Visual Recognition and Motion Perception

• Processes in recognizing objects, motion, and depth involve specific cortical areas and pathways (MT/V5 for motion).
• Saccades (rapid eye movements) help in retaining visual clarity during shifts in gaze.

Conclusion

• Vision is a complex interplay of anatomical structures and neural processing, allowing for detailed perception, motion detection, and color discrimination.
• Understanding vision involves integrating anatomy with physiological psychology for comprehensive insights into visual perception.