Lecture+9+Eye

Psychology 454: Behavioral Neuroscience

  • Instructor: Yuri Saalmann

  • Institution: University of Wisconsin-Madison

Anatomy of the Eye

  • Key Structures:

    • Retina: Contains photoreceptors and processes visual information.

    • Optic Nerve: Transmits visual signals to the brain.

    • Other Components: Pupil, iris, cornea, sclera.

Retinal Circuits

  • Types of Cells:

    • Photoreceptors: Rods and cones that detect light.

    • Horizontal Cells: Integrate signals from photoreceptors.

    • Bipolar Cells: Connect photoreceptors to ganglion cells.

    • Amacrine Cells: Modulate signals and contribute to contrast detection.

    • Ganglion Cells: Output neurons sending signals to the brain.

  • Functionality:

    • Rods: Function best in dim light.

    • Cones: Function in brighter light and are responsible for color vision.

Photoreceptor Function

  • Rods vs. Cones:

    • Rods: High sensitivity to light, but no color detection.

    • Cones: Three types for color detection, each sensitive to different wavelengths (S: blue, M: green, L: red).

Center-Surround Receptive Fields

  • Organization:

    • Bipolar cells and ganglion cells have center-surround organization, enhancing contrast and edge detection.

    • ON-center Cells: Respond more to light in the center.

    • OFF-center Cells: Respond more to light in the surround.

Color Processing

  • Trichromacy:

    • Involves three cone types that combine to create the full spectrum of colors.

  • Color Opponency:

    • Red-green and blue-yellow oppositional cones facilitate color perception.

Ganglion Cell Responses

  • Contrast Sensitivity: Ganglion cells are tuned to detect edges and contrast, responding robustly to changes between light and dark areas.

Visual Angle and Perception

  • Visual Angle (θ): Related to the size of an object (S) and its distance (D) from the eye, described mathematically as tan θ = S / D.

Retina Anatomy

  • Fovea: Area of highest cone density, responsible for sharp vision and color distinction.

  • Blind Spot: The optic disk lacks photoreceptors, where the optic nerve exits the retina.

Membrane Potentials in Phototransduction

  • In Darkness:

    • Photoreceptors are depolarized and release the neurotransmitter glutamate.

  • In Light:

    • Photoreceptors hyperpolarize, decreasing the release of glutamate.

    • Light affects sodium channels via cyclic GMP pathways.

Key Features of the Fovea

  • Design Optimizations:

    • Displacement of non-photoreceptor cells and absence of blood vessels enhance light access to the photoreceptors.

Summary of Visual Processing Pathways

  • Retina to Brain Pathways:

    • Magnocellular (M-type) pathway: luminance information.

    • Parvocellular (P-type) pathway: red-green color information.

    • Koniocellular pathway: blue-yellow color information.

Assignments and Readings

  • Textbook: "Neuroscience: Exploring the Brain" by Bear, Connors, Paradiso, 2015, 4th edition.

  • Assigned Chapters: Chapter 9 (Eye), Chapter 10 (Central Vision System).

  • Interactive Content: www.sumanasinc.com/webcontent/animations/content/receptivefields.html