Cell Biology Quiz

Course Title: Color Vision (UE 10)

• Course is titled UE 10
• Course is about color vision
• Course instructor is Karen Ponton

Color Definition

• Color is the quality of light reflected from an object.
• It is a visual impression associated with light.
• Physicists define color as a spectral color, related to the wavelength of light perceived by the human eye.
• Color characteristics are defined by three elements: hue, saturation, and value (or brightness).

Color Attributes

• Hue (or tone): The most recognizable characteristic of color. The eye can distinguish about 200 different hues, which correspond to distinct wavelengths.
• Saturation (or chroma): A measure of purity or intensity of a color. High saturation (vivid colors) means a color is strong and pure; low saturation (pale colors) means a color is mixed with white or gray.
• Value (or brightness): Describes how light or dark a color is. High value means light, low value means dark.

Color Classification

• Primary colors: Basic colors that cannot be created by mixing other colors. Usually red, yellow, and blue.
• Secondary colors: Created by mixing two primary colors. Usually orange, green, and violet.
• Tertiary colors: Created by mixing a primary color with a neighboring secondary color.

Color Wheel

• A circular diagram that arranges colors based on their relationships.
• It illustrates relationships between primary, secondary, and tertiary colors.
• Complementary colors sit opposite each other.
• Warm colors are usually warmer and cool colors are usually cooler.

Physical Aspects of Color

• Light can be separated into different wavelengths by prisms. This was demonstrated by Newton in 1666.

• Different wavelengths correspond to different colors in spectrum.

• White light's appearance is composed of all wavelengths, each corresponding to a specific color.

• A monochromatic light source/beam emits only one wavelength.

• Transmission: A filtering material that transmits some wavelengths and blocks others.

• Reflection: An object absorbs all wavelengths of light, including some in the visual spectrum, except for the wavelength or wavelengths that are reflected to the eye.

• The visible portion of the electromagnetic spectrum is a small part of the spectrum detected by the human eye (380nm to 780nm).

Anatomical Aspects of Color Vision

• Retina: A thin membrane lining the inside of the eye, the Retina perceives images and transmits them to the brain.
• Photoreceptors: Cells in the retina that react to light. There are two types
• Cones: Cone cells are responsible for color vision and best functioning in bright light ('photopic'). There are three types of cones, with varying sensitivities to three primary colors; Long-wavelength (L), medium wavelength (M), and short wavelength (S).
  • They are more concentrated in the fovea.
• Rods: Rod cells detect light and dark, crucial for night vision ('scotopic').
  • They are more abundant in the periphery of the retina.

Anomalies of Color Vision

• Defects in color vision can be congenital (present at birth) or acquired (develop later in life).
• Congenital color vision defects: Affect the cones' ability to detect wavelength differences.
  • Achromatopsia: A complete inability to distinguish colors.
  • Dichromatism (typical problem): The inability to perceive one of the three basic colors (red, green, or blue).
    • Protanopia: Inability to see red
    • Deuteranopia: Inability to see green.
    • Tritanopia: Inability to see blue.
• Acquired color vision defects: Result from damage to eye structures or disease.
  • Chromatopsia: A perception of a color overload.
  • Color central defects: Loss or weakening of color perception
• "Low discrimination": A reduced ability to discriminate colors, commonly resulting in hesitation when making color judgments.