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                Images] Sensation & Perception: Vision I  (Outline)

The World of Sensations (after Kardas)

Imagine what the world is like if you are not a human being?

Cats: Do not perceive color  Humans: Perceive color

Bees and Butterflies: See ultraviolet light  Humans: Do not see ultraviolet light Visible vs. Ultraviolet Light

Snakes: See infrared light  Humans: Do not see infrared light
Dogs: Recognize smells 1/1000 weaker than humans do

Bats: Hear ultrasonic sound (> 20 kH)  Humans: Cannot hear ultrasonic sound (< 20 kH)

[Human vs. Dog Vision]

Energy Sources Perceived by the Senses
  • Vision (= seeing)

[Light Spectrum]

Sound: pressure waves
  • Audition (= hearing)
Chemicals: Dissolved in liquid or free-floating as volatile molecules
  • Gustation/taste
  • Olfaction/smell
Mechanical Forces: e.g., heat, cold, pressure, pain
  • Cutaneous senses
Gravity & Forces of Acceleration/Deceleration


This orderly sequence codes the visual field in such a way that
125 million photoreceptor cells (cones & rods)
send their information
over the 1 million axons of the optic nerve.

A. The Structure of the Eye

[Human Eye]

B. The Retina

[The Retina]

Cones & rods

Cones --> color, fine discrimination (high visual acuity), adapted to bright/strong light (daylight); around the fovea. Rods are sensitive to low levels of light (night vision)

Adaptation: Dark
vs. Light


C. The Visual Pathways

Visual Pathway

D. Information Processing in the Visual Cortex

[Hubel-Wiesel Procedure]

  • Simple cell
  • Complex cell
  • Hypercomplex cell
  • = Feature Detection

              & Wiesel]
[Visual Streams]

E. Seeing Color

What are other qualities of light and its perception?

[Color Qualities]

E. Color Perception

1. Trichromatic Color Perception (at the level of the cones in the retina) is an additive process

[Color Mixing]

2. Opponent-Process Color Perception (at the level of the ganglion cells) = excitation/inhibition process

   Note that the Trichromatic Color Perception theory does not explain:

A. Negative (Inverted) Afterimages

Inverted US Flag

B. Contrast Effects

[Contrast Effect]

C. Colorblindness

Color-Blind R/G

Colorblind Achromatopsia

[Trichromatic & Opponent-Process Vision]

This page originally posted on 02/02/04 and updated on 09/20/2011


Colavita, F. (2006). Sensation, Perception, and the Aging Process: Guidebook, Pt. 1. The Teaching Company.

Kardas, E. Physical forces and associated sensory systems. Retrieved February 1, 2004 from the World Wide Web: http://peace.saumag.edu/faculty/kardas/Courses/GPWeiten/C4SandP/Forces.html.

WebExhibits.Com. Causes of Color.