Visual Constancies

Modified: 2024-06-12 5:20 AM CDST

• Size constancy occurs because we know the sizes that characterize familiar objects.
  • Cars are bigger than people, buildings are bigger than cars.
  • So when we see a car and it is far away, the image of that car takes up less space on our retinas.
  • As the car comes closer, its image takes up more space on our retinas, and we say it is getting closer.
  • As noted earlier, when we view new or unfamiliar objects, we may have some trouble perceiving their distance from us.
  • The man in the photo is the same size (check it out)
  • In the left photo size constancy makes us perceive him as normal size because he is further away. (Note that the photo also illustrates perspective)

• Shape constancy refers to our knowledge about the shapes of objects.
  • Again, we know that most objects do not change their shape, at least not very quickly.
    • Perhaps that is why we are so fascinated with the recent computer graphic technique of morphing.
    • Through that technique, objects (on film or computer monitor) can be made to appear to change their shape quickly.
    • In Terminator 2: Judgment Day that movie made heavy use of morphing.
    • However, in the real world, objects tend to retain their shapes, and we know that.
  • Look at the link below. It illustrates shape constancy nicely
    • The coin does not lose its perceptual shape but the circle and the ellipse do
    • Coins vs shapes
• Color constancy is a product of the difference between the action of the cones cells and the rod cells.
  • Remember that the cones are responsible for color vision, and the rods for black-and- white-vision.
    • When we are in a dark enough setting, we cannot see color because our cone cells are not getting enough light to work.
    • They are below their threshold.
    • But, we perceive the colors anyway. Why? Because we know what the colors should be.
    • We perceive the mug below as uniformly blue despite the other colors shown.

Interested? Want to see more about Brainard's research? CLICK HERE

• So the constancies provide firm evidence that perception and sensation are not the same.
• Perception is more than the simple reporting of sensations.
• Perception is profoundly altered by our experience.