PSYC 1200 Lecture 3b
Chapter 4: Colour Perception
Trichromatic/ All colours result from combined responses of these three types of cones:
Young-Helmolz 1. Prefers Blue (sensitive to short wavelengths)
Theory 2. Prefers Green (sensitive to medium wavelengths)
3. Prefers Red (sensitive to long wavelengths)
Colour Blindness One or more of cone types missing.
Problem is distinguishing red from green. Sometimes the problem is distinguishing blue from yellow.
Opponent-Process Opponent-Process cells in the retina, thalamus, and visual cortex increase firing rate when exposed to wavelength for
Theory one colour, but decrease firing rate when exposed to wavelength of a different colour.
In opposition are:
Red and Green
Blue and Yellow
Black and White
Colour Afterimages 1. Cells inhibited when exposed to one colour (e.g. Red) will “bounce back” after that colour is removed
leading to perception of the opposing colour (e.g. Green).
2. Cells that fire when exposed to one colour (e.g. Red) will be temporarily inhibited after that colour is
removed leading to perception of the opposing colour (e.g. Green).
Bottom-Up Involves the information that is out there in the world and how we access that to make sense of what is actually out
Processing there and to figure out its meaning.
Detect specific features of stimulus.
Combine specific features into more complex forms.
Top-Down Involves a hypothesis based on experience and higher order parts of the brain that influences the interpretation of
Processing what is going on out there in the world.
Formulate perceptual hypothesis about the nature of the stimulus as a whole.
Select and examine features to check hypothesis.
Bottom-Up vs. Top- 1. The sensory input can be identical, but the interpretation of that input can differ based on one’s knowledge
Down Influences on and expectations.
Perception e.g. of top-down processing
The “H” in the “THE” and the “A” in the “CAT” is the identical sensory input, yet the interpretation of the
input differed depending on what you expected.
Since you wanted to make it meaningful you interpreted it as the “THE CAT”; instead of “THE CHT.”
2. The sensory input can be identical, but the interpretation of that input can differ based on how one
organizes the input.
e.g. of bottom-up processing leading to different perceptions
The image can be viewed as a duck or rabbit interchangeably based on how one organizes the input.
Subjective Contours The Law of Pragnanz: reality is organized to the simplest form possible.
To the left, the simplest interpretation is a circle on top of blue squares, but it is actually 4 blue objects.
To the right, the simplest interpretation is a triangle on top of circles, but is actually 3 pacman-like shapes.
Form Perception Involves segmenting visual input into objects and backgrounds.
Gestalt Psychology People use several rules (Gestalt Principles) to group visual information into objects:
Proximity: elements that are close to one another tend to be grouped together.
Closure: viewers tend to supply missing elements to close or complete a familiar figure.
Similarity: elements that are similar tend to be grouped together.
Simplicity: viewers t