1. (Do Now) Journal
What is psychophysics? How does it connect sensation with perception?
What is an absolute threshold?
What are some implications of Signal Detection Theory?
What does Weber’s Law suggest about difference thresholds?

2. Ms. Saint-Paul A.P. Psychology
Chapter 4(C): Vision
Ms. Saint-Paul
A.P. Psychology

3. The Stimulus Input: Light Energy
The Electromagnetic Energy Spectrum
Visible
Spectrum

4. The Stimulus Input: Light Energy & Physical Property of Waves
Wavelength:
The distance from the peak of one light or sound wave to the peak of the next
Hue:
Dimension of color that is perceived
Determined by the wavelength of light
E.g. green, blue

5. Different wavelengths of light result
Wavelength (Hue)
Violet
Indigo
Blue
Green
Yellow
Orange
Red
400 nm
700 nm
Short wavelengths
Long wavelengths
Different wavelengths of light result
in different colors.

6. The Stimulus Input: Light Energy& Amplitude
Intensity:
The amount of energy in a light or sound wave
Determined by the wave’s amplitude
E.g. brightness (vision), loudness (hearing)

7. Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”

8. Vision Our most dominating sense
Vision is the most complex, best developed and most important sense for humans and other highly mobile creatures.
Think of the eye as the brain’s camera.
It gathers light, focuses it, converts it to a neural signal and sends these signals on for further processing.

9. Structure of The Eye

10. The Retina Photoreceptors
Photoreceptors: Light-sensitive cells (neurons) in the retina that transduce light energy into neural energy.
Rods (120 millions Photoreceptors):
responsible for peripheral vision, or non-color ( Gray, Black and white) sensitivity to low levels of light for night vision.
found all over the retina except fovea

11. The Retina Photoreceptors
Cones: (5 million Photoreceptors)
responsible for color and sharpness of vision
Concentrated in and around the fovea
work best in bright light, therefore requires more light to function than rods
Three (3) types of cones red, green and blue
sensitive to different wavelengths of light

12. The Optic Nerve and The Blind Spot
Optic Nerve: The bundle of neurons that carries the visual information from the retina to the brain.
This is where the stimulus, once changed into a neural impulse, gets passed onto the brain.
Blind Spot: The point where the optic nerve exits the eye and where there are no photoreceptors.
Any stimulus that falls on this area cannot be seen.

13. Demonstration: Test Your Blind Spot
Directions:
Looking at your sheet, close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

14. How the Eye Works???

15. The Retina

16. How the eye works

17. Pathways from the eyes to the visual cortex
Light enters the eye triggers a reactions in rods and cones at the back of the retina.
Chemical reaction in turn activates bipolar cells (Connect receptor cells to ganglion)
Bipolar cells then activate the ganglion cells (The axons of the ganglion cells form the optic nerve).
The optic nerve travels to the thalamus.
After leaving the thalamus, the optic nerve runs to the visual cortex in the occipital lobe

18. Visual Information Processing

19. Visual Information Processing Special Feature & Shape Detectors
Nerve cells in the brain that respond to specific features of stimulus such as edges, lines, angles and movements
Different parts of the visual cortex are used to identify different images

20. Parallel Processing
In the visual cortex, the brain divides a visual scene into several subdivisions and works on each aspect simultaneously

21. Color Vision
Our visual system is very good at detecting minor differences in color (about 7 million hues).

22. Young-Helmholtz Trichromatic (three color) Theory
Cones are sensitive to red, green, or blue light and by the combination of light waves these colors create different colors.
RED
BLUE
GREEN
*Most colorblind people simply lack cone receptor cells for one or more of these primary colors.
ENCROMA GLASSES

23. After Images
Stare at the eye of the red parrot while you slowly count to 20, then immediately look at one spot in the empty birdcage. The faint, ghostly image of a blue-green bird should appear in the cage.

24. After Images The ghostly birds are called afterimages.
As you stare at the red bird, light-sensitive cells at the back of your eyes become less responsive to red light. This is called the opponent processing theory.
Opponent processing theory: Color is processed by cones organized in opponent pairs; light that stimulates one half of the pair inhibits the other half.
Red-green, blue-yellow, black-white
**When a red cone is activated, then the green cone is off, which is why we don’t describe color as reddish-greenish.

25. Do Now (Turn in)
When looking at an object, what determines the color and brightness that we perceive?
What are the receptors in the Human eye and their function?
Explain “ how the eye works (process) from the moment light enter the eye and reaching the brain.
What are Feature Detectors?
What is the concept of parallel processing?
Differentiate between the Young-Helmholtz Trichromatic Theory and the Opponent-Process Theory of vision.