(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?

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

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

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

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.

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)

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

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.

Structure of The Eye

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

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

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.

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.

How the Eye Works???

The Retina

How the eye works https://youtu.be/YcedXDN6a88

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

Visual Information Processing

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

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

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

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 https://www.youtube.com/watch?v=o6QuYiY1EJg

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.

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.

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.