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Vision How does our body construct our conscious visual experience?

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1 Vision How does our body construct our conscious visual experience?
How de we transform particles of light energy to another? We do this by receiving light energy and transforming it into neural messages that our brains process into what we consciously see.

2 The Stimulus Input- Light Energy
What strikes are eyes IS NOT color, but rather electromagnetic energy that we perceive as color. The next slide shows the range from imperceptibility short waves of gamma rays to the narrow band we see as visible light, to the long waves of radio transmission and AC circuits.

3 The Stimulus Input: Light Energy
Visible Spectrum Both Photos: Thomas Eisner

4 Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next. The amount of energy in light waves or intensity, determined by a wave’s amplitude, or height, influences the brightness of the light

5 Intensity (Brightness)
Intensity Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

6 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.

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

8 Purity (Saturation) Monochromatic light added to green and red
Saturated Saturated Monochromatic light added to green and red makes them less saturated.

9 Represents all three characteristics of light stimulus on this model.
Color Solid Represents all three characteristics of light stimulus on this model.

10 The Eye OBJECTIVE 5| Describe the major structure of the eye, and explain how they guide the incoming ray of light toward the eye’s receptor cells.

11 Parts of the eye Cornea: Transparent tissue where light enters the eye. Pupil- a small adjusting opening that allows light to pass through Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses the light rays on the retina. Retina: Contains sensory receptors that process visual information and sends it to the brain.

12 The Lens Lens: Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

13 Retina Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information. OBJECTIVE 6| Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light.

14 Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster.

15 Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

16 Bipolar & Ganglion Cells
The neural signals produced in the rods and cones activate the neighboring BIPOLAR cells, which then activate a network of GANGLION cells. The axons of ganglion cells converge to from the OPTIC NERVE, which carries visual information to the BRAIN. Where the nerve leaves the eye, there are no receptors; thus, the area is called the BLIND SPOT

17 Test your Blind Spot Use your textbook (E-BOOK). 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.

18 Fovea, Rods and Cones Most cones are clustered around the retina’s point of central focus called the FOVEA, whereas the rods are concentrated in more peripheral visions of the retina. Many cones have their own bipolar cells to communicate with the visual cortex. Cones- enable color Rods- enable black and white vision Unlike cones, rods are sensitive. Adapting to a darkened room will take the retina approximately 20 minutes.

19 Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex. OBJECTIVE 7| Discuss the different levels of processing that occur as information travels from the retina to the brain’s cortex.

20 Feature Detection Hubel and Wiesel discovered that specific features called Feature Detectors. Examples include - respond to specific features, such as edges, angles, and movement. Ross Kinnaird/ Allsport/ Getty Images

21 Feature Detection Feature detectors pass the information to higher level cells in the brain, which respond to specific visual scenes. Research has shown that in monkey brains such cells that specialize in responding to specific gazes, head angles, posture, or body movements. In may cortical areas, teams of cells supercell clusters respond to complex patters.

22 Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. Other brain damaged people may demonstrate blind sight by responding to a stimulus that is not consciously perceived. OBJECTIVE 8| Discuss parallel processing and discuss its role in visual processing.

23 From Sensation to Recognition
Tim Bieber/ The Image Bank

24 Theories of Color Vision
Trichromatic theory: Based on behavioral experiments, Helmholtz suggested that the retina should contain three receptors that are sensitive to red, blue and green colors. An object appears to be red in color because it rejects the long wavelengths of red and because of our mental construction of the color. Standard stimulus OBJECTIVE 9| Explain how the Young-Helmholtz and opponent-process theories help us understand color vision. Comparison stimulus Max Medium Low Blue Green Red

25 Theories of Color Vision
One out of every 50 people is color deficient; this is usually a male because the defect is genetically

26 Subtraction of Colors If three primary colors (pigments) are mixed, subtraction of all wavelengths occurs and the color black is the result.

27 Addition of Colors If three primary colors (lights) are mixed, the wavelengths are added and the color white is the result. Fritz Goro, LIFE magazine, © 1971 Time Warner, Inc.

28 Photoreceptors Blue Cones Green Cones Red Cones MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans. Short wave Medium wave Long wave

29 Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test

30 Opponent Colors Gaze at the middle of the flag for about 30
Seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

31 Opponent Process Theory
Hering proposed that we process four primary colors combined in pairs of red-green, blue-yellow, and black-white. Cones Retinal Ganglion Cells

32 Color Constancy Color of an object remains the same under different illuminations. However, when context changes the color of an object may look different. OBJECTIVE 10| Explain the importance of color constancy. R. Beau Lotto at University College, London

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