1. Sensation and Perception
Chapter Three
Sensation and Perception
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2. Sensation What is sensation?
The process that detects stimuli from the from the external world and converts them onto neural impulses.
Sensory receptors- specialized cells that detect stimuli
Eyes
Ears
Nose
Mouth
Joints, muscles
Skin
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4. “Here’s Lookin at you kid”
Perception- The process that organizes sensations into meaningful patterns
Not mechanical at all, unlike a neural impulse
Meaningful patterns are inner representations of the world
Schemas- Different experiences and expectations and ways we organize information about the world.
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5. How do we study sensation and perception?
A change in environment triggers chemical and electrical activity in receptors. Sequential processing in the nervous system forms a pattern of activity in a certain area of the brain.(Sensation)
Brain assembles bits and pieces of sensory information into meaningful impressions of the world (Perception)Psychophysics-
Psychophysics-the study of the relationship between sensation and perception.
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6. Absolute Thresholds for Humans Reading: Ernst Weber – Classic Experiments in Psychology
SENSE
STIMULUS
RECEPTORS
THRESHOLD
Vision
Electromagnetic Energy
Rods & Cones in the retina
A candle flame viewed from a distance of about 30 miles on a dark night
Hearing
Sound Waves
Hair cells of the inner ear
The ticking of a watch from about 20 feet away in a quiet room
Smell
Chemical substances in the air
Receptor cells in the nose
About one drop of perfume diffused throughout a small house
Taste
Chemical substances in saliva
Taste buds on the tongue
About 1 teaspoon of sugar dissolved in 2 gallons of water
Touch
Pressure on the skin
Nerve endings in the skin
The wing of a fly falling on a cheek from a distance of about 0.4 inches

7. Absolute and Difference Thresholds
How much sugar is needed for you to taste it in 2 gallons of water?
The odor of a perfume in a room?
How loud does your name have to be called out for you to hear it?
Absolute threshold- the minimum amount of stimulation an individual can detect through a given sense.
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8. Subliminal Perception
Stimuli presented below level of conscious awareness
Subliminal perception- the unconscious perception of stimuli that are to weak to exceed the absolute threshold for detection
Can it influence attitudes or behavior?
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10. How soon can you detect changes in light or temperature?
Difference threshold, just-noticeable difference (jnd)-minimal differences between two stimuli that people can reliably detect.
Weber’s law- minimum change in stimulation that can be detected 50% of the time by a given person
Weight 1/50th
Light 1/60th
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11. TYPE OF DISCRIMINATION WEBER’S CONSTANT (WEBER’S FRACTION)
WEBER's Constant/Fraction
SENSE
TYPE OF DISCRIMINATION
WEBER’S CONSTANT (WEBER’S FRACTION)
VISION
Brightness of light
1/60
HEARING
Pitch (frequency) of a tone
1/333
Loudness of a tone
1/10
TASTE
Difference in saltiness
1/5
SMELL
Amount of rubber smell
TOUCH
Pressure on the skin surface
1/7
Deep pressure
1/77
Difference in lifted weights
1/53

12. Sensitized vs. Desensitized
Sensory adaptation-sensory receptors respond less and less to an unchanging stimulus
Lets us detect important changes in the env while ignoring unchanging ones
You will not adapt to extreme sensations because to ignore these could be harmful
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13. Responder Bias How ready are you to report the presence of a stimulus?
Biology vs. nurturing
Some individuals’ N . S. are more in tune with certain senses
While some learn to use these more like Helen Keller
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14. Seeing the Light Light Physical energy, electromagnetic radiation
Wavelength corresponds to color
nanometers
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15. Electromagnetic spectrum visible to humans
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16. Parts of the Eye (Figure 3.3)
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17. The Eye Cornea- clear covering on the eye surface
Iris-a muscle that contracts or expands to regulate the amount of light that enters the eye. (Reflex action)
Pupil-black opening inside the iris, size adjusts to the amount of light
Lens: accommodation-process by which the lens changes its shape to images more clearly
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18. Fovea- area in the retina where images are sharpest in focus
Retina: inner surface of the eye that receives the image as light strikes it through its photoreceptors
Fovea- area in the retina where images are sharpest in focus
Bipolar cells, ganglion cells
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20. Photoreceptors: convert physical energy of light into neural signals
Cones-
color vision and detail in bright light
Rods
detect objects in low light
Perception of brightness
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21. Light to Neural Impulses (Figure 3.5)

22. Where is your blind spot?
The part of the retina where the optic nerve leaves the eye
Why?
Contains no rods or cones
Why didn’t you notice before?
Eyes constantly move and they work together
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24. Where are the following?
Blind spot
Iris
Pupil
Lens
Cornea
Optic Nerve
Retina
FIGURE 4.3 In the human eye, light travels
through the pupil to the lens and is then reflected onto the retina. The optic nerve sends the visual information to the brain.

25. How does the brain translate light into visual images?
Feature Detectors are neurons that respond to specific features of the visual stimulus such as horizontal and vertical lines, movement, depth, colors, etc
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26. Color Vision Helmholtz: Trichromatic theory
3 types of color receptors: Red, green, blue-violet
By these 3 responding we are able to see colors
Hering: Opponent-process theory
Afterimages
3 Pairs of opposite colors- they transmit color for either one at a time
Red-Green
Blue-Yellow
Black-White
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27. VISUAL PROBLEMS Color Blindness
Color Blind – sensitive to only black & white
Dichromat – only sensitive to certain colors – partially color blind
Trichromat – normal color vision

28. Color blindness
Color blindness is caused by a defect in the retina or in the cones. Partial color blindness, called dichromatism, consists generally of the inability to differentiate between the reds and the greens or to perceive either reds or greens.
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