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Sensation and perception. Sensory psychology. How we know about the world General principles Transduction receptors Adequate stimulus Law of specific nerve energies Battery experiment Physical properties give rise to perceptual features Color is NOT a property of light.
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Sensory psychology • How we know about the world • General principles • Transduction • receptors • Adequate stimulus • Law of specific nerve energies • Battery experiment • Physical properties give rise to perceptual features • Color is NOT a property of light
Physical versus perceptual characteristics • Need to determine relationship between physical and perceptual characteristics • Vision – light travels in waves • Definition of wavelength
Wave characteristic of light Differences in wavelength are perceived as differences in color
Wave characteristic of light A and B have same wavelength B has higher amplitude Differences in amplitude are perceived as differences in brightness
Relationship between physical and perceptual characteristics of light
Visual transduction • Cornea • Light enters eye • Pupil • Contraction and dilation • Iris • Pigmented part • Lens • Focuses light on retina
Visual transduction • Optic disc • How to find your blind spot • Retina • Photoreceptors • Rods • Cones
Visual transduction • Photochemicals in rods and cones respond to light • Fire action potential • Are carrots really good for your eyes?
Properties of rods and cones • Cones (about 7 million in each retina) • Respond best to bright light • Respond to color • Difficult to see color in dark • Rods (about 120 million in each retina) • Respond best to dim illumination • Do not respond to color
From retina to perception • Optic nerve • Occipital lobe • Feature detectors in the brain • Respond (fire action potential) only for very specific stimuli • Some will fire if see horizontal but not vertical line • Some will fire if see “L” but not for straight line
Summary of visual transduction • Adequate stimulus for vision is light • Enters the eye and is focused on retina • Retina has receptors (neurons) with photochemicals • Fire action potential when exposed to light • AP to occipital lobe via optic nerve
Color perception • Not in the stimulus • Species differences • No brain; no color • Different brain; different color • Question: What processes give PERCEPTION of color?
The spectrum of light • White light combination of all colors • ROYGBIV • Longest to shortest wavelenths • Red, orange, yellow, green, blue, indigo, violet • Infrared and ultraviolet
Theories of color vision • Do not know exactly how perceive color • Trichromatic theory (Young-Helmholtz) • Found three different kinds of cones • Each has different photochemical • 3 different photochemicals respond best to 3 primary colors (red, green blue) • Any color can be made from combination of primary colors
Trichromatic theory of color vision • Show a color (pink) • All three cones types respond (fire) • Cone type most responsive to red fires most • Cone types most responsive to green and blue fire less • INTERPRETATION of pattern is pink
Trichromatic theory and color blindness • How does color blindness result according to theory? • Selective color blindness • Problems for the trichromatic theory • After images
The opponent process theory • Photochemicals in cones arranged in opposed pairs • Red-Green • Blue-Yellow • Black – White • Colors oppose one another • When see red prevents from seeing green
Opponent process theory • Explanation for after images
Factors affecting color blindness • Gender • Race • Age
Hearing • General questions same as for vision (and all other senses) • What is adequate stimulus ? • How does adequate stimulus get transduced (cause action potential) • Physical properties map on to perceptual characteristics
Adequate stimulus • Changes in air pressure • Tuning fork example • Compression and expansion of air molecules
Physical properties of sound • Changes in air pressure can be fast or slow • Many or few cycles (compression-expansion) per second (Hertz –Hz) • Frequency • Air pressure changes can be high or low • Amplitude • Measured in decibels (after AGB)
Different pitches 10,000 (10 kHz) 2000 Hz 200 Hz 16,000 Hz
Changes in loudness Base sound 10 dB louder 20 dB louder 30 dB louder
The outer ear Pinna • Pinna • External auditory canal
The middle ear Pinna • Tympanic membrane (ear drum) • Ossicles – hammer, anvil and stirrup
The inner ear Pinna • The cochlea- filled with fluid not air • Basilar membrane • Hair cells on the basilar membrane
Transduction in the auditory system • Changes in air pressure enter the external auditory canal • Vibrate the tympanic membrane • Vibrate the ossicles • Ossicles “bang” on the cochlea • Movement of fluid in cochlea • Bending of hair cells
Hearing without hair cells • Cochlear implants • Electrodes implanted in cochlear next to auditory nerve • Microphone (on belt) receives sound and transmits to electrodes • Electrodes directly stimulate the auditory nerve
Cochlear implants • What do they sound like? Normal Implant
Cochlear implants • Who should get them • Potential disadvantages • Controversy in deaf community
Factors that can affect hearing • Things that can’t control • Age • Gender • Things that can control • Noise • Duration and amplitude both important • Frequency • What frequencies important for speech • What frequencies noise damages • Environmental noise vs. loud music • “walkman” phenomenon