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LP 4B Color Perception 1 03/23/09 The Basic Senses and What They Detect Energy senses • Vision (electromagnetic energy—light waves) • Hearing (sound waves) LP 4B Color Perception 2 03/23/09 Chemical senses • Smell (airborne chemical molecules) • Taste (dissolvable chemical molecules) The skin and body senses • pressure/touch • temperature • pain • Position (kinesthetic) • Balance (vestibular) LP 4B Color Perception 3 03/23/09 Sensory Processes There are some basic concepts that psychologists use when talking about the sensitivity of the senses (pages 93 – 94). • Sensory adaptation: The decline in sensitivity to a constant stimulus. Therefore, a stronger stimulus is required to activate the sensors. Why is understanding sensory adaptation important (in what cases would sensory adaptation be “bad”)? LP 4B Color Perception 4 03/23/09 How do we see? LP 4B Color Perception 5 03/23/09 The Trichromatic Theory of Color Perception Cones are responsible for color perception. According to the theory, there are three types of cones in the fovea that are very sensitive to certain wavelengths of light and not very sensitive to the other wavelengths of light. • Blue light (short wavelength) • Green light (medium wavelength) • Red light (long wavelength) The perception of other colors (such as yyeellllo w) is the ow stimulation of a combination of cones (green and red). LP 4B Color Perception 6 03/23/09 The Trichromatic Theory of Color Perception What does the trichromatic theory of color perception explain? People with red/green color blindness cannot distinguish between the two colors because their red and green cones are sensitive to the same color. Technically, this should be called color deficiency, but is commonly called being color blind (about 8% for men, and % for women). • Blue sensitive • Green sensitive • Red sensitive • Blue sensitive • Green or Red sensitive • Green or Red sensitive True color blind people see the world in shades of gray, and are rare (about 1 out of 1,000,000 people). LP 4B Color Perception 7 03/23/09 The Opponent Process Theory The trichromatic theory of color perception cannot explain an afterimage such as seeing a faint red, white and blue flag after staring at a yellow/green flag. According to the opponent process theory, there are three types of color sensitive neurons that are sensitive to a certain pair of colors: n 1. red / g grreeeen w ow 2. blue / yyeellllo 3. black / white red / ggrreeeenn blue / yyeelllloow w red / ggrreeeenn blue / yyeelllloow w red / ggrreeeenn blue / yyeelllloow w black / white black / white black / white One single receptor can only be activated to a single color, while the other color is inhibited (blue can be activated, w is inhibited). With multiple receptors, ow while the yyeellllo some receptors can be sensitive to blue, while others can be sensitive to yellow. LP 4B Color Perception 8 03/23/09 All color perceptions are a combination of these receptors. For example, yeellllo w ow • Orange = red/green + blue/y • Purple = red/green + blue/yellow LP 4B Color Perception 9 03/23/09 How does the opponent process theory explain an afterimage? Afterimages are explained when it is combined with the general principle of sensory adaptation—the weakening of the sensitivity of your senses when they become adapted to a stimulus. Before staring at the “yellow/green” flag Normal sensitivity Yellow / Blue Green / Red Black / White Staring at the “yellow/green” flag Reduced sensitivity Normal sensitivity Y Yeelllloow w Green Black / Blue / Red / White Looking at a white background that RedOrangeY Yeelllloow wGreenBlueIndigoViolet reflects all colors of light RedOrangeYYeelllloowwGreenBlueIndigoViolet Since the red and blue receptors are sensitive, they will activate and accentuate those colors when you look at a white background, producing a weak afterimage of a red, white and blue flag. LP 4B Color Perception 10 03/23/09 Which theory of color vision is “right”, they both can’t be right? Which theory of color perception explains how we perceive color? This is the wrong question to ask about color perception. Both theories explain color perception, but at a different level of color perception. • The trichromatic theory primarily explains perception within the structure of the eye (the cones and retina) before being transmitted to the brain via the optic nerve. • The opponent process theory explains perception within the ganglion cells, thalamus and visual cortex. LP 4B Color Perception 11 03/23/09 Why is understanding the process of color perception important for understanding psychology, science, and perhaps life in general. • No one theory explains complex behavior—it involves multiple processes. • Sometimes asking the wrong/right question is important for understanding the world around you. The question that is given to you may be the “wrong” question. • Even though they “appear” to be inconsistent, the two theories are consistent. Science needs to be internally consistent Where will you see this again? • Motivation and Emotion • Personality LP 4B Color Perception 12 03/23/09 Theories of Sound Perception How do we perceive • low frequency sounds • mid-frequency sounds • high frequency sounds What are examples of low frequency sounds? What are examples of high frequency sounds? Perception of low frequency sounds (below 500 hertz): • The basilar membrane vibrates at the same frequency as the sound wave • Therefore, if the sound wave vibrates 300 times per second (or 300 hertz), the membrane vibrates at 300 times per second. Perception of high frequency sounds: • Different frequencies cause larger vibrations at different locations along the basilar membrane. • High frequency sounds causes maximum vibrations near the stirrup end of the basilar membrane. • Lower frequency sounds cause maximum vibrations at the other end. LP 4B Color Perception 13 03/23/09 Conduction deafness: the bones in the middle ear become brittle and have a difficult time amplifying the sound. Hearing aids can help with conduction deafness. Nerve deafness: damage to hair cells in the cochlea. Hearing aids cannot help with nerve deafness.