Hockenbury Discovering Psychology 5th txtbk

Hearing101Afterimages can be explained when the opponent-processtheory is combined with the general principle of sensoryadaptation (Jameson & Hurvich, 1989). If you stare continuouslyat one color, sensory adaptation eventually occurs andyour visual receptors become less sensitive to that color. Whathappens when you subsequently stare at a white surface?If you remember that white light is made up of the wavelengthsfor all colors, you may be able to predict the result.The receptors for the original color have adapted to theconstant stimulation and are temporarily “off duty.” Thusthey do not respond to that color. Instead, only the receptorsfor the opposing color will be activated, and you perceivethe wavelength of only the opposing color. For example,if you stare at a patch of green, your green receptors eventually become“tired.” The wavelengths for both green and red light are reflected by the whitesurface, but since the green receptors are “off,” only the red receptors are activated.Staring at the green, black, and yellow flag in Figure 3.6 should have producedan afterimage of opposing colors: a red, white, and blue American flag.Figure 3.6 Experiencing an After imageStare at the white dot in the center of thisoddly colored flag for about 30 seconds,and then look at a white wall or whitesheet of paper. What do you see?An Integrated Explanation of Color Vision At the beginning of this section wesaid that current research has shown that both the trichromatic theory and theopponent-process theory of color vision are accurate. How can both theories beright? It turns out that each theory correctly describes color vision at a differentlevel of visual processing.As described by the trichromatic theory, the cones of the retina do indeed respondto and encode color in terms of red, green, and blue. But recall that signals fromthe cones and rods are partially processed in the ganglion cells before being transmittedalong the optic nerve to the brain. Researchers now believe that an additionallevel of color processing takes place in the ganglion cells.As described by the opponent-process theory, the ganglion cells respond to andencode color in terms of opposing pairs (DeValois & DeValois, 1975). In thebrain, the thalamus and visual cortex also encode color in terms of opponent pairs.Consequently, both theories contribute to our understanding of the process ofcolor vision. Each theory simply describes color vision at a different stage of visualprocessing (Hubel, 1995; Werner & others, 2007).HearingFrom Vibration to SoundKey Theme• Auditory sensation, or hearing, results when sound waves are collected inthe outer ear, amplified in the middle ear, and converted to neural messagesin the inner ear.Key Questions• How do sound waves produce different auditory sensations?• What are the key structures of the ear and their functions?• How do place theory and frequency theory explain pitch perception?We have hiked in a desert area that was so quiet we could hear the whir of a singlegrasshopper’s wings in the distance. And we have waited on a subway platformwhere the screech of metal wheels against metal rails forced us to cover our ears.