Hockenbury Discovering Psychology 5th txtbk

Vision99FOCUS ON NEUROSCIENCEVision, Experience, and the BrainAfter Mike’s surgery, his retina and optic nerve were completelynormal. Formal testing showed that Mike had excellent colorperception and that he could easily identify simple shapes andlines that were oriented in different directions. These abilitiescorrespond to visual pathways that develop very early. Mike’smotion perception was also very good. When thrown a ball, hecould catch it more than 80 percent of the time.Perceiving and identifying common objects, however, was difficult.Although Mike could “see” an object, he had to consciouslyuse visual cues to work out its identity. For example,when shown the simple drawing above right, called a “Neckercube,” Mike described it as “a square with lines.” But whenshown the same image as a rotating image on a computerscreen, Mike immediately identified it as a cube. Functional MRIscans showed that Mike’s brain activity was nearly normal whenshown a moving object.What about more complex objects, like faces? Even threeyears after his surgery, Mike recognizes his wife and sons by theirhair color, gait, and other clues, not by their faces. He can’t tellwhether a face is male or female, or whether its expression ishappy or sad. Functional MRI scans revealed that when Mike isNecker CubeNecker Cube Shown a stationaryimage of a Necker cube, Mikedescribed it as “a square withlines.” Only when the image beganto rotate did Mike perceiveit as a drawing of a cube.shown faces or objects, the part of the brain that is normallyactivated is silent (see brain scans).For people with normal vision, recognizing complex threedimensionalobjects—like tables, shoes, trees, or pencils—isautomatic. But as Mike’s story shows, these perceptual conclusionsare actually based on experience and built up over time.Neuroscientist Ione Fine and her colleagues (2003), who havestudied Mike’s visual abilities, believe that Mike’s case indicatesthat some visual pathways develop earlier than others. Color andmotion perception, they point out, develop early in infancy. Butbecause people will continue to encounter new objects andfaces throughout life, areas of the brain that are specialized toprocess faces and objects show plasticity. In Mike’s case, thesebrain centers never developed.Scanning Mike’s Brain The red, orange,and yellow colors in the left fMRI scanshow the areas of the occipital lobe thatare normally activated in response tofaces. Blue and purple indicate the typicalpattern of brain activity in responseto objects. In contrast to a normalsighted individual, Mike’s fMRI scan onthe right shows virtually no response tofaces and only slight brain activation inresponse to objects.Normal ControlMike Maycolors, of the visible part of the electromagnetic spectrum. A glass prism placed insunlight creates a rainbow because it separates sunlight into all the colors of the visiblelight spectrum.So we’re back to the question: Why is an orange orange? Intuitively, it seemsobvious that the color of any object is an inseparable property of the object—unlesswe spill paint or spaghetti sauce on it. In reality, color is a sensation perceived in thebrain (Werner & others, 2007).Our perception of color is primarily determined by the wavelength of light thatan object reflects. If your T-shirt is red, it’s red because the cloth is reflecting onlythe wavelength of light that corresponds to the red portion of the spectrum. TheT-shirt is absorbing the wavelengths that correspond to all other colors. An objectappears white because it reflects all the wavelengths of visible light and absorbs none.An object appears black when it absorbs all the wavelengths of visible light andreflects none. Of course, in everyday life, our perceptions of color are also stronglyaffected by the amount or type of light falling on an object or the textures and colorsthat surround it (Shevell & Kingdom, 2008).colorThe perceptual experience of differentwavelengths of light, involving hue, saturation(purity), and brightness (intensity).hueThe property of wavelengths of light knownas color; different wavelengths correspondto our subjective experience of differentcolors.saturationThe property of color that corresponds tothe purity of the light wave.brightnessThe perceived intensity of a color, whichcorresponds to the amplitude of the lightwave.