Hockenbury Discovering Psychology 5th txtbk

98 CHAPTER 3 Sensation and Perceptionthalamus. This secondary pathway seems to be involved in processing informationabout the location of an object.Neuroscientists now know that there are several distinct neural pathways in thevisual system, each responsible for handling a different aspect of vision (Zeki,2001). Although specialized, the separate pathways are highly interconnected.From the thalamus, the signals are sent to the visual cortex, where they are decodedand interpreted.Most of the receiving neurons in the visual cortex of the brain are highly specialized.Each responds to a particular type of visual stimulation, such as angles, edges,lines, and other forms, and even to the movement and distance of objects (Hubel& Wiesel, 2005; Livingstone & Hubel, 1988). These neurons are sometimes calledfeature detectors because they detect, or respond to, particular features or aspects ofmore complex visual stimuli. Reassembling the features into a recognizable imageinvolves additional levels of processing in the visual cortex and other regions of thebrain, including the frontal lobes.Understanding exactly how neural responses of individual feature detection cellsbecome integrated into the visual perceptions of faces and objects is a major goal incontemporary neuroscience (Martin, 2007; Peissig & Tarr, 2007). As the Focus onNeuroscience illustrates, experience plays a key role in perception.Color VisionWe see images of an apple, a banana, and an orange because these objects reflectlight waves. But why do we perceive that the apple is red and the banana yellow?What makes an orange orange?The Experience of ColorWhat Makes an Orange Orange?When Red + Blue + Green = White Whenlight waves of different wavelengths arecombined, the wavelengths are addedtogether, producing the perception of adifferent color. Thus, when green light iscombined with red light, yellow light isproduced. When the wavelengths of red,green, and blue light are added together,we perceive the blended light as white. Ifyou’re wondering why mixing paintstogether produces a muddy messrather than pure white, it’s becausethe wavelengths are subtractedrather than added.Each color of pigment absorbsa different part of thecolor spectrum, and eachtime a color is added,less light is reflected.Thus, the mixed colorappears darker. If youmix all three primarycolors together, theyabsorb the entirespectrum—so we perceivethe splotch as black.Color is not a property of an object, but a sensation perceived in the brain (Werner& others, 2007). To explain how we perceive color, we must return to the originalvisual stimulus—light.Our experience of color involves three properties of the light wave. First, what weusually refer to as color is a property more accurately termed hue. Hue varies withthe wavelength of light. Look again at Figure 3.2. Different wavelengths correspondto our subjective experience of different colors. Wavelengths of about 400 nanometersare perceived as violet. Wavelengths of about 700 nanometers are perceived as red.In between are orange, yellow, green, blue, and indigo.Second, the saturation, or purity, of the color corresponds to the purity ofthe light wave. Pure red, for example, produced by a single wavelength, is moresaturated than pink, which is produced by a combination of wavelengths (redplus white light). In everyday language, saturation refers to the richness of acolor. A highly saturated color is vivid and rich; a less saturated color is fadedand washed out.The third property of color is brightness, or perceived intensity.Brightness corresponds to the amplitude of the light wave: the higherthe amplitude, the greater the degree of brightness.These three properties of color—hue, saturation, and brightness—are responsible for the amazing range of colors we experience. Aperson with normal color vision can discriminate from 120 to150 color differences based on differences in hue, or wavelength,alone. When saturation and brightness are also factoredin, we can potentially perceive millions of different colors (Bornstein& Marks, 1982).Many people mistakenly believe that white light contains nocolor. White light actually contains all wavelengths, and thus all