Sensation and Perception Lecture 4

Explaining Color Vision • Opponent-process theory of color vision: receptor cells for color are linked in pairs, working in opposition to each other: blackwhite, yellowblue, green-red. Figure 5.16 Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper. What do you see? This is known as a negative afterimage, and it provides empirical support for th opponent-process theory of color vision. Depth Perception: Translating 2-D to 3D • Depth perception: the ability to view the 1 • • • world in three dimensions and to perceive distance. We use a variety of cues in a visual scene to establish our sense of depth. Some of these are binocular cues, which means that they rely on the use of both eyes. Ex: Binocular disparity is the difference in the images seen by the left eye and the right eye. The difference between the images in the two eyes provides us with a way of determining distance. • • Depth Perception: Translating 2-D to 3-D 2 Monocular cues permit humans to obtain a sense of depth and distance with just one eye. EX: Linear perspective: objects in the distance appear to converge. Sound Waves Frequency ~ pitch • • the number of wave cycles that occur in a second. Low frequencies are very low in pitch—the characteristic that makes sound seem “high” or “low.” Amplitude ~ loudness • The range of sound we can hear is measured in decibels. MODULE 10 FIGURE 2 • The sound waves produced by different stimuli are transmitted—usually through the air —in different patterns, with lower frequencies indicated by fewer peaks and valleys per second. Sensing Sound • • 1 Sound localization: the process by which we identify the direction from which a sound is coming. Location of the outer ears on different sides of the head helps. • Sound: the movement of air molecules brought about by a source of vibration. • Eardrum: the part of the ear that vibrates when • sound waves hit it. Vibrations are then transferred into the middle ear, which contains three bones—the hammer, anvil, and stirrup—that transmit vibrations to the oval window leading to the inner ear. Sensing Sound (2) • • • • The inner ear changes the sound vibrations into a form transmittable to the brain. Cochlea: a coiled tube in the ear filled with fluid that vibrates in response to sound. Basilar membrane: a vibrating structure through the center of the cochlea, containing sense receptors for sound. Hair cells: tiny cells covering the basilar membrane that, when bent by vibrations entering the cochlea, transmit neural messages to the brain. © McGraw Hill LLC 37 Ear Decibels The Physical Aspects of Sound 3 • Place theory of hearing: different areas of basilar membrane respond to different frequencies. • Frequency theory of hearing: the entire basilar membrane acts like a microphone, vibrating as a whole in response to a sound. • After an auditory message leaves the ear, it is • • transmitted to the auditory cortex of the brain. Auditory neurons respond to specific types of sounds. Speech perception requires fine discriminations among sounds. • Echolocation The Physical Aspects of Sound • • • Several structures of the ear are related more to our sense of balance than to our hearing. This vestibular system responds to the pull of gravity and allows us to maintain our balance. Semicircular canals: three tube-like structures of the inner ear containing fluid that sloshes when the head moves, signaling rotational or angular movement to the brain. 4