Introductory Psychology

Chapter 4Sensation and Perception How We Sense and Conceptualize the World Sensation and Perception Sensation is the detection of physical energy by our sense organs, which send that in" rel="nofollow">information to the brain" rel="nofollow">in. Perception is the brain" rel="nofollow">in's in" rel="nofollow">interpretation of raw sensory data. Sensation Despite their differences, all our senses rely on a handful of prin" rel="nofollow">inciples. The external stimulus is converted by a sense receptor in" rel="nofollow">into neural activity via transduction. Activation is highest when stimulus is first detected, then sensory adaptation occurs. Psychophysics Study of how we perceive sensory stimuli based on their physical characteristics Absolute threshold is the lowest level of a stimulus we can detect 50% of the time A sin" rel="nofollow">ingle candle 30 miles away 50 odorant molecules The just noticeable difference is the smallest amount of stimulus change we can detect. Weber's law—the stronger the stimulus, the greater the change necessary for the detection of a difference. Signal Detection Theory Theory regardin" rel="nofollow">ing how stimuli are detected under different conditions Cross-Modal Effects Phosphenes, the McGurk effect, and the rubber hand illusion all demonstrate sensory cross-modality. This may help to explain" rel="nofollow">in synesthesia—the experience of cross-modal sensations, like hearin" rel="nofollow">ing sounds when one sees colors. The Role of Attention Selective attention allows us to choose which sensory in" rel="nofollow">inputs to focus on and which to "turn down." The other "channels" are still bein" rel="nofollow">ing processed at some level, though. Cocktail party effect We're poor at detectin" rel="nofollow">ing stimuli in" rel="nofollow">in plain" rel="nofollow">in sight if our attention is focused elsewhere. Inattentional blin" rel="nofollow">indness and change blin" rel="nofollow">indness are two similar phenomena. Blin" rel="nofollow">indin" rel="nofollow">ing Problem One of the great mysteries of psychology is just how our brain" rel="nofollow">ins combin" rel="nofollow">ine all the various stimuli around us in" rel="nofollow">into a coherent whole. The look, feel, smell, and taste of an apple all rely on different areas of the brain" rel="nofollow">in to process, but we just see an apple! Light The human visible spectrum is a narrow band of light that we respond to. Other animals may have a more restricted or broader spectrum. The Visible Spectrum Is a Subset of the Electromagnetic Spectrum. Visible light is electromagnetic energy between ultraviolet and in" rel="nofollow">infrared. Humans are sensitive to wavelengths rangin" rel="nofollow">ing from slightly less than 400 nanometers (violet) to slightly more than 700 nanometers (red). We perceive brightness (in" rel="nofollow">intensity) and hue (color). Mixin" rel="nofollow">ing lights produces white (additive). Mixin" rel="nofollow">ing pigments produces black (subtractive). Additive and Subtractive Color Mixin" rel="nofollow">ing. Additive color mixin" rel="nofollow">ing of light differs from subtractive color mixin" rel="nofollow">ing of pain" rel="nofollow">int. The Eye Sclera is the white portion of the eye Iris is the colored portion and controls how much light enters the eye Pupil is the hole where light enters the eye Cornea contain" rel="nofollow">ins transparent cells that focus light on the back of the eye The lens changes curvature (accommodation) to retract light onto back of eye. Glasses change the way light enters the eye to help correct myopia or hyperopia. The Retin" rel="nofollow">ina The retin" rel="nofollow">ina is a thin" rel="nofollow">in membrane at the back of the eye. The fovea in" rel="nofollow">in its center is responsible for acuity. Light hits two types of sense receptors on the retin" rel="nofollow">ina—rods and cones. Dark adaptation The Key Parts of the Eye The Eye The optic nerve exits the back of the eye and is composed of the axons of the ganglion cells. Causes a blin" rel="nofollow">ind spot Most of the axons go to the thalamus and then the visual cortex, but some go to midbrain" rel="nofollow">in. Perception and the Visual Cortex - Visual in" rel="nofollow">information from the retin" rel="nofollow">ina travels to the visual thalamus. Next, the visual thalamus sends in" rel="nofollow">inputs to the primary visual cortex (V1), then along two visual pathways to the secondary visual cortex (V2; see p. 136 ). One pathway leads to the parietal lobe, which processes visual form, position, and motion; and one to the temporal lobe, which processes visual form and color. Perceivin" rel="nofollow">ing Shape and Contour Different cortical cells respond maximally to different types of stimuli. Feature detector cells allow us to detect lin" rel="nofollow">ines and edges. Simple cells—detect orientation-specific slits of light in" rel="nofollow">in a particular location Complex cells—also orientation-specific, but less dependent on location than simple cells Color Perception Different theories of color perception explain" rel="nofollow">in different aspects of our ability to detect color. Trichromatic theory says color vision is based on our sensitivity to three primary colors. Consistent with three types of cones in" rel="nofollow">in eyes Explain" rel="nofollow">ins color blin" rel="nofollow">indness Opponent process theory sees color vision as a function of complementary, opposin" rel="nofollow">ing colors: red v. green or blue vs. yellow. As an example, stare at the white dot in" rel="nofollow">in the middle of the flag on the next slide see what happens. Opponent Processes in" rel="nofollow">in Action. Fin" rel="nofollow">ind a patch of blank white wall or place a blank sheet of white paper nearby before you begin" rel="nofollow">in. Then relax your eyes and fix your gaze on the white dot in" rel="nofollow">in the image above for at least 30 seconds without lookin" rel="nofollow">ing around or away. Afterward, stare at the white wall or paper for a few seconds. What do you see? When We Can't See Blin" rel="nofollow">indness—results in" rel="nofollow">in heightened touch, reorganization of visual cortex Blin" rel="nofollow">indsight—above-chance visual performance of cortically blin" rel="nofollow">ind in" rel="nofollow">individuals with damage to area V1 Visual agnosia—object recognition deficit; damage to higher visual cortical areas Hearin" rel="nofollow">ing and Sound Audition (our sense of hearin" rel="nofollow">ing) is the sense we rely on most after sight. Sound is simply vibration travelin" rel="nofollow">ing through a medium (usually air) and has: Pitch—wave frequency (Hz) Loudness—amplitude of the sound waves (dB) Timbre—complexity of sound The Ear The outer, middle, and in" rel="nofollow">inner ear do different jobs to transduce sound in" rel="nofollow">into neural activity. The outer ear (pin" rel="nofollow">inna and ear canal) tunnels sound waves onto the eardrum. On the other side of the eardrum, the ossicles (hammer, anvil, stirrup) vibrate and transmit sound to the in" rel="nofollow">inner ear. In the in" rel="nofollow">inner ear, the cochlea converts vibration in" rel="nofollow">into neural activity. The organ of Corti and basilar membrane convert auditory in" rel="nofollow">information in" rel="nofollow">into action potentials. The Human Ear and Its Parts. A cutaway section through the human ear and a close-up diagram of the hair cells. Pitch Perception Place theory – Different tones excite different areas of the basilar membrane and primary auditory cortex. Explain" rel="nofollow">ins perception of high-pitched tones Frequency theory and volley theory – Neurons' rate of firin" rel="nofollow">ing reproduces the frequency of the sound. Explain" rel="nofollow">ins perception of low and middle pitches Smell and Taste Olfaction (smell) and gustation (taste) work hand in" rel="nofollow">in hand. Work together to enhance likin" rel="nofollow">ing or dislikin" rel="nofollow">ing of some foods. Described as the "chemical senses" Odors and Flavors Odors are airborne chemicals that in" rel="nofollow">interact with lin" rel="nofollow">inin" rel="nofollow">ing in" rel="nofollow">in our nasal passages. We are sensitive to five basic tastes: Sweet, salty, sour, bitter, umami There is some evidence for a "fatty" taste as well. Smell and Taste Sense Receptors Each olfactory neuron contain" rel="nofollow">ins a sin" rel="nofollow">ingle type of receptor, which recognizes odorants based on their shape. The tongue contain" rel="nofollow">ins separate taste buds for each basic taste. 25% of people are supertasters, with more taste buds. Olfactory and Gustatory Perception Although they take different paths, our smell and taste senses converge in" rel="nofollow">in the orbitofrontal cortex. Smell and Taste. Our senses of smell and taste enter the brain" rel="nofollow">in by different routes but converge in" rel="nofollow">in the orbitofrontal cortex. Our Body Senses Three body systems that work in" rel="nofollow">in tandem: Somatosensory (touch and pain" rel="nofollow">in) Proprioception (kin" rel="nofollow">inesthetic sense – body position) Vestibular sense (equilibrium and balance) Somatosensory System - Responds to pressure, temperature, and in" rel="nofollow">injury. We sense these with specialized nerve endin" rel="nofollow">ings in" rel="nofollow">in the skin" rel="nofollow">in and with free nerve endin" rel="nofollow">ings. The Sense of Touch. The skin" rel="nofollow">in contain" rel="nofollow">ins many specialized and free nerve endin" rel="nofollow">ings that detect mechanical pressure, temperature, and pain" rel="nofollow">in. Somatosensory Pathways - Somatic nerves carry in" rel="nofollow">info to spin" rel="nofollow">inal cord -> Spin" rel="nofollow">inal reflexes may be activated -> Connects in" rel="nofollow">in brain" rel="nofollow">in stem, thalamus -> Touch: somatosensory, association cortices -> OR -> Pain" rel="nofollow">in: somatosensory cortex, limbic areas Pain" rel="nofollow">in Sensations Pain" rel="nofollow">in comes in" rel="nofollow">in many types, usually related to the pain" rel="nofollow">in-causin" rel="nofollow">ing stimulus. Gate control model – pain" rel="nofollow">in is blocked from consciousness by neural mechanisms in" rel="nofollow">in the spin" rel="nofollow">inal cord. Pain" rel="nofollow">in is in" rel="nofollow">influenced by emotional and cultural factors. Body Position and Balance Proprioception, our kin" rel="nofollow">inesthetic sense, helps us keep track of where we are, allowin" rel="nofollow">ing us to move efficiently. Muscle stretch receptors vs. tendon force detectors Vestibular sense, our sense of equilibrium, enables us to sense and main" rel="nofollow">intain" rel="nofollow">in our balance as we move about. Due to three fluid-filled semicircular canals in" rel="nofollow">in the in" rel="nofollow">inner ear. Our awareness of this sense is limited. Ergonomics: Human Engin" rel="nofollow">ineerin" rel="nofollow">ing Human factors – field that optimizes technology to better suit our sensory and perceptual capabilities. Uses what we know about psychology and sensory systems to build more ergonomic gadgets and tools. When Senses Meet the Brain" rel="nofollow">in After bein" rel="nofollow">ing transduced, our brain" rel="nofollow">ins then organize the sensory data in" rel="nofollow">into meanin" rel="nofollow">ingful concepts. Our brain" rel="nofollow">ins piece together: What's in" rel="nofollow">in our sensory field What was there a moment ago What we remember from our past The Multitaskin" rel="nofollow">ing Brain" rel="nofollow">in We attend to multiple senses at once, called parallel processin" rel="nofollow">ing. Bottom-up vs. top-down processin" rel="nofollow">ing Perception depends on sensory data and beliefs/expectations. What Do You See? Due to the in" rel="nofollow">influence of top-down processin" rel="nofollow">ing, readin" rel="nofollow">ing the caption "saxophone player" beneath this ambiguous figure tends to produce a different perception than readin" rel="nofollow">ing the caption "woman." Perceptual Hypotheses Perceptual sets occur when our expectations in" rel="nofollow">influence our perceptions. Perceptual constancy allows us to perceive stimuli consistency across conditions. We don't see the size, shape, or color of an object changin" rel="nofollow">ing despite the objective fact that they do. Color perception in" rel="nofollow">in particular derives from context. Shape Constancy - We perceive a door as a door whether it appears as a rectangle or a trapezoid. The Checker-Shadow Illusion - We perceive a checkerboard pattern of black and white alternatin" rel="nofollow">ing squares, and because of color constancy, we ignore the dramatic change due to the shadow cast by the green cylin" rel="nofollow">inder. Believe it or not, the A and B squares are identical. (Source: © 1995 Edward H. Adelson) Color Perception Depends on Context- Gray can appear like a color dependin" rel="nofollow">ing on surroundin" rel="nofollow">ing colors. The blue-colored squares on the top of the cube at the left are actually gray (see map below the cube). Similarly, the yellow-colored squares on the top of the cube at the right are actually gray (see map below the cube). (Source: © Dale Purves and R. Beau Lotto, 2002) Gestalt Prin" rel="nofollow">inciples Rules that govern how we perceive objects as wholes within" rel="nofollow">in their overall context Gestalt Prin" rel="nofollow">inciples of Perception- As Gestalt psychologists discovered, we use a variety of prin" rel="nofollow">inciples to help us organize the world. Face Perception Depends on neurons in" rel="nofollow">in the lower part of the temporal lobe and in" rel="nofollow">in the hippocampus. Though some neurons respond selectively to specific faces, face perception depends on broad neural networks. Motion Perception To determin" rel="nofollow">ine motion, the brain" rel="nofollow">in compares visual frames of what is to what was. Phi phenomenon Motion blin" rel="nofollow">indness—in" rel="nofollow">inability to perceive seamless motion Localizin" rel="nofollow">ing Sound We rely on bin" rel="nofollow">inaural cues to tell us where sounds are comin" rel="nofollow">ing from. These cues in" rel="nofollow">include differences between the two ears in" rel="nofollow">in the timin" rel="nofollow">ing and in" rel="nofollow">intensity of sound waves. Depth Perception Monocular depth cues rely on one eye: Relative size, texture gradient, in" rel="nofollow">interposition, lin" rel="nofollow">inear perspective, height in" rel="nofollow">in plane, light and shadow Bin" rel="nofollow">inocular depth cues require both eyes. Bin" rel="nofollow">inocular disparity and bin" rel="nofollow">inocular convergence When Perception Deceives Us We often misperceive in" rel="nofollow">information around us and understandin" rel="nofollow">ing why provides in" rel="nofollow">insight in" rel="nofollow">into how we make sense of our surroundin" rel="nofollow">ings. Examples of such misperception in" rel="nofollow">include the moon illusion; the Ames room; and the Muller-Lyer, Ponzo, vertical-horizontal, and Ebbin" rel="nofollow">inghaus illusions. Sublimin" rel="nofollow">inal Perception We process many sensory in" rel="nofollow">inputs unconsciously and many of our actions occur with little to no forethought or deliberation. If we can detect stimuli without knowin" rel="nofollow">ing it, does that change our behavior? The processin" rel="nofollow">ing of sensory in" rel="nofollow">information that occurs below the level of conscious awareness Can have a brief, short-term impact on behaviors and attitudes Effect disappears when subjects are aware of or suspect sublimin" rel="nofollow">inal in" rel="nofollow">influences Sublimin" rel="nofollow">inal Persuasion Fairly unlikely to produce large-scale or endurin" rel="nofollow">ing changes in" rel="nofollow">in attitudes or decisions Sublimin" rel="nofollow">inal self-help tapes have been shown to be in" rel="nofollow">ineffective. Reversed sublimin" rel="nofollow">inal messages are also in" rel="nofollow">ineffective. Extrasensory Perception The perception of events outside the known channels of sensation Accordin" rel="nofollow">ing to parapsychologists, there are three major types: Precognition Telepathy Clairvoyance Evidence for ESP Early studies by Rhin" rel="nofollow">ine (1934) usin" rel="nofollow">ing Zener cards reported positive results. But, methodological problems plagued the study and no one could replicate his results. Ganzfield technique studies, fMRI studies, and others all fail to fin" rel="nofollow">ind positive effects for ESP. ESP proponents explain" rel="nofollow">in away negative fin" rel="nofollow">indin" rel="nofollow">ings, citin" rel="nofollow">ing such factors as experimenter effects. These are ad-hoc explanations, though Why People Believe Over 40% of American adults believe in" rel="nofollow">in ESP. Why? Illusory correlations Not understandin" rel="nofollow">ing chance events Underestimatin" rel="nofollow">ing the likelihood of coin" rel="nofollow">incidences The "Birthday Paradox." As we reach a group size of 23 people, the probability that at least two people share the same birthday exceeds 0.5, or 50 percent. Research demonstrates that most people markedly underestimate the likelihood of this and other coin" rel="nofollow">incidences, sometimes leadin" rel="nofollow">ing them to attribute these coin" rel="nofollow">incidences to paranormal events. Failed Psychic Predictions Specific predictions ("Nazi flag found on moon!") do not come true. So "psychics" use other methods to make it seem as if they are accurate. Multiple end poin" rel="nofollow">ints Cold readin" rel="nofollow">ing techniques