Sensing and Perceiving Sensing and Perceiving • • • • • We Experience Our World Through Sensation Seeing Hearing Tasting, Smelling, and Touching Accuracy and Inaccuracy in Perception Sensing and Perceiving Sensation • stimulation of sense organs Transduction • conversion of stimuli detected by receptor cells to electrical impulses transported to the brain Perception • organization and interpretation of sensations We Experience Our World Through Sensation We Experience Our World Through Sensation • Learning Objectives 1. Review and summarize the capacities and limitations of human sensation. 2. Explain the difference between sensation and perception and describe how psychologists measure sensory and difference thresholds. Measuring Sensation • Psychophysics – branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states – founded by the German psychologist Gustav Fechner in the 19th century Measuring Sensation • Absolute Threshold – the intensity of a stimulus that allows an organism to just barely detect it Measuring Sensation • Signal Detection Analysis – technique used to determine the perceiver’s ability to separate true signals from background noise – yields two measures: • sensitivity – the true ability to detect the presence of absence of signals • response bias – behavioral tendency to respond ‘yes’ Measuring Sensation • Possible trial outcomes in a signal detection experiment. Correct rejections and hits are accurate responses; misses and false alarms are errors. Measuring Sensation • • Difference Threshold – the change in a stimulus that can just barely be detected by the organism – also called the just noticeable difference, or jnd Weber’s Law – the just noticeable difference is a constant proportion of the original intensity of the stimulus Influence Without Awareness subliminal stimuli blindsight perception without awareness? Subliminal Stimuli • • Stimuli below the absolute threshold may have some effect on behavior. The influence of subliminal advertising is weak, though. Blindsight • Visual cortex damage may render people unable to consciously report on visual stimuli, even though they can answer questions about what they are seeing. We Experience Our World Through Sensation • Key Takeaways – Sensation is the process of receiving information from the environment through our sensory organs. Perception is the process of interpreting and organizing the incoming information in order that we can understand it and react accordingly. – Transduction is the conversion of stimuli detected by receptor cells to electrical impulses that are transported to the brain. – Although our experiences of the world are rich and complex, humans – like all species – have their own adapted sensory strengths and sensory limitations. – Sensation and perception work together in a fluid, continuous process. We Experience Our World Through Sensation • Key Takeaways, continued – Our judgments in detection tasks are influenced by both the absolute threshold of the signal as well as our current motivations and experiences. Signal detection analysis is used to differentiate sensitivity from response biases. – The difference threshold or just noticeable difference is the ability to detect the smallest change in a stimulus about 50 percent of the time. According to Weber’s law, the just noticeable difference increases in proportion to the total intensity of the stimulus. – Research has found that stimuli can influence behavior even when they are presented below the absolute threshold (that is, subliminally). The effectiveness of subliminal advertising, however, has not been shown to be of large magnitude. Seeing Seeing Learning Objectives: 1. Identify the key structures of the eye and the role they play in vision. 2. Summarize how the eye and the visual cortex work together to sense and perceived the visual stimuli in our environment, including processing colors, shape, depth, and motion. • Vision detects electromag-netic radiation. • Only a small portion of the electromagnetic spectrum is seen as visible light. Seeing: Perceiving Depth • Depth Cues: messages from our bodies and the environment that tell us about space and distance; may be monocular (requiring one eye) or binocular (requiring two eyes) binocular depth cues retinal disparity convergence accommodation the two eyes receive different images inward turning of the eyes to focus on objects changes in curvature of the lens Seeing: Perceiving Depth Seeing: Perceiving Depth • Figure-Ground: Some fence posts seem more distant because they are higher up in the picture. • Relative Size: The smaller –looking cars appear more distant than do the largerlooking ones. Seeing: Perceiving Depth • • Linear Perspective: We know that the tracks are parallel. As they appear to converge, we determine that they are farther away. Light and Shadow: We see the images as extending and indented according to their shadowing. If we invert the picture, the images will reverse. Seeing: Perceiving Depth • Interposition: Because the blue star covers the pink bar it is seen as closer than the yellow moon which does not. • Aerial Perspective: The clouds appear hazy and thus seem distant. Seeing: Perceiving Motion Beta Effect • • Perception of motion that occurs when different images are presented in succession Used in movies to create the impression of motion Phi Phenomenon • • We perceive motion based on the appearance and disappearance of adjacent objects. Identified by the Gestalt psychologists Seeing • Key Takeaways – Vision is the process of detecting the electromagnetic energy that surrounds us. Only a small fraction of the electromagnetic spectrum is visible to humans. – The visual receptor cells on the retina detect shape, color, motion and depth. – Light enters the eye through the transparent cornea, and passes through the pupil at the center of the iris. The lens adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina are excited or inhibited by the light and send information to the visual cortex through the optic nerve. – The retina has two types of photoreceptor cells; rods, which detect brightness and respond to black and white, and cones that respond to red, green and blue colors. Color blindness occurs when people lack function in the red or green-sensitive cones. Seeing • Key Takeaways, continued – Feature detector neurons in the visual cortex help us recognize objects, and some neurons respond selectively to faces and other body parts. – The Young-Helmholtz Tri-Chromatic Color Theory proposes that color perception is the result of the signals sent by the three types of cones, whereas the Opponent Process Color Theory proposes that we perceived color as three sets of opponent colors; red-green, yellow-blue, and white-black. – The ability to perceive depth occurs through the result of binocular and monocular depth cues. – Motion is perceived as a function of the size and brightness of objects. The beta effect and the phi phenomenon are examples of perceived motion. Hearing Hearing • Learning Objectives: 1. Draw a picture of and label the key structures and functions of the ear and the role they play in hearing. 2. Describe the process of transduction in hearing. The Ear frequency wavelength of the sound wave humans can detect wavelengths from 20 Hz -20,000 Hz pitch perceived frequency of a sound higher frequency = higher pitch The Ear amplitude height of the sound wave humans can detect wavelengths from 20 Hz 20,000 Hz loudness degree of sound volume larger waves= louder • Sounds in Everyday Life • The human ear can comfortably hear sounds up to 80 dB. • Prolonged exposure to sounds above 80dB can cause hearing loss. • The Ear • Sound waves enter the outer ear and are transmitted through the auditory canal to the eardrum. The resulting vibrations are moved by the ossicles into the cochlea, where they are detected by hair cells and sent to the auditory nerve. • The Ear 1. pinna draws in sound waves 2. sound waves strike tympanic membrane 3. vibrations relayed through ossicles 6. hair cells bend 5. fluid in cochlea moves 4. oval window vibrates The Ear Frequency Theory of Hearing • As the pitch of a sound wave increases, nerve impulses of a corresponding frequency are sent to the auditory nerve. – Neurons cannot fire fast enough to code pitches as high as we can hear. Place Theory of Hearing • Different areas of the cochlea respond to different frequencies. – Higher tones excite areas at the opening of the cochlea near the oval window. – Lower tones excite areas near the narrow tip of the cochlea. Hearing Loss Conductive Hearing Loss • • Caused by physical damage to the ear, reducing the ability of the ear to transfer vibrations from the outer to the inner ear May be lessened by hearing aids that amplify the sound Sensorineural Hearing Loss • • • • Caused by damage to the cilia or the auditory nerve Increases with age May be created by prolonged exposure to loud noise May be remediated by cochlea implants if the auditory nerve is intact Hearing • Key Takeaways – Sound waves, vibrating through media such as air, water, or metal, are the stimulus energy that is sensed by the ear. – The hearing system is designed to assess frequency (pitch), and amplitude (loudness). – Sound waves enter the outer ear (the pinna) and are sent to the eardrum via the auditory canal. The resulting vibrations are relayed by the three ossicles, causing the oval window covering the cochlea to vibrate. The vibrations are detected by the cilia (hair cells) and sent via the auditory nerve to the auditory cortex. Hearing • Key Takeaways, continued – There are two theories as to how we perceive pitch: Frequency theory suggests that as a sound wave’s pitch increases, nerve impulses of a corresponding frequency enter the auditory nerve. Place theory suggests that we hear different pitches because different areas of the cochlea respond to higher and lower pitches. – Conductive hearing loss is caused by physical damage to the ear or eardrum may be improved by hearing aids or cochlear implants. Sensorineural hearing loss, caused by damage to the hair cells or auditory nerves in the inner ear, may be produced by prolonged exposure to sounds over 85db. Tasting, Smelling, and Touching Tasting, Smelling, and Touching • Learning Objectives: 1. Summarize how the senses of taste and olfaction transduce stimuli into perceptions. 2. Describe the process of transduction in the senses of touch and proprioception. 3. Outline the gate control theory of pain. Explain why pain matters and how it may be controlled. Tasting sweet bitter sour Basic Tastes piquancy salty spicy unami savory Tasting • • • • 2,000 to 10,000 taste buds – Each bud contains 50-100 receptor cells. – Some are found on the walls of the mouth and the back of the throat. Taste buds are activated quickly. – A sweet or salty taste will trigger a neural impulse within 1/100 second. Taste buds live for about 5 days. The rate of taste bud creation slows down as we age. Smelling • • • 10 million to 20 million olfactory receptor cells embedded in the olfactory membrane of the upper nasal passage – 1,000 types of receptor cells detect 10,000 different odors Women have a more sensitive sense of smell than do men. Our sense of smell peaks in early adulthood then declines. Touching • pressure warmth Basic Touch Sensations cold pain • Thousands of nerve endings in the skin respond to four basic sensations. Other sensations reflect combinations of these four. Touching cold pressure wetness Touching • Proprioception – the ability to sense the position and movement of our body parts – accomplished by specialized neurons in the skin, joints, bones, ears, and tendons Touching • Vestibular System – set of liquid-filled areas in the inner ear that monitors our head’s position and movement – allows us to maintain balance • semicircular canals – sense rotational movements • vestibular sacs – sense linear accelerations Experiencing Pain • Gate Control Theory of Pain – Pain is determined by two types of nerve fibers in the spinal cord. • Small fibers carry pain from the body to the brain. • Larger fibers can open or shut the flow of pain to the brain. – By massaging a painful area, we activate the larger fibers, shutting off the flow of pain from the small fibers. Experiencing Pain • Both neurochemical and cognitive factors influence the experience of pain. – endorphins – neurotransmitters that act as the brain’s natural painkillers – Challenging activities or humor can distract attention from pain. Tasting, Smelling, and Touching • Key Takeaways – The ability to taste, smell, and touch are important because they help us avoid harm from environmental toxins. – The many taste buds in our tongue and mouth allow detect six basic taste sensations: sweet, salty, sour, bitter, piquancy, and umami. – In olfaction, transduction occurs as airborne chemicals that are inhaled through the nostrils are detected by receptors in the olfactory membrane. Different chemical molecules fit into different receptor cells creating different smells. – On average, women have a better sense of smell than men, and the ability to smell diminishes with age. Tasting, Smelling, and Touching • Key Takeaways, continued – We have a range of different nerve endings embedded in the skin, combinations of which respond to four basic sensations of pressure, warmth, cold, and pain. But only the sensation of pressure has its own specialized receptors. – Proprioception is our ability to sense the positions and movements of our body parts. Postural and movement information is detected by special neurons in the skin, joints, bones, ears and tendons, which pick up messages from the compression and the contraction of muscles throughout the body. – The vestibular system in the inner ear, monitors our head’s position and movement and allows us to maintain balance. – Gate control theory explains how large and small neurons work together to transmit and regulate the flow of pain to the brain. Accuracy and Inaccuracy in Perception Accuracy and Inaccuracy in Perception • Learning Objectives: 1. Describe how sensation and perception work together through sensory interaction, selective attention, sensory adaptation and perceptual constancy. 2. Give examples of how our expectations may influence our perception, resulting in illusions and potentially inaccurate judgments. How the Perceptual System Interprets the Environment • Sensory Interaction – Different senses work together to create experience. • the McGurk effect -- sounds are misperceived when the auditory and visual parts of the speech are mismatched • Selective Attention – The ability to focus on some sensory inputs while tuning out others • the cocktail party effect – important stimuli may be processed even when they are not the focus of selective attention How the Perceptual System Interprets the Environment • Sensory Adaptation – decreased sensitivity to stimuli after constant and prolonged exposure – enhances our ability to perceive important changes in the environment • Perceptual Constancy – the ability to perceive stimuli as unchanging despite changes in sensation Illusions • • • Illusions occur when the processes that normally help us perceive the world correctly are fooled by a particular situation so that we see something that is incorrect or nonexistent. Illusions demonstrate that our perception of the world may be influence by our prior knowledge. Illusions do not suggest that perception is generally inaccurate. Illusions • The Mueller-Lyer illusion makes the line segment at the top appear shorter than the one on the bottom. • The illusion reflects monocular depth cues– the bottom line looks like an edge that is normally farther away from us, while the top one looks like an edge that is normally closer. Illusions • The Moon Illusion – The moon always looks larger on the horizon than when it is high above. – When you take away the surrounding distance cues of the horizon, the illusion disappears. Illusions • The Ponzo Illusion – caused by a failure of the monocular depth cue of linear perspective – Both bars are the same size even though the top one looks larger. The Important Role of Expectations in Perception contexts emotions expectations culture motivations perception desires Accuracy and Inaccuracy in Perception • Key Takeaways – Sensory interaction occurs when different senses work together, for instance when taste, smell and touch together produce the flavor of food. – Selective attention allows us to focus on some sensory experiences while tuning out others. – Sensory adaptation occurs when we become less sensitive to some aspects of our environment, freeing us to focus on more important changes. Accuracy and Inaccuracy in Perception • Key Takeaways, continued – Perceptual constancy allows us to perceive an object as the same, despite changes in sensation. – Cognitive illusions are examples of how our expectations can influence our perceptions. – Our emotions, motivations, desires, and even our culture can influence our perceptions.