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Sensation and Perception Unit 3 Sensation and Perception Basic concepts of Sensation I. Sensation 1. 2. The detection of physical energy from the environment, it is then encoded into neural signals Occurs when energy in the external environment or the body stimulates receptors in the sense organs Sensory receptors- specialized cells that detect sensory stimuli (light, sound, odors) & convert them into neural impulses Found throughout body in eyes, ears, nose, mouth & joints & muscles Basic concepts of Sensation II. Thresholds 1. Absolute threshold- the smallest amount of a stimulus that a person can sensed Vision The flame from a single candle flickering about 30 miles away on a dark, clear night Hearing The ticking of a watch placed about twenty ft. away from a listener in a quiet room taste About one teaspoon of sugar dissolved in 2 gallons of water smell About one drop of perfume dispersed in a small house touch The wing of a bee falling on the cheek from about one centimeter away Basic concepts of Sensation 2. Difference threshold (just-noticeable difference)- minimal difference in the magnitude of energy needed for people to detect a difference between stimuli (comparing) Weber’s Constant Weber’s law- Sensation Principle: difference thresholds grow with Saltiness of food the magnitude of the Pressure on skin stimulus Loudness of sounds (approximate) 1/5 (20%) 1/7 1/10 (10%) odor 1/20 Heaviness of weights 1/50 (2%) Brightness of lights 1/60 Pitch of sounds 1/333 Absolute & Difference Threshold Select a sense Design an experiment to find an absolute threshold test the just noticeable difference for an increase or decrease in the intensity of the stimulus. Create a hypothesis about the intended results Basic Concepts of Sensation III. IV. V. VI. Signal-detection theory- detection of a stimulus depends on factors such as the intensity of the stimulus, the level of background stimulation, and the biological and physical characteristics , and expectations of the perceiver. Sensory Adaptation-process by which sensory receptors adapt to constant stimuli by becoming less sensitive to them. Sensory Deprivation-absence of normal levels of sensory stimulation Sensory overload- too much stimuli ASD Conservative or liberal Vision I. 1. Process by which light energy is converted into neural impulses that the brain interprets to produce the experience of sight Light- physical energy in the form of electromagnetic radiation Colors are caused by different wavelengths within the visible spectrum red = longest Violet = shortest Roy G. Biv Vision II. 1. The Eye Cornea- transparent covering on the eye’s surface through which light enters Iris- regulates the size of the pupil to adjust to changes in the level of illumination 2. 3. Pupil- allows light to enter the eye 4. Lens- focuses light rays on the retina 5. Accommodation-process by which the lens changes its shape (thickness) to focus images more clearly on the retina Fovea- center of focus for clearer vision Structure of the Eye Vision 6. Retina-Neural tissue lining the back of the eyeball’s interior containing the receptors for vision; retina contains: Photoreceptors- light-sensitive cells in the eye that register light a) Rods- Visual receptors that are sensitive to intensity of light (dim) b) Cones- Visual receptors involved in color vision & fine details; humans have 3 types: blue, green, red 7. Optic nerve- carries neural impulses generated by light stimulation from the eye to the brain 6. Blind spot- contains no photoreceptor cells; Place where the optic nerve leaves the eye Structures of the Retina Vision III. Color vision 2 major theories~ Trichromatic theory- the ability to see different colors depends on the relative activity of three types of color receptors in the eye (red, green, and blue-violet) all other colors derived by a combination Opponent-process theory-assumes that the visual system treats pairs of colors as opposing or antagonistic. Opponent-process cells are inhibited by a color, and have a burst of activity when it is removed. 1. 2. a) Color vision: Afterimage- image remains after stimulus is removed; cones become tired o Trichromats-people with normal color vision o Monochromats- no color vision o Dichromats- some color vision Hearing I. Audition (sense of hearing): 1) Travels in waves; exists only in mediums such as air, liquids, gases & solids 2) Vibration Amplitude, Pitch 3) Auditory Localization Sounds from different directions are not identical as they arrive at left and right ears. The brain calculates a sound’s location by using these differences. Loudness (Intensity, amplitude {height of wave}, measured in decibels) Pitch(frequency{number of cycles per second}, hertz) Hearing II. The Ear: structured to capture sound waves 1. Eardrum- vibrates in response to external stimuli & transmits waves to middle ear 2. Ossicles- tiny bones (hammer, anvil, & stirrup) in the middle ear that vibrate in response to eardrum 3. Cochlea- contains sensory receptors for hearing Nerve (hair) cells- receptors that transform vibrations into neural impulses that are transmitted to the brain via the… 4. Auditory nerve- carries neural impulses from ear to brain Hearing Hearing How You Hear When an object makes a noise, it sends vibrations (better known as sound waves) speeding through the air. These vibrations are then funneled into your ear canal by your outer ear. As the vibrations move into your middle ear, they hit your eardrum and cause it to vibrate as well. This sets off a chain reaction of vibrations. Your eardrum, which is smaller and thinner than the nail on your pinky finger, vibrates the three smallest bones in your body: first, the hammer, then the anvil, and finally, the stirrup. The stirrup passes the vibrations into a coiled tube in the inner ear called the cochlea. The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into messages that are sent to the brain via the auditory nerve. The auditory nerve carries messages from 25,000 receptors in your ear to your brain. Your brain then makes sense of the messages and tells you what sounds you are hearing. 2 types of deafness: 1. Conductive Deafness: • Caused by damage to middle ear; prevent people from hearing sounds that aren’t loud enough • Hearing aids provide amplification 2. Sensorineural (nerve) deafness: • Can be mild, moderate or severe • Damage to cells or auditory nerve in inner ear • Cochlear implants will help “Ringing sensation” is nerve damage Deafness Conductive Deafness • Conductive deafness occurs because of damage to the middle ear, which is the part that amplifies sound. • Hearing aids can provide for the function of the middle ear by amplifying sound. Sensorineural Deafness • Sensorineural deafness occurs when sounds of certain frequencies are not heard. • It is usually caused by damage to the inner ear. • Loud sounds can destroy neurons in the ear. • Cochlear implants can help people with sensorineural deafness. Chemical Senses I. Olfaction (sense of smell) Airborne chemical molecules enter the nose and circulate through the nasal cavity. Vapors can also enter through the mouth and pass into nasal cavity. Receptors (olfactory hairs) on the roof of the nasal cavity detect these molecules. Intensity depends on # of receptors firing. Passes through the olfactory nerve, olfactory bulb, to the olfactory cortex and also structures in the Limbic System (memory and emotion) Chemical Senses II. Taste 1. Depends on odor, texture, & temperature; role in adaptation & survival 2. Papillae (taste receptors) 1. taste buds- pores or openings on the tongue containing taste cells (receptors) inside the bud; 50 to 100 receptors/bud Regenerate in 5-10 days 2. Genetic factors, expectations, and context play a significant role in taste sensitivities and preferences 3. Five basic tastes: Sweet Salty Sour Bitter Umami Taste 1. Decrease with age 2. Supertasters- 2 or more times the taste buds, Hypersensitive, 1 in four people 3. Medium tasters 4. Non-tasters ALERT: receptors are actually mixed and located throughout the mouth…back of throat, roof, cheeks and tongue Skin Senses III. Skin Senses (largest sensory organ) 1. The senses of pressure, temperature, and pain that involve stimulation of sensory receptors in the skin 2. Pressure a) Sensory receptors at the root of body hair b) Pressure sensitivity varies throughout the body Fingertips, lips, nose, & cheeks 3. Temperature a) Receptors are just beneath the skin (warm & cold) 4. Pain a) Pain sensitivity varies b) Prostaglandins: chemical that carries pain messages; Aspirin production c) Pain message sent from spinal cord to thalamus to cerebral cortex (somatosensory cortex) Skin Senses Brain generates pain 1. a. b. c. Phantom Pain Injured athlete doesn’t feel pain No Pain??? Gate Theory 2. a. Only a certain amount of information can be processed by the brain at one time Pain Disorders Hereditary Sensory Autonomic Neuropathy Pain and temp nerve fibers (receptors) never developed Insensitivity to pain means that the painful stimulus is not even perceived: a patient cannot describe the intensity or type of pain. Indifference to pain means that the patient can perceive the stimulus, but lacks an appropriate response: they will not flinch or withdraw when exposed to pain Body Senses (Balance) 1. 2. Kinesthesis (Greek: to move & perception)- sense that informs people about the position of their bodies a) Sensory info is fed from receptor cells in joints, tendons and muscles to the brain Allows for navigation, movement coordination, & feel muscle contraction; interacts with vision Vestibular sense- movement, the sense that keeps us informed about balance and the position of our body in space, equilibrium, enables you to keep your balance; cerebellum, head position a) Semicircular canals- in the inner ear; crystals; sense changes in the direction & movement of the head Senses speed, motion and balance Dizzy b) Vestibular sacs- fluid filled, send messages to the cerebellum Controversies in Perception I. Subliminal perception: perception of stimuli that are presented below the threshold of conscious awareness Controversies in Perception II. A. Parapsychology- seeks to investigate the existence and the causes of psychic abilities Extrasensory perception (ESP):perception that occurs without benefit of the known senses 1. 2. 3. 4. Telepathy- communication of thoughts from one mind to another that occurs without using the known senses Clairvoyance- ability to perceive objects and events without using the known senses Precognition- ability to foretell the future Psychokinesis (telekinesis)-ability to move objects by mental effort only Psychic test #1 Psychic test #2 Ganzfeld experiment Perception Perception- process by which the brain integrates, organizes, & interprets sensory impressions to create representations of the world Perceptual set- tendency for perception to be influenced by one’s expectations or preconceptions • context effects l3 Mary had a a little lamb Perception Perception Principles I. Gestalt (whole) principles: the brain organizes sensory information into meaningful units and patterns 1. Visual field is organized into figure (shapes) and ground (no shape) stand out from surroundings Principles of grouping/organization: 2. Proximity-things near are grouped 3. Closure- brain fills in gaps 4. Continuity- lines & patterns continue into space Perception Depth Perception- see objects in 3D (visual cliff) Cues for depth: perspective, clearness, overlap, shadow, texture 1. Binocular cues: visual cues that require the use of both eyes a) Convergence -Turning inward of the eyes, which occurs when they focus on a nearby object b) Retinal disparity - The slight difference in lateral separation between two objects as seen by the right and left eyes; 2 ½ in. apart 2. Monocular cues (depth): visual cues that can be used by one eye a) Relative height, motion, size; interposition, linear perspective, light & shadow Perception 1. Perceptual Constancy- The accurate perception of objects as stable or unchanged; context Shape, size, color shape constancy color constancy size constancy Monocular cues Perception Visual Illusions • The cats in (a) are the same size. • The diagonal lines in (b) are parallel. • You can create a “floating fingertip frankfurter” by holding hands as shown, 5–10 inches in front of face. Perception Visual Illusions: I. I. The Müller-Lyer illusion