Sensation Chapter 5

Sensation Sensing the World: Some Basic Principles Vision Threshold Sensory Adaptation Vision The Stimulus Input: Light Energy The Eye

Sensation Vision Hearing Visual Information Processing Color Vision The Stimulus Input: Sound Waves The Ear Hearing Loss and Deaf Culture

Sensation Other Important Senses Touch Taste Smell Body Position and Movement

Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organize, and interpret our sensations, the process is called perception. OBJECTIVE 1| Contrast sensation and perception, and explain the difference between bottom-up and top-down processing.

Sensation Stimulation of the senses is mechanical; results from sources of energy like light and sound are from presence of chemicals, as in smell and taste

Perception Not mechanical but interpreted Def: the process by which sensations are organized into an inner representation of the world

Perception It reflects learning and expectations and the ways in which we organize incoming information about the world.

Top-Down Processing The use of contextual information or knowledge of a pattern in order to organize parts of the pattern Ex:puzzles Box picture=“top” Finding pieces=“top down process”

THE CHT Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT

Bottom-up Processing The organization of the parts of a pattern to recognize, or form an image of, the pattern they compose Start with bits and pieces of info and become aware of the pattern formed by the assembled pieces only after you have labored a while Ex: puzzles without the box picture

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

Senses are nature’s gift that suit an organism’s needs. Sensing the World Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

Exploring the Senses What stimuli cross our threshold for conscious awareness? Could we be influenced by stimuli too weak (subliminal) to be perceived? Why are we unaware of unchanging stimuli, like a band-aid on our skin?

Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them. Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet

Detection Absolute Threshold Intensity No No No Yes Yes Detected Observer’s Response Detected Tell when you (the observer) detect the light.

Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) OBJECTIVE 2| Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute thresholds and be influenced by them.

Absolute Threshold The weakest amount of a stimulus that can be told apart from no stimulus at all Ex: Taste About 1 teaspoon of sugar dissolved in 2 gallons of water

Absolute Threshold There are individual differences in absolute thresholds Ex: Pitch -the highness or lowness of a sound, as determined by the frequency of the sound waves

Subliminal Threshold Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock

Difference Threshold Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). Difference Threshold No No Yes Observer’s Response Tell when you (observer) detect a difference in the light.

Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I. Stimulus Constant (k) Light 8% Weight 2% Tone 3%

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a faint stimulus (signal) amid background noise (other stimulation). SDT assumes that there is no single absolute threshold and detection depends on: Person’s experience Expectations Motivation Level of fatigue Carol Lee/ Tony Stone Images

Signal-Detection Theory The degree to which the signal can be distinguished from background noise Ex: easier to hear a friend’s voice in a quiet room rather than a room filled with people clinking silverware and chatting “Cocktail Party Effect”

SDT Matrix The observer decides whether she hears the tone or not, based on the signal being present or not. This translates into four outcomes. Decision Yes No Signal Present Hit Miss Absent False Alarm Correct Rejection

Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. OBJECTIVE 3| Describe sensory adaptation, and explain how we benefit from being unaware of changing stimuli. Put a band aid on your arm and after awhile you don’t sense it.

Desensitization Becoming less sensitive to ongoing stimulation constant light appears to grow dimmer Live in city, become desensitized to traffic sounds

Now you see, now you don’t

Vision

Transduction In sensation, the transformation of stimulus energy into neural impulses. Phototransduction: Conversion of light energy into neural impulses that the brain can understand. OBJECTIVE 4| Define transduction, and specify the form of energy our visual system converts into neural messages our brain can interpret.

The Stimulus Input: Light Energy Visible Spectrum Both Photos: Thomas Eisner

Light Characteristics Wavelength(hue/color) Intensity (brightness) Saturation (purity)

Wavelength (Hue) Hue (color) is the dimension of color determined by the wavelength of the light. Wavelength is the distance from the peak of one wave to the peak of the next.

Different wavelengths of light result Wavelength (Hue) Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Short wavelengths Long wavelengths Different wavelengths of light result in different colors.

Intensity (Brightness) Intensity Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”

Purity (Saturation) Monochromatic light added to green and red Saturated Saturated Monochromatic light added to green and red makes them less saturated.

Represents all three characteristics of light stimulus on this model. Color Solid Represents all three characteristics of light stimulus on this model. http://www.visionconnection.org

The Eye OBJECTIVE 5| Describe the major structure of the eye, and explain how they guide the incoming ray of light toward the eye’s receptor cells.

Parts of the eye Cornea: Transparent tissue where light enters the eye. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. Lens: Focuses and adjusts the light rays on the retina. Retina: Contains sensory receptors (rods and cones) that process visual information and sends it to the brain.

The Lens Lens: Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

The Lens Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects. Farsightedness: A condition in which faraway objects are seen more clearly than near objects.

Retina Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information. OBJECTIVE 6| Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light.

Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster. http://www.bergen.org

Test your Blind Spot Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

Rods Rod-shaped photoreceptors that are sensitive only to the intensity of light They allow us to see in black and white

Cones Cone-shaped photoreceptors that transmit sensations of color Provide color vision

Light Adaptation Dark adaptation: adjusting to lower lighting Movie theater: -Cones: permit perception of color, reach maximum adaptation to darkness in 10 minutes -Rods: allow perception of light and dark only, are more sensitive and continue to adapt to darkness for up to about 45 minutes

Light Adaptation cont… Adaptation to brighter lighting conditions takes place more rapidly Emerging from dark theater: at first you’ll be surprised by featureless blaze around you. Within a minute or so, the brightness will have dimmed and objects will have regained their edges

Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which are for the optic nerve.

Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex. OBJECTIVE 7| Discuss the different levels of processing that occur as information travels from the retina to the brain’s cortex.

Vision Pathway 1. Cornea 2. Iris 3. Pupil 4. Lens 5. Retina/Fovea 6. Bipolar Cells 7. Ganglion Cells 8. Optic Nerve 9. Thalamus 10. Visual Cortex (Occipital Lobe)

Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. Ishai, Ungerleider, Martin and Haxby/ NIMH

Perception in Brain Our perceptions are a combination of sensory (bottom-up) and cognitive (top-down) processes.

Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc. OBJECTIVE 8| Discuss parallel processing and discuss its role in visual processing.

From Sensation to Recognition Tim Bieber/ The Image Bank

Theories of Color Vision Trichromatic theory: Based on behavioral experiments, Helmholtz suggested that the retina should contain three receptors that are sensitive to red, blue and green colors. Standard stimulus OBJECTIVE 9| Explain how the Young-Helmholtz and opponent-process theories help us understand color vision. Comparison stimulus Max Medium Low Blue Green Red

Subtraction of Colors If three primary colors (pigments) are mixed, subtraction of all wavelengths occurs and the color black is the result.

Addition of Colors If three primary colors (lights) are mixed, the wavelengths are added and the color white is the result. Fritz Goro, LIFE magazine, © 1971 Time Warner, Inc.

Photoreceptors Blue Cones Green Cones Red Cones MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans. Short wave Medium wave Long wave

Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test

Opponent Colors Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

Opponent Process Theory Hering proposed that we process four primary colors combined in pairs of red-green, blue-yellow, and black-white. Cones Retinal Ganglion Cells

Color Constancy Color of an object remains the same under different illuminations. However, when context changes the color of an object may look different. OBJECTIVE 10| Explain the importance of color constancy. R. Beau Lotto at University College, London

Feature Detection Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. Ross Kinnaird/ Allsport/ Getty Images

Audition

The Stimulus Input: Sound Waves Sound waves are composed of compressed air molecules. OBJECTIVE 11| Describe the pressure waves we experience as sound. Acoustical transduction: Conversion of sound waves into neural impulses in the hair cells of the inner ear.

Sound Characteristics Frequency (pitch) Intensity (loudness) Quality (timbre)

Frequency (Pitch) Frequency (pitch): The dimension of frequency determined by the wavelength of sound. Wavelength: The distance from the peak of one wave to the peak of the next.

Intensity (Loudness) Intensity (Loudness): Amount of energy in a wave, determined by the amplitude, relates to the perceived loudness.

Loudness of Sound Richard Kaylin/ Stone/ Getty Images 120dB 70dB

Pitch and Loudness The pitch of a sound is determined by its frequency, or the number of cycles per second as expressed in the unit Hertz (Hz). Hz=one cycle per second The greater the number of cycles per second (Hz), the higher the pitch of the sound (women vs. men)

Loudness Amplitude:loudness of a sound that is determined by its height of sound waves Decibel (dB): a unit expressing the loudness of a sound (Sound waves of various frequencies and amplitudes)

Loudness Tones (musical sounds) Consonant:when a combination of tones are pleasant; in harmony Dissonant:incompatible; not harmonious, discordant

White Noise Discordant sounds of many frequencies, often producing a lulling effect

Overtones: Makes the distinction among musical instruments possible.

The Ear Dr. Fred Hossler/ Visuals Unlimited OBJECTIVE 12| Describe the three regions of the ear, and outline the series of events that triggers the electrical impulses sent to the brain.

The Ear Outer Ear: Collects sounds. Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window. (HAS) Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

Cochlea Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

Theories of Audition Place Theory suggests that sound frequencies stimulate the basilar membrane at specific places resulting in perceived pitch. OBJECTIVE 13| Contrast place and frequency theories, and explain how they help us to understand pitch perception. http://www.pc.rhul.ac.uk

Theories of Audition Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. Auditory Nerve Action Potentials Sound Frequency 200 Hz 100 Hz

Other Important Senses The sense of touch is a mix of four distinct skin senses: Touch Pressure Warmth Cool Pain OBJECTIVE 17| Describe the sense of touch. “Touch is both the alpha and omega of affection” (James, 1890). Bruce Ayers/ Stone/ Getty Images

Skin Senses Only pressure has identifiable receptors. All other skin sensations are variations of pressure, warmth, cold and pain. Pressure Vibration Vibration Burning hot Cold, warmth and pain

Touch and Pressure Sensory receptors at the roots of hair cells appear to fire in response to touching the surface of the skin “get the feel of”-touching fabric by running our hands over it. Sensation fade quickly if held still

Touch and Pressure Two-point threshold:the least distance by which two rods touching the skin must be separated before the person will report that there are two rods, not one, on 50% of occasions. Assess our sensitivity to pressure (fingertips, lips, noses, and cheeks are much more sensitive than our shoulders, thighs, and calves)

Touch and Pressure Differential sensitivity occurs for 2 reasons: Nerve endings are more densely packed in the fingertips and face than in other locations A greater amount of sensory cortex is devoted to the perception of sensations in the fingertips and face -sense of pressure, like the sense of touch, undergoes rather rapid adaptation

Ashley Blocker (right) feels neither pain Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain. OBJECTIVE 18| State the purpose of pain, and describe the biopsychosocial perspective on pain. AP Photo/ Stephen Morton Ashley Blocker (right) feels neither pain nor extreme hot or cold.

Biopsychosocial Influences

Gate-Control Theory Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed. One way to treat chronic pain is to stimulate it through massage by electrical stimulation or acupuncture. Rubbing causes competitive stimulation to pain thus reduces its effect. Gary Comer/ PhototakeUSA.com

Pain Control Pain can be controlled by a number of therapies including, drugs, surgery, acupuncture, exercise, hypnosis, and even thought distraction. Burn victims can be distracted by allowing them to engage in illusory virtual reality. Their brain scans show differences in pain perceptions. Todd Richards and Aric Vills, U.W. ©Hunter Hoffman, www.vrpain.com

Phantom Limb Pain The pain occurs in the absence of (present) tissue damage, but the pain itself is real enough (war veterans) Sometimes involves activation of nerves in the stump of missing limb Pain reflect activation of the neural circuits that store memories connected with the missing limb

Taste Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”. OBJECTIVE 19| Describe the sense of taste, and explain the principle of sensory interaction. Sweet Sour Salty Bitter Umami (Fresh Chicken)

Sensory Interaction When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor.

Taste Flavor of food involves taste but is more complex Apples and onions same taste qualities but their flavors differ greatly

Taste Flavor cont… Depends on its odor, texture, temperature as well as its taste

Taste Cells Receptor cells that are sensitive to taste Located on taste buds

Taste buds the sensory organs for taste. They contain taste cells and are located on the tongue 10,000 taste buds-located near the edges of tongue and the back of tongue

Taste Buds Specialized a bit Sweetness: tip of tongue Bitterness: back of tongue Sourness: along sides of the tongue Saltiness: overlaps the areas sensitive to sweetness and sourness

Taste buds We all have different taste worlds By eating hot foods and scraping tongue, you regularly kill off many taste buds, Taste buds reproduce rapidly and completely renew once a week

Taste buds Elderly complain their food has little or no taste-more likely to experience a decline in the sense of smell Older people experience the loss of flavor.

Smell Like taste, smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. Unlike taste, there are many different forms of smell. OBJECTIVE 20| Describe the sense of smell and explain why specific odors so easily trigger memories.

Smell Smell and taste are the chemical senses With smell and taste, we sample molecules of the substance being sensed Humans are underprivileged when compared to dogs

Smell Smell makes crucial contribution to the flavor of foods Ex: If you did not have a sense of smell, then an onion and an apple would taste the same to you