Basic Concepts of Sensation

1. Basic Concepts of Sensation

2. Important Terms • What is sensation? The process by which we receive, transform, and process stimuli from the outside world to create sensory experiences of vision, touch, hearing, taste, smell, etc. • Sensation—receiving the information; Perception—interpreting the information • Sensory Receptors-- Specialized nerve cells in our sense organs that detect stimuli from the outside world (light, sound, etc.) and transform them into neural impulses that the brain uses to create sensations of vision, hearing, etc. • Vision--Rods and cones in the eyes • Hearing--Hair cells in the inner ear • Taste--Taste buds on the tongue • Smell--Receptor cells in the upper nostrils • Touch--Nerve endings in the skin

3. Important Terms • Absolute Threshold-- the smallest amount of a given stimulus a person can sense. • Vision--the flame from a candle flickering 30 miles away • Hearing--the ticking of a watch 20 feet away in a quiet room • Taste--1 teaspoon of sugar dissolved in two gallons of water • Smell--1 drop of perfume dispersed in a small house • Touch--the wing of a bee falling on the cheek from 1 cm. away • Difference Threshold (Just Noticeable Difference)--The minimal difference in the magnitude of energy needed for people to detect a difference between two stimuli.

4. Important Terms • Weber’s Law--The amount you must change a stimulus to detect a difference is given by a constant fraction or proportion of the original stimulus. • Brightness of lights=1.67% (1/60) • Difference in weights=2% (1/50) • Loudness of sounds=10% (1/10) • Saltiness of food=20% (1/5)

5. Important Terms • Signal-Detection Theory--Theory that says that the threshold for detecting a signal depends on more than the properties of the stimulus. It also depends on background stimulation, and the biological and psychological character- istics of the perceiver. • What happens through sensory adaptation? • With repeated exposure to the same stimuli, we become less sensitive to them (odors, hot/cold water). But it doesn’t always work with certain strong stimuli (car alarm) Sensation and Perception

6. Some Review Videos Video #1Video #2Video #3Video #4Video #5

7. How the eye works

8. Anatomy of the Eye • Cornea: transparent covering through which light enters. • Iris: muscle which regulates the size of the pupil to determine the amount of light that enters. • Pupil: black opening inside iris that allows light to enter the eye • Lens: focuses light rays on the retina

9. How the Eye Works • Retina: Light sensitive layer of the inner surface of the eye that contains photoreceptor cells. • Photoreceptors: light sensitive cells • RODS: sensitive to the intensity of light (light v. dark) • CONES: sensitive to color • Optic Nerve: The nerve that carries visual information to the brain where it is routed to the thalamus then to the visual cortex where vision is produced.

10. Color Theories Trichromatic--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) • Trichromatic Theory vs Opponent Process Theory Opponent-Process (based on work with afterimage--see p. 94)--We have 3 types of color receptors BUT each type of receptor consists of a pair of opposing receptors. Red-green and blue-yellow receptors process color and black-white receptors detect brightness.

11. Colorblindness • TRICHROMATS--people with normal color vision • MONOCHROMATS 1 in 40,000 (completely colorblind) only see in black and white • DICHROMATS people who lack one of the three types of cones making it difficult to distinguish between colors • Red-Green color blindness (8% of men, less than 1% of women) • Blue-Yellow--much less common Colorblind Test

12. Hearing Amplitude or height of sound waves determines their perceived loudness (decibels). For each 10 decibels, loudness increases 10x Frequency--the higher the frequency of the sound wave, the higher the pitch. (Women’s voice, shorter strings on piano--vibrate more rapidly). Light travels 186,000 miles per second; sound 1,130 feet per second.

13. Anatomy of the Ear • Eardrum: between the outer & middle ear; vibrates and transmits sound waves to the middle ear • Ossicles: 3 tiny bones; the hammer, anvil and stirrup (middle)--vibrate in response to vibrations of the eardrum. • Oval Window: Membrane covered opening; separates the middle ear from the inner ear • Cochlea: Snail shaped organ in the inner ear that contains sensory receptors for hearing • Basilar membrane--structure within cochlea that vibrates in response to movement of fluid in the cochlea • Organ of Corti (hair cells that act as auditory receptors--they bend in response to the vibrations in Basilar membrane--they trigger neural impulses) Auditory Nerve: carries neural impulses from the ear to the brain (temporal lobes) Hearing

14. Anatomy of the Ear

15. How does the ear enable us to hear? • Sound waves are funneled by the outer ear to the eardrum, causing it to vibrate • Vibrations are transmitted through the ossicles (three tiny bones in the ear) then to the oval window, then they are transmitted to the cochlea within the inner ear

16. How does the ear enable us to hear? 3. Vibration of the oval window causes movement of fluid in the cochlea, causing the basilar membrane to vibrate 4. Hair-cell receptors in the organ of Corti bend in response to the vibration, triggering the neural impulses that travel through the auditory nerve to the brain.

17. Deafness and Hearing Loss • Conduction Deafness: involves the middle ear--loss of conduction of sound vibrations through the ear. Either a punctured eardrum or three bones that amplify sound waves lose ability to vibrate properly. • Nerve Deafness: associated with nerve damage--damage to hair cells (cochlear implants) or to the auditory nerve itself Decibal Chart Hearing Loss

18. Our Other Senses

19. The Nose • Olfaction: Our sense of smell • Olfactory Nerve: Nerve that carries impulses from olfactory receptors in the nose to the brain • Olfactory Bulb: Area in the front of the brain (above the nostrils) that receives sensory input from receptors in the nose • Pheromones-chemicals we pick up on; sexual attraction? Pheromones • What happens when people’s senses mix? Synesthesia—A rare condition in which stimulation in one sensory modality triggers sensations in another sensory modality. synesthesia

20. Taste • Taste Cells: Nerve cells that are sensitive to taste (receptors) • Taste Buds: Pores or openings on the tongue containing thousands of taste cells (bumps on tongue) • Most taste buds are found near the edges and back of the tongue. • Why do we have certain likes and dislikes of food? • Cultural Background • Genetic factors (sweet/bitter) • Supertasters--1/4 of people who experience more intense tastes than other people

21. Touch • Skin senses: The senses of touch, pressure warmth, cold and pain that stimulate receptors in the skin • Skin=Largest Sensory Organ! • Gate Control Theory of Pain—Pain signals that have originated in areas of injury do NOT travel directly to the brain.  Rather, there exists within the spinal cord a gate mechanism which determines the degree to which pain signals are transmitted to the brain. 

22. Gate Control Theory (con’t) • When the gate is wide open, more pain signals get through than when it is closed.  Generally, rather than being completely open or shut, the gate is open to varying degrees.

23. Gate Control Theory (con’t) • Some Factors Which Open the Pain Gate • Extent of injury or trauma • Inappropriate Activity level • Depression, Worry, Anxiety, Tension, Anger • Focusing on the pain • Boredom due to minimal involvement in life activities

24. Gate Pain Theory (con’t) • Some Factors Which Close the Pain Gate • Application of Heat or Ice • Massage • Medication • Managing stress properly • Distraction away from pain—increased social activities • Practicing Positive Attitude • Appropriate Exercise • Healthy Eating • Having a communicative outlet to share thoughts and feelings

25. Balance • Kinesthesis (kinesthetic sense): keeps us informed about movement of the parts of the body and their position in relation to each other • i.e.--riding a bike without watching legs, type without looking at keyboard, touch our nose when blindfolded • Vestibular Sense- monitors position in space; helps us maintain sense of balance • i.e.--detects acceleration and orientation of your body as you move and whether, and by how much, your head is rotating.

26. Perceiving Our World

27. Perception--Definition • What is Perception? • The process by which the brain interprets sensory information, turning it into meaningful representations of our world. (The brain is bringing order to the sensations we experience--i.e., this power point)

28. Perception vs. Reality • Do perceptions always reflect external reality?

29. Selective Attention--The 1st Step • Selective Attention: The process by which we limit our attention to certain stimuli while filtering out other stimuli. We pay attention to stimuli that are meaningful or emotionally significant. Also, motivational states like hunger and thirst affect our attention. • Selective Attention Test

30. Perceptual Set • Perceptual Set: Tendency for our perceptions to be influenced by our expectations or preconceptions.

32. Bottom-Up vs. Top-Down Processing Bottom-Up: Mode of perceptual processing by which our brain recognizes patterns by piecing bits and pieces of sensory information together. If you understand concepts and ideas by starting with the details and then working your way up to the main idea of overall concept, you're a bottom-up processor. Top-Down: Mode of perceptual processing by which our brain identifies patterns as meaningful wholes (information processing based on previous knowledge) I.e.--THE MHN RHN

35. Laws of Perceptual Organizing: Principles identified by Gestalt psychologists that describe the ways in which the brain groups bits of sensory stimulation into meaningful wholes or patterns. • Figure--that which takes shape (part we pay attention to) • Ground--background, that which has no shape • FIGURE defines GROUND and GROUND defines FIGURE.

37. Figure and Ground

38. Similarity: Objects that are similar will be perceived as belonging to the same group.

39. Gestalt Laws of Grouping • Proximity: Objects that are near each other will be perceived as belonging to a common set (we tend to group nearby objects)

40. Continuity: A series of stimuli will be perceived as representing a unified form.

41. Closure: People tend to piece together disconnected bits of information to perceive whole forms.

42. Connectedness: Objects positioned together or moving together will be perceived as belonging to the same group.

43. Perceptual Consistencies • Tendency to perceive the size, shape color and brightness of an object as remaining the same even when the image it casts on the retina changes.

44. Shape Constancy • Tendency to perceive an object as having the same shape despite differences in the images it casts on the retina as the viewer’s perspective changes.

45. Size Constancy • The tendency to perceive an object as having the same size despite changes in the images casts on the retina as the viewing distance changes.

46. Color Constancy • Tendency to perceive an object as having the same color despite changes in lighting conditions (if your car is red, you perceive it to be red even though it may look grayish as evening falls).

47. Brightness Constancy • Tendency to perceive objects as retaining their brightness even when they are viewed in dim light.

48. Cues for Depth Perception • Binocular Cues for Depth: Cues for depth that involve both eyes • Retinal Disparity--each eye sees the same scene but from a slightly different perspective (disparity is greater at close distances)

49. Cues for Depth Perception • Binocular Cues for Depth: Cues for depth that involve both eyes • Convergence--the degree to which the eyeballs must turn toward the nose (converge) in order to focus on an object. The closer an object is to you, the greater the convergence. If the object is more than 20 feet away, however, the degree of convergence is zero

50. Cues for Depth Perception • Monocular Cues for Depth: Cues for depth that involve one eye only • Relative size--When two objects are believed to be the same size, the one that appears larger is perceived to be closer.