Sensation & Perception

1. 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 give meaning by selecting, organizing, and interpreting our sensations, the process is called perception.

2. Sensation vs. Perception • Sensation • The experience of sensory stimulation. • Sensation involves transducers-specialized receptor cells. • Transduction – converting stimuli into neural impulses

3. Perception • The process of creating meaningful patterns from raw sensory information

6. Perception: Top-Down Processing -analysis based on experience and expectation (starts with the brain) Sensation: Bottom-up Processing -analysis that starts with the senses

7. 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.”

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

9. Example of Top-Down Processing • Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

10. The Basic Process • Receptor cells • Specialized cells that respond to a particular type of energy • Doctrine of specific nerve energies • One-to-one relationship between stimulation of a specific nerve and the resulting sensory experience • For example, applying pressure with your finger to your eye results in a visual experience

11. Sensory Thresholds • Absolute threshold • The minimum amount of energy that can be detected 50% of the time between two stimuli.

12. Absolute Thresholds • Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water • Smell: 1 drop of perfume diffused throughout a three-room apartment • Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch) • Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions • Vision: a candle flame seen from 50km (30 miles) on a clear, dark night

13. Sensory Thresholds • Sensory adaptation • An adjustment of the senses to the level of stimulation they are receiving • Ever forgotten you are wearing a watch? • Ever gotten used to a smell? • Then why don’t things disappear from your vision?

14. Sensory Thresholds • Difference threshold • The smallest change in stimulation that can be detected 50% of the time • Also called the just noticeable difference (jnd)

15. 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 Yes No Observer’s Response Tell when you (observer) detect a difference in the light.

16. Weber’s Law • Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. dR=Difference needed for detection (perception). Constant Original stimulus amount.

17. Sensory Thresholds • Weber’s Law • States that the difference threshold is a constant proportion of the specific stimulus • Senses vary in their sensitivity to changes in stimulation .

18. 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

20. Subliminal Messages Subliminal Threshold: When energy of the stimulus is below one’s absolute threshold for conscious awareness. Subliminal= stimuli that sensory system responds to, but due to short duration or subtle form, don’t reach threshold of cognition Quick Survey • Do you think you are influenced by subliminal messages in advertising? • Do you think you are influenced by everyday advertisements that you perceive consciously (e.g. laundry detergent, beverages)?

21. Can we a) sense unconsciously stimuli below threshold and b) can we be influenced by it?Cited Research: • 1956: NJ Movie Audiences (Eat Popcorn, Drink Coca-Cola)-false report! • By definition we can sense stimuli below absolute threshold up to 49% of the time. • What if sense stimuli 0% of the time? Negative & Positive images (only perceived as a flash of light) can influence future perceptions. • Subliminal Priming: subliminal bread allows detection of butter faster than bottle.

22. Back masking • A recording studio technique where backward messages are deliberately superimposed on the soundtrack • The fear . . . “Human brains are capable of receiving, scanning, deciphering, storing and later reacting to subliminal or subconscious messages”

23. Another One Bites the Dust • http://www.backmaskonline.com/music/Queen%20-%20Another%20One%20Bites%20the%20Dust%20FOR.mp3 • (Forward) • http://www.backmaskonline.com/music/Queen%20-%20Another%20One%20Bites%20the%20Dust%20REV.mp3 • (Backward) • "It's fun to smoke marijuana"

24. Sexual imagery in ads? • Wilson Bryan Key: “sex” in ice cubes, nude figures in images from butter to icing in cake mix ads. • Even if images aren’t consciously perceived, they put us in good mood and pay more attention to ad • http://www.youtube.com/watch?v=PVrOFt-0-e0

25. Vision

27. Acuity- the sharpness of vision • Nearsightedness • nearby objects seen more clearly • lens focuses image of distant objects in front of retina • Farsightedness • faraway objects seen more clearly • lens focuses near objects behind retina

28. Retina’s Reaction to Light-Receptors • Cones • near center of retina (fovea) • fine detail and color vision • daylight or well-lit conditions • Rods • peripheral retina • detect black, white and gray • twilight or low light

29. Dark & Light Adaptation • Adaptation - process by which the eye becomes more or less sensitive to light

30. Retina’s Reaction to Light • Optic nerve- nerve that carries neural impulses from the eye to the brain • Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there • Fovea- central point in the retina, around which the eye’s cones cluster

31. Vision - Receptors Receptors in the Human Eye Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitive? Yes No

32. Visual Information Processing • Feature Detection + Parallel Processing • Feature Detection + Parallel Processing • Color • Motion • Form • Depth All processed separately but simultaneously

33. Parallel Processing • simultaneous processing of several dimensions through multiple pathways • color • motion • form • depth

34. STIMULUS: Light Energy Wavelength: Distance from the peak on one light (or sound) wave to the peak of the next. Wavelength = Hue (blue, green, red, yellow, orange, etc.)

35. Intensity=Amplitude of light wave (height)=Brightness STIMULUS: Light Energy

36. 1. All the invisible colors of sunlight shine on the apple.2. The surface of a red apple absorbs all the colored light rays, except for those corresponding to red, and reflects this color to the human eye.3. The eye receives the reflected red light and sends a message to the brain.

37. Trichromatic Theory of Color Vision Helmholtz 1852 Human eye has 3 types of cone receptors sensitive to different wavelengths of light. Medium Long Short People see colors because the eye does its own “color mixing” by varying ratio of cone neural activity

38. Color-Deficient Vision People who suffer red-green blindness have trouble perceiving the number within the design

39. Opponent-Process Theory- opposing retinal processes enable color vision “ON” “OFF” redgreen greenred blueyellow yellowblue black white white black

41. Opponent Process- Afterimage Effect

45. Audition- The Ear

46. Outer Ear • Auditory Canal • Eardrum • Middle Ear • hammer • anvil • stirrup • Inner Ear • oval window • cochlea • basilar membrane • hair cells

47. 2. The eardrum vibrates and the vibrations are transmitted to the inner ear (hammer, anvil, stirrup). 1. Sound waves cause air pressure changes in the auditory canal. 3. The stirrup vibrates the wall of the cochlea, creating waves in the fluid inside. 4. Fluid moves hair cells on the basilar membrane generating a nerve impulse.

48. How do we determine pitch? PLACE THEORY This section contains hair cells sensitive to high frequencies (short wavelengths) This section of the cochlea’s basilar membrane contains hair cells sensitive to low frequencies (long wavelengths)

49. FREQUENCY THEORY • 1000 Waves per Second = 1000 Nerve impulses per second • VOLLEY PRINCIPLE: Nerves take turns sending sound waves over 1000 waves per second.

50. NERVE DEAFNESS CONDUCTION DEAFNESS