Sensation and Perception

1. Sensation and Perception

2. What does this picture show? Random dots??? Still can’t see it? Here’s some help.

4. Why??? Try to explain this craziness……

5. Some interesting phenomena Kanizsa illusory contoursWestheimer effect Orientation afterimageStepping feet illusion Motion blindnessRotating snake Stereokinetic phenomenonWaterfall effect Spoke illusionEye jitter effect Motion perceptionAn enigma Motion bounce illusionMotion binding Herman gridWertheimer-Koffka Pyramid illusionMunker-White illusion Adelson’s checker shadowContrast gain control Lilac chaserPoggendorf illusion Café wallMuller-Lyer illusion Blur effectsBlotted letters Rotation effect“Magic Eye”

6. Sensation and Perception • Sensation • a process by which our sensory receptors and nervous system receive and represent stimulus energy • Perception • a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

7. Sensation • Bottom-Up Processing • analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • Top-Down Processing • information processing guided by higher-level mental processes • as when we construct perceptions drawing on our experience and expectations

8. Sensation- Basic Principles • Psychophysics • study of the relationship between physical characteristics of stimuli and our psychological experience of them • Light - brightness • Sound - volume • Pressure - weight • Taste - sweetness

9. Sensation- Thresholds • Absolute Threshold • minimum stimulation needed to detect a particular stimulus • usually defined as the stimulus needed for detection 50% of the time (example: candlelight at 30 miles) • Difference Threshold • minimum difference between two stimuli that a subject can detect 50% of the time • just noticeable difference (JND)

10. Sensation- Thresholds • Signal Detection Theory • predicts how and when we detect the presence of a faint stimulus (signal) • assumes that there is no single absolute threshold • detection depends partly on person’s • experience • expectations • motivation • level of fatigue

11. 100 Percentage of correct detections 75 50 Subliminal stimuli 25 0 Low Absolute threshold Medium Intensity of stimulus Sensation- Thresholds • When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.

12. Sensation- Thresholds • Weber’s Law - to perceive a difference between two stimuli, they must differ by a constant proportion • light intensity - 8% • Weight - 2% • tone frequency - 0.3% • Sensory adaptation - diminished sensitivity with constant stimulation

13. Vision • Transduction - conversion of one form of energy to another • Wavelength - the distance from the peak of one wave to the peak of the next • Hue - dimension of color determined by wavelength of light • Intensity - amount of energy in a wave determined by amplitude • brightness • loudness

14. Vision • Pupil - adjustable opening in the center of the eye • Iris - a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening • Lens - transparent structure behind pupil that changes shape to focus images on the retina

16. Vision • Accommodation • change in shape of lens • focus near objects • Retina • inner surface of eye • light sensitive • contains rods and cones • layers of neurons • beginning of visual information processing

17. Vision • Acuity - the sharpness of vision • Normal focus • Farsightedness • lens focuses on near objects behind retina • Nearsightedness • lens focuses image of distant objects in front of retina

18. 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

19. 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

21. 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 Vision- Receptors

22. Cell’s responses Stimulus Visual Information Processing • Feature Detectors • neurons in the visual cortex respond to specific features • shape • angle • movement

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

24. Visual Information Processing • Trichromatic (three color) Theory • Young and Helmholtz • three different retinal color receptors • red • green • blue

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

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

28. Opponent Process- Afterimage Effect

30. Audition • Audition • the sense of hearing • Frequency • the number of complete wavelengths that pass a point in a given time • Pitch • a tone’s highness or lowness • depends on frequency

31. Audition- The Ear

32. Audition- The Ear • Outer Ear • Auditory Canal • Eardrum • Middle Ear • hammer • anvil • stirrup • Inner Ear • oval window • cochlea • basilar membrane • hair cells

33. Audition • Place Theory • the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated • Frequency Theory • the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

34. Audition • Conduction Deafness • hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea • Nerve Deafness • hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve

35. Audition • Older people tend to hear low frequencies well but suffer hearing loss for high frequencies Amplitude required for perception relative to 20-29 year-old group 1 time 10 times 100 times 1000 times 32 64 128 256 512 1024 2048 4096 8192 16384 Frequency of tone in waves per second Low Pitch High

36. Touch • Skin Sensations • pressure • only skin sensation with identifiable receptors • warmth • cold • pain

37. Pain • Gate-Control Theory • theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain • “gate” opened by the activity of pain signals traveling up small nerve fibers • “gate” closed by activity in larger fibers or by information coming from the brain

38. Taste • Taste Sensations • sweet • sour • salty • bitter • Sensory Interaction • the principle that one sense may influence another • as when the smell of food influences its taste

39. Smell

40. Body Position and Movement • Kinesthesis • the system for sensing the position and movement of individual body parts • Vestibular Sense • the sense of body movement and position • including the sense of balance