Sensation and Perception

1. Sensation and Perception Chapter 4

2. The Basics • Sensation – Involves the stimulation of sensory receptors and the transmission of sensory information to the central nervous system • i.e. spinal cord and brain • Things that tip off sensory receptors: • Light, sound, smells, etc.

3. The Basics • Perception – How we interpret sensory stimulation • Football field example • Perception reflects learning, expectations and attitudes

4. Absolute Threshold • The weakest amount of a stimulus that can be tested • Dogs v. Humans • Thresholds are different amongst people • More sensitive than others

5. Some established absolute thresholds are: vision: a candle flame 30 miles away on a clear night. hearing: a watch ticking 20 feet away taste: 1 teaspoon of sugar dissoved in 2 gallons of water smell: a single drop of perfume in a three-room house touch: a bee's wing falling a distance of 1 centimeter onto the cheek.

6. Difference Threshold • The minimum amount of difference detected between two stimuli • Tone • Hue • Piles of sand

7. Signal-Detection Theory • Distinguishing sensory stimuli that takes into account all factors of self and environment • We focus on what we consider important

8. Sensory Adaptation • Process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli • Eyes adapting to darkness • Waves on a beach • Traffic

9. Section 2 - Vision • Color spectrum – Roy G. Biv

10. The Eye • Similar to a camera • Light enters the eyes, and then is projected onto a surface • The amount of light that enters is determined by the opening in the colored part of the eye • The pupil

11. The Eye • Once light enters, it meets the lens • The lens adjusts to distances of objects by changing its thickness • Finger test – near / far

12. The Eye • The changes in thickness and light project a clear image onto the retina • The retina acts like the film of a camera • Neurons in your retina that are sensitive to light are called photoreceptors • Once the photoreceptors are activated a nerve carries the information to the brain – occipital lobe

13. The Blind Spot • We need the blind spot to see • A point left empty of photoreceptors – room for information to travel • Circle test

14. Rods and Cones • 2 kinds of photoreceptors • Rods – sensitive only to the brightness of light • Cones – provide color

15. Dark and Light Adaptation • Your ability to see in low light improves for 45 minutes • Sundown • Adaptation to light happens much more quickly

16. Visual Acuity • Vision tests for sharpness • 20/20 • As you age your lenses become brittle, and you may become farsighted • Holding reading material further away

17. Color Vision • Human beings can see up to 1 million different hues • Animals are more sensitive to certain colors • The color circle • Afterimages • Color blind – distinguishing colors from each other • Total color blindness is extremely rare

18. Section 3 • Hearing – a series of vibrations in the form of sound waves in its own unique pitch or loudness • Hearing experiment

19. Pitch • The more cycles (sound waves) per second, the higher the pitch (high or low) • Women’s voices are at a higher pitch than men’s because their vocal cords tend to be shorter • Humans – 20 to 20,000 per second • Dogs / Dolphins / other animals in excess of 20,000

20. Loudness • Measured in dB (decibels) • Loudness is determined by the height / amplitude of sound waves • 0 decibels is the threshold (a watch heard ticking at 20 feet away)

21. Locating Sound • Perception of sound • Infinite possibilities • How your body / senses react to sound

22. Deafness • Inherited / Disease / Injury / Old Age • Conductive Deafness – • Damage to middle ear, sound is not amplified • Helped with hearing aides • Sensorineural Deafness • Damage or elimination of neurons, damage to auditory nerve • Cannot be helped if nerve itself is damaged • Cochlear implants can help neuron loss

23. Section 4 • Other Senses – • Smell – incredibly important, apples and onions would be relatively the same otherwise • Taste – Spheres of the tongue • Smell and taste work together when eating

24. Skin Senses • Touch • Infants grow quickly and stay healthier if touched • Older people do better if they have pets (cats / dogs) • Body is covered in hairs, many too small to see • Sensory receptors lie at the base of the hair • Do we actually “touch”?

25. Temperature • Differences are all relative • Fevers • Outside heat (Summer) • Swimming pools • A/C

26. Pain • The more pain receptors are located in a certain body, they more we will feel • Point of contact > Spine > Thalamus > Brain (processing) • Prostaglandins help transmit messages • Ibuprofen and aspirin help slow prostaglandins

27. Pain • Why does rubbing or scratching painful areas help? • Mixed signals • Phantom limb pain

28. Body Senses • Vestibular Sense • Sensory organs in your ears monitor your motion and relation to gravity • Balance, standing, changing speeds, etc. • Kinesthesis • Position and motion of your body • Copying body motions

29. Section 5 • Perception – the way our body makes sense of our sensory impressions • Gestalt psychology – “The whole is more than the sum of its parts”

30. Rules of Perceptual Organization • Closure – filling in the gaps to get a complete picture • Fig 4.11 (p. 93) • Filling in the blanks because dogs are familiar to you

31. Rules of Perceptual Organization • Figure-Ground Perception • What do we perceive as the figure and what do we perceive as the background • Fig 4.12 (Vases or Faces)

32. Rules of Perceptual Organization • Other Rules - • Laws of: • Proximity • Similarity • Continuity • Common Fate

33. Rules of Perceptual Organization • Perception of Movement • To sense movement we need a change of position • Your senses need clues to tell you that you are moving • Trees, road bumps, etc.

34. Rules of Perceptual Organization • Stroboscopic Motion • The illusion of movement • Flipbooks • Movies on reels • Subliminal messages • Perception smoothes out the gaps • Humans prefer smooth images

35. Rules of Perceptual Organization • Depth Perception • The “distance away” • Monocular clues – the appearance of 3-D on 2-D surfaces • i.e. paintings • Clearness, shadow, texture, overlapping, perspective • This is done through stimulation of retina

36. Monocular Cues • Clearness – faraway objects seem less detailed • Perspective – parallel lines coming together or moving apart • Overlapping – placing of one object in front of another • Shadows and highlights – give a 3-D feel • Texture Gradient – closer objects have more texture (gradient – progressive change) • Motion parallax – the tendency of objects to seemingly move forward or backward depending on distance away • Moon, stars v. trees and rocks while driving

37. Binocular Cues • Need both eyes v. one eye for monocular • 2 cues in binocular: • Retinal Disparity • Convergence

38. Binocular Cues • Retinal Disparity – only works on objects that are very close • Difference of angles of an object as seen by both retinas • Convergence – associated with a tightness of the eye muscles on things up close • Magic Eye puzzles

39. Perceptual Constancies • Size Constancy – Comes through experience • Perceiving an object as one size no matter the distance • Pygmy example p. 98

40. Perceptual Constancies • Color Constancy • The tendency for objects to maintain color no matter the light quality • Brightness Constancy • Tendency to find an object equally bright even when its surroundings change

41. Perceptual Constancies • Shape Constancy • The knowledge an item has one shape • i.e. top of a glass from different angles

42. Visual Illusions • When the rules of constancies are violated