Sensation & perception

1. Sensation & perception

2. How do we sense our worlds? • Sensation • Detection of external stimuli • Response to the stimuli • Transmission of the response to the brain • Perception • Processing, organizing and interpreting sensory signals • Internal representation of the stimulus

3. The Sensing Process • Stimulus • Sensation • Sensory receptors in the eye detect the stimulus

4. The Sensing Process • Sensory Coding • Stimulus is transduced (translated into chemical & electrical signals that are sent to the brain) • Perception • The brain processes the neural signals and constructs a representation of the green light – a signal to go

5. The Stimuli, receptors & pathways The 5 Senses

6. Taste • Stimuli • Molecules on the tongue • Receptors • Cells in taste buds on the tongue • Pathways to the brain • Portions of facial, glossopharyngeal, and vagus nerves

7. Smell • Stimuli • Molecules on mucus membranes in the nose • Receptors • Sensitive ends of olfactory neurons • Pathways • Olfactory nerves

8. Touch • Stimuli • Pressure on the skin • Receptor • Sensitive ends of touch neurons in skin • Pathway • Cranial nerves for touch above the neck, spinal nerves for touch elsewhere

9. Hearing • Stimuli • Sound waves • Receptors • Pressure-sensitive hair cells in the cochlea of the inner ear • Pathways • Auditory nerve

10. Vision • Stimuli • Light waves • Receptor • Light sensitive rods and cones in the retina of the eye • Pathway • Optic nerve

11. Sensory thresholds Sensory organs constantly acquire information from the environment

12. Absolute Threshold • The minimum intensity of stimulation that must occur before you experience a sensation • Approximate Absolute Sensory Threshold • Taste – 1 tsp. of sugar in 2 gallons of water • Smell – 1 droplet of perfume in a standard size room • Touch – a fly’s wing falling on your cheek • Hearing – the tick of a clock at 20ft in quiet conditions • Vision – a candle flame seen at 30 miles on a dark, clear night

13. Difference Threshold • The just noticeable difference between 2 stimuli • Minimum amount of change required for a person to detect a difference • Example: • If you’re reading a book and watching TV, a commercial comes on that is louder than the show – you look up and notice something has changed • The DT is the minimum change in volume required to detect a difference

14. Signal detection theory sdt

15. SDT • Detecting a stimulus requires making a judgment about its presence or absence • The detection of a faint stimulus requires a judgment • Example • A hearing test • Person wears headphones and is told to raise their hand when they hear the tone in that ear

16. Sensory Adaptation • A decrease in sensitivity to a constant level of stimulation • Example • You are studying and your neighbor starts mowing their lawn • After a few minutes the noise seems to blend in or fade into the background

17. How we experience the sense of sound

18. Hearing • The 2nd sense to vision • Sound waves – pattern of changes in air pressure • Amplitude – loudness • Frequency – pitch

19. Process of Hearing • Sound waves arrive at the outer ear • Travel down the auditory canal to the eardrum • Then to the middle ear • Sound waves make the eardrum vibrate • Vibrations transfer to 3 tiny bones • Hammer • Anvil • Stirrup • Then to the auditory nerve

20. How we experience the sense of sight

21. Vision • Most important source of knowledge • Does a place look safe or dangerous? • Does a person look friendly or hostile?

22. Process of Seeing • Light first passes through the cornea (transparent outer layer) • Cornea focuses incoming light, which enters the lens • Forms an image on the retina(thin inner surface of the back of the eyeball) • THE RETINA IS THE ONLY VISIBLE PART OF THE BRAIN OUTSIDE THE SKULL! • Pupil – dark circle at the center • Contracts – gets smaller • Dilates – gets larger

23. Process of Seeing • Iris – eye color • Behind the iris, muscles change the shape of the lens • Lens – focuses images through accomodation

24. 2 Types of Cells in the Retina • Rods • Respond to extremely low levels of light • Used primarily in night vision • Cones • Respond in bright levels of light • Used for seeing color and detail

25. Color • Determined by wavelength • An object appears to be a particular color because of the wavelength it reflects • Color is always a product of our visual system; there is no color in the physical world!

26. Color Spectrum ROYGBIV

27. Trichromatic Theory • 3 different types of cones that are sensitive to different wavelengths • 1. Short (blue-violet) • 2. Medium (yellow-green) • 3. Long (red-orange)

28. Opponent-Process Theory • Some colors seem to be opposites • Stare at a red image – see a green afterimage • Stare at a green image – see a red afterimage • Stare at a blue image – see a yellowafterimage • Stare at a yellow image – see a blue afterimage

29. 3 Dimensions of Color • Hue • Distinctive characteristics of a color • Ex. – blue, light blue, navy blue, turquoise • Saturation • Color’s purity, vividness • Ex. – lime green, fluorescent yellow • Brightness • Perceived intensity • Two of the same exact colors can be perceived differently in different light

30. Gate control theory

31. Pain • Brain regulates the experience of pain • Producing it • Suppressing it • Depends on biological, psychological, and cultural factors

32. Gate Control Theory of Pain • For a person to experience pain: • Pain receptors must be activated • A neural gate in the spinal cord must allow the signals through to the brain • Eventually, the “gate” closes and no more pain signals reach the brain

33. Visual Illusions • Illusions are tools used by psychologists to determine how the brain understands information

34. Gestalt psychology “Organized whole”

35. Figure & Ground

36. Proximity & Similarity

37. Closure

38. Continuation

39. Depth perception

40. Depth Cues • Binocular • Both eyes • Monocular • Each eye separately • 1. Accommodation – change in the shape of the lens that varies with distance (1 eye) • 2. Convergence – the way the eyes rotate inward and outward with changes in distance (2 eyes) • 3. Binocular disparity – difference between the images provided by each eye

41. Figure and Ground • 3 Principles • 1. The figure is more “thinglike” and more memorable than the ground • 2. The figure is seen as being in front of the ground • 3. The ground is seen as unformed material and seems to extend behind the figure

42. Monocular Depth Perception • Occulsion • A near object blocks an object that is farther away • Relative Size • Far-off objects project a smaller retinal image than close objects • Linear perspective • Parallel lines appear to converge in the distance • Texture gradient • Shows depth or looks dense • Position relative to the horizon • Objects below the horizon that appear higher in the visual field are perceived as being farther away

43. Perception of Motion • Different kinds of movement: • A figure moving against a stationary background • Objects at rest against a moving background • Objects moving at different speeds in relation to each other • Observer’s own movements in relation to his/her surroundings • Induced movement • perception of movement of an object that is not moving

44. Illusions

45. Muller-Lyer • Which line appears longer?

46. Ponzo Railroad Track Illusion • Which of the two horizontal lines on the track appear longer?

47. The Necker Cube • The cubes seem to shift and another side seems closer to you. • Then it shifts back again

48. The Boring Figure • Designed by E.G. Boring • Ambiguous figure • Young girl/old woman

49. The Ames Room • Albert Ames • Appears to be a normal room • Actually shaped so the left corner is almost twice as far from the viewer as the right corner • The viewer perceives the nearer person as being much larger than the other, although both are exactly the same height

50. What do you see?