Sensation and Perception: Understanding the Detection and Interpretation of Stimuli

3. Defining Sensation and Perception • Sensation • The detection of physical energy emitted or reflected by physical objects. • It occurs when energy in the external environment or the body stimulates receptors in the sense organs. • Perception • The process by which the brain organizes and interprets sensory information.

4. Sensation and Perception • Sensation • Vision, taste, and touch • Psychophysics • Organization • Top-down • Bottom-up • Context • Vision • Depth • Constancies • Illusions • Car Accidents

5. Sensation is fundamentally biological • Rod and Cone Cells • Colorblindness • Taste • Touch • Psychophysics

6. A Camera’s View

7. An Eye’s View

8. Two Types of Colorblindness • Monochromats: • People who are totally colorblind • Dichromats: • People who are blind to either red-green or yellow-blue

9. Test of Color Deficiency

12. Are you a supertaster?

13. Sensation • Sensory Thresholds • How Much Stimulation is Enough? • Sensory Adaptation • “It Feels Great Once You Get Used to It”

14. Psychophysics Study of the relationship between physical events and the experience of those events • Thresholds • Absolute threshold • Difference threshold • Just-noticeable difference (JND) • Weber’s law

15. Sensory Thresholds • Absolute threshold: • minimum stimulation needed to detect a particular stimulus 50% of the time • Difference threshold (jnd): • minimum difference between two stimuli that one can detect 50% of the time • increases with magnitude of stimulus

16. Absolute Sensory Thresholds • Vision: • A single candle flame from 30 miles on a dark, clear night • Hearing: • The tick of a watch from 20 feet in total quiet • Smell: • 1 drop of perfume in a 6-room apartment • Touch: • The wing of a bee on your cheek, dropped from 1 cm • Taste: • 1 tsp. Sugar in 2 gal. water

17. 1 lb 1 lb 1/10 Suppose you have a 1 lb weight in your left hand and something heavier in your right hand. Anything less than 1.1 lbs in your right hand, and you won’t be able to tell the difference. Weber’s Law • The principle that the JND for any given sense is a constant fraction or proportion of the stimulation being judged.

18. Will people detect the same difference (1/10 lb) between 5 and 5.1 lbs? 5 lb 5 lb 5 lb 5 lb 1/10 1/2 No – a 10% difference is 1 JND for weight, so the weight must be raised to 5 ½ lbs before the two can be distinguished. Weber’s Law

19. Subliminal Perception • Definition: • Below threshold • Effect of subliminal stimulation: • Most research finds no perception • A small number of studies find subtle, fleeting effect on thinking

20. Does subliminal advertising work? • No. The goal of using subliminal advertising is to increase the likelihood that you will buy a particular product. • Research has repeatedly demonstrated that subliminal messages have no effect on behavior.

21. Sensory Adaptation and Deprivation • Adaptation • The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious. • Prevents us from having to continuously respond to unimportant information.

22. Rods, Cones, and Dark Adaptation

23. Sensation and Perception • Sensation • Vision, taste, and touch • Psychophysics • Organization • Top-down • Bottom-up • Context • Vision • Depth • Constancies • Illusions • Car Accidents

24. Organization • Bottom-Up Processing • An analysis of the action of feature detectors in a sensory experience • Top-Down Processing • An analysis of the effects of expectations and prior learning on a sensory experience

25. Top (Whole) Bottom (Features) CAT C A T  /\   / \ 

26. Top-down Processing Bottom-up Processing • Identify the whole (top) using built-in perceptual biases and previous experience - CAT • Examine/find the relations among features - Letters • Examine/find the features - /-\ • Identify the individual features (bottom) • Relations among features • \/- and A aren’t the same • Relations among relations • CAT, ACT, TAC, etc. are all different • Identify Object - CAT

34. Feature Detection On the next slide, locate the red T

35. T

36. Feature Detection On the next slide, locate the red T (Again)

37. T L T L T L T L T T L T T L T T L T L T L T T L T L T L T T LL T T L T L T T T L T T L T T T L

38. Bottom-up Processing • Much visual processing is done in the brain. • Some cortical cells respond to lines in specific orientations (e.g. horizontal). • Other cells in the cortex respond to other shapes (e.g., bulls-eyes, spirals, faces). • Feature-detectors • Cells in the visual cortex that are sensitive to specific features of the environment.

39. Hubel & Wiesel’s Experiment

40. Gestalt Psychology The whole is greater than the sum of its parts - Max Wertheimer

41. The Gestalt Laws of Perceptual Grouping Figure-Ground Proximity Similarity Continuity Common fate

42. Figure-Ground Distinction • Figure: • Entity perceived to stand apart from the background • Ground: • Background against which a figure appears

44. Figure-Ground Distinction

45. Look at the shapes

46. Did you see this shape?

47. How about this one?

48. Figures have shape, but ground doesn't