Understanding Sensation and Perception: The Brain's Interpretation of Stimuli

1. Sensation & Perception Myers Chapter 6 Additional information from Lilienfeld, Lynn, Namy, & Wolf (2011)

2. Sensation vs. Perception • Sensation: how our sensory receptors and nervous system receive and represent stimulus energies from our environment • Perception: how we organize and interpret sensory information

3. What Illusions Suggest • What we sense is not necessarily what we perceive • The sensory information must be manipulated in some way to create our mental representations • Our representations depend upon our viewpoint

4. Sensation • The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment

5. Bottom-up Processing • Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • Construct a whole stimulus from its parts

6. Top-down Processing • Information processing guided by our experience and expectations • Starts with our beliefs and expectations

7. Top-down Processing • Aoccdrnig to rscheearch at Cmabrigde uinervtisy, it deosn't mttaer waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteres are at the rghit pclae. The rset can be a tatol mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae we do not raed ervey lteter by it slef but the wrod as a wlohe.

8. Transduction • The process by which the nervous system converts an external energy or substance into electrical activity within neurons

9. Sensing the World: Basic Principles • Psychophysics: the study of the relationship between physical energy and psychological experience

10. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) Absolute Threshold • The minimum stimulation needed for the nervous system to detect a stimulus 50% of the time

11. Absolute Threshold • Variability in the absolute threshold • Changing sensitivity • Lapses of attention • Slight fatigue • Psychological changes • Age

12. Just-noticeable Difference (jnd) • The minimum difference between two stimuli that a person can detect 50% of the time • Difference threshold

13. Weber’s Law • There is a constant proportional relationship between the jnd and the intensity of the original stimulus • Light intensity 8% • Weight 2% • Tones .3%

14. Signal Detection Theory (Green & Swets, 1966) • Predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) • No single absolute threshold

15. Signal Detection Theory (Green & Swets, 1966) • Individual threshold depends upon several variables • Experience • Expectations • Motivation • Level of fatigue

16. Signal Detection Theory (Green & Swets, 1966)

17. Subliminal Threshold When stimuli are below one’s absolute threshold for conscious awareness

18. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) Priming • The activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response

19. Sensory Adaptation • Activation of our senses is greatest when we first detect a stimulus • Diminished sensitivity as a consequence of constant stimulation

20. Sensory Adaptation

21. Sensory Interaction • Multi-modal Perception • One sense may influence another • Smell of food influences its taste • McGurk Effect

22. Perceptual Set • Set formed when expectations influence perceptions

23. Perceptual Constancy • The process by which we perceive stimuli consistently across varied conditions Changes in stimulus + Constants = Precise info.

24. Size Constancy • Our perception that the size of a stimulus remains the same although our proximal stimulus has changed in size

25. Shape Constancy • An object retains the same shape although the proximal stimulus has changed in shape • As when a door opens toward us

26. Color Constancy • Our ability to perceive color consistently across different levels of lighting

27. Selective Attention • Process of selecting one sensory channel and ignoring or minimizing others • Cocktail party effect • Inattentional blindness (Simons & Chabris, 1999, 2010)

28. Perceptual Organization • Gestalt: an organized whole • Psychological perspective: emphasized our tendency to integrate pieces of information into meaningful wholes Our brain does more than register information about the world

29. Figure-Ground

30. Proximity O O O O O O O

31. Similarity X O X O X O X O X O X O X O X O

32. Continuity or Connectedness

33. Closure

34. Depth Perception • Depth: the distance from a surface • Use of depth extends beyond our body as we interact with the world • Driving - when to brake • Walking across the parking lot - how loudly do greet friend

35. Visual cliff: experimental apparatus that gives an illusion of a sudden drop-off between one horizontal surface and another (Gibson & Walk, 1960) Depth Perception 35

36. Texture Gradient

37. Relative Size

38. Interposition/Occlusion

39. Linear Perspective

40. Aerial Perspective

41. Location in the Picture Plane

42. Binocular Cues (2) • Binocular Convergence • Item perceived as closer when our eyes are pulled toward our nose • Item perceived as farther away when our eyes relax more toward our ears • Binocular Disparity • Huge discrepancy between L and R eye as object appears closer • Less discrepancy between eyes as object appears farther away

43. Ames Room • Perceived distance (based on the cues of the environment) influences the apparent size of the children • Size and distance are interdependent