What is stressful for a given individual?

1. Stress and Disease Dr. Donald B. Giddon Harvard University, Fall 2013Perception and Psychophysics

2. What is stressful for a given individual? Objective vs. Subjective Stressors Stimulus/object R1 Stimulus/subjective PERCEPTION Rx

3. Key Concepts • Sensation vs. Perception • Perception - • the key intervening variable between psychosocial stressors and coping methods • Psychophysics – • relating subjective to objective measures

4. PRINCIPLES OF PERCEPTION Dr. Anderson Gestalt Principles of Perceptual Organization Illustrated Through the Use of Illusions • Ambiguity - Figure /Ground, Old/Young Lady, Necker Cube • Completion – Kanzisa triangles • Context/framing –Ponzo illusion (railroad tracks/vertical lines), Muller Lyer (“wings” at ends of lines) • Camouflage - Hidden groups of bird, Dalmations • Distortion - Size constancy • Facial illusions - Inverted face (Thatcher/Clinton/Gore)

5. Ambiguity

6. Ambiguity

7. Ambiguity or Bistable percept

8. Ambiguity or Bistable percept

9. Completion/Closure

10. Closure Completion

13. The angle affects the strength of the illusion

14. Context/Framing

15. Camouflage

16. Detail from left side of scrotum

20. Sensation The process by which our sense organs respond to and translate stimuli into nerve impulses sent to the brain

21. Perception Organizing the stimulus input and giving it meaning

22. Translation of sensation into perception • Stimuli activate sensory receptors • Sensory receptors translate information into nerve impulses (transduction) • Specialized (2nd and 3rd order) neurons integrate stimuli features • Stimulus pieces are reconstructed and compared to stimuli in memory • Perception is then the conscious experience of an organized and meaningful message

23. The Perception of Letters --see whiteboard

24. The Sensory Systems: Vision • Lens: • Becomes thinner to focus on distant objects and thicker to focus on closer ones • Rods: Black and white receptors • Cones: Color receptors

25. The Sensory Systems: Vision • Transduction • Absorption of light by photopigments produces a chemical reaction changing the rate of neurotransmitter release at the synapses

26. Light • Wavelength • Frequency • Intensity • Color • Hue • Brightness

27. Brain Visual Pathways

28. The Sensory Systems: Audition • Characteristics of sound waves • Frequency/Pitch: the number of sound waves, or cycles, per second (measured in Hz) • Amplitude/Loudness : the magnitude of the sound waves (measured in dB)

29. Decibel Scaling of Common Sounds iPods 85-100

30. Examples of Relation of Physical Energy to Perception • Sound • Wavelength • Frequency • Volume/Decibels • Tone • Timbre

31. Subliminal Perception: Research Results • Stimuli above threshold influence behavior much more than subliminal stimuli • Subliminal stimuli may influence attitudes with or without changing behavior • Effects may be due to • Anticipation and/or • Expectations

32. Importance of Audition in Interpersonal Communication * Communication facilitation and interference - Clinicians’ masks -Distortion of context - “Masking” of affect and - Relation to facial expression - Burqa effect - Patient compliance - Cooperation - Adherence to treatment - Health literacy - Relation to Psychopathology

33. The Sensory Systems: Olfaction More important in animals (drug dogs, bloodhounds) evolutionary significance • Menstrual Synchrony • Tendency of women who live together or are close friends to become similar in their menstrual cycles • May be due to pheromones (Preti et al., 1986), but synchrony not found in cohabiting lesbian couples (Weller & Weller, 1997, 1998) • Recall vs. Recognition • Cannot conjure up or recall smells/taste; only recognize

34. The Sensory Systems • Skin Sensations • Humans are sensitive to: • Pressure (touch) • Tactile • Pain • Temperature • Warm • Cold • Body Senses • Kinesthesis – movement • Proprioception • Provides us with feedback about the position of our muscles and joints

35. Psychophysics: Relation of Objective to Subjective World • The Absolute Threshold (R. Limen): The lowest magnitude at which a stimulus can be detected • Dimmest light in which we can see objects • Softest sound we can hear • Lowest chemical concentration detected • Gustation • Olfaction

36. The Difference Threshold (D.Limen) • The difference threshold (just noticeable difference or JND) is the smallest difference between two stimuli. • Point of subjective equivalence • Weber’s Law: the JND is directly proportional to the magnitude of the stimulus with which the comparison is made (e.g 1/50 for weight)

37. Weber/Fechner Fractions for Sensory/Perceptual Systems • Vision (brightness) 1/60 • Vision (hue) varies • Audition (pitch) 1/333 • Audition (loudness) 1/20 • Tactile 1/7 • Pain (heat) 1/30 • Taste (salt) 1/3 • Smell (India Rubber) ¼ • Changes in facial dimensions • Recognize diastema (space between teeth) • Recognize angulation (slant of mouth) • Each sensory system has a Power Function relating physical • to subjective world.

38. Difference threshold (D. Limen) • How much objective change in the stimulus before it can be subjectively detected • Smallest difference in brightness or hue detectable • Recognizing differences between tones or intensity • Differences in concentration • Differences in angular proportional measures related to body image • Esthetics • Orthodontics • Plastic surgery

39. Sensory Adaptation (Habituation) • Activation of sensory neurons decreases in response to a constant stimulus

40. Other applications • Relation to word choice • e.g., “acceptable” • Psychodiagnostics • e.g. Rorschach (see next two slides)

44. Signal Detection Theory Decision criterion: A personal standard of certainty before indicating that one detects the presence, absence or change of a stimulus • Willingness to respond • Affected by: • Conservativeness or boldness • Increasing rewards for hits or costs for misses e.g. response bias • Correction by standard scores

45. The Role of Perception in Life Experiences • Perceptual schemata: Allow us to classify sensory input in a top-down fashion • Perceptual set: A readiness to perceive stimuli in a particular way • Perceptual constancies: E.g., stereotype response set/rigidity. Allow us to recognize familiar stimuli under varying conditions • Perceptual defense • Need determines perception, e.g. Rorschach • Hunger • Sex

46. Practical Applications of Perceptual Tenets Cosmetic Surgery Fashion Architecture/Interior Design Eyewitness Identification “Mis”perceptions about life events importance of losing a tennis game - line calls -- “Quality of life” (education, housing, recreation, health care, employment, security, food)