Stress and Disease

Dr. Donald B. Giddon Harvard University, Fall 2013

Perception and Psychophysics

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What is stressful for a given individual?

Objective vs. Subjective Stressors

Stimulus/object

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Stimulus/subjectiveStimulus/subjectivePERCEPTIONPERCEPTION

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Key Concepts

• Sensation vs. Perception

• Perception - – the key intervening variable between psychosocial

stressors and coping methods

• Psychophysics –– relating subjective to objective measures

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Gestalt Principles of Perceptual Organization Illustrated Through the Use of Illusions

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1. Ambiguity - Figure /Ground, Old/Young Lady, Necker Cube

2. Completion – Kanzisa triangles

3. Context/framing –Ponzo illusion (railroad tracks/vertical lines), Muller Lyer (“wings” at ends of lines)

4. Camouflage - Hidden groups of bird, Dalmations

5. Distortion - Size constancy

6. Facial illusions - Inverted face (Thatcher/Clinton/Gore)

PRINCIPLES OF PERCEPTIONPRINCIPLES OF PERCEPTION

Dr. AndersonDr. Anderson

AmbiguityAmbiguity

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AmbiguityAmbiguity

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Ambiguity orAmbiguity orBistable perceptBistable percept

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Ambiguity orAmbiguity orBistable perceptBistable percept

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Completion/Closure

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Closure Completion

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The angle affects the strength of the illusion The angle affects the strength of the illusion

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Context/Framing

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Camouflage

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Detail from left side of scrotumDetail from left side of scrotum

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Sensation

The process by which our sense organs respond to and translate stimuli into

nerve impulses sent to the brain

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Perception

Organizing the stimulus input and giving it meaning

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• Translation of sensation into perceptiono Stimuli activate sensory receptorso Sensory receptors translate information into nerve

impulses (transduction)o Specialized (2nd and 3rd order) neurons integrate

stimuli featureso Stimulus pieces are reconstructed and compared

to stimuli in memoryo Perception is then the conscious experience of an

organized and meaningful message

The Perception of Letters

--see whiteboard

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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

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The Sensory Systems: Vision

Transduction

– Absorption of light by photopigments produces a chemical reaction changing the rate of neurotransmitter release at the synapses

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•Light

oWavelength

o Frequencyo Intensity

o Color

o Hue

o Brightness

Brain Visual PathwaysBrain Visual Pathways27

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)

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Decibel Scaling of Common Sounds

iPods 85-100iPods 85-100

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Examples of Relation of Physical Energy to Perception

• SoundoWavelengthoFrequencyoVolume/DecibelsoToneoTimbre

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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 tooAnticipation and/oro Expectations

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Importance of Audition in Interpersonal CommunicationImportance of Audition in Interpersonal Communication

* Communication facilitation and interference * Communication facilitation and interference

- Clinicians’ masks- Clinicians’ masks-Distortion of context-Distortion of context

- “Masking” of affect and- “Masking” of affect and- Relation to facial expression- Relation to facial expression- Burqa effect- Burqa effect

- Patient compliance- Patient compliance- Cooperation- Cooperation- Adherence to treatment- Adherence to treatment- Health literacy- Health literacy

- Relation to Psychopathology- Relation to Psychopathology

The Sensory Systems: Olfaction

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

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More important in animals (drug dogs, bloodhounds) evolutionary significance

The Sensory Systems

• Skin Sensationso Humans are sensitive to:

o Pressure (touch)o Tactileo Paino Temperature

WarmCold

• Body Senseso Kinesthesis – movement

o ProprioceptionProvides us with feedback about the position of our

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Psychophysics: Relation of Objective to Subjective World

• The Absolute Threshold (R. Limen):

The lowest magnitude at which a stimulus can be detected

o Dimmest light in which we can see objectso Softest sound we can hearo Lowest chemical concentration detected

Gustation Olfaction

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)

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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

o Recognize diastema (space between teeth)o Recognize angulation (slant of mouth)

Each sensory system has a Power Function relating physical to subjective world.

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•Difference threshold (D. Limen) How much objective change in the stimulus before it can be subjectively detected

oSmallest difference in brightness or hue detectableoRecognizing differences between tones or intensityoDifferences in concentrationoDifferences in angular proportional measures related to body image

Esthetics Orthodontics Plastic surgery

Sensory Adaptation (Habituation)

• Activation of sensory neurons decreases in response to a constant stimulus

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•Other applications

o Relation to word choicee.g., “acceptable”

oPsychodiagnosticso e.g. Rorschach (see next two slides)

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Signal Detection Theory

Decision criterion: A personal standard of certainty before indicating that one detects the presence, absence or change of a stimuluso Willingness to respondo Affected by:

Conservativeness or boldnessIncreasing rewards for hits or costs for misses

e.g. response bias Correction by standard scores

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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

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Practical Applications of Perceptual TenetsPractical Applications of Perceptual Tenets

• Cosmetic SurgeryCosmetic Surgery• FashionFashion• Architecture/Interior DesignArchitecture/Interior Design• Eyewitness IdentificationEyewitness Identification• “ “Mis”perceptions about life eventsMis”perceptions about life events

– importance of losing a tennis gameimportance of losing a tennis game

- line calls - line calls

-- -- ““Quality of life” (education, housing, recreation, health Quality of life” (education, housing, recreation, health care, employment, security, food)care, employment, security, food)

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