Sensation and Perception

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• Sensation and Perception
• All is not as it appears!!

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Sensation and Perception

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

• Perception
• Organizing the stimulus input and giving it
  meaning

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Sensation and Perception

• Stages of sensation and perception
• Stimuli activate sensory receptors
• Sensory receptors translate information into
  nerve impulses
• Specialized neurons analyze stimuli features
• Stimulus pieces are reconstructed and compared to
  stimuli in memory
• Perception is then consciously experienced

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Psychophysics Studies of Sensitivity to Stimuli

• Absolute limits of sensitivity
• Dimmest light in which we can see objects
• Softest sound we can hear

• Recognizing differences between stimuli
• Smallest difference in brightness detectable
• Recognizing differences between tones

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Stimulus Detection

• The Absolute Threshold
• The lowest intensity at which a stimulus can be
  detected 50 of the time

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Signal Detection Theory

• Decision criterion A personal standard of
  certainty before a person will say that they
  detect a stimulus
• Affected by
• Conservativeness or boldness
• Increasing rewards for hits or costs for misses

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Subliminal Perception

• A subliminal stimulus cannot be perceived
  consciously but do register in the nervous system
• subliminal perception

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Subliminal Perception Research Results

• Stimuli above threshold influence behavior much
  more than subliminal stimuli
• Subliminal stimuli have stronger effects on
  attitudes
• Effects may be due to placebo effects

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The Difference Threshold

• The difference threshold (just noticeable
  difference or JND) is the smallest difference
  between two stimuli that people can perceive 50
  of the time
• Webers 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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Sensory Adaptation (Habituation)

• Sensory neurons respond to a constant stimulus by
  decreasing their activity

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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 receptors
  synapse
• The greater the change in release, the stronger
  the signal passed into the optic nerve

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The Sensory Systems Vision

• Dark Adaptation
• Photopigment molecules are regenerated,
  increasing receptor sensitivity
• Cones reach maximum sensitivity in 5 minutes
  rods take 1/2 hour

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The Sensory Systems Vision

• Opponent Process Theory (Hering, 1870)
• Three cone types respond to two different
  wavelengths
• Red/Green
• Blue/Yellow
• Black/White

• Young-Helmholtz trichromatic theory
• Individual cones are most sensitive to
  wavelengths corresponding to
• Blue
• Green
• Red

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The Sensory Systems Vision

• Dual-Process Theory
• Trichromatic theory confirmed
• Opponent processes occur in the ganglion cells of
  the retina rather than the cones

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The Sensory SystemsColor Blindness

• Dichromat
• Blind in Red - Green or Yellow - Blue systems or
  both

• Monochromat
• Sensitive only to the Black - White system

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The Sensory Systems Audition

• Characteristics of sound waves
• Frequency the number of sound waves, or cycles,
  per second (measured in Hz)
• Amplitude the vertical size of the sound waves
  (measured in dB)

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The Sensory Systems Auditory Transduction

• 1. Sound waves strike eardrum, setting cochlear
  fluid into motion
• 2. Fluid waves vibrate the basilar membrane,
  bending the hair cells in the organ of Corti
• 3. Neurotransmitters are released into the
  synapse, resulting in a nerve impulse

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Audition Theories of Pitch

• Frequency Theory
• Nerve impulses sent to the brain match the
  frequency of the sound wave

• Place Theory
• There is a specific point in the cochlea where
  the fluid wave peaks and most strongly bends the
  hair cells

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The Sensory Systems Audition

• Sound localization
• Sounds arrive first at the ear closest to the
  sound
• Judgments of sound intensity also affect
  localization

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The Sensory Systems Audition

• Types of Deafness
• Conduction
• Caused by problems transmitting sound waves to
  cochlea
• Nerve deafness
• Caused by damaged receptors in inner ear or
  damaged auditory nerve

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The Sensory Systems Gustation

• A taste results from complex patterns of neural
  activity produced by the four types of taste
  receptors

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The Sensory Systems Olfaction

• Humans have about 40 million olfactory receptors.

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The Sensory Systems Olfaction

• Menstrual Synchrony
• The 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 was not found in cohabiting lesbian
  couples (Weller Weller, 1997, 1998)

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The Sensory Systems The Tactile Sensations

• Humans are sensitive to
• Pressure (touch)
• Pain
• Warmth
• Cold

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The Sensory Systems The Body Senses

• Kinesthesis
• Provides us with feedback about our muscles and
  joints positions and movements

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Perception The Creation of Experience

• Bottom-up processing
• Taking individual elements of a stimulus and
  combining them into a perception
• Top-down processing
• Using existing knowledge in perception

• Attention
• Focusing on certain stimuli
• Filtering out other information

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Perception The Creation of Experience

• Stimulus factors in attention
• !!!Intensity!!!
• Novelty
• Movement
• Contrast
• Repetition Repetition

• Personal factors in attention
• Motives
• Interests

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Gestalt Principles of Perceptual Organization
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Gestalt Principles of Perceptual Organization
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Gestalt Principles of Perceptual Organization

• Figure-Ground Relations

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Perception The Creation of Experience

• 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 Allow us to recognize
  familiar stimuli under varying conditions

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Depth Perception

• Monocular cues
• Light and shadow
• Linear perspective
• Interposition
• Height in the horizontal plane
• Texture
• Clarity
• Relative size
• Motion parallax

• Binocular cues
• Binocular disparity
• Convergence

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Perception The Creation of Experience

• Illusions are false perceptions

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Understanding Pain

• Endorphins Natural opiates inhibit the release
  of neurotransmitters involved in pain perception
• Stress-induced analgesia A reduction in
  perceived pain that occurs under stressful
  conditions
• Adaptive for functioning so that a person can
  deal with the stressful stimulus

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Psychology and Pain

• Can psychology help people
• suffering from pain?
• http//www.crha-health.ab.ca/clin/adultpsy/feature
  s/chronic.htm