Sensation and Perception

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Sensation and Perception

• Chapter 4

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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.

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Ambiguous Figure

• Colored surface can be either the outside front
  surface or the inside back surface
• Cannot simultaneously be both
• Brain can interpret the ambiguous cues two
  different ways

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The Riddle of Separate Sensations

• Sense receptors
• Specialized cells that convert physical energy in
  the environment or the body to electrical energy
  that can be transmitted as nerve impulses to the
  brain.

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Sensation Perception Processes
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Sensory Overload

• Overstimulation of the senses.
• Lets play an observation game!
• Can use selective attention to reduce sensory
  overload.
• Selective attention
• The focusing of attention on selected aspects of
  the environment and the blocking out of others.
• Inattentional blindness

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Measuring Senses

• Absolute threshold
• Difference threshold
• Signal-detection theory

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Absolute Threshold

• The smallest quantity of physical energy that can
  be reliably detected by an observer.

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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

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Pledge of Allegiance

• I pledge allegiance

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• to the flag

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• of the United States of America

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• and to the republic

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• for which it stands

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• one nation under God

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• indivisible

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• with liberty

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• and justice for all

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JND

• Each slide of the Pledge of Allegiance increased
  the font size.
• Did you notice?

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Stimulus Discrimination

• Just Noticeable Difference (JND)
• The smallest amount of change in a stimulus that
  can be detected half the time.

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Webers Law

• JND is proportional to the magnitude of the
  stimulus
• The larger the stimulus the larger the change
  must be to be noticed!!

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Webers Law

• For a difference to be perceptible, 2 stimuli
  must differ by a constant proportion, not amount

• Light 8
• Weight 2
• Tone .3

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Backmasking!!

• Secret messages hidden in musical lyrics?
• Lets find out!!
• Jeffmilner.com

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Signal-Detection Theory

• A psychophysical theory that divides the
  detection of a sensory signal into a sensory
  process and a decision process. (expectations,
  experience, anticipation)

Stimulus is Present Stimulus is Absent
Response Present Hit False Alarm
Response Absent Miss Correct Rejection
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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.
• Deprivation
• The absence of normal levels of sensory
  stimulation.