Sensation and Perception

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Sensation and Perception

• 19th October 2007
• tomesova_at_ftvs.cuni.cz

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Information-processing system

• Sensation stimulation of receptors - registered
  in the brain
• Perception brain interprets sensations

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Differences in sensory and perceptual capabilities

• Among species (dog x mens range of hearing)
• Among individuals (taste preferences)
• Why?
• Variations in how sensory systems are structured
• Higher order processes

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Processing information

• bottom-up, or data driven processing
• top-down, or conceptually driven processing

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Stimulus

• The quality of a stimulus (color, musical pitch)
• The quantity of a stimulus (brightness, loudness)

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Stimulus detection

• Sensory threshold
• Distracting factors
• Background noise
• Spontaneous activities of sensory cells
• Motivation (costs)
• Expectations

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Stimulus discrimination

• Weber - Fechners law
• the amount by which a stimulus must be increased
  to produce a just noticeable difference tends to
  be a constant proportion of the initial stimulus
  intensity

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Sensory adaptation

• Reduced ability to provide information after
  prolonged, constant stimulation
• Why?
• Sensitivity to CHANGES

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Perceiving a complex world

• Direct perspective all the information comes
  from the outer world
• Constructivist perspective we must supplement it
  with additional information stored in memory
• schemas

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Expectations and perceptions

• Perceptual set
• Expectations based
• on schemas

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Basic perceptual processes

• Form perception
• Perceptual constancy
• Depth perception

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Form perception

• Gestalt psychologists (Max Wertheimer, Kurt
  Koffka, Wolfgang Kohler)
• Subjective contours
• Rules or principles of perceptual grouping
• Overestimation of bottom-up processing

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Figure and groundBottom-up and top-down
processing
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Depth perception

• Binocular disparity
• Monocular depth cues
• Motion parallax
• Relative size
• Relative closeness to horizon
• Linear perspective
• Texture gradient
• Partial overlap
• Light and shadow

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Disorders of perception

• Sensory distortions
• changes in quality, intensity, spatial form of
  perception (toxic state, depression, migraine)
• Sensory deceptions
• Illusions
• Hallucinations

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Hallucinations

• Perceptions which arise in the absence of any
  external stimulus (false perception)
• unwilled - not subject to conscious manipulations
• same qualities as a real perception
• perceived as being located in the external world
• auditory, visual, olfactory, gustatory
• hypnogogic (visual or auditory)
• palinopsia (reappearance - Parkinsons)
• of bodily sensations (temperature, touch, fluid)

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Illusions

• involuntary false perception consequent on a real
  object in which a transformation of the object
  takes place
• distortions of real objects
• extreme tiredness and emotions
• completion (banished by attention)
• affective (fear)
• pareidolic (shapes in clouds)