Sensation and Perception

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Sensation and Perception

• By Sarah Fredericks
• Period 1

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What are sensation and perception?

• Sensation- relationship between physical
  stimulation and its psychological effects
• Perception- how we recognize, interpret, and
  organize our sensations

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Thresholds

• Detection- the act of sensing a stimulus
• Absolute threshold- the level of stimulation that
  is right on our perceptual borderline. We cannot
  detect lower levels of stimuli, but we can detect
  higher levels.
• Just Noticeable Difference-the minimum amount of
  distance between two stimuli that can be detected
  as distinct
• Measuring detection thresholds- signal detection
  theory- the signal (stimulus) is either present
  or it is not
• Webers Law- the observation that JND is a
  proportion of stimulus intensity. The greater the
  magnitude of the stimulus the larger the
  differences must be to be noticed.

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Receptor Process

• Receptor cells- designed to detect specific types
  of energy
• Receptive field- the area from which our receptor
  cells receive input
• Transduction- takes place at the level of the
  receptor cells, and then the neural message is
  passed to the nervous system
• Contralateral shift- level of the thalamus. Most
  of the sensory input from one side of the body
  travels to the opposite side of the brain
• No matter what the form of input at the level of
  receptor, it must be converted, transduced

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Sensory Mechanisms

• Sensory coding- the process by which receptors
  convey such a range of information to the brain
• Wavelengths of light and frequency of sound are
  hue and pitch
• Amplitude brightness for light and loudness of
  sound
• Single cell recording- technique by which the
  firing rate and pattern of a single receptor cell
  can be measured in response to varying sensory
  input
• Visual sensation- occurs when the eye receives
  light input from the outside world
• Distal stimulus- the object as it exits in the
  environment
• Proximal stimulus- the image of that object on
  the retina. Is inverted so the brain can
  interpret the image

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Ear
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How the ear functions

• Auditory input- in the form of sound waves enters
  the ear by passing the outer ear and into the ear
  canal
• Outer ear collects and magnifies sound waves
• Vibration enters the tympanic membrane, hit the
  ossicles, and vibrates them
• Last of the three ossicles, stapes, vibrate
  against the oval window (beginning of the inner
  ear)
• Further vibrate the cochlea, which contain
  receptor cells located structures, basilar
  membrane and organ of corti
• Inner ear- responsible for balance and has
  vestibular sacs-receptors sensitive to tilting

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Sensory Adaptation

• Detect changes in stimuli intensity and quality
• Adaptation- unconscious, temporary change in
  response to environmental stimuli
• Habituation- process by which we become
  accustomed to a stimulus, and notice it less and
  less over time
• Dishabituation- occurs when a change in the
  stimulus, even a small change, causes us to
  notice it again

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Attention

• Attention- processing through cognition of a
  select portion of the massive amount of
  information incoming from the senses and
  contained in memory
• Selective attention- attend to one thing while
  ignoring another
• Divided attention- trying to focus n more than
  one task at a time, is most difficult when
  attending to two or more stimuli that activate
  the same sense. Declines with age

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Eye
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How the eye functions

• Light passes through the cornea (protective
  layer)
• Under the cornea, Lens (bends in order to focus
  an image of the outside world on the retina).
  This focusing- accommodation
• Retina at the back of the eye and is covered
  with receptor cells, rods and cones
• Rods- sensitive in low light
• Cones- bright light and color vision
• Cones clustered in the fovea- greatest visual
  acuity
• Information travels to the visual association
  areas for processing
• Young Helmholtz theory- the cones in the retina
  are activated by light waves associated with
  blue, red, and green.
• Opponent process theory- black/white,
  blue/yellow, red/green operates in theses color
  sets. If one color is activated the other isnt

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Perception

• Perceptual processes- how our mind interprets
  these stimuli
• Bottom-up processing- achieves recognition of an
  object by breaking it down into its component
  parts
• Top-down processing- relies on prior experience
  with an object
• Theory of constructive perception- states that we
  create perceptual constructs out of their pieces
  or elements with the involvement of higher
  cognitive functions. If we are missing part of
  something we are still able to figure out the
  whole
• Direct perception- takes the view that our
  sensations and sensory context are all we need
  for perception. Prior knowledge or learning is
  not necessary.
• Depth perception- perceive depth, size, shape,
  and motion. Is facilitated by various perceptual
  cues
• - Monocular depth cues- are those that we need
  only one eye to see
• - Binocular depth cues- rely on both eyes viewing
  an image

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Continued

• Relative size- refers to the fact that images
  that are farther from us project a smaller image
  on the retina than do those that are closer to
  us.
• Texture gradient- textures, or patterns of
  distribution of objects, appear to grow more
  dense as distance increases
• Interposition- which occurs when a near object
  partially blocks the view of an object behind it
• Linear perspective- a monocular cue based on the
  perception that parallel lines seem to draw a
  closer together as the lines recede in to the
  distance
• Vanishing point- as your looking at two rails and
  they are moving away from you they draw closer
  together
• Aerial perspective- another perceptual cue, which
  is based on the observation that atmospheric
  moisture and dust tend to obscure objects in the
  distance more than they do nearby objects. Things
  look more distant than they actually are

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Finally

• Gestalt approach- top-down theory. Most
  perceptual stimuli can be broken down into
  figure-ground relationships.
• Proximity- the tendency to see objects near to
  each other as forming groups
• Similarity- the tendency to prefer to group like
  objects together
• Symmetry- the tendency to perceive preferentially
  forms that make up mirror images
• Continuity- the tendency to perceive
  preferentially fluid or continuous forms, rather
  than jagged or irregular ones
• Closure- the tendency preferentially to close up
  object that are not complete
• Law of Pragnanz- minimum tendency, meaning that
  we tend to see objects in their simplest forms
• Features- different orientations
• Feature detectors- neurons that respond to
  specific features