Sensation and Perception

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Sensation and Perception

• Unit 3
• Chapter 4

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Basic Concepts

• sensation- stimulation of sense organs
• converted into neural impulses
• perception- selection, organization, and
  interpretation of sensory input
• meaningful experiences
• psychophysics- study of how physical stimuli are
  translated into psychological experiences

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Thresholds Looking for Limits

• thresholds- dividing point between energy levels
  that do and do not have a detectable effect
• absolute threshold minimum stimulus intensity
  detected
• just noticeable difference smallest difference
  in stimulus intensity that a specific sense can
  detect

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Examples of Absolute Thresholds
Sense Absolute Threshold
Vision A candle flame seen at 30 miles on a dark clear night
Hearing The tick of a watch under quiet conditions at 20 feet
Taste One teaspoon of sugar in two gallons of water
Smell One drop of perfume diffused into entire volume of a six room apartment
Touch The wing of a fly falling on your cheek from a distance of 1 centimeter
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Signal Detection Theory

• proposes that detection of stimuli involves
  decision processes as well as sensory processes,
  both influenced by variety of factors besides
  stimulus intensity
• expectations
• level of noise

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Perception Without Awareness

• subliminal perception- registration of sensory
  input without conscious awareness
• below threshold
• money, sex,
• religion

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Sensory Adaptation

• gradual decline in sensitivity to prolonged
  stimulation
• continued exposure adaptation to stimulus
• automatic process that keeps people tuned into
  changes rather than constants in their sensory
  input

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Our Sense of Sight The Visual System

• Unit 3

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The Stimulus Light

• light- form of electromagnetic radiation that
  travels as a wave
• Varies in both amplitude and wavelength
• Amplitude affects perception of brightness
• Wavelength affects perception of color

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The Eye A Living Optical Instrument

• cornea- provides 2/3 of eyes total power
• lens- focuses light rays on the retina
• retina- absorbs light, processes images, sends
  visual info to brain
• pupil- permits light to pass into eye

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Visual Receptors Rods and Cones

• CONES
• 5-6.4 million cones
• daylight vision and color vision
• visual acuity- sharpness and precise detail

• RODS
• 100-125 million rods
• night vision and peripheral vision
• sensitive to dim light

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Visual Deficiencies

• Nearsightedness
• close objects seen clearly but distant objects
  appear blurry
• light falls short of retina
• eyeball is too long

• Farsightedness
• distant objects seen clearly but close objects
  appear blurry
• light falls behind retina
• eyeball is too short

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Visual Adaptation

• Dark Adaptation
• process by which the eyes become more sensitive
  to light in low illumination
• Complete in 30 minutes

• Light Adaptation
• process whereby eyes become less sensitive to
  light in high illumination
• Improves visual acuity

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Viewing the World in Color

• trichromatic theory- human eye has three types of
  receptors with differing sensitivities to
  different light wavelengths
• red, green and blue
• color mixing allows for all colors
• afterimage- visual image that persists after a
  stimulus is removed
• color will be complement of original color

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Perceiving Forms, Patterns, and Objects

• Unit 3

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Perceptions are Subjective

• same visual input can result in radically
  different perceptions
• perceptual set- readiness to perceive a stimulus
  is a particular way
• inattentional blindness- involves failure to see
  visible objects or events because attention is
  focused elsewhere

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Looking at the Whole Picture Gestalt Principles

• Figure and Ground
• figure is thing being looked at, while ground is
  background against which it stands
• figures appear closer, stand out and have more
  substance

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Gestalt Principles

• Proximity
• things that are near one another seem to belong
  together

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Gestalt Principles

• Closure
• group elements to create completeness
• fill in gaps

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Gestalt Principles

• Similarity
• tendency to group stimuli that are similar
• same characteristics

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Gestalt Principles

• Simplicity
• Tendency to group elements that combine to form a
  good figure
• Organize forms in simplest way possible

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Gestalt Principles

• Continuity
• follows in direction led
• connect points that result in straight or gently
  curved lines that create smooth paths

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Perceiving Depth of Distance

• depth perception- interpretation of visual cues
  that indicate how near or far away objects are

• Binocular Cues
• clues about distance based on differing views of
  the two eyes
• retinal disparity- images projected to different
  locations on right and left retinas
• convergence- sensing the eyes converging toward
  each other as they focus on closer objects

• Monocular Cues
• clues about distance based on the image in either
  eye alone
• motion parallax- images projected at different
  distances moving across retina at different rates
• pictorial depth cues-
• clues about distance
• given in a flat picture

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Phi Phenomenon

• illusion of movement created by presenting visual
  stimuli in rapid succession
• our perceptions fill in the gaps to perceive
  motion

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Stroboscopic Photography
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Our Sense of Hearing The Auditory System
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The Stimulus Sound

• sound waves are vibrations of molecules that
  travel through physical medium
• wavelength described in terms of frequency
• cycles per second, hertz (Hz)
• amplitude described in terms of loudness
• measured in decibels (dB)

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Sensory Processing in the Ear

• external ear
• vibration of air molecules
• middle ear
• vibration of movable bones
• inner ear
• waves in a fluid

https//www.youtube.com/watch?vflIAxGsV1q0
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The human ear

• pinna- sound collecting bone
• hammer, anvil, stirrup- amplify tiny changes in
  air pressure
• cochlea- contains receptors for hearing

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Our Chemical Senses Taste and Smell

• https//www.youtube.com/watch?vEJud8MKrvBE

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Taste The Gustatory System

• Chemical substances that are soluble
• Receptors are clusters of taste cells on taste
  buds
• short life of 10 days
• perception depend on patterns from receptors
• Four primary tastes
• sweet, sour, salty, bitter

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Smell The Olfactory System

• chemical substances-volatile ones that evaporate
  and spread throughout the air
• dissolved in fluid, mucus in the nose
• olfactory cilia- hairlike structures in upper
  portion of nasal passages
• short life (30-60 days)
• Sensory adaptation 4 minutes

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Our Sense of Touch

• conversion of physical sensation into a
  psychological experience
• mechanical, thermal and chemical energy
• pressure of touch in warmth, cold and pain

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Puzzles in Pain Perception

• Pain Pathways
• Fast- registers localized pain and relays it to
  cortex in fraction of a second
• Slow- conveys longer lasting, aching or burning
  pain that comes after initial injury

• Gate Control Theory
• Incoming pain sensations must pass through gate
  in spinal cord that can be closed, blocking
  ascending pain signals
• Cognitive and emotional processes block pain
  signals

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Our Other Systems

• Kinesthetic
• monitors positions of various body parts
• receptors located in joints and muscles

• Vestibular
• responds to gravity and keeps you informed about
  you bodys location in space
• provides the sense of balance and equilibrium
• receptors located within semicircular canals of
  ear