Sensation and Perception
Chapter 4
The Basics
• Sensation – Involves the stimulation of
sensory receptors and the transmission of
sensory information to the central nervous
system
» i.e. spinal cord and brain
• Things that tip off sensory receptors:
• Light, sound, smells, etc.
The Basics
• Perception – How we interpret sensory
stimulation
• Football field example
– Perception reflects learning, expectations and
attitudes
Absolute Threshold
• The weakest amount of a stimulus that
can be tested
• Dogs v. Humans
– Thresholds are different amongst people
– More sensitive than others
Some established absolute thresholds are:
vision: a candle flame 30 miles away on a clear night.
hearing: a watch ticking 20 feet away
taste: 1 teaspoon of sugar dissoved in 2 gallons of water
smell: a single drop of perfume in a three-room house
touch: a bee's wing falling a distance of 1 centimeter onto the cheek.
Difference Threshold
• The minimum amount of difference
detected between two stimuli
• Tone
• Hue
• Piles of sand
Signal-Detection Theory
• Distinguishing sensory stimuli that takes
into account all factors of self and
environment
• We focus on what we consider important
Sensory Adaptation
• Process by which we become more
sensitive to weak stimuli and less sensitive
to unchanging stimuli
– Eyes adapting to darkness
– Waves on a beach
– Traffic
Section 2 - Vision
• Color spectrum – Roy G. Biv
The Eye
• Similar to a camera
• Light enters the eyes, and then is
projected onto a surface
– The amount of light that enters is determined
by the opening in the colored part of the eye
» The pupil
The Eye
• Once light enters, it meets the lens
– The lens adjusts to distances of objects by
changing its thickness
» Finger test – near / far
The Eye
• The changes in thickness and light project
a clear image onto the retina
– The retina acts like the film of a camera
– Neurons in your retina that are sensitive to
light are called photoreceptors
– Once the photoreceptors are activated a
nerve carries the information to the brain –
occipital lobe
The Blind Spot
• We need the blind spot to see
• A point left empty of photoreceptors –
room for information to travel
– Circle test
Rods and Cones
• 2 kinds of photoreceptors
– Rods – sensitive only to the brightness of light
– Cones – provide color
Dark and Light Adaptation
• Your ability to see in low light improves for
45 minutes
• Sundown
• Adaptation to light happens much more
quickly
Visual Acuity
• Vision tests for sharpness
– 20/20
• As you age your lenses become brittle,
and you may become farsighted
• Holding reading material further away
Color Vision
• Human beings can see up to 1 million
different hues
• Animals are more sensitive to certain colors
• The color circle
• Afterimages
• Color blind – distinguishing colors from
each other
• Total color blindness is extremely rare
Section 3
• Hearing – a series of vibrations in the form
of sound waves in its own unique pitch or
loudness
– Hearing experiment
Pitch
• The more cycles (sound waves) per
second, the higher the pitch (high or low)
– Women’s voices are at a higher pitch than
men’s because their vocal cords tend to be
shorter
– Humans – 20 to 20,000 per second
– Dogs / Dolphins / other animals in excess of
20,000
Loudness
• Measured in dB (decibels)
– Loudness is determined by the height /
amplitude of sound waves
» 0 decibels is the threshold (a watch heard ticking at
20 feet away)
Locating Sound
• Perception of sound
• Infinite possibilities
– How your body / senses react to sound
Deafness
• Inherited / Disease / Injury / Old Age
• Conductive Deafness –
– Damage to middle ear, sound is not amplified
• Helped with hearing aides
• Sensorineural Deafness
– Damage or elimination of neurons, damage to
auditory nerve
• Cannot be helped if nerve itself is damaged
• Cochlear implants can help neuron loss
Section 4
• Other Senses –
– Smell – incredibly important, apples and
onions would be relatively the same otherwise
– Taste – Spheres of the tongue
• Smell and taste work together when eating
Skin Senses
• Touch
• Infants grow quickly and stay healthier if
touched
– Older people do better if they have pets (cats
/ dogs)
• Body is covered in hairs, many too small
to see
– Sensory receptors lie at the base of the hair
• Do we actually “touch”?
Temperature
• Differences are all relative
– Fevers
– Outside heat (Summer)
– Swimming pools
– A/C
Pain
• The more pain receptors are located in a
certain body, they more we will feel
• Point of contact > Spine > Thalamus >
Brain (processing)
– Prostaglandins help transmit messages
» Ibuprofen and aspirin help slow prostaglandins
Pain
• Why does rubbing or scratching painful
areas help?
• Mixed signals
• Phantom limb pain
Body Senses
• Vestibular Sense
– Sensory organs in your ears monitor your
motion and relation to gravity
– Balance, standing, changing speeds, etc.
• Kinesthesis
– Position and motion of your body
– Copying body motions
Section 5
• Perception – the way our body makes
sense of our sensory impressions
• Gestalt psychology – “The whole is more
than the sum of its parts”
Rules of Perceptual Organization
• Closure – filling in the gaps to get a
complete picture
– Fig 4.11 (p. 93)
» Filling in the blanks because dogs are familiar to you
Rules of Perceptual Organization
• Figure-Ground Perception
– What do we perceive as the figure and what
do we perceive as the background
» Fig 4.12 (Vases or Faces)
Rules of Perceptual Organization
• Other Rules – Laws of:
•
•
•
•
Proximity
Similarity
Continuity
Common Fate
Rules of Perceptual Organization
• Perception of Movement
– To sense movement we need a change of
position
– Your senses need clues to tell you that you
are moving
– Trees, road bumps, etc.
Rules of Perceptual Organization
• Stroboscopic Motion
– The illusion of movement
• Flipbooks
• Movies on reels
– Subliminal messages
– Perception smoothes out the gaps
– Humans prefer smooth images
Rules of Perceptual Organization
• Depth Perception
– The “distance away”
– Monocular clues – the appearance of 3-D on
2-D surfaces
– i.e. paintings
» Clearness, shadow, texture, overlapping, perspective
– This is done through stimulation of retina
Monocular Cues
• Clearness – faraway objects seem less detailed
• Perspective – parallel lines coming together or moving
apart
• Overlapping – placing of one object in front of another
• Shadows and highlights – give a 3-D feel
• Texture Gradient – closer objects have more texture
(gradient – progressive change)
• Motion parallax – the tendency of objects to seemingly
move forward or backward depending on distance away
• Moon, stars v. trees and rocks while driving
Binocular Cues
• Need both eyes v. one eye for monocular
– 2 cues in binocular:
• Retinal Disparity
• Convergence
Binocular Cues
• Retinal Disparity – only works on objects
that are very close
– Difference of angles of an object as seen by
both retinas
• Convergence – associated with a
tightness of the eye muscles on things up
close
– Magic Eye puzzles
Perceptual Constancies
• Size Constancy – Comes through
experience
– Perceiving an object as one size no matter
the distance
– Pygmy example p. 98
Perceptual Constancies
• Color Constancy
– The tendency for objects to maintain color no
matter the light quality
• Brightness Constancy
– Tendency to find an object equally bright even
when its surroundings change
Perceptual Constancies
• Shape Constancy
– The knowledge an item has one shape
» i.e. top of a glass from different angles
Visual Illusions
• When the rules of constancies are violated