Sensation and Perception
Sensation and perception are not the same thing!
§ The human brain is predisposed to find recognizable
§ Our sensory and perceptual processes work together to
help us sort out what we are experiencing
a process by which our sensory receptors and nervous
system receive and represent physical stimulus energy
§ a process of organizing and interpreting sensory
information, enabling us to recognize meaningful objects and events
is transformed into neural impulses, sent to the brain, then interpreted
receptors - specialized neurons.
§ Top-Down Processing
§ information processing guided by higher-level mental processes
§ when we construct perceptions by drawing on our
experience and expectations
§ Often imposes a meaning that does not exist in the
physical stimulus (not veridical)
§ Bottom-Up Processing
§ analysis that begins with the sense receptors and works up to
the brains integration of sensory information
§ reflects physical stimuli veridically
Sensation - Thresholds
threshold - The minimum amount of energy our senses can consciously detect 50%
of the time.
flame at 30 miles
watch at 20 feet
Taste 1 tsp
sugar in 1 gal water
Smell 1 drop
perfume through 3 rooms
Touch bee wing
falling on face at 1 cm
§ Difference Threshold
§ Also called just noticeable difference or JND
§ the smallest difference between two stimuli that is
detectable 50 percent of the time
§ Smallest detectable difference between two stimuli
§ Webers Law
§ Governs the JND stimuli must differ by a constant
proportion in order to be detected
light intensity- 8%
tone frequency- 0.3%
Energy that is below
absolute threshold (below conscious awareness)
no awareness of the
effect or persuasion on behavior
adaptation - tendency
of sensory receptors to fatigue and stop responding to an unchanging
why dont objects just disappear when we stare at them?
Visual saccades tiny eye movements that
change the visual scene just enough to prevent adaptation
Advantage of adaptation?
Allows us to focus on informative changes
Lesson? Our perceptions are not always veridical, but
they are (often) useful.
§ Habituation - tendency of the brain to stop
noticing constant, unchanging information.
§ Example your clothing, fan noise, perfume!
study of the relationship between physical characteristics
of stimuli and our psychological experience of them
X-rays? Radio waves? Infrared light?
The visible spectrum
We see very little!
Bees see UV
light, but not red
Dogs do not see
red, but they do see some colors
§ amount of energy in a wave determined by its amplitude
(height of the wave)
Brightness for light waves
Loudness for sound waves
The Psychology of Color Vision
The human eye can
see 7,000,000 colors
appropriate use of color can maximize productivity, minimize
visual fatigue, relax the whole body
Yellow is the
most fatiguing color because bright colors reflect more light, resulting in
excessive stimulation of the eyes
such as blues and browns, are more soothing to the eye because it has to do
Color Perception Simplified
light) shines on the apple.
surface absorbs all light wavelengths except for those corresponding to
red; those are reflected to the human eye.
The eye receives
the reflected wavelengths and sends a red color message to the brain.
Anatomy of the Human Eye
that admits light
Iris - round
muscle (colored part) surrounding the pupil
Conracts to change pupil size, letting in more or less light
clear membrane that covers the surface of the eye
80% of eyes
accommodation to supply the other 20%
accommodation - the process by which
the eyes lens changes shape to help focus near or far objects on the retina
through the pupil and is focused by the cornea and lens onto the retina at the
back of the eye
consists of three layers of cells
1. Photoreceptor layer
2. Bipolar cell layer
3. Ganglion cell layer
the light-sensitive surface at the back of the eye
photoreceptors transduce the light stimulus into neural impulses
receptors on the back of the retina; they account for nearly 3/4 of all human
photoreceptors responsible for noncolor and
sensitivity in dim light
Cones - photoreceptors responsible for color
vision and acuity (sharpness)
additional layers of neurons that refine the neural processing of visual
Bundle of ganglion cell axons that carries neural impulses from the retina to
the visual cortex in the brain
The Blind Spot
Spot on the
retina where the axons of the retinal cells exit the eye to form the optic
insensitive to light (no rods or cones)
a small object that falls on the blind spot is
What you see in
your blind spot is an image created by your own brain, not an accurate reflection
of the environment. Think about what
Functions of Color Vision
organization organizing the visual world into separate entities
functions (contrived, red for danger)
survival, natural selection
importance for foraging individuals
importance of color vision
Dr. Nordby (monochromat from birth)
Mr. I (monochromat in adulthood)
What might be the
underlying causes for each?
Reasons that the
pattern of activity in 3 different retinal color receptors (cones) yields
normal color perception
red green blue
Opponent Process Theory
primary colors arranged in pairs:
When one is
activated, the other is inhibited
Lateral geniculate nucleus (LGN) of thalamus
when red is on, green is off
Color Deficient Vision
Monochrome colorblindess -
either have no cones, cones that are not working, or damage to color-processing
blue-yellow color deficiency - either
the red or the green OR ELSE the blue cones are not working. Why not yellow?
Visual Processing in the Cortex
§ Feature Detectors
§ nerve cells in the cortex that respond to specific features
of what you see
§ (think of a clock face)
What happens to
color under different types of illumination? (bright
light vs. shadow)
Receptor sensitivity to higher intensity wavelengths
In sunlight, all wavelengths are approximately equal
Red wavelengths are more intense in light bulbs
Demonstrate by adapting one eye to lamplight
Background - color constancy works only when the entire visual scene is
familiar objects as having consistent color, even if changing illumination
alters the wavelengths reflected by the object
simultaneous processing of several aspects of a stimulus
The Binding Problem
representations (e.g., color, shape, motion) are physically separated in the
responses from different areas indicate whole-ness
and mental codes!
Some support from
Sound & Audition!
Psychological Properties of Sound
interpreted as frequency or pitch (high, medium, or low).
interpreted as volume (how soft or loud a sound is).
(aka complexity) interpreted as timbre (a richness in the tone of the
hertz (Hz) - cycles or waves per second, a measurement of
Anatomy of the Ear
Pinna (outer ear)
tympanic membrane (eardrum)
canal - short tunnel that runs from the pinna to the
eardrum (tympanic membrane).
- thin section of skin that tightly covers the opening into the middle ear
sound waves hit the eardrum and vibrate three tiny bones in
the middle ear (ossicles)
§ chamber between eardrum and cochlea containing three tiny
bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum
onto the cochleas oval window
§ innermost part of the ear, containing the cochlea, semicircular
canals, and vestibular sacs
§ Cochlea - snail-shaped structure of the inner ear that
is filled with fluid.
long, thin membrane in the cochlea that moves up and down in response to
sound vibrations; resting place for the organ of Corti
Organ of Corti rests in the basilar membrane; contains receptor
(hair) cells for sense of hearing.
Auditory nerve -
bundle of axons from the hair cells in the inner ear; receives neural message
from the organ of Corti.
Types of Hearing Impairments
hearing impairment - can
result from either:
damaged eardrum (prevents sound waves from being carried into
the middle ear properly), or
damage to the bones of the middle ear (prevents sounds from
being conducted from the eardrum to the cochlea).
impairment can result from either:
damage in the inner ear (hair cells), or
damage in the auditory pathways and/or cortical areas of the
Surgery to Help Restore Hearing
Implant - a microphone implanted
behind the ear picks up sound from the environment.
Speech processor selects and arranges the sound
Implant receives the sound and converts it into
electrical impulses sent to the cochlea
electrical impulses are
converted to neural impulses and sent to the brain, as usual.
taste receptor cells in mouth; responsible for sense of taste
Olfactory bulbs -
areas of the brain just above the sinus cavity and just below the frontal lobes
that receive information from the olfactory receptors
least 1,000 olfactory receptors.
individual receptors are equally sensitive
only takes 1 odor molecule to cause transduction in
an olfactory receptor.
humans can differentiate around 10,000 odors
Somesthetic senses - the body senses consisting of:
1. Skin senses - the sensations of touch,
pressure, temperature, and pain.
in the skin
endings, networks within the skin that respond to intense pressure, heat,
acids, and capsaicin (the active ingredient in hot peppers)
Pain serves a
functional role for survival
pain receptors are at great risk
Pain is a
motivational force that can activate behavior
Pain involves an
emotional component that can increase or decrease pain perception
sensory & cognitive factors
theory that the spinal cord contains a neurological gate
that blocks pain signals or allows them to continue to the brain
§ gate opens by activity in
small nerve fibers
§ gate closes by activity in
Large fibers are
activated by rubbing AND by pleasant thoughts, SO
mom was right!
2. Kinesthetic sense - sense of the location
of individual body parts in relation to the ground and each other.
Proprioceptive receptors (proprioceptors)
3. Vestibular senses - whole body sensations
of motion, balance, position arising from fluid motion in middle ear
sensory conflict theory - says motion sickness happens when
information from the eyes conflicts with vestibular information, resulting in
dizziness, nausea, etc.
Top- down process
(individualized by experience)
how your brain makes sense of the world, which includes
hiding from you certain changes in stimuli so that the stimuli continue to
appear constant to you
Size constancy -
the tendency to interpret a familiar object as always being the same actual
size, regardless of its distance from the eyes (retinal size)
the tendency to interpret the shape of a familiar object
as being constant, even when its actual shape changes on the retina.
the tendency to perceive the apparent brightness
of an object as the same even when the light conditions change
Figureground - the tendency to perceive objects (figures) as
standing out from their surroundings (ground). Reversible figures -
visual illusions in which the figure and ground can be reversed.
Gestalt Grouping Principles
§ proximity-group nearby figures together
§ similarity-group figures that are similar
§ continuity-perceive patterns as continuous
§ connectedness-spots, lines, and areas are seen as a single, connected
§ closure-fills in the gaps; the tendency to complete figures that
§ Contiguity - the tendency to perceive two things that
happen close together in time as being related (e.g., thunder and
Perception of Depth
Images on the
retina are 2-D
How do we
perceive 3-D (depth)?
CUE approach we
learn the connection between cues and depth through experience, yielding 3-D
(pictorial depth cues) cues for perceiving depth based on one eye only.
Accommodation - as a monocular clue, the brains use of information
about the changing thickness of the lens of the eye in response to looking at
objects that are close or far away.
perspective the tendency for parallel lines to appear to converge as distance
increases. (Items closer to convergence are perceived as being farther away.)
Relative size - when objects a person expects to be of
a certain size appear to be smaller, they are interpreted to be farther away.
Interposition (overlap) - assumption that an object
appearing to block part of another object is in front of the second object and
closer to the viewer.
Relative clarity - the haziness that surrounds objects
that are farther away causes the distance to be perceived as greater.
Texture Gradient - tendency for
textured surfaces to appear to become finer (smoother) as distance from the
Motion parallax - perception of objects in motion
where close objects appear to move faster than far objects.
Binocular cues - cues for perceiving depth based on both eyes.
1. retinal disparity
images from the two
closer the object, the
larger the disparity
two eyes move inward
(converge) more as objects get nearer
Mόller-Lyer illusion - illusion of line length where
inward-turning or outward-turning corners on the ends of the lines cause two
equal lines to appear to be different in length.
the horizon moon
appears larger than the zenith moon, but visual angles on the retina are
autokinetic effect - a
small, stationary light in a darkened room will appear to move or drift because
there are no surrounding cues to indicate that the light is not moving.
stroboscopic motion - seen in motion pictures, in which a rapid series of
still pictures will appear to be in motion.
phi phenomenon lights turned on in a sequence appear to move.
Factors that Influence Perception
processing - the use of preexisting knowledge to organize individual features
into a unified whole.
Perceptual set (perceptual expectancy) - the tendency
to perceive things a certain way because previous experiences or expectations
influence those perceptions.
Set- tendency to perceive things in a particular way because of previous