Chapter 3: Sensation, Perception and Conscious Experience
Sensation: theprocess of receiving sensorydata from the environment and
translating it to the brain.
Perception: The sorting out, interpretation, analysis, and integration of
stimuli by the sense organs and brain.
Stimuli: Energy that produces a response in a sense organ.
Psychophysics:thestudy ofthe relationship between the physical aspects of
stimuli and our psychological experience ofthem.
Receptorcell:a specialized cell that responds to a particular type ofenergy.
Absolute threshold:theleast amount ofenergy that can be detected as a
stimulation50percentof the time; the smallest intensity ofa stimulus that
must be present for the stimulus to be detected.
Noise: background stimulation that interferes with the perception ofother
The approximate absolute thresholds under ideal circumstances are as
Hearing The tick of a watch from 6 meters (20 feet).
Vision A candleflameseen from 50 km (30miles) on a clear,dark night.
Taste 1 gram (.0356 ounce) oftable salt in 500 liters (529 quarts) of
Smell One drop of perfume diffused throughout a three-room
Touch The wing of a bee falling on thecheek from a height of1 cm (0.39
Differencethresholdor just-noticeabledifference(jnd): thesmallest change
in stimulation that can be detected 50percentofthe time; the smallest level
of added or reduced stimulation required to sense that a change in
stimulation has occurred.
Weber’s law: the principle that the jnd for any given sense is a constant
fraction or proportion of the stimulation being judged.
Adaptation: anadjustmentofthe senses tothelevelofstimulation they are
A cross section of the human
eye. Light enters the eye
through the cornea, passes
through the pupil, and is
focused by the lens onto the
The retina. A view ofthe retina through
an ophthalmoscope, an instrument used
to inspect blood vessels in the eye. The
small dark spot is the fovea. The yellow
circle marks the blind spot, where the
optic nerve leaves the eye.
o Cornea –the transparentprotective coating over the
front part ofthe eye
o Pupil –a smallopening inthe iris through which light
enters the eye.
o Iris –the colored partofthe eyethat regulates thesize
o Lens –the transparent partoftheeyebehind the pupil
that focuses light onto the retina.
o Retina –thelining ofthe eye containing receptor cells
that are sensitive to light.
o Fovea –the area oftheretina that is the center ofthe
o Rods –receptor cells in theretina responsiblefor night
vision and perception ofbrightness.
o Cones – receptor cells in the retina responsible for
Rods and Cones. As you can
see, the rods and cones are
named for their shape.
The basic cells oftheeye. Light enteringthe eye travels through the ganglion
and bipolarcells andstrikes the light-sensitive rods and cones located at the
back ofthe eye. The rods andcones thentransmit nerve impulses to the brain
via the bipolar and ganglion cells.
o Bipolar cells –neurons that have only one axon and
one dendrite; inthe eye, these neurons connect the
receptors on the retina to the ganglion cells.
o Visual acuity –the ability to distinguish fine details
o Dark adaptation –increased sensitivity ofrods and
cones in darkness.
o Light adaptation –decreased sensitivity ofrods and
cones in bright light.
o Afterimage –sensory experience that occurs after a
visual stimulus has been removed.
o Ganglion –neurons that connect the bipolar cells in
the eyes to the brain.
o Optic nerve –the bundle ofaxons ofganglion cells that
carries neural messages from each eye to the brain.
o Blind spot–the placeon theretina wheretheaxons of
all the ganglioncells leavetheeye andwherethereare
o Optic chiasm – the point near the base ofthe brain
where some fibers in the optic nerve from each eye
cross to the other side ofthe brain.
o Feature detectors –specialized brain cells that only
respond toparticular elements in the visual field such
as movement or lines ofspecific orientation.
o Additive colormixing –the process ofmixing lights of
different wavelengths to create new hues.
o Trichromatic theory –the theory ofcolor vision that
holds that all color perception derives from three
different color receptors in the retina (usually red,
green, and blue receptors).
o Color blindness –partial ortotal inability to perceive
o Opponent-process theory–theory ofcolor vision that
holds that three sets ofcolor receptors (yellow-blue,
red-green, black-white) respond to determine the
color you experience.
Stare at the dot
on this flag for
about a minute
and then look at
a piece of plain
What do you
people see an
afterimage that converts the colors in the figure into the traditional red,
white, and blue U.S. flag.
The electromagnetic spectrum. The eye is sensitive to only a very small
segment ofthe spectrum, known as visible light.
COMMON PROBLEMS OF VISION
Condition Description Treatment
objects ata distance
Corrective lenses or
Difficulty seeing close
or highly detailed
Corrective lenses or
Astigmatism Blurred vision due to
irregularities in the
shape ofthelens or
Corrective lenses or
Cataract A thin cloudy covering
develops on the
Surgery to removethe
Glaucoma Build up ofpressure
lead to blindness
Diet and/or medication
Macular degeneration Degenerationofretinal
cells, usually in and
Retinitis pigmentosa Hereditary disorder
the retina; eventually
o Sound: a psychologicalexperiencecreated by the brain
in responseto changes in air pressure that arereceived
by the auditory system.
o Eardrum: thepart oftheearthat vibrates whensound
waves hit it.
o Sound waves: changes in pressure caused when
molecules ofair or fluidcollide with one another and
then move apart again.
o Frequency: thenumber ofcycles per second ina wave;
in sound, the primary determinant ofpitch.
o Pitch: auditoryexperience corresponding primarily to
frequency ofsound vibrations,resulting in a higher or
o Amplitude: the magnitude of a wave; in sound, the
primary determinant ofloudness.
Sound waves. As the tuning fork vibrates, it alternately compresses and
expands the molecules of air, creating a sound wave.
o Timbre: the quality or texture of sound; caused by
o Oval window: membraneacross theopening between
the middleearandinnerear thatconducts vibrations
to the cochlea.
o Cochlea: part ofthe inner earcontaining fluidthat can
vibrate,whichin turn causes thebasilar membrane to
o Basilar membrane: membrane in the cochlea ofthe
inner earthat responds tovibrations; itcontains sense
receptors for sound.
o Organ ofCorti: structureon thesurface ofthe basilar
membrane that contains thereceptor cells for hearing.
o Auditory nerve: the bundleofaxons thatcarries signals
from each ear to the brain.
Prolonged exposure to sounds above 85 decibels can cause permanent
damage to ears, as can even brief exposure to sounds near the pain
How we hear?
1. Sound waves enter the outer ear and travel to the eardrum,
causing it to vibrate.
2. The vibrating eardrum causes the bones of the middle ear (the
hammer, anvil, and stirrup) to strike each other, amplifying and
carryingthe vibrations to the oval window and on to the fluid in
the coiled cochlea ofthe inner ear.
3. Now, the moving fluid sets the basilar membrane, inside the
4. The organ of Corti, on top ofthe basilar membrane, moves too.
Inside the organ of Corti, thousands of tiny receptor cells are
topped by a bundle ofhair-like fibers. As the basilar membrane
vibrates, the fibers bend, stimulating the receptor cells to send a
signal through the afferentnerve endings, which join to form the
5. The auditory nerve carries impulses to the brain.
6. When the nerve impulses reach the temporal lobe, they are
interpreted as sounds.
At the top of each hair cell is a bundle offibers. Ifthe fibers bend as much as
100 trillionths of a meter, the receptor cells transmit a sensory message to
o SMELL (olfaction)
The human olfactory system. The sense of smell is triggered when odor
molecules inthe air reach the olfactory receptors located inside the top ofthe
nose. Inhalingandexhalingodor molecules fromfood does muchto give food
its flavorful “taste.”
1. As we breathe, molecules from theflowerreach thereceptor cells
high in each nasal cavity.
2. The axons fromthese millions ofreceptors carry nerve impulses
to the olfactory bulb.
3. The olfactory bulb transmits these impulses to thetemporallobes
of the brain where they are experienced as smell.
o Olfactory bulb: the small center in the brain.
o Pheromones: chemicals thatcommunicateinformation
to other organisms through smell.
o TASTE (gustatory)
Taste buds: structures on the tongue that
contain the receptor cells for taste.
1. Different areas on the tongue are slightly more sensitive to
2. When we eat, chemicals in the food dissolve in saliva and come
into contact withthe taste cells (receptors) within the taste buds.
3. Now, adjacent neurons fire,sending nerve impulses to the brain’s
parietal lobe, where the messages are perceived as taste.
There are 10,000taste
buds on the tongue
and other parts ofthe
mouth. Taste buds
wear out and are
replaced every ten
o SKIN SENSES - the senses of touch, pressure,
temperature, and pain.
o Gate-controltheory ofpain: thetheory that particular
nerve receptors inthespinal cord lead tospecific areas
of the brain related to pain.
Perception: thebrain’s interpretationofsensory information so as to give it
Gestalt laws of organization: a series ofprinciples that describe how we
organize bits and pieces ofinformation into meaningful wholes.
An illusory triangle.Whensensory informationis
incomplete, we tend tocreate a complete
perceptionby supplying the missingdetails. In this
figure we will fillinthe lines thatlet us perceive a
white triangle in the center ofthe pattern.
Perceiving a pattern. Knowing beforehand
that the block blotches in this figure
represent a person riding a horse changes
our perception ofit.
An optical illusion. In the case of the
trident we go beyondwhat is sensed (black
lines on flat white paper) to perceive a
three-dimensional object that isn’t really
see a vase or the
silhouettes ofa man
and a woman? Both
possible, but not at
the same time.
like this work
because it is unclearwhichpart ofthe stimulus is the figure and which is the
neutral ground against which the figure is perceived.
Although at first it is difficult to distinguish
anything in this drawing, keep looking, and
eventually you’ll probably be able to see the
figure ofa dog. The dogrepresents a gestalt,
or perceptual whole, which is something
greater than the sum of the individual
Gestalt principles ofperceptual organizations
1. Proximity –Whenobjects are close to one another, we tend to
perceive them together rather than separately.
2. Similarity–Objects that areofa similar color, size, or shape are
usually perceived as part ofa pattern.
3. Closure –we areinclined tooverlook incompleteness in sensory
information and to perceive a whole object even where none
4. Continuity –items thatcontinuea pattern ordirection tend to be
grouped together as part ofthe pattern.
PERCEPTUAL CONSTANCY: a tendency to perceive objects as
stableand unchanging despite changes in sensory stimulation.
o Shape constancy: the tendency to see an object the
same shape no matter what angle it is viewed from.
Shape constancy. Even though
the image of the door on the
retina changes greatly as the
door opens, we stillperceive the
door as being rectangular.
o Size constancy: the
perception of an object as the same size
regardless ofthe distance from which it is
DEPTH PERCEPTION: The ability to view the world in three
dimensions and to perceive distance.
o Monocularcues: visual cues requiring the use ofone
o Binocular cues: visual cues requiring the use ofboth
monocular distance cuein which oneobject,
by partly blocking a second object, is
perceived as being closer.
Because the king of clubs appears to have
been interposed on the king of spades, we
perceive it to be closer to us.
Because of the higher
elevation and the suggestion
of depth provided by the
road, the tree on the right is
perceived as being more
distant and about the same
size as the tree at lower left.
Actually, it is appreciably
smaller, as you cansee ifyou
measure the heights of the two drawings.
Railroad tracks that seem to join together in
the distance are an example of linear
o Perspective: monoculardistanceand depth cues that
involve the convergence of lines, the haziness of
images, and the relative elevation objects.
o Texture gradient: monocular cueto distanceanddepth
based on the fact that objects seen at greater
distances appear to be smoother and less textured.
monocular cue to distance and
depth based on the fact that
shadows often appear ontheparts
ofobjects that are more distant.
VISUAL ILLUSIONS: physical stimuli that consistently produce
errors in perception.
1. Do you think it is possibleto havesensationwithout perception?
Is it possibleto haveperception withoutsensation? Explain why.
2. Describe the basic mechanisms involved in vision, hearing, and
the other major senses.
Feldman, R. S. (2010). Understanding Psychology. 9th
Edition. McGraw Hill Companies,
Morris, C.G.,et al. (2007). Psychology Concepts and Applications. Pearson Education, Inc.
Mrs. Maria Angela L. Diopol