INTRODUCTION TO

PSYCHOLOGY
PSYCH01X
Sensation
and
Perception
LESSON 4

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Learning Objectives
• Define sensation and perception.
• Explain how we sense and perceive the world.
• Define transduction.
• Discuss the different gestalt principles.
• Discuss the different factors that influence perception.
How eyes see and how eyes see colors
Factors that influence perception
 Sensation and the central nervous system

Sensation
• It is the activation of receptors in the various sense organs.
• It is the physiological arousal of a sense organ by a stimulus
• Stimuli are energy patterns which are registered by the senses.
Any object that elicits or accelerates a physiological or psychological
activity or response.
• Sensory receptors - specialized forms of neurons.
• It is a sensory nerve ending that responds to a stimulus in the internal or
external environment of an organism.
• a cell or group of cells that receives stimuli : SENSE ORGAN
Sense organs:
•eyes
•ears
•nose
•skin
•taste buds
Characteristic of Sensation: Specificity
of Sensory Stimulation

• Each sense organ is stimulated by a specific form of

physical energy.
Ex: The eye is stimulated by electromagnetic energy
called light waves; The ear by soundwaves and the skin
senses of touch and pain by pressure.
How sensation works:
• The sense organ detect this energy then transform it into
a code that can be transmitted to the brain.
• First step in “sensing” is the work of the receptors which
respond to certain forms of energy.
Ex: The retina of the eye is sensitive to light and special
cells in the ear are sensitive to the vibrations that make
up sound
• The physical energy is transformed into electrical
impulses; the information carried by these electrical
impulses travels through the nerve fibers that connect
the sense organs with the central nervous system.
• Information about the external world then travels to the
appropriate area of the cerebral cortex.
 Transduction:
• The process by which information is
transmitted to the brain is same for all
senses.
• Ex: Eye respond to light waves and
the ear to sound waves. Light and
sound are foreign language to the
brain, Thus, the sensation to be
useful, the energy whatever its form,
must be changed by the sense organ
into a form that the brain can
understand. This conversion process
is called transduction.
Transduction as the
transmission Process
to the Brain
• Conversion takes place at
the receptor cells, which
receive energy produced by
the stimulus and convert it
into the electrochemical
energy, the brain’s
language.
Sensation and the central nervous system
Perceptions:
• Is the brain’s process of organizing and interpreting sensory
information to give it meaning.
• The process of interpreting sensations and events as influenced by
set and prior experience-making them meaningful.
• The retinas in our eyes record a fast moving-silver object in the sky,
but they do not “see” a passenger jet, our eardrum vibrates in a
particular way, but it does not “hear” a Beethoven symphony.
• Organizing and interpreting what is sensed, that is “seeing” and
“hearing” meaningful patterns in sensory information is perception.
Sensation and the central nervous system
• Sensation and perception are inseparable. When
the brain receives sensory information through
afferent nerves, it automatically interprets the
information.
• Sensation and perception then is called a unified
information-processing system.
Sensory Thresholds
• How far away does a brewing coffeepot have to be for
you to detect the smell of coffee?
• How much of a stimulus is necessary for you to see,
hear, taste, smell or feel something?
• Thresholds: is the approximate point at which a stimulus
becomes strong enough to produce a response in an
individual.
 Sensation and the central nervous system

Sensory Thresholds
• Just noticeable difference (jnd or the difference threshold) - the
smallest difference between two stimuli that is detectable 50
percent of the time. (ex: candle light, volume of music)
• Absolute threshold - the smallest amount of energy needed for a
person to consciously detect a stimulus 50 percent of the time it
is present. Or minimum amount of energy that we can detect.
Determining the absolute
Thresholds:
• When a stimulus has less energy than absolute thresholds, we
cannot detect its presence, more energy, we can.
• Ex: wristwatch that ticks (20ft at 50 percent of the time; 25 ft at
38 percent of the time)
• People have different thresholds because people have better
hearing than others and some have better vision than others.
 LO 3.1 Sensation and the central nervous system

Subliminal Sensation
• Subliminal stimuli - stimuli that are below the level of
conscious awareness.
• Just strong enough to activate the sensory receptors but not strong
enough for people to be consciously aware of them.
• Limin - “threshold”
• Sublimin - “below the threshold.”
• Subliminal perception – process by why subliminal stimuli act
upon the unconscious mind, influencing behavior.
 How sensations can be ignored

Habituation and Sensory Adaptation

• Habituation or stimulus boredom- tendency of the brain to

stop attending to constant, unchanging information. (ex:
unpleasant stimuli- rotting garbage/superb taste of gourmet)
• Sensory adaptation - tendency of sensory receptor cells to
become less responsive/less sensitive to a stimulus that is
unchanging.
How eyes see and how eyes see colors

Menu
Sense of touch and experiencing pain
 Perception and perceptual constancies

Perception and Constancies

• Perception - the method by which the sensations experienced at
any given moment are interpreted and organized in some
meaningful fashion.
• Size constancy - the tendency to interpret an object as always
being the same actual size, regardless of its distance.
• Shape constancy - the tendency to interpret the shape of an
object as being constant, even when its shape changes on the
retina.
• Brightness constancy – the tendency to perceive the apparent
brightness of an object as the same even when the light
conditions change.
Perception and perceptual constancies
 Perception and perceptual constancies
Shape constancy
 Gestalt principles of perception

Gestalt Principles
• Figure–ground - the tendency to perceive objects, or
figures, as existing on a background.
• Reversible figures - visual illusions in which the figure
and ground can be reversed.
Gestalt principles of perception

Menu
 Gestalt principles of perception

Do you see
an old lady
or a young
lady?
Do you see a rabbit or a duck?
 Gestalt principles of perception

Gestalt Principles
• Similarity - the tendency to perceive things that look
similar to each other as being part of the same group.
• Proximity - the tendency to perceive objects that are close
to each other as part of the same grouping.
• Closure - the tendency to complete figures that are
incomplete.
• Continuity - the tendency to perceive things as simply as
possible with a continuous pattern rather than with a
complex, broken-up pattern.
• Contiguity - the tendency to perceive two things that
happen close together in time as being related.
Gestalt principles
of perception
 Perceiving the world in three dimensions

Depth Perception
• Depth perception - the ability to perceive the
world in three dimensions.
• Studies of depth perception
• Visual cliff experiment
Perceiving the world in three dimensions

Menu
 Perceiving the world in three dimensions
Pictorial depth cues
 Perceiving the world in three dimensions

Linear Perspective
 LO 3.16 Visual illusions

Perceptual Illusions
• Müller-Lyer illusion - illusion of line length that is distorted by inward-
turning or outward-turning corners on the ends of the lines, causing
lines of equal length to appear to be different.
• Moon illusion – the moon on the horizon appears to be larger than the
moon in the sky.
• Apparent distance hypothesis
• Illusions of Motion:
• 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.
Visual illusions
Visual illusions
 Visual illusions
Ame’s room illusion
 Factors that influence perception

Factors that Influence Perception

• Perceptual set (perceptual expectancy) - the tendency to
perceive things a certain way because previous experiences
or expectations influence those perceptions.
• Top-down processing - the use of preexisting knowledge to
organize individual features into a unified whole.
• Bottom-up processing - the analysis of the smaller features to
build up to a complete perception.
Factors that influence perception
 Factors that influence perception

Applying Psychology
• Extrasensory Perception (ESP) - claim of
perception that occurs without the use of
normal sensory channels such as sight,
hearing, touch, taste, or smell.
• Telepathy - claimed ability to read another person’s thoughts, or
mind reading.
• Clairvoyance - supposed ability to “see” things that are not
actually present.
• Precognition - supposed ability to know something in advance
of its occurrence or to predict a future event.
• Parapsychology - the study of ESP, ghosts,
and other subjects that do not normally fall
into the realm of ordinary psychology.
INTRODUCTION TO
PSYCHOLOGY
PSYCH01X