Sensation and Perception Chapter 3

Sensation • Sensation - the activation of receptors in

the various sense organs.

• Sensory receptors - specialized forms of neurons.

• Sense organs:

• Eyes – Visual Sensation

• Ears – Auditory Sensation

• Nose- Olfactory Sensation

• Skin – Tactile Sensation

• Taste buds (tongue) – Gustatory Sensation

So where do vision and

hearing (& the other senses)

happen? • The Brain! • The physical energy in

the environment is

detected by the eyes,

ears, etc. but we can‘t

see, hear, etc. until the

brain interprets them—

i.e., makes sense of

them. So in a way, we

see, hear, smell, etc. in

our brains!

Transduction • Transforming

signals into neural

impulses.

• Information goes

from the senses to

the thalamus , then

to the various areas

in the brain.

Remember Ethan in Sky High. He changes his body to slime. Solid form to liquid form. Change from one form of energy to another.

Transduction is transforming physical

energy into neural impulses

Sensory Thresholds • Just noticeable difference or the difference threshold) - the smallest difference between two stimuli that is detectable 50 percent of the time.

Sensory Thresholds • Absolute threshold - the smallest

amount of energy needed for a person to consciously detect a stimulus 50 percent of the time it is present.

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.

Perception of Minimal Stimuli

• Subliminal Perception

• The concept of subliminal perception is

well known to the general public.

• Subliminal perception is the idea that a stimulus

can influence behavior even when it is so weak

or brief that we do not perceive it consciously.

• There is concern that subliminal perception can

powerfully manipulate human behavior.

Perception of Minimal Stimuli • What does ―subliminal‖ mean?

• When the term ―subliminal‖ is used, it

refers to the quality of being ―below the

(sensory) threshold.‖

• Scientists use it to indicate that the

stimulus was not consciously detected in a

given presentation.

• Because the only way to know if a stimulus

has been detected is to ask, it is very

difficult to interpret the results of research

on subliminal stimuli.

Perception of Minimal Stimuli • What subliminal perception cannot

do

• Claims that subliminal stimuli in

advertisements can make people buy

things are unsupportable.

• This claim has been tested repeatedly

and no evidence has been found.

• Advertisements in American culture

have little need of subliminal stimuli.

They are overtly and effectively

manipulative.

Perception of Minimal Stimuli • What subliminal perception cannot do

• Messages in music (recorded backwards

or superimposed) cannot make people do

anything, evil or otherwise.

• This claim has also been repeatedly tested

under controlled conditions.

• No one listening to the messages can discern

these messages.

• No one‘s behavior has been changed after

listening to music containing messages.

Perception of Minimal Stimuli • What subliminal perception cannot do

• Subliminal audiotapes just don‘t work

• Claims that addictions can be overcome, self-

esteem can be improved, and general self-

improvement can be achieved through the use

of subliminal audiotapes are also unsupported.

• Any results achieved through the use of these

tapes can be attributed to the placebo effect or

to the individual user‘s motivation to improve.

Perception of Minimal Stimuli • What subliminal perception can do

• Some subtle effects on subsequent

perception and emotion have been

supported

• ―Priming‖ individuals to see an object in

subsequent presentations has been achieved

through repeated presentations (Bar &

Biederman, 1998)

• Emotional states can be influenced by

subliminal presentation of messages that may

be perceived as emotionally loaded (Masling et

al., 1991)

Perception of Minimal Stimuli

• Subliminal perception

• The fact that subliminal perception can

influence behavior at all is interesting.

• But the effects overall are much smaller

than people hope or fear.

Habituation and Sensory

Adaptation • Habituation - tendency of the brain

to stop attending to constant,

unchanging information.

• Sensory adaptation - tendency of

sensory receptor cells to become

less responsive to a stimulus that is

unchanging.

Somesthetic Senses • Somesthetic senses - the body senses

consisting of the skin senses, the kinesthetic sense, and the vestibular senses. • ―Soma‖ – body

• ―Esthetic‖ - feeling

1. Skin senses - the sensations of touch, pressure, temperature, and pain. • Sensory receptors in the skin

• Gate-control theory - pain signals must pass through a ―gate‖ located in the spinal cord.

Somesthetic Senses

2. Kinesthetic sense - sense of the location

of body parts in relation to the ground

and each other.

• Proprioceptive receptors (proprioceptors)

3. Vestibular senses - the sensations of

movement, balance, and body position.

Tells us where our body is oriented in

space.

Vestibular Sense

• Tells us where our

body is oriented in

space.

• Our sense of

balance.

• Located in our

semicircular canals

in our ears.

Kinesthetic Sense

• Tells us where our body parts are.

• Receptors located in our muscles and joints.

Perception and Constancies • Perception - the method by which

the sensations experienced at any given moment are interpreted and organized in some meaningful fashion.

• Mental interpretation of sensation results in perception

Perception and Constancies

PERCEPTION = SENSATION + MEANINGFUL INTERPRETATION

Ex: Smell we experience due to the burning of an object is sensation and understanding that the burning object is rubber is PERCEPTION

Sensation and Perception

Sensation: your window to the world

Perception: interpreting what comes

in your window.

Perception and Constancies • 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.

Shape constancy

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.

Do you see

an old lady

or a young

lady?

Do you see a

rabbit or a

duck?

The white and black stripes on

these zebras can be reversed –

both can serve as either figure or

ground.

Some Laws of Perceptual Organization

Gestalt Principles

• Closure - the tendency to complete figures that are incomplete.

Ex : While proof reading missing

letters escape from our attention & our minds fill up the gap !

Laws of Perceptual Organization

Gestalt Principles • Continuity - the tendency to

perceive things as simply as possible with a continuous pattern rather than with a complex, broken-up pattern.( Organization of perception appears to be going infinitely in the same direction)

Ex : Cinema scenes though not individually, when they run in a sequence at the rate of 15 frames per second, they appear to be one and continuous

Laws of Perceptual Organization

Gestalt Principles • Pragnanz – Pragnanz means compact but

significant. In perceiving we do not add the different sensations received and edit them so as to get at the meaningful interpretation of the object perceived. We always perceive anything as a whole configuration or pattern so that it is simple, meaningful and stable.

Ex: On seeing a man riding a cycle, we do not perceive the cycle and the rider separately, it appears as a whole unit to us. The mental act of ‗organizing‘ takes place during perception

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Laws of Perceptual Organization

• 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. Menu

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Depth Perception • Depth perception - the ability to

perceive the world in three dimensions.

• Studies of depth perception

• Visual cliff experiment

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Perceptual Illusions • Illusions are wrong / mistaken

perceptions

• Our perceptions are not always true and accurate. Sometimes errors do creep in our perception when our mind wrongly interpret the sensory input, which is otherwise known as ILLUSION

Perceptual Illusions

• Illusion of movement : Ex: A spot of light in dark appears to be moving around

• Illusion of perceptive : Ex: Two parallel lines appears to meet at along distance

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

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.

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.

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The Doorway to Psychology

You cannot know anything except through

the senses –

Anaxagoras