Sensation and

Perception

SensationSensation: • The process of detecting a stimulus (something that

attracts the attention of a sensory organ)

• the stimulation of sensory receptors and the transmission of sensory information to the central nervous system

Five Traditional Senses:• Vision• Hearing• Touch• Taste• Smell

SensationSensory Receptors: located in the sensory organs (eyes, ears, nose, tongue, hands)

cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain

Definition

Five Sensory Receptors:

• Temperature• Pressure• Pain• Balance• Motion

Sensation

PerceptionPerception: • process by which the brain organizes & interprets sensory information• using sensory information to form a meaningful pattern • final, organized, meaningful experience of sensory information

An example:Have you ever started the car and had to quickly turn down the volume on the radio from where it was set last time you were in the car? The level of energy (I.e., loudness) of the radio hasn’t changed (the volume know remains in the same place as when you last had it on), but your perception of the loudness has changed drastically!

The Process

ThresholdsDefinition:– minimum amount of any given sensation that

has to be present for us to notice it

Just Noticeable Difference: (Difference Threshold)

– Smallest amount of difference in amount of stimulation that a specific sense can detect (difference in shades of two colors)

Absolute Threshold:- minimum amount of a

stimulus that is necessary for us to notice it 50% of the time

1 drop of perfume in a small house

Ticking of a watch from 20 ft away

Smallest difference in the shades of red your eye can see

Sensory Adaptation

Sensory Adaptation:• process by which we become less aware of weak stimuli• if a stimulus is unchanging, we become desensitized to it

We adapt to lying on a beach by becoming less aware of weak stimuli like the sounds of the ocean

We adapt to living near a highway by becoming less aware of the sounds of traffic

Sensory OverloadDefinition:• Overstimulation of the senses.• Can use selective attention to reduce sensory overload

– Selective Attention• focusing of attention on selected aspects of the environment and

the blocking out of others

Light

Red Orange Yellow Green Blue Indigo Violet“Our Visible Spectrum”

• Hue determines color– Depends on length of the distance

from one peak to the next on the wave• Brightness

– Lightness and luminance; the visual experience related to the amount of light emitted from or reflected by an object.

• Saturation– Vividness or purity of color; the visual

experience related to the complexity of light waves.

The Eye• Cornea– Protects eye and bends

light toward lens.• Lens– Focuses on objects by

changing shape.• Iris– Controls amount of light

that gets into eye.• Pupil– Widens or dilates to let

in more light.

The Eye

• Retina– Neural tissue lining the back of

the eyeball’s interior, which contains the receptors for vision.

• Rods– Visual receptors that respond

to dim light.• Cones– Visual receptors involved in

color vision. Most humans have 3 types of cones.

The Ear• Loudness– The dimension of auditory experience related to

the intensity of a pressure wave.• Pitch– The dimension of auditory experience related to

the frequency of a pressure wave.• Timbre – The distinguishing quality of sound; the

dimension of auditory experience related to the complexity of the pressure wave.

The Ear

The Ear

• Sounds from different directions are not identical as they arrive at left and right ears– Loudness– Timing– Phase

• The brain calculates a sound’s location by using these differences.

Auditory Localization:

The Ear

• Three theories on how we perceive sound:– Frequency Theory• Neural impulses are stimulated more with higher

frequencies of air waves• More plausible for small frequencies, rather than high

frequencies because we can hear freqs higher than the maximum rate of neural firing (1,000 neurons a second)

– Place Theory• Different frequencies of air waves activate different places

along the basilar membrane

– Volley Theory• Neurons fire out of sequence to add up to a certain Hz

Smell

• Olfaction– Detects molecules in the air

• Lock-and-key– Olfactory receptors (i.e., the locks) are built so that

only molecules (the keys) with particular shapes will fit in particular receptors

– Receptors send neural signals to the brain, passing the thalamus (memory) and the limbic system (emotions) along the way• This is why odors often trigger emotional memories

Taste

• Detects molecules of substances that have dissolved in saliva

• Taste Buds– Clusters of hair-like receptor cells• Within each bud is a cluster of 50 to 150 receptor cells

– We have about 10,000 (most on tongue)– Four types: sweet, sour, salty & bitter

taste

The Process• Sense of taste combines with the sense of

smell to produce perception of flavor of food– Research suggests that neural impulses for both senses

converge to some degree in brain area associated with the perception of flavor

– When the sense of smell is blocked, we have a harder time detecting most flavors

Skin Senses

• Touch– Skin is the body’s largest sensory organ– Millions of skin receptors mix and match to produce

specific perception– Four basic types of sensations• Pressure, warmth, cold, and pain

Skin Senses

• Temperature– Two separate sensory systems – one for signaling

warmth and the other for signaling cold– Also have distinct spots on the skin that register only

warmth or cold• If you activate both at the same time, the person

perceives ‘hot’!

Skin Senses

• Pain– Pain serves a function – it warns

us of impending danger– Endorphins• Neurotransmitters in the brain that have a pain-killing

effect– Gate-control theory• Pain impulses can be inhibited by closing of neural gates in

the spinal cord

Sensitivity to touch

Body Senses

• Kinesthetic sense– Provides info about position of joints, muscles, limbs• Gives us control over body movements

• Vestibular sense– Provides info about body’s orientation relative to

gravity and head’s position in space• Helps us maintain balance• Relies on semicircular canals in the inner ear

Influences on Perception

• Our needs affect our perception because we are more likely to perceive something we need

• Our beliefs can affect what we perceive• Emotions, such as fear, can influence perceptions

of sensory information• All are influenced by our culture.• Expectations based on our previous experiences

influence how we perceive the world.

Perceptual Set

• What you see in the centre figures depends on the order in which you look at the figures:– If you scan from the left, see an old woman– If you scan from the right, see a woman’s figure

Context Effects

• The same physical stimulus can be interpreted differently

• We use other cues in the situation to resolve ambiguities

• Is this the letter B or the number 13?

Rules of Perceptual Organization

Gestalt Principles of Vision: notes the various ways people make sense of sensory information through:• Figure-Ground– The recognition of objects against

a background– What we perceive as the object &

perceive as the background influence our perception

Rules of Perceptual Organization

• Proximity– Grouping together visual &

auditory stimulus which are near to one another

– Marks near one another tend to be grouped together What do you see?

- 3 rows of dashes or 36 dashes

• Similarity– Tendency to group elements

together that look alike– Marks that look alike tend to

be grouped togetherWhat do you see?- 3 columns of red or a 4 x 6 pattern

Rules of Perceptual Organization

• Closure– We tend to fill in gaps in

what your senses tell you

• Continuity– Marks that tend to fall along a

smooth curve or a straight line tend to be grouped together

– People prefer to see smooth continuous patterns not disrupting ones

Depth and DistanceBinocular Cues: Visual cues to depth or distance that require the use of both eyes.

Depth and Distance

– Convergence: Turning inward of the eyes, which occurs when they focus on a nearby object.

– Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

Depth and DistanceMonocular Cues: visual cues to depth or distance that can be used by one eye alone.

– Cues create the illusion of three dimensions or depth on two dimensional or flat surfaces

– Cause certain objects to appear more distant than others

Visual Constancies

• The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce.– Size constancy– Color constancy– Brightness constancy– Shape constancy

Size Constancy

• the tendency to perceive an object as being of one size no matter how far away the object is

Color Constancy

• the tendency to perceive an object as keeping their color even though different light may change the appearance of their color

Brightness Constancy

• the tendency to perceive an object as being equally bright even when the intensity of the light around it changes

Shape Constancy• the knowledge that an item has only one shape

no matter what angle you view it from• even though these images cast shadows of

different shapes, we still see the quarter as round

Visual Illusions Illusions are valuable in understanding perception because

they are systematic errors that reveal our experiences – Illusions provide hints about perceptual strategies.

• In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.

• In the Ponzo Illusion (above) side lines seem to converge and top line seems farther away, but the retinal images of the red lines are equal!