SENSATION AND PERCEPTION

Unit IV

Sensation: the process of absorbing information, in the form of energy, from our environment

Uses sensory organs and nervous system

Perception: the process of organizing and interpreting information to determine what is meaningful

Happens in brain

http://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L10/PS1061_10.htm

What’s in this picture?

http://www.shutterstock.com/pic-84801493/stock-vector-optical-illusion-forces-to-see-a-spiral-when-actually-figures-are-located-on-a-circle.html

Spiral or circles?

Bottom-Up Processing

Analysis that starts with sensory receptors and works up to the brain’s integration of information

Happens when we have no prior knowledge of something

usslave.blogspot.com

Top-Down Processing

Analysis that uses prior knowledge and experience to construct meaning

Focusing on details requires effort EX: Aoccdring to rscheearch at

CmabrigdeUinervtisy, it deosn’tmttaer in wahtoredr the ltteers in a wrod are, the olnyiprmoetnttihng is taht the frist and lsatltteer be at the rghitpclae. The rset can be a total mses and you can still raed it wouthit a porbelm. Tihs is bcuseae the huamnmniddeos not raederveylteter by istlef but the wrod as a wolhe.

Theories on top-down processing Likelihood principal: we perceive the

most likely object based on context and experience

Hypothesis testing: perception uses sensory data to make and revise hypotheses about the world

Selective Attention

We consciously focus on a very small amount of the sensory information we take in and ignore the rest

Ex: you can have a conversation with one person in a crowded room

ADHD may be a lack of selective attention

Demonstration!

Inattentional blindness

We often don’t notice things, especially if we are focused on one thing in particular

Video break: a famous experiment on inattentional blindness

Research suggests the unconscious may pick up on unnoticed information

Change Blindness

We often fail to notice changes in our environment Happens when we are distracted

from the changed object More quickly noticed when the object

is central to the scene You must pay attention to the object

at some point to notice a change Paying attention to an object is not

always enough to notice a change

Video break: Mind Games “Pay Attention”

Mindsight?

Some people may be able to “sense” change before they find exactly what the change is Using secondary visual system? Or verifying conscious detection of

change?

Thresholds

Absolute threshold: minimum stimulation necessary for detection 50% of the time May change slightly because of lapses of

attention, slight fatigue, or other factors Ex: hearing tests

Signal Detection Theory

Says signal detection depends on experience, expectations, motivations, and alertness

Predicts how often weak signals will be picked out of “background noise”

Would mean that absolute thresholds vary significantly

Ex: TSA agents looking for guns in suitcases

Subliminal Stimuli

We do sometimes unconsciously sense stimuli below the absolute threshold

Priming with images or smells can shape people’s responses to other people

This effect is short-lived and mild (doesn’t work for advertising)

Difference Thresholds

AKA just noticeable difference Three ways to test (discovered by

Gustav Fechner): Method of limits: start with a standard

stimulus and increase the difference between it and another stimulus until someone notices

Method of right and wrong cases: present a pair of stimuli and ask if they are different

Method of adjustment: Adjust a stimulus until it is identical to the standard and measure the error

Weber’s Law

Two stimuli must differ by a constant percentage (not amount) to be perceived as different

Weight: 2% Pitch: 0.3% Light intensity: 8% Also applicable to economics Demonstration!

Sensory Adaptation

Our sensitivity decreases with constant/repetitive stimulation

Helps us to focus on changes to the environment - more informative/important than things that are always present

Ex: disappearing disc

Vision

Vision

Light Energy Wavelength - distance from one peak to

another (determines color) Intensity - amount of energy, depends on

height of wave, influences brightness

Figure 4.10The eye Light rays reflected from the candle pass through the cornea, pupil, and lens. The curvature and thickness of the lens change to bring either nearby or distant objects into focus on the retina. Rays from the top of the candle strike the bottom of the retina and those from the left side of the candle strike the right side of the retina. The candle’s retinal image is thus upside-down and reversed.

© 2010 by Worth Publishers

Figure 4.11 The retina’s reaction to light

© 2010 by Worth Publishers

The Eye cont.

Light goes through the lens, which focuses light for different distances (accommodation)

Image hits retina upside-down Light goes to rods and cones at the back

of the retina, causes chemical reaction bipolar cells (middle layer of retina)

activate and pass signal to ganglion cells (upper layer of retina)

Ganglion cells converge into optic nerve

The Eye Cont.

Blind spot exists where optic nerve leaves the eye Usually eyes work together to get complete

picture and brain will fill in a gap Cones: mostly in/around fovea, spot of

central focus on retina; detect color and detail

Rods: mostly on peripheral of retina, detect black-and-white, work in dim light

Visual Processing

Retinal cells send initial information through thalamus to visual cortex

Feature detectors respond to specific characteristics - lines, movements, angles

Supercell clusters of neurons interpret more complex patterns - faces, complete objects Some supercells are specialized Some integrate information from others

Parallel processing: The brain processes color, movement, form, and depth simultaneously

Damage to specific areas will disrupt these specific functions Blindsight: research on patients with

damage suggests a secondary, intuitive visual system

Visual Processing

Color Vision

Color is a construct of our minds Young-Helmholtz trichromatic theory: the

eye has 3 types of cones for seeing red, blue, and green

All other colors are combinations of those - green and red light make yellow, etc.

Color-deficient vision is caused by a lack of one or two types of cones (usually red and/or green)

Color-deficiency test

Opponent Colors

Opponent Process Theory

Opponent colors: red-green, blue-yellow, black-white

Some neurons are turned off by red and on by green and vice versa

Modern color theory uses both Young-Helmholtz and opponent-process: color is seen by combinations of cones and then goes through opponent-process cells to visual cortex

Hermann Grid

Problems with Vision

Color deficiency Nearsightedness – lens focuses objects

in front of the retina instead of on the retina (see things better up close)

Farsightedness – lens focuses objects behind the retina (see things better far away)

Blindness due to damage or from birth

Hearing

Hearing

Audition is very sensitive, esp. to human-created sounds

Sound waves are air molecules moving in pressurized waves - vibrations

Frequency of sound waves determines pitch

Amplitude of sound waves determines volume Measured in decibels - 0 = absolute

threshold, 10 decibels is a 10x increase in intensity

Ex: Conversation at 60 db is 10,000x more intense than 20 db whisper

Structure of the Ear

Outer Ear: moves sound through auditory canal to eardrum

Middle Ear: transfers vibrations from eardrum through 3 tiny bones - hammer, anvil, and stirrup - to cochlea

Inner Ear: Hair cells inside the cochlea sway when the cochlea vibrates, triggering neurons to fire Most hearing loss is because of damage to hair cells Loudness is perceived based on the number of hair

cells that fire

Sensorineural hearing loss Damage to hair

cells caused by Sustained noise

above 85 decibels Aging Heredity Disease

Hearing can be restored with cochlear implants – mechanical device wired into ear

http://health.howstuffworks.com/human-body/systems/ear/loud-noise-ear.htm

Theories on Perceiving Pitch

Place theory - different pitches trigger activity on different parts of the cochlea Explains high pitches but not low ones

Frequency theory - pitch determines how often neural cells all over the cochlea will fire (higher frequency = faster firing) Explains low sounds but not high ones

Volley principle - cells alternate firing to get a faster combined frequency

Modern sound theory uses a combination of place and frequency theory

Locating Sounds

Having two ears means we can determine the location of sound

Our brains can detect minute differences in the timing and intensity of sound waves between the ears

We struggle to identify sounds that are equidistant to both ears (overhead, directly behind, etc) because there is no time lag Cope by cocking your head

Other Senses

Touch

4 types of skin sensations: pressure, warmth, cold, and pain (only pressure receptors have been identified

Hairy skin detects movement and pressure

Galbrous skin (no hair) is more sensitive Touch is influenced by top-down

processing and expectations (rubber hand experiments)

Kinesthesis and Vestibular Senses Kinesthesis is the sense of body position

and movement Measured by sensors in joints, tendons,

bones, and ears Interacts with vision Related to vestibular sense, which

monitors head position and movement Determined by fluid in the semicircular

canals of the inner ear – moving fluid activates hair cells

Essential for balance

Pain

Pain alerts us to problems so we can take care of them

Many causes of pain trigger the same receptors

Some pain signals come from the brain, as with phantom limbs

Level of pain depends on social-cultural context We perceive more pain when others are

also feeling pain

Gate-Control Theory

Pain signals travel through spinal cord in small nerve fibers

Other sensory signals travel in large nerve fibers

Small fiber signals open a “gate” in the spinal cord and you feel pain

Large fiber signals or messages from the brain close the gate Stimulating area by rubbing can block pain

signals Endorphins limit experience of pain

Psychological effects on pain Distraction limits perception of pain We remember peak moment of pain and

level of pain at the end of a painful experience Medical procedures can seem less painful if

they are longer but the level of pain tapers off

Taste

5 taste sensations: sweet, sour, salty, bitter, and umami (savory, meaty)

Humans have >200 taste buds, each with 50-100 receptor cells

Receptors are mostly specific to one taste sensation, reproduce every 2 weeks

Taste sensitivity decreases with age, smoking, and alcohol use

Taste Perceptions

Brain responds more negatively to a taste when you are warned it will be bad

Price of food influences our perception of how good it will taste

People prefer familiar foods to unfamiliar ones

Tastes (and taste aversions) may be acquired or learned over time

Smell (Olfaction)

Smell and taste are both chemical senses Molecules of substances are caught in

receptor cells in the top of the nasal cavity Different odors activate different

combinations of receptors Smell does not go through the thalamus,

but it does go past the prefrontal cortex, which helps process emotional memories This may explain why smells are associated

so strongly with memories

Infants and mothers identify each other by smell

The ability to identify scents peaks in early adulthood

Attractiveness of smells depends on learned associations

Women have slightly better senses of smell than men

Sensory Interaction

Our senses influence each other, especially smell and taste (ex: no flavor when you have a cold)

Vision and hearing work together to help understand language

Synesthesia: stimulating one sense causes the perception of another sense Ex: tasting shapes, seeing letters in specific

colors