sensation and perception

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  • Created by: shauna
  • Created on: 06-12-12 19:43



Pupil (Cornea)

Refracted by lens


stimulates rods and cones

Bipolar - Ganglion cells

Optic nerve


BRAIN (Occipital lobe)!!

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Eye Anatomy

  • Cornea:light admitting, transparent layer
  • Pupil: adjustable opening
  • Iris: muscle controlling size of pupil 
  • Lens: bends/refracts light rays onto retina
  • Retina : group of light receptors
  • Optic nerve: transports neural messages to Brain
  • Fovea: located in retina filled with cones, hence sharp vision
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Colour Vision

Do we see colour?

  • No!! we see electromagnetic waves and the differences in the wavelength of light is interpreted as colour.
  • We see a limited range on the electromagnetic spectrum (450-700nm), we can't see infa-red, x-rays gamma-rays for exapmle.

Physical properties of light

  • Length of wavelength= colour     short=bluish     long= reddish
  • Amplitude of wavelength= Intensity   Great= bright   small= dull
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Trichromatic Theory (Helmholtz)

  • 3 receptors in retina (cones) responsible for colour:

One for green 

one for red

one for blue

  • These colours are mixed to create the complexity of colour we see
  • Colur TV works on basis of vision being tricromatic, as only the three colours above are on the screen. Intensity of the three are varied to produce illusion of complex colours.
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X  Can't explain afterimages, we see an image of another colour whilst staring prolonged

X  Cannot explain colour-blindness

     Monochrome colourblindess (Total colourblindness): No cones or defective cones

     Colour weakness (inablilty to distinguish some colours): Red-Green (most common men)        Blue-Yellow (less common)

  • Correct account of how colour is processed by cones in retina
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Opponent- Process Theory ( Hering)

  • 3 mechanisms producing antagonistic responses to three colour pairings:


B-W               R-G               B-Y

  • One stimulated, other inhibited
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  • Explains afterimages - overstimulation of one produces afterimage of other
  • Correct account of how colour vision is processed after it leaves the retina

Both theories are complementary to one another.

Our current view on colour vision is based on both theories

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Ear Anatomy

Outer Ear

  • channels soundwaves into inner structures
  • Ear drum at the end of auditory canal vibrates upon receival of sound waves

Middle Ear

  • amplifies soundwaves
  • 3 tiny bones (ossicles) hammer, anvil, stirrup, move to amplify soundwaves beforee set to inner ear

Inner Ear

  • transforms sound into neural response
  • Contains cochlea (fluid-filled chamber of inner ear, with hair cells(sound receptors) that trigger nerve impulses (once hair cells die they are NEVER REPLACED)
  • transforms pressure signals into nerve impulses.
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Physical properties of soundwaves

  • soundwaves created when an object vibrates


  • Great amplitude = Loud
  • Smallamplitude = Soft


  • short wavelength = high frequency (high pitch)
  • long wavelength = low frequency (low pitch
  • Most sounds are combination of different waves of different frequency (timbre)
  • Sound waves measured in hertz
  • Sound loudness measured in decibels ( human range from 20Hz - 20,000Hz
  • Sound localisation results from sound lag, also intensity of sound on one ear
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Hearing Things

Pinna (channels sound to)

Ear Drum (hammer, anvil, stirrup vibrate onto oval window)

Cochlea/ Inner Ear (transduction of air pressure into vibrations)

Basilar membrace vibrates (hair cells bend)

Auditory nerve (hair cells connect to fibres here)

Cerebral cortex (auditory cortex)

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Pitch Perception Theories

Place Theory

  • hear different pitches as different sound waves trigger hair cells in different regions of Cochlea's Basilar membrane
  • Best explains high frequency sounds

Frequency Theory

  • pitch determined by frequency with which Basilar membrane vibrates
  • Best explains low frequency sounds
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Hearing Loss

Conduction Deafness

  • middle-ear deafness due to problems transferring sound waves to inner ear, due to ear drum or bone damage

Also possibly result of ear wax or infection

Nerve Deafness

  • inner ear deafness dut to damage to cochlea, hair cells or auditory nerve
  • Disease, Age & exposure to loud music can cause this too
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Smelling things

Chemical Molecule

Olfactory receptors (neurons with dendrites extended to the)

Olfactory epithelium (initiation of neural impulse)

Olfactory Bulb


  • Only sense that doesn't send info through hypothalmus
  • Processes in severeal brain regions
  • Relationship between olfaction and emotional memory
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Lock & Key Theory

  • Odours are related to the shape of chemical molecules
  • Each 3-D molecule has its own  receptor
  • Humans have 1,000 receptors from wich theyd distinguish 10,000 smells

Age , Gender & Smell

  • women and young kids have acutest sense of smell
  • smell sesitivity decreases with age
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Taste Bud

  • Bitter
  • Sour 
  • Salty
  • Sweet

Flavour = combination of taste and smell

  • 10,000 receptor cells in mouth, die in 10 days, however constantly renewed, occurs slowly in elderly, hence they have less acute taste
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How we taste

Chemical Molecules

Taste Cells (trigger neural impuses)

Thalmus - primary gustatory cortex( taste identification)

Limbib system (enables quick response to taste) i.e spit out sour milk

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Skin Senses and Receptors




Cold (near skin surface)

Warmth (deeper in skin)

Intensity of stimulus coded by: 

  • Firing rate of individual neurons
  • No. of neurons stimulated
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  • Pain results from skin damage or over-stimulation of sensory receptors
  • Two nerve fibres carry pain signals from skin to Spinal Cord
  • Cerebral cortex plays role in how we experience pain
  • Rare disease in which afflicted person feels no pain
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Gate - Control Theory

Spinal Cord contains neurological (gates) that either block pain or allow it to be sensed.(Melzack and Wall)

Short nerve fibres

  • Conduct pain signals (open gate)

Long nerve fibres

  • conduct other sensory information (close gate)

Explains why when we rub our hurt arm (activate long nerve fibres) pain is lessened. (Wall,2000)

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Biopsychosocial influences in experience of pain

Biological influences

  • genetic differences in endorphin production
  • activity in spinal cords short and long fibres
  • Brains interpretation of CNS activity

Psychological influences

  • attention to pain
  • learning via expereince
  • expectation of pain relief

Social-cultural influences

  • presence of others
  • empathy for others pain
  • cultural expectations (i.e culturally expected for men to tolerate pain better than women)
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The Body Senses (Spatial Orientation)

Vestibular System (Balance)

  • Provides info about the bosy in space and head movement by sensing gravity and motion
  • Sensory conflict Theory states motion sickness results from mismatch between sensations from eye and body.

Kinesthetic Sense (relation of body parts)

  • Provides info about body posture, orientation and movement/ location of body parts with respect to one another and the ground (receptors in muscles, joints and ligaments)

Synesthaesia (union of senses)

  • Expereince of a secondary sese whilst expereincing another (1 in 23 people)

Grapheme :letters/ numbers associated with colour (most common)

Music: Tones associated with colour

Lexical: words associated with taste

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The Detection Question

  • Concerned with limits to detecting faint signals
  • Each sensory system has miniumum energy required to activate system (threshold)

Absolute Threshold

  • smallest level of stimuli one can detect half the time
  • Thresholds can change in a person over time and due to hormone status (e.g thresholds for senses increase with age, olfactory sensitivity during pregnancy.)

Absolute sensory Thresholds

  • Vision ~ candle flame from 30 miles at night
  • Hearing ~ ticking watch 20ft away in quiet room
  • Taste ~ 1 tspn sugar in 2 gallons water
  • Smell ~ 1 drop of perfume in small house
  • Touch ~ wing of fly on cheek from 4 inches
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Measuring Absolute Thresholds

Method of Limits (Fechner)

  • experimenter contorls intensity in ascending or descending order
  • some trials start above, others below threshold
  • Average crossover from yes to no's = Absolute Threshold

Method of adjustment (Fechner)

  • participant controls intesnsity of stimulus
  • repeated for average
  • Threshold for ascending trials usually higher than descending trials

Method of constant stimuli

  • presentation of stimuli intensity randomised
  • Threshold is 50% detection at given intensity

x laborious but most accurate

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Subliminal Threshold

  • stimuli below absolute threshold (conciouslly) detectable less than half the time
  • strong enought to activate sensory recpetors, but not enought to make one conciously aware of it

Subliminal Perception

  • subliminal stimuli acts on unconcious mind to influence behaviour
  • Priming the effect of this: frequently used or recent words/ ideas come to mind influencing interpretation of new information. (shor-term) 

Evidence (Strathan et al 2002)

Hypothesis: we perceive subliminal cues, but only act on them when motivated to

Method: Thirsy/ not thirsty pp's exposed to either thirst related or neutral words Tested on amount of kool aid consumed on taste test

Results: Thirsty pp's when primed with thirst related word consumed more kool-aid, than when given neutral word.

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Signal-detection Theory

  • Detection of a stimuli depends on both its intensity and the psycholgical or physical state of the individual. (e.g car parked at night, you'll likely hear minute noises as you're situation is threatening, however in daytime possibly wouldn't be attending to these noises)

Signal setection dependent on:

  • signals strength
  • observers sensitivity
  • observers response criterion

Factors affecting likelihood of detection

  • probability of it occuring
  • sensitivity at time
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The difference Question

  • Concerened with our ability to detect minute differences between stimuli

Just noticeable difference

  • minimum difference in stimulation that a person can detect 50 percent of the time. (e.g adding amounts of sand to palm, point of detecting weight change that is the JND.)
  • how much can a stimulus increase before we detect change

Weber's Law (Fechner)

  • JND grows in size proportionally to the size of stimulus
  • more intense the stimulus is, more intense the increment must be to detect change
  • two stuli must differ by a constant minimum percentage to be perceived as different
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The scaling Question (Magnitude estimation)

  • Magnitude estimation is how our perception of stimulus intensity is related to actual stimuli strength

Response compression

  • as intensity increases, magnitude increases, though not as rapidly.

Response expansion

  • as intensity increases, perceptual magnitude increases more than intensity. sensation grows mroe rapidly than the physical stimulus. (i.e electric shock doubled in intensity, we perceive at as 10 times more intense)
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Habituation and sensory adaptation

  • Habituation: tendency of the brain to stop attending to constant unchanging information.
  • Sensory Adaptation: tendency of receptor cells to become less responsive to an unchanging stimulus, allowing you to shift your attention to whats importanct, thus conveying survivial advantages (important to detect new stimuli)

Normally our sensations and perceptions agree → we make meaning of our sensations.

  If sensations and perceptions do not agree we experience an ILLUSION 

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