Sensation and perception
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Sensation and Perception. Chapter 4. The Basics. Sensation – Involves the stimulation of sensory receptors and the transmission of sensory information to the central nervous system i.e. spinal cord and brain Things that tip off sensory receptors: Light, sound, smells, etc. The Basics.

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The basics
The Basics

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

    • i.e. spinal cord and brain

  • Things that tip off sensory receptors:

    • Light, sound, smells, etc.

  • The basics1
    The Basics

    • Perception – How we interpret sensory stimulation

      • Football field example

    • Perception reflects learning, expectations and attitudes

    Absolute threshold
    Absolute Threshold

    • The weakest amount of a stimulus that can be tested

      • Dogs v. Humans

    • Thresholds are different amongst people

      • More sensitive than others

    Sensation and perception 1273549

    Some established absolute thresholds are:

    vision: a candle flame 30 miles away on a clear night.

    hearing: a watch ticking 20 feet away

    taste: 1 teaspoon of sugar dissoved in 2 gallons of water

    smell: a single drop of perfume in a three-room house

    touch: a bee's wing falling a distance of 1 centimeter onto the cheek.

    Difference threshold
    Difference Threshold

    • The minimum amount of difference detected between two stimuli

      • Tone

      • Hue

      • Piles of sand

    Signal detection theory
    Signal-Detection Theory

    • Distinguishing sensory stimuli that takes into account all factors of self and environment

    • We focus on what we consider important

    Sensory adaptation
    Sensory Adaptation

    • Process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli

      • Eyes adapting to darkness

      • Waves on a beach

      • Traffic

    Section 2 vision
    Section 2 - Vision

    • Color spectrum – Roy G. Biv

    The eye
    The Eye

    • Similar to a camera

    • Light enters the eyes, and then is projected onto a surface

      • The amount of light that enters is determined by the opening in the colored part of the eye

        • The pupil

    The eye1
    The Eye

    • Once light enters, it meets the lens

      • The lens adjusts to distances of objects by changing its thickness

        • Finger test – near / far

    The eye2
    The Eye

    • The changes in thickness and light project a clear image onto the retina

      • The retina acts like the film of a camera

      • Neurons in your retina that are sensitive to light are called photoreceptors

      • Once the photoreceptors are activated a nerve carries the information to the brain – occipital lobe

    The blind spot
    The Blind Spot

    • We need the blind spot to see

    • A point left empty of photoreceptors – room for information to travel

      • Circle test

    Rods and cones
    Rods and Cones

    • 2 kinds of photoreceptors

      • Rods – sensitive only to the brightness of light

      • Cones – provide color

    Dark and light adaptation
    Dark and Light Adaptation

    • Your ability to see in low light improves for 45 minutes

      • Sundown

  • Adaptation to light happens much more quickly

  • Visual acuity
    Visual Acuity

    • Vision tests for sharpness

      • 20/20

    • As you age your lenses become brittle, and you may become farsighted

      • Holding reading material further away

    Color vision
    Color Vision

    • Human beings can see up to 1 million different hues

      • Animals are more sensitive to certain colors

  • The color circle

  • Afterimages

  • Color blind – distinguishing colors from each other

    • Total color blindness is extremely rare

  • Section 3
    Section 3

    • Hearing – a series of vibrations in the form of sound waves in its own unique pitch or loudness

      • Hearing experiment


    • The more cycles (sound waves) per second, the higher the pitch (high or low)

      • Women’s voices are at a higher pitch than men’s because their vocal cords tend to be shorter

      • Humans – 20 to 20,000 per second

      • Dogs / Dolphins / other animals in excess of 20,000


    • Measured in dB (decibels)

      • Loudness is determined by the height / amplitude of sound waves

        • 0 decibels is the threshold (a watch heard ticking at 20 feet away)

    Locating sound
    Locating Sound

    • Perception of sound

      • Infinite possibilities

    • How your body / senses react to sound


    • Inherited / Disease / Injury / Old Age

    • Conductive Deafness –

      • Damage to middle ear, sound is not amplified

        • Helped with hearing aides

    • Sensorineural Deafness

      • Damage or elimination of neurons, damage to auditory nerve

        • Cannot be helped if nerve itself is damaged

        • Cochlear implants can help neuron loss

    Section 4
    Section 4

    • Other Senses –

      • Smell – incredibly important, apples and onions would be relatively the same otherwise

      • Taste – Spheres of the tongue

        • Smell and taste work together when eating

    Skin senses
    Skin Senses

    • Touch

    • Infants grow quickly and stay healthier if touched

      • Older people do better if they have pets (cats / dogs)

    • Body is covered in hairs, many too small to see

      • Sensory receptors lie at the base of the hair

    • Do we actually “touch”?


    • Differences are all relative

      • Fevers

      • Outside heat (Summer)

      • Swimming pools

      • A/C

    Sensation and perception 1273549

    • The more pain receptors are located in a certain body, they more we will feel

    • Point of contact > Spine > Thalamus > Brain (processing)

      • Prostaglandins help transmit messages

        • Ibuprofen and aspirin help slow prostaglandins

    Sensation and perception 1273549

    • Why does rubbing or scratching painful areas help?

      • Mixed signals

  • Phantom limb pain

  • Body senses
    Body Senses

    • Vestibular Sense

      • Sensory organs in your ears monitor your motion and relation to gravity

        • Balance, standing, changing speeds, etc.

  • Kinesthesis

    • Position and motion of your body

    • Copying body motions

  • Section 5
    Section 5

    • Perception – the way our body makes sense of our sensory impressions

    • Gestalt psychology – “The whole is more than the sum of its parts”

    Rules of perceptual organization
    Rules of Perceptual Organization

    • Closure – filling in the gaps to get a complete picture

      • Fig 4.11 (p. 93)

        • Filling in the blanks because dogs are familiar to you

    Rules of perceptual organization1
    Rules of Perceptual Organization

    • Figure-Ground Perception

      • What do we perceive as the figure and what do we perceive as the background

        • Fig 4.12 (Vases or Faces)

    Rules of perceptual organization2
    Rules of Perceptual Organization

    • Other Rules -

      • Laws of:

        • Proximity

        • Similarity

        • Continuity

        • Common Fate

    Rules of perceptual organization3
    Rules of Perceptual Organization

    • Perception of Movement

      • To sense movement we need a change of position

      • Your senses need clues to tell you that you are moving

        • Trees, road bumps, etc.

    Rules of perceptual organization4
    Rules of Perceptual Organization

    • Stroboscopic Motion

      • The illusion of movement

        • Flipbooks

        • Movies on reels

          • Subliminal messages

      • Perception smoothes out the gaps

      • Humans prefer smooth images

    Rules of perceptual organization5
    Rules of Perceptual Organization

    • Depth Perception

      • The “distance away”

      • Monocular clues – the appearance of 3-D on 2-D surfaces

        • i.e. paintings

          • Clearness, shadow, texture, overlapping, perspective

    • This is done through stimulation of retina

    Monocular cues
    Monocular Cues

    • Clearness – faraway objects seem less detailed

    • Perspective – parallel lines coming together or moving apart

    • Overlapping – placing of one object in front of another

    • Shadows and highlights – give a 3-D feel

    • Texture Gradient – closer objects have more texture (gradient – progressive change)

    • Motion parallax – the tendency of objects to seemingly move forward or backward depending on distance away

      • Moon, stars v. trees and rocks while driving

    Binocular cues
    Binocular Cues

    • Need both eyes v. one eye for monocular

      • 2 cues in binocular:

        • Retinal Disparity

        • Convergence

    Binocular cues1
    Binocular Cues

    • Retinal Disparity – only works on objects that are very close

      • Difference of angles of an object as seen by both retinas

    • Convergence – associated with a tightness of the eye muscles on things up close

      • Magic Eye puzzles

    Perceptual constancies
    Perceptual Constancies

    • Size Constancy – Comes through experience

      • Perceiving an object as one size no matter the distance

      • Pygmy example p. 98

    Perceptual constancies1
    Perceptual Constancies

    • Color Constancy

      • The tendency for objects to maintain color no matter the light quality

    • Brightness Constancy

      • Tendency to find an object equally bright even when its surroundings change

    Perceptual constancies2
    Perceptual Constancies

    • Shape Constancy

      • The knowledge an item has one shape

        • i.e. top of a glass from different angles

    Visual illusions
    Visual Illusions

    • When the rules of constancies are violated