Light the Eye and the Visual System

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P2 Visual - Perception
LIGHT THE EYE AND THE VISUAL SYSTEM
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PART I WHAT DOES IT MEAN TO SEE? PART
IILIGHT PART IIITHE HUMAN VISUAL SYSTEM
11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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PART I WHAT DOES IT MEAN TO SEE?
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SENSATION, PERCEPTION AND COGNITION
11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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Sensation, Perception and Cognition
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• Sensation, Perception and Cognition are
  fundamental processes in the human visual
  system!
• How do you understand these terms?

• Sensation refers to immediate experiences
  generated as stimuli fall on our sensory system.

• Perception involves the interpretation of those
  sensation, giving them meaning and organization

• Cognition involves the aquisition, storage and
  retrievel, and use of information

11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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Example 1 The Kanizsa triangle
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• What do you see?
• What is the sensation part?
• What is the perception part?
• Is there cognition involved?

11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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Example 2 Colour Illusion

• What do you see?
• What is the sensation part?
• What is the perception part?
• Is there cognition involved?

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Example 3 Illusionary Objects

• What do you see?
• What is the sensation part?
• What is the perception part?
• Is there cognition involved?

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Hierarchy
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• These three concept form a hierarchy of tasks
  done by the human visual system
• One builds on top of each other
• Is there always a clear boarder between these
  activities?
• So how does this fit in to the model of general
  vision system?

Cognition
Perception
Sensation
11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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PART II - LIGHT
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THIS YOU SHOULD ALREADY KNOW!
11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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Definition of light (recap)
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• Light is part of the electro magnetic spectrum
  (EMS)
• Different animals are sensitive to different
  parts of the EMS
• Light is understood sometimes as particles
  (photons) and sometimes as a wave
• Different colours are associated to different
  wavelengths

11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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Visible Light
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• Light is visible for humans between 350-700
  nano-meter (nm)
• What is white light?
• Is black and white a colour? (Find argument for
  both positions)

11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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PART III AN OVERVIEW OF THE HUMAN VISUAL SYSTEM
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THE EYE VISUAL PATHWAYS NEURONS AND BRAIN
11/09/06
Florian Pilz (fpi_at_imi.aau.dk)
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The Eye

• What is that for
• Iris
• Retina
• Lense
• What is the equivalent in a camera?
• What are dimilarities, what are differences
  between cameras and eyes.

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Eye Movements
MR - Medial Rectus LR - Lateral Rectus SR -
Superior Rectus IR - Inferior Rectus SO -
Superior Oblique IO - Inferior Oblique
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Resume The Eye

• Parts visible from the outside sclera, cornea
  iris, pupil.
• Cornea clear membrane, bends light to bring it
  in focus in the retina
• The shape of the lens brings both distant and
  near objects in focus
• The retina contains the fovea, where vision is
  sharpest, and the optic disc which is a blind
  spot due the absence of light receptors

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Visual Pathways

• The visual pathway describes the way of the
  visual information from the eye (light), via
  neurons (electricity) to the visual cortex.
• The visual cortex does the majority of visual
  processing

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The Retina

• Retina consist of cells photo-receptors, bipolar
  cells, ganglion cells, horizontal cells and
  amacrine cells.
• Light breaks down in the photo-pigments found in
  rods and cones
• Rod and cones differ in color and reaction time

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Cones Rods
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Retina
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The Retina

• Light energy breaks down the photo-pigments found
  in rods and cones (hyperpolarized). This
  generates a neural signal indicating sensory
  experience of vision.
• Photo-receptors pass their information to
  bi-polar cells. These connect to a single cone or
  small number of cones.
• These pass the information to ganglion cells,
  which collectively form the optic nerve between
  the eye and brain.
• The receptive field of a ganglion is the area of
  the retina which produces a change in activity
  when stimulated.

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Midget and Parasol Ganglion Cells
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Visual Pathways
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Visual Pathways

• The visual system has to kind of cross-overs
  visual material is reversed in the eye and in the
  chiasm where all information is split into left
  visual field and right visual field.
• Optic tract is the optic nerve behind the
  chiasm.
• The lateral geniculate is organized into six
  layers dividing left from right eye and parvo
  and magno pathway.

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Neuron Doctrine

• Galvani (1737-1798)
• Living muscle and nerve cells produce
  electricity
• Camillo Golgi (1843-1926) Ramon y Cajal
  (1852-1934)
• Neurons are the discrete basic entities the brain
  consists of
• DuBois-Reymond, Mueller and von Helmholtz (after
  1950)
• electrical activity of one nerve cell affects the
  activity of another adjacent nerve cell

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Neurons in a microscope
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Neurons Generate Spikes

• Axons of other neurons connect with dendrites and
  soma (100-150000 contacts)
• Their output increase the action potential of the
  neuron
• If a certain threshold is exceeded a spike is
  generated and travels with a speed of 1-100m/s
• The strength of the signal is constant

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PE-Questions

• Describe in your own words how you see the
  difference between sensation, perception and
  cognition.
• How do rods and cones differ?
• Why do we need eye movement?
• Explain the difference and similarities of the
  eye and a camera in terms of iris, lens, retina,
  CCD chip, ...
• Describe briefly the visual pathway!