Graphics 2 Cognitive Science, Visual Perception and Graphics

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Graphics 2Cognitive Science,Visual
Perceptionand Graphics
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Introduction can Cognitive Science contribute to
graphics related fields?

• what is Cognitive Science?
• scope of the discipline
• history of development
• superficial structure of the visual system
• revision - visual pathways
• distribution of photoreceptor cells in the retina
• conclusion
• discussion can the study of the visual system
  tell us anything about designing signs?

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Cognitive Science

• Study of the Mind
• draws on many disciplines
• Psychology, philosophy, computer science,
  neuroscience, anthropology, mathematics
• established in the 1970s building on work carried
  out during previous two decades
• Term coined in 1973 - commentary by
  Longuet-Higgins following publication of the
  Lighthill Report - state of AI research
• Journal Cognitive Science first published 1977
• The Cognitive Science Society founded 1979
• many areas of research
• Perception, attention, comprehension, attitudes
  and beliefs, memory, artificial intelligence,
  human-computer interaction, linguistics, abnormal
  psychology, natural language processing, etc, etc

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Cognitive Science and Graphics

• training, experience and established practices
  provide the designer with rules on how best to
  arrange graphic elements
• Can the study of cognitive science predict any of
  these rules?
• Are there any low-level / computational
  approaches to the mind that can predict graphics
  principles?
• If so, could the study of cognitive science guide
  us towards better design, eg for signs and
  pictograms?
• Example - mechanism of the perception of colour.
• structure and function of the eye in colour
  vision
• colour perception in the brain

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revision - vision

• mechanical operation of the eye well understood
• ranges and limits of the normal eye well
  established
• visible colour spectrum of light
• visual acuity - resolving two objects at a
  standard distance 20/20 vision
• common defects are well known, eg
• myopia - short-sightedness distant objects
  blurred
• presbyopia - long-sightedness inability to focus
  on near objects
• astigmatism - varying refraction across visual
  field
• colour blindness - difficulty distinguishing
  certain colours

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vision

• image falls on retina
• photoreceptor cells excited, begin firing
• rod cells fire at light intensity
• good for movement and low light levels, not
  colour sensitive, poor acuity
• cone cells fire at differing wavelength
• require good light levels
• provide high resolution of detail at the focal
  point

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vision

• optic nerve carries information from the retinas
  to the brain - right field of view to left
  hemisphere, and vice versa
• first to the projection areas
• lateral geniculate nucleas (LGN)
• superior colliculus
• then on to the visual cortex

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example - saccadic movement

• the eyes are constantly moving
• four or five times a second the eyes jerk to
  adjust the field of view, in movements called
  saccades
• afterimage from staring at an object - as cells
  recharge, a shadow of the field of view remains
  to our perception
• prevent the field of view from flooding - rods
  and cones become exhausted from firing and need
  time to recharge
• focal point fixes on a feature in the field of
  view for each saccade
• strong features selected, eg gazing at a face
  eyes, mouth, nose, eyebrows, periphery of the
  face / head
• perceptual system fills in the gaps as the eyes
  skip around
• narrow field of view - enlarges our breadth of
  visual awareness
• eliminates blind spots, in particular where optic
  nerve leaves retina

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saccadic movements whilst observing an image of a
face
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saccadic movements broaden perception of limited
field of view
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example - eliminating saccades

• What would happen if the saccadic movements were
  stopped, or their function rendered ineffective?
• habituation perceptual system tunes out
  artefacts that do not change thats why you
  dont usually see your nose!
• anaesthetising eye muscles with head steady,
  field of view fades eye surgery
• image drawn onto a contact lens image fades,
  field of view remains
• Ganzfeld effect
• Startling demonstration of habituation eg
  Wackerman et al (2002)
• noticed by polar explorers - sudden blindness in
  a featureless landscape
• can be repeated with cut-in-half ping pong ball
  placed over the eyes with constant illumination
  adaptation in 5 7 mins

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electromagnetic and visible spectrum
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colour - types of cell

• cone cells - trichromatic three types of cone
  cells, exhibit peak activity at three different
  wavelengths
• L-type - respond most to long wavelengths
• Peak activity for yellow (ie covers reds,
  oranges, yellows)
• make up approximately two-thirds of cone cells
• M-type - respond most to medium wavelengths
• Peak activity for green
• make up approximately one-third of cone cells
• S-type - respond most to short wavelengths
• Peak activity for violet
• make up only 2 of all cone cells

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response of cone cells
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response of rod cells

• respond to all wavelengths, but
• response much reduced for long wavelengths
• little or no activity for red light - instrument
  lights on ship
• maximum response at shorter wavelengths
• Purkinje shift
• maximum visual acuity shifts from yellow to green
  as eye adapts to reduced light levels
• can be seen when flowering plants are viewed at
  dusk

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colour - retinal cell distribution

• rod cells
• no rod cells at the centre of the field of view
  (fovea)
• hence rod cells do not contribute much to visual
  acuity when light levels are good
• distributed around the fovea and out towards the
  periphery
• mostly responsible for peripheral vision and
  vision when light levels are poor
• cone cells
• concentrated in the fovea
• hence cone cells responsible for visual acuity
  sharp focus, resolution of detailed image
• S-type cells are distributed both inside and
  outside fovea
• no L-type or M-type cells outside the fovea

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conclusion

• possible lessons for graphics related fields
• How should letters, words and other elements be
  spaced?
• eye does not move smoothly
• high visual acuity in only a very narrow area
• saccades settle on strong features during a
  period of observation
• What colour should emergency exit signs be?
• likely to be required in reduced light levels
• rod cells exhibit little activity at the red end
  of the spectrum
• S-type cone cells (that respond to the blue end
  of the spectrum) make up only 2 of total number
• Any other suggestions?

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Further information

• Structure and function of the eye
• Vast number of sources all useful
• Anatomy
• Neuroscience
• finding information searching and browsing helps
  to consolidate learning - see what you can find
  on the web
• Ganzfeld effect
• Jir L Wackermann, Peter Putz, Simone Buchi, Inge
  Strauch and Dietrich Lehmann (2002) Brain
  electrical activity and subjective experience
  during altered states of consciousness ganzfeld
  and hypnagogic states, International Journal of
  Psychophysiology, 46(2), pp. 123-146, online
  Available from http//ejournals.ebsco.com/direct.
  asp?ArticleIDE68T149ECE4PPND5AL31.  
• Cognitive Science
• Cognitive Science Society http//www.cognitivesci
  encesociety.org/
• past issues of the Journal of Cognitive Science
  are available to non members up to 2004 vast
  resource
• Ten classic papers http//cognitrn.psych.indiana.
  edu/rgoldsto/cogsci/classics.html
• chosen by the editorial board provides an
  excellent idea of the scope of the discipline
• What is cognitive science? http//ls.berkeley.edu
  /ugis/cogsci/major/about.php
• introduction from Berkelys department of
  cognitive science
• The Chinese Room argument http//www.bbsonline.org
  /Preprints/OldArchive/bbs.searle2.html
• One of the most important papers on the
  Philosophy of Mind - generated years of
  discussion.