Docstoc

Graphics

Document Sample
Graphics Powered By Docstoc
					      Graphics 1

Cognitive psychology and
        Graphics
Introduction

 • recap – the story so far…
 • introduction to psychology and graphics; example -
   what does colour ‘mean’
 • cognitive science and a brief look at the structure of
   the visual system;
    • visual perception pathways
    • saccadic movements
    • distribution of photoreceptor cells in the retina

 • conclusion;
    • can the study of the visual system tell us anything about designing
      signs?
recap – the story so far…
• using the computer for graphics
   • input and output of graphics – raster images
   • creation, manipulation and storage – vector graphics

• sign systems
   • graphic design – effective visual communication
   • some signs evolve through use, some are carefully designed
   • some owned privately, some carefully regulated by authorities and
     agreed internationally as standards
   • provide information using familiar symbols from shared cultures and
     simple images from which we can discern meaning
   • smallest graphical units of meaning, from which more complex
     communication is possible, eg Fairtrade logo
recap – the story so far…
• signs and pictograms
   • Kapitzki’s classification of signs - what is and isn’t a pictogram
   • need for language to analyse and discuss graphics
• semiotics – the study of signs
   • introduction to the work of Sausserre and Peirce
   • Morris’s extension of Peirce’s classification;
       • semantics, sigmatics, syntax, pragmatics

• designing pictograms – key issues
   • intention of the designer versus interpretation of the viewer
   • minimising representation; shared repertoire
   • context, message, theme, motif, format, style, systematisation
what do colours ‘mean’ to us?

in some societies red is associated with evil, but in others with good luck
and prosperity and protection against evil…




            satanic symbols and
            depictions of the Devil


                                      Chinese Red
                                      Envelope, Ang Pow,
                                      and red banners and
                                      lanterns to bring good
                                      luck and ward off evil
what do colours ‘mean’ to us?
we often associate red with DANGER…
what do colours ‘mean’ to us?

 …but also frequently associated with the sensual; from romantic - red
 roses; to harsh - ‘red light district’; and in between - luxurious, decadent,
 alluring…




          ‘Mae West’s Lips’ sofa;
          Salvador Dahli, Edward
          James, 1938
what do colours ‘mean’ to us?
       …perhaps leading to secondary responses;
       excitement, bravery, passion, seduction, thrill-
       seeking…
what do colours ‘mean’ to us?
  but the colour red has also gained meaning
  through association with familiar objects;
      public facilities provided by government
      authorities in the 20th Century;
          a utilitarian purpose for red as an
          information sign…




                                                         Edward VII pillar box
                                                         K6 Telephone Box

                                                 Routemaster Bus
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 .
cognitive science and graphics
• training, experience, established practices; provide the
  designer with rules on arranging graphic elements…
• …can study of cognitive science predict 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 .
visual perception
• mechanical operation of the eye quite 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 (distance at which subject can resolve two objects compared
     to ‘normally sighted’ person)

• common defects of perception 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 .
visual
pathways
  visual process

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

• 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’ .
saccadic movements whilst
observing an image of a face
 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
   • there is an afterimage from staring at an object - as cells recharge, a
     ‘shadow’ of the field of view remains to our perception
   • it prevents the field of view from flooding - rods and cones become
     ‘exhausted’ from firing and need time to ‘recharge’
• focal point fixates 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 .
 saccadic movements broaden
perception of limited field of view
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
     – that’s why you don’t 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 in the lab with cut-in-half ping pong ball placed over
     the eyes with constant illumination – adaptation in 5 to 7 minutes .
electromagnetic and visible spectrum
types of retinal cell in humans
• rod cells - monochromatic; respond to all wavelengths
• 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 .
response of cone cells
  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 ships
• 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 red flowering
     plants are viewed at dusk…
   • …flowers become black, foliage
     retains brightness .
  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 ships
• 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 red flowering
     plants are viewed at dusk…
   • …flowers become black, foliage
     retains brightness .
 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 ‘violet’ cells are distributed both inside and outside fovea,
     however…
   • …no L-type ‘yellow’ or M-type ‘green’ cells outside the fovea .
 conclusion
• possible lessons for graphics related fields;
• ‘What colour should fire 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
• ‘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
                           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?ArticleID=E68T149ECE4PPND5AL31.


•   Cognitive Science
           •   Cognitive Science Society; http://www.cognitivesciencesociety.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 Berkely’s 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.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:21
posted:8/9/2011
language:English
pages:27