Level 1: the first 6 vision lectures

Constructionist Data not enough; add knowledge of the world. Focusses on recognition and understanding.

Computational Who cares? find out how a vision system could work. Has often (but not necessarily) tended to focus on bottom-up processing (see below); may be the least neglectful of the uses of vision for detecting surprises and danger.

Sample exam question

Aspects of the lectures

• The core material, summarised in the handbook and repeated above. If you know this material, you will do the exams well. Exam and essay questions are likely to be constructed around the learning objectives listed e.g. "Describe the nature of sensory systems, with special emphasis on the visual system". This core material is fully covered in the textbook. The lectures are an alternative to reading, and include some examples and demonstrations that may help you understand and remember.
  
• Fundamental concepts associated with them. Listed below, these are concepts that are important and will recur repeatedly in later lectures and later years, even though they may only be introduced quite briefly here. If you want to know which are the deep ideas worth further thought, start with these.
  
• Critical thinking questions. These questions usually do not have answers we agree on, but are interesting to try to answer. You are recommended to try to answer them both because you may find them interesting, and because you will end up understanding and remembering the associated issues (that you will be tested on) better.

Fundamental Concepts

1. Representation (coding)

2. A lot of our theory is easiest to think about as if perception consisted of a linear assembly-line of processing from light waves to final percept. One aspect of this is the old terminology of sensation vs. perception: reflecting an old and wrong idea that first there are physical stimuli, which are converted into sensations, which are then converted into percepts. Although an important part of the story, that is NOT really how it is: various different sources of data are combined. Examples of things that don't fit this include:
   • Why are there nerve paths back from the cortext to the LGN?
   • If you press your eyeball with your finger, the world seems to move: that is because your visual perception uses not only signals from the optic nerve but also signals from your eye muscles.
   • Our sense of balance and motion, and of motion sickness, comes from the combination and comparison of what we see, what we sense in our joints (proprioception), and what we sense in the vestibular system of our inner ears.
   In the end, we should be thinking about overall systems, and the convergence (and competition) of different sources of information.

3. Types of observation (types of psychology)

   Physics - (neuro)physiology - information processing (computation) - perception. These are 4 perspectives, often pursued using quite different research techniques in different departments, on the same topic of perception. Realising which perspective is being used, and understanding how the different perspectives relate, is non-trivial and you can sometimes detect even experts making errors in this.

   These involve at least these kinds of research: Physical measures, neurophysiological observations, brain damage observations, perceptions (introspection, what the subject becomes conscious of), behavioural experiments, computational models.

   And they are used in various combinations. For instance psychophysics is when you do experiments that vary the physical input, and report the perceptual experience (or perhaps the behaviour) of the participant. These lectures are also about the relationship (for vision) of physics, neurophysiology, and the resulting perception; and how these revolve around and perhaps can be explained by representations.

4. Schools of theory of perception

   The textbook (and lecture 6) talk about the constructionist, ecological, and computational approach to visual perception. These are not different disciplines or research techniques but different kinds of theory, which lead to focussing on different cases as particularly important. Although their most fervent proponents see these as incompatible and opposed to each other, others have seen the best view as lying in some combination of these views.

5. Diagrams of neurophysiology

   Some of the different aspects involved in understanding perception fully are implied by the different kinds of diagram you see, or want to see, of the neurophysiology:
   • Physical layout: 3D facts, and how to recognise it for dissection
     
   • Sequence and connectivity: how the cells are connected together (NOT just to neighbours, but often to distant cells in very particular ways).
   • Function from high/overall perspective. I.e. what are the cells doing? What function do they carry out? What are they computing?
   • Evolution and development ("phylogeny" and "ontogeny"). How an anatomical structure relates to one in other animals

Questions (Critical thinking)

• What is vision for? For instance some plants have a kind of vision (to tell which way is up for a seed to grow). You can use vision for: day/night; time of day; motion; which way is up; ...
• What other senses are there / could there be?
  
• How else could vision have been implemented?
  (What is particular/accidental/implementation detail; individual differences; What is possible; What is true of all systems i.e. necessary.)
  Completely different kinds of eyes from ours have evolved.
  We focus by changing the shape of our lens; but cameras focus by moving the lens forwards and backwards.
  
• Why not 5 colour systems?
  
• Colour language terms. Do people agree on what words like "blue" really mean?.
  
• Is colour blindness a disadvantage?
  What can't you do if you are colour blind?
  Sometimes people with colour anomalies can see through camouflage the rest of us are fooled by.
  
• Are there colours you could experience, but never have?
  
• Why can't we see vividly our blind spot? E.g. like a black disk obscuring our vision? Even though we can't see there, surely it would be safer for our visual system to tell us there is a gap in its abilities?
• Why should our judgement of light intensity follow Fechner's law, when our judgement of the intensity of electric shock does not?
• Using pencil and paper, work out some examples that set the 8 Gestalt principles in conflict (predicit different groupings for the same example picture). With 8 principles, there are in theory 8*7/2 = 28 possible conflicts to explore; but attempting even a few will get you thinking about these principles from a new angle.
• Try the same thing for depth cues. In fact impossible objects can sometimes be generated like this; but in other cases, one cue just seems to win over another.
• Think of cases where you think your expectations have affected what you saw. Are these cases support for the constructionist view of perception, or did they operate at another level?

Steve's Questions

• Why aren't the rods integrated into the colour vision system? e.g. why don't we use the rods instead of one of the cone types. Even if there is some reason why the cell types of rods and cones must be different, why don't we use the same photopigment in rods and one of the cones? As it is, we have 4 photopigments but only a 3 colour perceptual system.

• What does a) "rod monochromacy" b) "cone monochromacy" mean? (?a) no cones b) only 1 not 3 types of cone?)

Reading

Bruce,V. & Green,P.R. (1990) Visual perception: physiology, psychology and ecology 2nd edition psy F10
[Especially useful for lectures 5 and 6]

Wandell, Brian A. (1995) Foundations of vision (Sunderland, Mass. : Sinauer Associates) Level 5 Main Lib Physiology RV8 1995-W
[This is much deeper than you need to go: but you may still find parts of it interesting especially p.315 onwards.]

R.N.Nesse & G.C. Williams "Evolution and the origins of disease" Scientific American Nov.1998 vol.279 no.5 pp.58-65
[For a brief but interesting point on the blind spot.]

Sacks,Oliver (1996) The island of the colour-blind (Picador) [Sacks is always interesting; and available in paperback.]

Dawkins, Richard (1995) River out of Eden : a Darwinian view of life Level 5 Main Lib Biology R30 1995-D
[This has a long discussion about evolution of the eye (roughly pp.65-84), and is easy to read. I believe it is also a Penguin paperback.]

Robert Sekuler, Randolph Blake. (1994) Perception (third edition) (New York ; London : McGraw-Hill)
Level 2 Short Loan Psychology F10 SEK
[The appendix "Behavioral methods for studying perception" is an excellent short piece of extra reading on psychophysics.]

The slides from another version of lectures 4-6.

Some web notes on Gibson (cf. lecture 6), originally for a level 4 course.

World wide web (WWW)

General instructions

To get at all this: Go to a computer cluster and log on.
Start up the WWW software (a "browser" like Netscape or Internet Explorer).
The address (called "URL") of the special page is:
http://www.psy.gla.ac.uk/~steve/courses/vision/level1.html
My own home page is:
http://www.psy.gla.ac.uk/~steve/

Notes:

• a) If you start typing at "www" i.e. omit the "http" the browser will probably fill that in for you
  
• b) The character "~" is called a "tilde". It is on every keyboard, but not in any standard position: you may take a minute to find it.
  
• c) You would also be able to find the page anyway: get to the university pages (probably where the browser starts up if you are using a university computer cluster), from there find the psychology department pages, from there find my page, from there find a link to the level 1 page.
  
• d) On the WWW, click buttons and links ONCE only, not twice.
  
• e) Accessing web pages from the USA can be slow: particularly on weekday afternoons. If you get frustrated, try weekends.

Unlike printed books, documents on the web may be modified or deleted at any time.
=>Because of this, you may need to check a page periodically to see if it has been updated: check the modification date if it has one (there is one at the top of this document).
=>Because of this, citing such documents should take account of this. A sample citation might be:
Draper (1997, April, 11) Adding (negotiated) learning management to models of teaching and learning [WWW document] URL: http://www.psy.gla.ac.uk/~steve/TLP.management.html (visited 1997, Nov, 5)
For more on how to cite web documents, click on this.

Related pages: [this page]         [lectures 4-6(last year's notes)]
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