1. Psychology 3680 Illusion Lecture

3. What is Vision?

4. Levels of Analysis in Vision Behaviour Systems Circuits Molecules Synapse Membranes, Ions, Biochemistry Neuron Micro-Circuits

5. Vision Light Sources Absorption Reflection Optics Retina Brightness Colour Everything Else Scatter Perception

6. Point #1: You “see” with your brain.

7. Perception: How do we do it? Experimental Psychology / Neuroscience: –Measurements, theories and phenomena (what) –Biological mechanisms (how, why) –Evolution (why) Also need to know more about the external world: –Physics of light and material –Statistics of the natural world. What is probable? For humans, “natural” means the hunter-gatherer environment before ~10,000 BCE.

8. Perception Difficult to impossible for computers Seems effortless to us Also fast Because: –Short-cuts, assumptions and compromises –Not aware of what we miss Big brain? Yes, and no. –All animals cope, to some extent

9. How do young animals recognize their parents? Genetic: Expensive Learned: Too slow Question:

10. Imprinting: Identify parent as first object that moves after hatching Will then follow that shape Example of simplifying assumption Instinct & Learning

11. Frog Vision Few specialized shape detectors cells “bug” detectors –Dark on light –Small –Moving But just about any shape. Can’t see legs. No detector, not “seen” Abstraction, simplification

12. Supernormal Stimulus An exaggerated stimulus that is elicits a larger (more frequent, preferential) response than does the normal (natural) stimulus Oystercatcher egg retrieval

13. Supernormal Stimuli for Humans? Joan Miró, Bleu II Geisha, Zanatta

14. Lessons from Ethology Some things are innate; some learned Rely on environmental consistencies Make simplifying assumptions Ignore some data Favour speed as much as accuracy “Odd” behaviour results when stimuli exceed natural limits.

15. Problems for Humans Must deal with theoretical infinities: –2D from 3D images –Shadows vs absorption –Colour –Video/Film motion –Stereopsis Size and orientation variations Motion, self and object Multiple objects & backgrounds Individuals and category

16. Basic Assumptions Objects do not change: –Identity(object constancy) –Color(color constancy) –Albedo(lightness constancy) –Size(size constancy) –Shape(shape constancy) –Etc.

17. Example of Our Assumptions Light is coming from 3D objects in a 3D world Light travels in a straight line Objects lie in the direction the light comes from Needed because it is a 3D world and we only get 2D retinal images

18. Ames Room

20. Infinite Ways to Produce a 2D image

21. Ellipse or Circle?

22. Coincidences Cooincidences are rare. Cooincidences are hard to detect. Brain does not waste time checking for them. Object constancy: –We expect an identified object to be the “same thing” as we, and it, move around.

25. Modules Not one big brain, but big collection of small brains (modules) A module does a simple calculation Limited input; ignorant of many things Makes assumptions about the world No conscious access into internal workings.

26. Bottom-Up Processing Start at low level modules –Brightness, color, edges, motion etc. Pass information up hierarchy Automatic, quick No effort required Always working

27. Top-Down Processing High-level modules –Knowledge & Memory –Attention –Context, Expectations –More general –Large scale High level modules influence low level modules –Affect how simple elements are perceived “Active” versus “Passive” Attention etc. –May require “effort” –Limited capacity, so maybe elsewhere.

28. Top-Down Effects

30. Ignoring Information

31. Ames Room Illustrates: There is more than one way in the 3D world to create any 2D image. Mostly low-level, bottom-up processing. –Makes assumptions (angles are square) –Ignores things (sizes of women) –Illusion is fast and automatic. We assume the view point is not critical. –Object constancy –Do not check for coincidences

32. Thompson Effect - RMD

34. That’s not the half of it!

43. Your visual system creates something out of nothing!