1. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.1 Shape, Pattern, Form What is needed for shape (pattern, form) ? Facts a theory must account for Organization Four categories of theories The Information Processing approach Bottom-up and Top-down processing

2. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.2 What Is Needed For Shape Contours –discontinuity, change, edge, border Contours are necessary for shape but do not equal the shape –ambiguous figures –sketches –illusory or anomalous contours shape without the retinal image of the shape need information to indicate the boundaries

3. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.3 Illusory or Anomalous Contours

4. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.4 Facts To Be Explained Retinal image is ambiguous –size and shape constancy the retinal images changes but perception remains the same –ambiguous figures retinal image remains the same but perception changes Segmentation of image into objects

5. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.5 Facts To Be Explained Perceptual Learning –learn new discriminations Figural Adaptation –figural affereffects

6. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.6 Organization Of The Retinal Image Figure/Ground segregation –separating objects from background Gestalt Grouping Principles –figuring out which parts of the image belong with which objects

7. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.7 Figure/Ground Segregation What part of the image becomes the figure –bounded (closed) area –smaller area –symmetric area –convex area –brighter area

8. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.8 Bounded and Smaller

9. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.9 Symmetric and Convex

10. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.10 Figure/Ground Qualities Figure –shape –bounded –near –identified –meaning –remembered Ground –shapeless –continuous –far –not identified –meaningless –forgotten

11. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.11 Gestalt Grouping Principles Proximity A A A AAA AAA A A A Similarity AAAAABBBBAAAAAAA AAAAAABBAAAAAAAA AAAAABBBBAAAAAAA

12. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.12 Gestalt Grouping Good continuation

13. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.13 Gestalt Grouping Closure –illusory contours are based on good continuation and closure

14. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.14 Gestalt Grouping Common fate –camouflage is broken by common fate

15. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.15 Gestalt Grouping Pragnanz –simplicity and regularity Set and past experience –familiarity and expectations –“Street figures” and ambiguous figures –perception organized by your expectations

16. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.16 Four Categories Of Theories Theories differ on –what is encoded –how the encoded information is stored and used Categories –analytic feature models –spatial frequency models –template models (prototype models) –cognitive construction models

17. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.17 Analytic Feature Models What is encoded? –Small local features or elements –based on Hubel and Wiesel feature detectors Theories within this category differ on how the features are reassembled Example: Selfridge’s Pandemonium Model –hierarchy of feature detectors –parallel processing (all features detected at once)

18. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.18 Selfridge’ Pandemonium Model

19. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.19 Spatial Frequency Model Fourier analysis (what is encoded) –break complex image into component sine waves –sine waves are a graph of the distribution of brightness over space (blurry bars) The components (blurry bars) can vary in –frequency –amplitude –orientation –phase

20. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.20 Sine Waves Sine wave patterns Also called blurry bars or gratings

21. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.21 Sine Waves Top pattern is low frequency, high amplitude The next three increase in frequency, but decrease in amplitude The first four patterns start in-phase, but quickly get out-of-phase (the peaks and valleys do not line up after the first peak) As you add the patterns together you get a square wave (black and white stripes)

22. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.22 Spatial Frequency Model Adding the components together reproduces the original image Theories in this category vary in –how the components are added together Examples of evidence –contrast sensitivity function –block portraits –selective adaptation

23. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.23 Template Model What is encoded –whole objects (but not whole scene) –model (template) stored in memory –Prototype Incoming image is compared to stored representation

24. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.24 Cognitive Construction Models What is encoded: –depends upon expectations –can encode an entire scene at a time if given proper schema –can encode local elements if no schema is available or if incoming information conflicts with schema Schemas –sets of expectations e.g. a living room

25. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.25 Cognitive Construction Models Image is processed in steps –make hypothesis based on schema (expectations) –if incoming information matches the hypothesis there is rapid identification –if incoming information does not make, must make new hypothesis and try again –cycle through matching procedure until get a match

26. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.26 Cognitive Construction Models Examples of evidence –ambiguous pictures –“Street” figures –scene perception research –research on the effects of “set” and context

27. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.27 Set and Context

28. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.28 Information Processing Approach Stages of processing of form through the memory and recognition system Not a separate theory of form perception The models of shape perception –refer to processing in LTM that results in recognition –propose different mechanisms that shape may be stored in LTM

29. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.29 Information Processing Approach Distal Stimulus –object in the environment Stage I Proximal Stimulus –transduction produces the retinal image Stage II Sensory Register –iconic storage for 1/4 sec Stage III Short Term Memory –factors that influence further processing Stage IV Long Term Memory

30. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.30 Sensory Register Sperling’s Partial Report Technique –can report 3 -5 letters before image fades –proves that entire image is available but fades fast

31. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.31 Short Term Memory Limited capacity –7 +/- 2 items Many factors influence either what gets further processing or the speed of further processing Any information that does not get further processing is lost

32. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.32 Factors That Influence Processing Task requirements –may not need to do a full analysis –global discrimination in which of the following would it be easier to find the letter Q? Why? –EKLXAVFTZ –ODCBGPRU

33. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.33 Factors that influence processing Instructional Set –process only the features you are instructed to attend to, such as color, location, form, or size

34. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.34 Factors That Influence Processing Familiarity –familiar things are processed faster word superiority –“m” presented alone –“aemg” m presented as part of a letter string –“game” m presented as part of a meaningful word the letter is detected fastest when part of a familiar word, even faster than if presented alone

35. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.35 Factors That Influence Processing Interference –slows down processing –features you can’t ignore –e.g. Stroop Task - color words presented in incongruous ink colors. The automaticity of reading interferes with color naming.

36. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.36 Stroop Blue Green Red Blue Green Yellow Red Blue Yellow Green Red Orange Green Red Blue Yellow Orange

37. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.37 Factors That Influence Processing Schemas and expectations –you are faster at processing things you expect to see –you are faster at processing things that fit your schemas

38. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.38 Long Term Memory Incoming sensory information is compared with the representation stored in LTM Each of the theories of form perception makes different predictions about: –what is stored in LTM –the mechanism of the comparison process

39. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.39 Direction of Processing Bottom-up (data driven) –the features encoded rom the environment determine the final representation –usually fast and automatic, relatively fixed –e.g. most feature models and spatial frequency models Top-down (conceptually driven) –the representations already stored in LTM determine what gets encoded from the environment –slower, more flexible –experience, expectations, schemas, and set influence encoding –e.g. cognitive construction models

40. Sensation and Perception - shape.ppt © 2001 Dr. Laura Snodgrass, Ph.D.40 Direction of Processing Both direction of processing are necessary –may use one or the other in different situations –sometimes both are needed e.g. ambiguous figures –abstract art