Human Perception. Topic Objectives. CS 725/825 Information Visualization Fall Dr. Michele C. Weigle.

Transcription

1 CS 725/825 Information Visualization Fall 2013 Human Perception Dr. Michele C. Weigle Topic Objectives! Define perception! Distinguish between rods and cones in the human visual system.! Define preattentive processing! Describe four preattentive visual tasks.! Distinguish between a preattentive feature and a feature that cannot be detected preattentively.! Explain why knowledge of the feature hierarchy and visual interference is important for visualization designers.! Explain change blindness and the implication for visualization designers.! Explain why perceptual balance and distinguishability are important characteristics in choosing colors.! Describe the three main types of memory! Explain the implication of Weber's Law for visualizations.! Explain the implication of Stevens' Law for visualizations.! Describe methods that could be used to expand humans' ability to perceive information accurately. 2

2 Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization Reading Assignment (due today): Ch 3 - Human Perception and Information Processing! Metrics Homework Assignment: Due next Tuesday 3 What is perception?! Recognizing! Organizing! Interpreting! Perception is how we interpret the world around us 4

3 Visual representations can be misinterpreted WGK, Fig 3.2 WGK, Fig Our visual system is often not under our full control WGK, Fig 3.6a WGK, Fig 3.6b 6

4 There's more to our visual system than meets the eye WGK, Fig 3.7a WGK, Fig 3.7b 7 Studying Perception! Measures - used to build a model! Models - predict future outcomes, which can be measured 8

5 Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization! Metrics 9 Electromagnetic Spectrum By Philip Ronan, Gringer [CC-BY-SA-3.0 ( licenses/by-sa/3.0)], via Wikimedia Commons 10

6 Human Eye via Wikimedia Commons 11 How Light Travels Through the Eye content/0/content/html/portal_ks2science/pg htm 12

7 The Retina - Rods and Cones via Wikimedia Commons 13 The Blind Spot 14

8 Eye Movements Smooth Pursuit Saccadic "Types of Eye Movements and Their Functions", Neuroscience. 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA): Sinauer Associates; Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization! Metrics 16

9 One Model of Perceptual Processing! Three stage process! Parallel extraction of low-level properties of scene! Pattern perception! Sequential goal-directed processing Stage 1 Features Stage 2 "What" system "Action" system Stage 3 Visual Working Memory Ware, Information Visualization 17 Preattentive Processing! How does human visual system analyze images?! Some things seem to be done preattentively, without the need for focused attention! Generally less than ms (eye movements take 200 ms)! Seems to be done in parallel by low-level vision system 18

10 How Many 3s? How Many 3s?

11 Example! Determine if a red circle is present 21 Hue Can be done rapidly (preattentively) by people! Surrounding objects called distractors 22

12 Example! Determine if a red circle is present 23 Shape Can be done preattentively 24

13 Example! Determine if a red circle is present 25 Hue and Shape Cannot be done preattentively! Must perform a sequential search! Conjunction of features (shape and hue) causes it 26

14 Example! Is there a boundary in the display? 27 Hue and Shape - Boundary Edition Left: Can be done preattentively since each group contains one unique feature! Right: Cannot (there is a boundary!) since the two features are mixed (hue and shape) 28

15 Example! Is there a boundary in the display? 29 Hue vs. Shape Both can be detected preattentively because of difference in hue 30

16 Christopher Healey at NC State! Nice on-line tutorial, table of preattentive feature examples, and example applet 31 Potential Preattentive Features 32

17 Potential Preattentive Features 33 Potential Preattentive Features 34

18 Preattentive Visual Tasks! Target detection! is something there?! Boundary detection! can the elements be grouped?! Region tracking! is there a set of items moving together?! Counting and estimation! how many elements of a certain type are present? 35 Theories of Preattentive Processing! Five theories of preattentive processing! Critical role that the viewer's state of mind plays in determining what is seen! Presents studies in which human perception has influenced the development of new methods in visualization and graphics 36

19 Postattentive Vision 37 Feature Hierarchy 38

20 Change Blindness 39 Gestalt Laws, or Principles of Perceptual Organization 40

21 Gestalt Laws! Proximity! Things close together are perceptually grouped together! Similarity! Similar elements get grouped together! Connectedness! Connecting different objects by lines unifies them! Continuity! More likely to construct visual entities out of smooth, continuous visual elements Figures from wikipedia. and 41 Gestalt Laws! Symmetry! Symmetrical patterns are perceived more as a whole! Closure! A closed contour is seen as an object! Parallelism! Elements that are parallel to each other appear more related than elements not parallel to each other! Figure & Ground! Figure is foreground, ground is behind Figures from wikipedia, 42

22 Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization! Metrics 43 Color Goals! Perceptual balance! Distinguishability! Flexibility 44

23 Color Models - RGB 45 Color Models - HSV Hue - what people think of as color! Saturation - intensity, ranges hue!" gray! Value (or brightness) - light/dark, ranges black!" white 46

24 Color Models - CIE LUV 47 Color Models - CIE Lab! L * a * b! L = luminance! a = red to green! b = blue to yellow Images from and 48

25 Texture! Appears to be combination of! orientation! scale! contrast 49 Weigle et al. (with Enns, Healey), Proceedings of Graphics Interface, Motion Flicker Direction of Motion Velocity of Motion 50

26 Memory Issues! sensory memory! "muscle memory"! short-term memory! limited to 30 seconds! chunking! long-term memory! theoretically limitless! access is slow and unreliable 51 Can you read this? Rinadeg Oedrr Aoccdrnig to a rscarhee at Cigdmabre Uinervtisy, it deosn't mtetar in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the fnst and lsat ltteer be at the rghit pclae. The rset can be a taotl mses and you can sit11 raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. 52

27 Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization! Metrics 53 Human Limitations! What graphical entities can be accurately measured by humans?! How many distinct entities can be used in a visualization without confusion?! With what level of accuracy do we perceive various primitives?! How do we combine primitives to recognize complex phenomena?! How should color be used to present information? 54

28 The Magical Number Seven Used information theory to explain results! number of levels that can be perceived mapped to bits of information! levels = 2 bits 55 Absolute Judgment of 1D Stimuli! Position on a line levels! Sizes of squares levels! Color - 10 levels of hue, 5 levels of brightness! Line length levels! Line orientation levels! Line curvature levels! In general, only about 6-7 levels of data value with accuracy for 1D signals 56

29 Absolute Judgment of Multidimensional Stimuli! Unfortunately, this is not additive! Dot in a square - 24 levels! Hue and saturation - 12 levels! additive - 39 levels! Size, brightness, and hue - 17 levels! additive levels 57 Relative Judgment WGK, Figs 3.33 a,b 58

30 Perception Accuracy - Tested length area angle volume slope hue position on common scale position on nonaligned scales WGK, Fig Perception Accuracy - Increasing Error position on common scale position on nonaligned scales length angle, slope area volume 60 hue, saturation, density WGK, Fig 3.34

31 Two Laws Weber's Law Stevens' Law WGK, Fig So, what can we do?! Require relative judgments instead of absolute! tick marks, grid lines can help! Increase dimensionality! but, only up to a point! Reconfigure problem! series of absolute judgments instead of simultaneous 62

32 Recoding! Short-term memory chunks data! ~6 chunks of varying complexity! Remember these 5 numbers:! ! Now, remember these 5 numbers:! Role of Focus and Expectation 64

33 Was there a red horizontal? 65 Role of Focus and Expectation 66

34 Outline! What is Perception?! Physiology! Perceptual Processing! Perception in Visualization! Metrics 67