Perception - definition

Transcription

1 Perception - definition Sensory impressions arise as a result of the interaction between stimuli in our environment and our sensory organs These impressions are transformed into a representation in our nervous system - a representation that can then be processed Perception is our experience of the information content in this representation We can compare them with previous experience 1

2 Perception - via our senses Vision visual perception Hearing auditive perception Smell Taste Touch haptic perception 2

3 Perception - vision The visual (iconic) system is extremely well-developed: Strong sunshine to dark night Still images and fast motion Long distance, tiny objects We recognize objects without any effort We see in 3D, ie, where objects are positioned in space 3

4 Perception - vision The eye is constantly moving: ms movement, 200 ms fixation, ie. 3-4 fixations per second Fixations give the eye time to focus Movements allow us to discover more of our environment perhaps we see something we had not inteded to look at These movements are called saccadic movements 4

5 The eye s saccadic movements Note the fixations and the saccadic movements 5

6 Eye cells cones black/white vision Light stimuli receptors rods colour vision cells attached to each other optic nerve that goes to the brain 6

7 Vision Stimuli distributed between right and left parts of the eye 7

8 The b/w system: rods The eye s three colour systems 2 colour systems: Blue-yellow Red-green cones Ganglia cells that lead to the optic nerv 8

9 Rods and cones We have 6 m cones (colour) and 100 m rods The number of rods means that we can see details when it is light and that we can see in the dark The cones are most dense in the middle of the retina where focus is best There are three types of cones that react to long-, mediumand short-waves (corresponding to red/blue/green), which means that the eye can create all other colours 9

10 Colours we can distinguish Electromagnetic radiation in this interval is converted to colour in the brain violet nm blue 480 nm green 520 nm red nm 10

11 The electromagnetic spectrum wavelength Gamma waves X-rays ultraviolet radiation We only see these wavelengths infrared radiation Micro-waves radar radio / TV 11

12 Colour Colour arises when photo-electric energy (electromagnetic radiation) of a certain wavelength is interpreted by the visual centre Colour is described by three componentes Hue (färgton) the actual colour is determined by the wavelength, eg. red or green Saturation (mätnad) a colour is more or less saturated if a certain wavelength dominates (is more intense, has more energy) than other wavelengths in the stimulus Brightness (ljusstyrka) how much light is reflected, general intesity 12

13 Hue (colour) and Saturation (mätnad) hue saturation 13

14 Brightness These colours are brighter than the ones above 14

15 Colour We perceive wavelengths between nm We can distinguish about 150 different colours (hues) ie. We notice a difference of 2 nm! 150 hues * saturation * brightness gives us 7 m colours! National Bureau of Standards (USA) has registered 500 names for colours Conclusion: Colour is important for humans 15

16 Names of some colours Aliceblue, antiquewhite, aqua, aquamarine, azure, beige, bisque, black, blanchedalmon, blue, blueviolet, brown, cadetblue, chartreuse, chocolate, coral, cornflowerblue, crimson, cyan, darkblue, darkcyan, darksalmon, deeppink, dimgray, deepskyblue, firebrick, gainsboro, ghostwhite, honeydew, lemonchiffon, mistyrose, papayawhip, peachpuff, saddlebrown, seashell, steelblue, thistle, whitesmoke 16

17 Colour All colours can be created using a mixture of one long-wavelength component (red) one medium-wavelength component (green) one short-wavelength component (blue) (These are the three colours used in TV- and computer- screens) 17

18 Colour - difference between paint and light Additive Subtractive 18

19 Complementary colours Colours in each colour system are received by the same receptors Blue-yellow, red-green, and black-white are complemenary 2 colours that produce grey when mixed If you stare at the flag... You can tire the receptors of a given colour 19

20 Experiencing colour in context This strip is unicoloured 20

21 Colour circle - normal vision 21

22 Blue and green are considered cool colours Colour psychology Red, orange and yellow are considered warm Blue and green can lower pulse and body temperature In red we secrete more adrenalin; blood pressure and breathing rate increase 22

23 Experiencing colour 23

24 Experiencing colour in context 24

25 Colour and language (Berlin & Kay, 1969) black green red blue white yellow 25

26 Perception - vision Which cognitive processes are active in visual perception Knowledge of eye structure, animal experimentation and computer simulations show that the following processes are involved : template matching feature recognition 26

27 Perception - vision template matching Template matching - stimuli are matched with predetermined patterns A detector cell stimulus template: connected neurons neurons that match a letter are connected so that there is one detector cell for each letter 27

28 Perception - template matching Template matching is data-driven, ie. stimuli from the environment activate the receptors Advantage: immediate perception Limitation: stimuli must match the template precisely A A A A hello 28

29 Perception - feature recognition Physical objects have critical features A A \ B C A D E 29

30 Feature recognition the demon model Source: Human Information Processing Lindsay & Norman 30

31 Critical features (example) Features Straight lines Horisontal Vertical A E F M Z x xxx xx xx x x xx You can expect confusing E och F Diagonal / Diagonal \ x x x x x Symmetry x x x x 31

32 Feature recognition Find Z in column 1. Find Z in column 2. Which was faster? (1) (2) ODUGQR IVMXEW QCDUGO EWVMIE CQOGRD EXWMVI QUGCDR ITEWNV URDGQO VXZEMI GRUQDO MXVEWI DUZGRO XVWEFI UCGROD MWTVIE DQRCGU VIMEXW QDOCGU EXVWIM 32

33 Nerv impulses in feature recognition same neuron with different stimuli 33

34 Feature recognition and distractors Find the vertical line 34

35 J J J J J J J J J J J J J Find a blue J J J J J J J J 35

36 Find a blue J J S S J J S J S J S S J J S J J S J S J 36

37 Feature recognition We just need a few clues to be able to recognize objects 37

38 Feature recognition 38

39 Limitations of 1. Template matching Visual perception Stimulus and template must match well How many templates do we need? 2. Feature recognition Easy to express in limited contexts (letters, reular shapes) In simulations you need to know what features are critical 39

40 Higher cognitive processes in visual perception constructivist theory Basic idea: sensory stimuli are not just received; they are actively processed in the brain which adds information based on previous experience. Sensory stimuli help us see an object; then we use a neural code to recognize it. 40

41 Constructivist theory Proof that further construction is performed by the brain : The image on the retina is 2-dimensional, but we experience 3 dimensions other processes must interpret the neural code of the retina and create a 3-dimensional image Gestalt theory has shown that we add information to see whole objects 41

42 Constructivist theory Clues that these higher processes use: Parallel lines seem to converge at a distance 42

43 Constructivist theory Other clues that higher cognitive proceeses use in visual perception: texture size interposition shadow 43

44 Constructivist theory texture: indistinct information appears further away texture: Precise information appears closer to the observer 44

45 Constructivist theory size: On the right: objects further away seem to be smaller 45

46 Size contributes to depth perception 46

47 Interposition The little elephant covers part of the middle elephant and is experienced as being closer 47

48 Interposition/distance The tree is closer to the camera than the building parallel lines seem to converge 48

49 Depth - shadow 49

50 Depth - shadow 50

51 Illusions Various mechanisms can collide when viewing contradictory information Illusions can teach us more about how we experience our environment Müller-Lyer illusion 51

52 Illusion and reality The black line is the same length in both pictures On the right the line is experienced as being farther away than the line on the left 52

53 53

54 What is foreground/background? 54

55 Illusion 55

56 Illusions Same line seems longer when vertical The rectangle does not exist we create it 56

57 Illusion - Kanizsas triangle We construct reality 57

58 a. Perspective b. Same tabletop - different perspective We see a rectangulär door even here 58

59 Controlling what you see Look at the triangles. What direction do they point in? Can you influence the direction? 59

60 Impossible figures Why are they impossible? 60

61 Visual perception and interface sdesign Colour Visual information graphs Text presentation Visual information icons 61

62 Perception and interface design - colour Avoid colour pollution oh no!! 62

63 Interfaces and text presentation oh-oh!! 63

64 Perception and interface design - colour yess! 64

65 Interfaces and presentation of information Mercedes Other cars average costs purchase Cost after 5 years 1 : 2,5 (visually) $ advert 65

66 costs $ k Mercedes Other cars average 1 : 1, purchase after 5 years 66

67 Interfaces and text presentation 67

68 Interfaces and text presentation 68