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  1. Humans

  2. Humans • Humans form an important part of human-computer interaction • The limitations of humans influence how computers must be designed to work well with humans • We will turn our attention to the human senses and brain to become familiar with the capabilities and limitations of each

  3. Input-Output Channels • Humans interact with the world via • Senses • Sight, hearing, touch, taste, & smell • Effectors • Limbs, fingers, eyes, head, & vocal system • The senses allow us to receive information from the computer while the effectors send information to the computer • The important senses from an HCI perspective are sight, hearing, and touch

  4. Vision • The human visual system depends on • The eye • Receiving the light and converting it into signals • Ganglia in the retina • Responsible for edge and shape detection • Visual cortex • Part of the brain • Responsible for understanding of scene

  5. The Eye * Human Computer Interaction, Dix et al, Prentice-Hall, 2004

  6. The Eye • Cornea & lens • Focus light onto the retina • Retina • Light sensitive part containing rods & cones • Rods • Highly sensitive to light • Cannot resolve fine detail • ~ 120 million around periphery of retina • Dominate low-light & peripheral vision

  7. The Eye • Cones • Less sensitive to light • 3 types corresponding to different colors that permit color vision • ~ 6 million, concentrated in the fovea • Blind spot • Where optic nerve exits eye where there are no rods or cones • Ganglion Cells • X-cells – in fovea for pattern detection • Y-cells – throughout retina for motion detection

  8. Edge Detection Detected Edges Original Image

  9. Visual Perception • Much of vision depends on visual angle • Objects with a large visual angle are closer • Visual angle is used to determine distance • Overlap helps to determine distance • Known object size also determines distance • The visual angle determines the detail which can be resolved • A line can be seen at 0.5 seconds of arc • Spaces between lines can be detected at 30-60 seconds of arc

  10. Visual Angle

  11. Perceiving Brightness • Brightness is determined by the luminance of objects • Contrast is the difference in brightness of objects • The visual system compensates for brightness so that most scenes look the same • As light decreases, the rods dominate and we lose color vision

  12. Perceiving Brightness • Visual acuity increases with brightness • On computer displays, flicker increases with brightness • Flicker is perceived is the screen is updated less than 50 Hz • Flicker is most often perceived in peripheral vision

  13. Perceiving Color • Color is made up of • Hue • Intensity • Saturation • We can perceive about 150 hues • We can vary the intensity & saturation to increase this to 7 million colors • Untrained individuals might be able to identify as few as 10 colors

  14. Perceiving Color • Approximately 8% of males and 1% of females suffer from some form of color blindness • Red / green color blindness is the most common

  15. Color Blindness 25, 6 45, 8 56, 29

  16. Visual Limitations • The eye compensates for changes in • Luminance • Location • It also makes interpretations based on what it expects to see, not what is actually there • This can lead to optical illusions

  17. The Muller-Lyer Illusion Which line is longer? * Dix, et al

  18. The Ponzo Illusion Are the blue rectanglesthe same size? * Dix, et al

  19. Text Illusions * Dix, et al Is this text correct?

  20. Reading • Reading is performed at about 250 words per minute • People recognize words in about the same time it takes to recognize a character • Fonts between 9 – 12 point are equally legible • Lines between 2.3 – 5.2 inches are easily read

  21. Reading • There is evidence to suggest that it is slower to read from a computer display • Line length too long or short • Unfamiliarity with the medium • Insufficient contrast • Dark characters on a light background provide higher luminance and higher acuity, but is more prone to flicker • In practice white letters on black is preferred and increases reading accuracy

  22. Reading Contrast This is preferred by Most people due to The high contrast and The lack of flicker In the background This is low contrast With the background And can be difficult To read

  23. Eye Fatigue • Eye fatigue results from letters with too low resolution • Professional printers use 1200 DPI since 600 DPI will cause fatigue • Displays have ~100 DPI • Scalable fonts should be used • Flicker increases fatigue

  24. Hearing • The ear drum vibrates in response to changes in air pressure • The vibration is transmitted via bones to the liquid-filled cochlea where it is detected by cilia • Humans can detect sound from 20 Hz to 15 KHz • Humans can detect subtle changes in pitch

  25. Sound in Interfaces • Sound is usually used for warnings • It could be used far more extensively • Music and speech can • Enrich the user’s experience • Provide the user with more information • Help people with poor vision

  26. Touch • Although touch, or haptic perception, is viewed as less important that sight and sound, it is vital in daily life • The skin has 3 types of receptors • Thermoreceptors for temperature • Nociceptors respond to intense pressure • Mechanoreceptors respond to lower pressure

  27. Touch • Different areas of the body have different numbers of receptors • Exercise • Touch various parts of the body with 1 and two objects • What parts of the body can tell whether they are being touched by one or two objects?

  28. Touch in the Interface • We use touch for a variety of feedback in real life • We can use it in interfaces • A click so we can feel a key press • Force feedback on a joy stick • Force feedback on keys of electronic musical instruments

  29. Novint Falcon • A device to let users feel weight, texture, motion, and force • The ball is held in the hand and moved • As it enters different parts of the virtual world, it provides tactile feedback to the user • Technology like this could be used to enhance e-shopping by letting you feel the goods * Novint Technologies,

  30. Movement • A user can respond to a • Sound – 150 ms • Visual signal – 200 ms • Pain – 700 ms • To respond the user has to quickly and accurately plan motion of a hand, finger, and arm • Requiring faster responses is often what is done to make levels in games more difficult

  31. Movement • In general, when the user gets a signal, they must respond and hit a button • This response depends on • How far they have to move • How big the target is • This is summarized by Fitt’s Law • movementTime = a + b log2(distance/size + 1) • Where a & b are empirically determined constants

  32. Movement • In terms of UI design this means • Place controls close to one another to minimize movement • Make controls large enough so that they can be accurately hit with little effort • Place frequently used menu items near to one another

  33. Memory • Humans have several forms of memory • Sensory memory • Retains input from senses for a brief period • Short-term memory • Allows us to retain what we are working on for a few seconds • Long term memory • Long term memories of events and facts

  34. Sensory Memory • There are 3 types • Iconic memory • Visual images retained for 0.5 s • Echoic memory • Aural stimuli retained for a few seconds • Haptic memory • Memory of touch • Sensory memory is continually overwritten as new input is received

  35. Short-term Memory • Acts as a scratch pad for temporary information • Used when we perform mental arithmetic • Can be accessed quickly, ~70 ms • Decays rapidly • Has limited capacity • 7 ± 2 items in short term memory

  36. Short-term Memory • Short term memory stores chunks of information • We can increase the amount retianed by grouping data into chunks • 265397620853 • Individual digits – hard to remember • 44 113 245 8920 • Chunks – easier to remember

  37. Long-term Memory • Stores information for years, possibly forever • Two types • Episodic – stores events • Semantic – stores facts • Episodic memory is processed to derive new facts to store in semantic memory • There are several models of how long-term memory works

  38. Semantic Network * Dix, et al A popular model to view memory as interconnected facts.

  39. Closure • When a task is completed, the mind often flushes short-term memory to make way for the next task • Early ATMs gave the money before returning the bank card • This caused many people to take the money, wipe their memories, and forget their card • Newer ATMs return the card before giving the money

  40. Memorable or Secure? • Random strings make the best passwords • Random strings are the hardest to remember • Therefore, people choose poor passwords that are easy to remember and use them for multiple sites

  41. Reasoning • Reasoning is the process we use to draw conclusions form the facts we know • There are three types of reasoning • Deductive • Inductive • Abductive

  42. Deductive Reasoning • Derives a logical conclusion from the facts • I go to work on Mondays • Today is Monday • Therefore, I go to work today • Common problems with deductive reasoning are that people can make mistakes of logic

  43. Inductive Reasoning • This allows us to generalize from what we have seen to infer what we have not seen • Every elephant I have seen has a trunk • Therefore, all elephants have trunks • This is not a proven fact and cannot be proven unless we see every elephant • It can be disproven by finding one trunkless elephant • People still rely on this type of logic

  44. Abductive Reasoning • This reasons from a fact to the action which caused it • Sam always drives fast when he drinks • We see Sam driving fast and assume he has been drinking • Sam could be in a hurry for other reasons, but our first thought is that it is because he was drinking

  45. Problem Solving • Problem solving involves inferring new information from what is already known • There are different theories as to how people solve problems • Gestalt Theory • Problem Space Theory

  46. Gestalt Theory • Early explanations of problem solving said that it involved trial and error • Gestalt theorists felt it was more complex than this and had two parts • Reproductive problem solving drawing on previous knowledge • Productive problem solving in which the problem is restructured to yield a new insight

  47. Maier’s Pendulum • A group of subjects is placed in a room with two strings hanging from the ceiling • The task is to tie the strings together • There are pliers and poles in the room • No one thinks to use the pliers as a weight to make one of the strings swing • The researcher brushes against a string, setting it in motion, and soon they come up with the idea

  48. Problem Space Theory • Newell & Simon created this as an alternative to Gestalt theory • Problems can exist in several states and solving them involves applying operators to move the problem from one state to another • Consider the problem of moving your desk

  49. Problem Space Theory • You can push it or carry it • You can only carry it if it is light but carrying is faster than pushing • Therefore, you try to solve how to lighten the desk • If you solve that, you solve the whole problem

  50. Mental Models • Whenever we deal with any complex system we create a mental model of how it works • Consider a car • It has an engine which makes it go • The engine needs gas to run • We push the accelerator to go faster and the brake to go slower • As long as the car performs according to our model, we can drive safely