Human Factors Engineering

1. Human Factors Engineering ECE 796/896 Text, Graphics, Symbols and Codes

2. Process of Seeing

3. Visual Capabilities • Accommodation: Ability of eye to focus light on the retina. • Visual Acuity:Ability to discriminate fine detail and it depends on the accommodation of the eye. • Contrast Sensitivity:

4. Accommodation • Near Point, Far Point: • Normal vision: Far point = infinity, near point = 14 inches. • Dark Focus: Arm’s length = 1m Generally measured in diopters (D). 1D = 1m, 2D = 0.5m, 3D = 0.33m

5. Accommodation • Nearsightedness / farsightedness • With age (40+) --> farsightedness

6. Visual Acuity • The ability to discriminate fine detail. • Common measure = minimum separable acuity • Measured as the reciprocal of the VA subtended at the eye by the smallest detail that can be distinguished.

7. Visual acuity • VA (minutes) = (3438 * H)/ D (H=ht.,D=dist.) • Normal acuity = 1.0 the higher the number the better the vision. Snellen acuity: 20 ft. or 6 m from the chart 20/20 normal … 20/30 -> a normal person could read at 30 what the subject barely reads at 20.

8. Acuity Testing

9. Types of Acuity • Vernier Acuity: differential one line offset from another. • Min. Perceptible acuity: Detect a spot from its background. • Steroscopic Acuity: differentiate the two images received by the two eyes. Differ most close, least further away.

10. Contrast Sensitivity • Spatial frequency: The number bars per unit distance. • 1 cycle = 1 dark + 1 light bar • The waveform of a grating’s luminance. • Square wave and sine wave versions.

11. Acuity Grating

12. Contrast Sensitivity • Modulation contrast or Michelson Contrast: C= (Lmax - Lmin)/(Lmax + Lmin) values between 0 and 1

13. Contrast Sensitivity • Threshold Contrast: The point at which you see the bars from the background. • Contrast Sensitivity = 1/ threshold • Most sensitive => 2 and 4 cycles per degree

14. Contrast Sensitivity • More detailed the target = high spatial frequency • Visual acuity tests use high contrast objects. Tells little about how a person sees in a low contrast environment

15. Factors Effecting Acuity and Contrast Sensitivity • Luminance Level: • Contrast: • Exposure Time: • Target Motion: • Age: • Training:

16. Adaptation • Changes to light sensitivity • Two phases, cones and rods

17. Color Discrimination • Normal color vision: Trichromats - 100’s of colors • Complete lack of color vision: monochromats • Color Deficiency: dichromats or anomalous trichromats

18. Reading • Complex eye movements: • Combination of (saccades)”fast movements”, and stationary periods (fixations) • Also regressions

19. Perception • Visual Displays: 1. Must be seen clearly 2. Help to viewer to correctly perceive the meaning 3. Horizontal-vertical illusion

20. Text: Hardcopy • Visibility: separation from surroundings • Legibility: (discriminability) • Readability: character grouping/ formating

21. Typography • Most type faces are very readable • 4 types of circumstances for “preferred” • Viewing conditions are unfavorable • Information is important or critical • Viewing is at a distance • People with poor vision use displays

22. Stroke Width • Ratio of thickness to height • Irradiation: white on black • Rule: black on white should be thicker

23. Font Samples

24. Stroke Width • With good illumination: B-W (1:6,1:8) W-B (1:8 to 1:10) • With reduced illumination: thick letters become more readable than thin ones. • Low levels and low contrast -> boldface type w/ low stroke w-to-h (1:5)

25. Stroke Width • Highly luminous letters (1:12-1:20) • For black letters on luminous background need to very thick strokes

26. Width to Height Ratio

27. Width-Height Ratio • Standard: 3:5 • Styles of Type: 30,000 • Roman: Most common, serifs • Gothic: uniform stroke width, sans serif • Script: simulate hand writing • Block: simple, German manuscript form

28. Different W-H Ratios

29. Size • Measured in points: 1 pt = 1/72 inch or 0.35 mm, this does not consider, ascenders and descenders. • Better measure 1 pt = 1/100 inch or 0.25 mm

30. Mil spec Text

31. Reading • 9-11 pt for newspapers / magazines • 22 to 27 min - viewing angle • If reading is critical or in low light than text height will need to be increased • Check table 4-2 for ranges

32. Distance Reading • National Bureau of Standards • Ws = 1.45 * 10(-5) * S * D • Hl = Ws / R • Ws = stroke width, S = denominator (snellen), D = reading dist.,Hl letter height, R stroke W-H (decimal)

33. Other Factors • Case: lower case in easier to read than upper case. A capital starting letter can make reading faster and more acurate. • Layout: interletter spacing, regular and dense spacing, dense is superior • interline spacing : spatial frequency may provoke eye strain, etc.

34. Reading Ease • Type of Sentence • Order of Words • Indices of Readability

35. Type of Sentence • The green button starts the motor. • The motor is started by the green button. • The red button does not start the motor. • Simple, affirmative,active are the easiest to understand.

36. Order of Words • “push the green button after turning off the gas” • Better: “Turn of the gas before pushing the green button”

37. Indices of Readability • Flesch Reading Ease Score • Based on an 100 word passage , the number of syllables(S) and average number of words per sentence (W). • Score = (0.846*S) - (1.015*W) • The book = 51 -> fairly difficult

38. Text : VDT Screens • Not the same as hard copy - image quality • Text represented by pixels • Better the quality = closed to hard copy

39. Typography • Dot matrix ( 5X7, 7X9, …15X24) • Pixel size and aspect ratio is a factor • Note figure 4-10 • Reading distance - greater than with hardcopy (24-36 --- 18-20) • Size: arc of 11-12 mins --> .06-.07 ANSI - .09 (.116,.128) max( .14)

40. Hardware Considerations • Refresh rate,jitter,flicker,phospher persistence • Polarity: dark on light or light on dark • Color: use as few colors as possible, avoid using the extremes, avoid color pairs of saturated red/blue, maximize the contrast between text and background

41. Screen Design Issues • Density: ( 24X80 available) percentage of spaces used. Most screens average about 25% with more than 40/50 rare. • Local Density: higher density in groupings

42. Grouping • Data items viewed to form well define groups 1 If groups subtend less then 5 degrees of VA (12/14 W X 6/7 lines H) - search time was a function of the number of groups. 2 If the VA is > 5 degrees, search time was a function of the size. • Recommendation: min. number of groups, make them as close to 5 degrees as possible.

43. Complexity • Arrangement (layout) complexity - Items placed on the screen follow a pattern. - Reduce complexity by lining up data into columns and/or rows.

44. Complexity

45. highlighting • Highlighting with validity leads to positive improvement. Higher the validity the higher the effectiveness of highlighting. (Validity is percentage of time that the target being searched is highlighted.) • Except for urgent critical information blinking should not be used.

46. Graphic Representation • Instructional materials:Combine text with pictures for speed, long-term retention and accuracy. ( ex: airline safety instruction card) • Representing data graphically - distort results

47. Distorting Data

48. Symbols • Symbol Vs. Verbal signs • Symbol is preferred generally Ex: deer crossing, rest rooms, etc.

49. Objectives of Symbolic Coding systems • Strongest connection between the symbol and the referent • Ease of learning the association - “recognizability”

50. Criteria for Selecting Symbols • Experimental testing may be required • Factors: Recogntion, Matching, Preferences and Opinions