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1 Ergonomics CS2352 Lecture 8 Robert Stevens

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1 1 Ergonomics CS2352 Lecture 8 Robert Stevens

2 2 Introduction Ergonomics or human factors is traditionally the study of the physical side of the interaction Design of controls (switches etc) Environment in which interaction takes place Layout and physical qualities of the screen Also psychological aspects of design

3 3 Grouping of Controls Physical as well as cognitive aspects Cognitive: Mapping from task language to input language Think broader than desktop workstation Having the right control in the right place maybe vital in safety critical situation Air traffic control: High pressure & huge number of controls Power button a nd disk eject button adjacent on PC Hidden buttons etc. on Web pages

4 4 Grouping (2) Logical grouping of controls: Standard keyboard, GUI menus Opposing controls separated Functionally related controls grouped Sequence on display reflects required task order – e.g., mandatory order in aviation Frequency influences position on display – most frequently Controls and displays as a whole must be physically accessible Most critical displays at eye-level Controls with adequate room for manoeuver Knocking one switch when reaching another

5 5 The MS Word User Interface

6 6 The QWERTY Keyboard Keyboard most common form of text entry device Known after the QWERTY keys Possibly better arrangements, but inertia prevents advance Move commonly used keys under strong fingers Alphabetic layout makes no difference, except to stop people typing! Keyboards can be split and/or curved to reduce strain

7 7 Keyboard Layout

8 8 Lap Top Keyboard

9 9 The Ergonomic Keyboard

10 10 DVORK Layout Based on commonly used keys Tries to alternate keystrokes 56% made by right hand Most commonly used keys on centre line – so no movement Stronger fingers make most movement Some conflict in constraints Less fatigue and 10 – 15% speed increase

11 11 DVORAK Keyboard

12 12 Chord Keyboard

13 13 Consistency Always advised to make UI consistent “Consistent with what?” Should be consistent with task – cf menus in GUI Consistent naming of commands in language If all else fails, become consistent to arbitrary standard or internally consistent

14 14 The Physical Environment Where will a system be used? Who will use the system? Is the user sitting, standing or moving? All domain dependent Not such a big question for the majority of applications Remember there are a spectrum of users

15 15 Basic Requirements The smallest user should be able to reach all controls Include those in wheelchairs Displays should be visible Prolonged use suggests seating; this should have back support When standing, should have room to reach all controls Important controls close; less used, less import controls further away Avoid glare, reflection, noise, etc.

16 16 Health Issues Physical environment important for health No prolonged standing Support given for rest when a posture has to be sustained (typing) Temperature extremes affect performance due to concentration difficulties Sufficient lighting to avoid eye strain; Flickering can cause problems for some people Noise can cause discomfort, pain and interference; it can also be harmful Time: Prolonged system usage with no rest should be avoided (pregnant women)Carpal tunnel syndrome; repetitive strain injury

17 17 Carpal Tunnel Syndrome Nerbes and tendons run through narrow channel at base of wrist The “carpal tunnel” Carpal tunnel syndrome happens when the median nerve becomes inflamed Numbness, tingling, pain (through whole arm), lack of grip, etc. Any repetitive task can bring this on, including mouse work and typing.

18 18 Use of Colour Ergonomics are not just about physical characteristics Perception also has its characteristics & limitations Colour in the UI is also an ergonomics issue Colours should be distinct and not affected by change in contrast Critical information not displayed in blues (can be used as background) Colour encoding should be supplemented with other cues: Written cues highlighted by colour and sounds (danger) Use common conventions – Traffic lights

19 19 Office Colour Scheme

20 20 Outdoor/Strong Sunlight Colour Scheme

21 21 Fitt’s Law Hitting a target a function of target size and distance to be moved to that target Captured in Fitt’s law Movement time = a + b log2(distance/size + 1)Targets should all be as big as possible and equi-distant from the start point No overly big menus Pie chart menu an alternative design

22 22 Pie Chart Menu New Open Close Save Save As Save as Pack and Go Page Setup Print Send to Properties Exit Page Web

23 23 Pie Chart Pros & Cons Minimises movement to target Large target areas for mouse click Very inefficient use of screen space More difficult to make Labels fit Placement of entries – “Exit” & “new” no longer separated

24 24 Summary Grouping and placement of controls Meeting of physical and cognitive aspects Purely physical considerations of the workplace environment Use of Colour a perceptual ergonomic issue Basic design considerations that cut across domain modelling

25 25 Further Reading HCI Dix, Abowd, Findlay & Beale Chapter 3.

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