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Chapter 6 ergonomics l.jpg

Chapter 6Ergonomics

6.1 Definition

6.2 Fitt’s Law

6.3 Types of Ergonomics

6.4 Physical ergonomics

6.5 Cognitive ergonomics

6.5.1 Cognitive fundamentals

6.5.2 Cognitive Science

6.5.3 Cognitive psychology

6.5.4 Human Memory

6.5.5 Human Memory organization

6.5.6 Psychology

6.5.7 Human Psychology

6.5.8 Classification of Memory by Information Type

6.5.9 Memory disorders

6.5.10 Human Perception

6.5.11 The Senses

6.5.12 Study of Perception

6.5.13 Perception and reality

6.5.14 Factors in Cognitive Ergonomics

6.6 Ergonomics of Computer Use

6.7 Human Factors Vs. Ergonomics

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Chapter 6Ergonomics

Ergonomics

Ergonomics is the study of people in relation to their working environment. It is concerned with the design of man machine interfaces to improve factors affecting health, efficiency, comfort and safety. In other words, ergonomics is the scientific foundation, both in terms of data and methodology, for a user-centered approach to design. The first definition from an IT dictionary gives a general definition stressing the physical aspects and dangers of poorly designed machinery and work practices. The second, from The Ergonomics Society, brings in methodologies especially user-centered approaches with which you will be familiar.

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Chapter 6Ergonomics

Types of Ergonomics

There are two types of ergonomics for computer use: the physical and cognitive ergonomics.

Physical ergonomics

Physical Ergonomics = the application of principles developed through kinesiology research to the design and evaluation of physical tasks.

Cognitive ergonomics

Cognitive Ergonomics = the application of principles developed through engineering psychology research to the design and evaluation of cognitive tasks and systems development.

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Chapter 6Ergonomics

Cognitive fundamentals

There is great diversity in individual abilities reflecting difference in education and experience but all of us seem to be subject to some basic related words on our thinking. These are a consequence of the way in which information is stored and modeled in our brains. An awareness of this model can help you understand some fundamental cognitive limitations which affect software engineering approaches.

Cognitive Science

The term cognitive in cognitive science is used for any kind of mental operation or structure that can be studied in precise terms. This conceptualization is very broad, and should not be confused with how cognitive is used in some traditions of analytic philosophy, where cognitive has to do only with formal rules and truth conditional semantics. (Nonetheless, that interpretation would bring one close to the historically dominant school of thought within cognitive science on the nature of cognition - that it is essentially symbolic, propositional, and logical.)

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Chapter 6Ergonomics

Cognitive psychology

Cognitive psychology is a framework in which to understand the mind more than a subject area, although it has traditionally focused on certain aspects of psychology. Perception, learning, problem solving, memory, attention, language and emotion are all well researched areas. Cognitive psychology is based on a school of thought known as cognitivism, which argues for an information processing model of mental function, informed by positivism and experimental psychology. Techniques and models from cognitive psychology are widely applied and form the foundation of psychological theories in many areas of both research and applied psychology.

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Chapter 6 Ergonomics

Human Memory

Human Memory is one of the activities of the human mind, much studied by cognitive psychology. It is the capacity to retain an impression of past experiences. There are multiple types of classifications for memory based on duration, nature and retrieval of perceived items. The main stages in the formation and retrieval of memory, from an information processing perspective, are:

  • Encoding (processing and combination of received information);

  • Storage (creation of a permanent record of the encoded information);

  • Retrieval (calling back the stored information);

  • Classification by duration.

    Continued…

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Chapter 6 Ergonomics

It may be that short-term memory, which is supported by transient changes in neuronal communication, whereas long-term memories are maintained by more stable and permanent changes in neural structure that are dependent on protein synthesis. Some psychologists, however, argue that the distinction between long- and short-term memories is arbitrary, and is merely a reflection of differing levels of activation within a single store.

For example, if we are given a random seven-digit number, we may remember it only for a few seconds and then forget (short-term memory). On the other hand, we can remember telephone numbers for many years, since we have stored them in our brain after long periods of consolidation and rehearsal (long-term memory).

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Chapter 6 Ergonomics

Human Memory organization

Software systems are abstract entities and engineers must remember their characteristics during the development process of the software system. For example, programmers must understand and remember the relationship between the source code and the dynamic behavior of the program. They apply this stored knowledge in further program development.

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Chapter 6 Ergonomics

The retention of information in the memory depends on the memory and suture. This seems to be hierarchical with three distinct, connected areas.

  • A limited capacity, fast access, short term memory. Input from the senses is received here for initial processing. This memory is comparable with registers in a computer; it is used for information processing and not information storage.

  • A larger capacity, working memory area.This memory area has longer access time than short term memory. It is used information processing but can retain information for longer periods than short term memory. It is not used for long-term information retention. By analogy with the computer, this is like RAM (random access memory) where information is maintained for the duration of a computation.

  • Long term memory. It has a large capacity, relatively slow access time and unreliable retrieval mechanisms (i.e. we sometimes forget things). Long-term memory is used for the ‘permanent’ storage of information. To continue the analogy, long-term memory is like disk memory on a computer.

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Chapter 6 Ergonomics

Classification of Memory by Information Type

Long-term memory, the largest part of any model, can be divided into declarative (explicit) and procedural (implicit) memories. The important conclusions are:

  • Declarative memory requires conscious recall, in that some conscious process must call back the information. It is sometimes called explicit memory, since it consists of information that is explicitly stored and retrieved.

  • Declarative memory can be further sub-divided into semantic memory, which concerns facts taken independent of context.

  • Episodic memory, which concerns information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract about the world, such as “Delhi is the capital of India”. Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time.

  • Autobiographical memory for particular events within one's own life - is generally viewed as either equivalent to, or a subset of, episodic memory.

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Chapter 6 Ergonomics

Human Psychology

Psychology is the practice of studying, teaching or applying an understanding of the mind, thought and behavior. It is largely concerned with psychology of humans, although the behavior and thought of non-human animals is also studied; either as a subject in its own, or more controversially, as a way of gaining an insight into human psychology by means of comparison. Psychology is conducted both scientifically and non-scientifically. Mainstream psychology is based largely on positivism, using quantitative studies and the scientific method to test and disprove hypotheses, often in an experimental context. Psychology tends to be varied, drawing on scientific knowledge from other fields to help explain and understand behavior. However, not all psychological research methods are scientific, and some may involve qualitative or interpretive techniques more allied to the humanities. Some psychologists, particularly adherents to humanistic psychology, may go as far as completely rejecting a scientific approach. However, mainstream psychology has a bias towards the scientific method, which is reflected in the dominance of cognitivism as the guiding theoretical framework used by most psychologists to understand thought and behavior.

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Chapter 6 Ergonomics

Human Perception

Perception often concerned with pattern recognition: how does the information-processing system (mind) categories and distinguish among objects (important in the development of icons for use on screen; and in the repetition and representation of icons). In psychology and the cognitive sciences, perception is the process of acquiring, interpreting, selecting, and organizing sensory information. Methods of studying perception range from essentially biological or physiological approaches, through psychological approaches to the often abstract thought-experiments of mental philosophy.

The Senses

Human perception depends on the senses. The classical five senses are sight, hearing, smell, taste and touch. Along with these there are at least four other senses:

  • proprioception (body awareness),

  • equilibrioception (balance),

  • thermoception (heat)

  • nociception (pain).

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Chapter 6 Ergonomics

Ergonomics of Computer Use

Ergonomics is concerned with attempts to ensure a good match between people and the things they use. A good fit is one that optimizes work efficiency, effectiveness, comfort, ease of use, health and safety. The detailed specifications of physical and cognitive ergonomics are as follows:

  • 1. Workstation design

    The workstation includes the desk, chair, screen, keyboard, and/or any other equipment needed. It should be highly adjustable because people require:

    • all adjustment controls for comfort;

    • equipment within easy reach;

    • things moving around.

      Continued…

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Chapter 6 Ergonomics

Desk

  • Height of the desk:

    • should allow forearm to be horizontal when typing;

    • should be adjustable independently of chair to allow for extremes of human height;

    • should be according to wheelchair users;

    • should be in such a way that the writing surface may need to be higher than typing surface.

  • The surface of the desk:

    • should be non-reflective, non-slip, not cold to touch;

    • large enough for documents etc;

    • deep enough for screen, keyboard not to be too close to user;

    • should not have sharp edges, protruding legs etc;

    • should keep cabling out of the way.

      Continued…

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    Chapter 6 Ergonomics

    Chair

    • The chair should be stable & movable, e.g. on 5-star casters.

    • The chair should be adjustable corresponding to

      • seat height;

      • back support height;

      • back/seat angle.

  • When chair is at correct height, thighs and feet should be supported.

  • The footrest may be necessary for some users.

  • The arm rests restrict movement, may help in rising from chair.

    Keyboard

  • The keyboard should be movable and separate from screen.

  • The keyboard should have non-slip feet.

  • The keyboard should be adjustable at an angle of about 10 degrees.

    Continued…

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    Chapter 6 Ergonomics

    • The keys should:

      • be of about 12-15 mm diameter;

      • be 18-20 mm apart;

      • be concave in shape;

  • The shaped keyboards may be more comfortable.

  • The non-standard key layouts can balance work between hands better.

  • The keyboard should have wrist rest or at least sufficient desk space in front of keyboard to rest hands.

    Copy holder

  • It can be useful for designers and programmers.

    Screen

  • It should be apart 500-750 mm from user’s eyes.

  • It should have adjustable height to suit sitting position at:

    • top of screen level with eyes;

    • center of screen 30 degrees below eyes;

      Continued…

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    Chapter 6Ergonomics

    • The adjustable angle :

      • avoids from reflections;

      • suits user's preference;

      • allows more than one viewer.

  • The quality of image very important in terms of:

    • brightness;

    • color;

    • resolution;

    • absence of shake, flicker, drift.

  • VDU should be resilient to knocks and vibration

    2. Working Environment

    Noise

  • The noise measured in decibels (dB):

    • The noise level of 50-70dB is allowed in offices.

    • The noise level of 70+dB causes stress if sustained.

    • The noise level of 90+dB causes harm if sustained.

      Continued…

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    Chapter 6 Ergonomics

    • The types of sound that irritates:

      • rhythmic or continuous sounds not so disturbing as irregular.

      • continuous hum can be very annoying.

      • silence can be worrying too.

  • The sources of noise that may irritate:

    • people.

    • office/computing machinery.

    • PC fans, disks, printers.

  • The other sources of noise that need to be controlled:

    • acoustic hoods for machines or move them out;

    • muffle sound with carpets, curtains, acoustic tiles, acoustic screens;

    • cover noise with music or white noise.

      Continued…

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    Chapter 6 Ergonomics

    Vibrations

    • The vibrations from machinery etc. should be controlled. These can be very disturbing.

      Temperature

    • The legal minimum temperature in some jobs is 16 degrees centigrade.

    • Good working temp is 18-22 degrees centigrade, but it should be adjustable:

      • individuals vary, individual control is best.

      • females prefer warmer than males.

      • outside this range, comfort is rapidly affected.

  • The effect of large cold surface nearby should be large.

  • The heat emitted by computer equipment means air-conditioning may be needed.

    Humidity

  • 30-40% is best or say ideal.

  • The offices with computers tend to get too dry.

    Ventilation

  • is must if air conditioner is not working;

  • air movement is helpful up to the point where paper moves;

  • complete absence of draughts is very stuffy.

    Continued…

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    Chapter 6 Ergonomics

    Lighting

    • bad lighting can have large effects on productivity:

      • flickering fluorescent lights are very annoying;

  • Some people prefer natural light or a close approximation to it.

  • Ideally lighting should come from behind the left shoulder for right-handed people and vice versa.

  • The color of light affects atmosphere in the room.

  • The eye tends to be attracted to the brightest thing in the field of vision.

  • The 'ambient lighting' is the general lighting in the room.

  • The 'task lighting' is normally specific to one person:

    • e.g. desk lamp;

    • shouldbe individually controllable.

  • The 'glare' occurs when there is too much light from one source, affecting the ability:

    • e.g. a light source behind the VDU.

  • The 'reflections' a problem especially when they occur on the screen:

    • reflections can also be a source of glare e.g. off a shiny desk top.

      Continued…

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    • The solutions to lighting problems are:

      • to place VDU perpendicular to window.

      • to keep screen low to avoid reflections of lamps.

      • to use diffusers on light fittings.

      • to use many small light sources rather than one very bright one.

      • to use indirect lighting (e.g. up-lighting).

      • to use window blinds (preferably vertical).

      • to use non-reflective surfaces wherever possible.

      • to choose a good color scheme for furniture and decoration.

      • not too bright.

        3. Room Layout

        Comfort and convenience

  • A legal minimum space of 11 cubic meters per person in some circumstances.

  • Some people like to have a view, but also like privacy.

    Continued…

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    • The personal space is important:

      • subjective, depends on individual, task, and environment.

      • it should be something like 5-10 sq meters.

      • but need at least 20 sq meters each for confidential privacy.

      • assuming good noise control.

  • The open plan offices (with or without computers):

    • hard to work in a void with no boundaries.

    • ideally have screening to left, right and front if working alone.

    • less screening if cooperative work.

    • need to plan for access to files, doors etc.

  • The people with many visitors should be near the door.

  • Arranging PCs/terminals in shared labs:

    • need at least 1 meter between machines side by side to allow for papers and for more than one user per screen.

    • should have 1 meter space between back of machine and wall to allow access, and to allow refocusing of eyes.

    • avoid machines back to back if possible.

      Continued…

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    Chapter 6 Ergonomics

    Fire regulations

    • The fire regulations specify:

      • widths of doors and corridors.

      • distances to doors and fire escapes from accident.

      • placing of extinguishers etc.

  • The corridors and access routes in rooms must be kept clear.

    Wiring

  • It may need to use proper insulation to avoid injuries.

  • It may need to use fire free wiring setup.

  • It may need to allow for room plan changes.

  • The good methods of wiring are to use

    • sockets (power, data, phone) in floor.

    • sockets suspended from ceiling.

  • can't put too much in one duct:

    • inductance and overheating problems.

    • maintenance is not easy.

      4. Health

  • No long-term data is available on health risks, there are no users with more than 20 or so years' use of VDUs.

    Continued…

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    Chapter 6 Ergonomics

    Radiation

    • Radiation emissions from VDUs have been blamed for lots of problems:

      • they do emit radiation of various kinds but at very low levels.

      • older VDUs are much worse.

      • most types of radiation (except light) are emitted more to the rear.

        Stress

    • A psychological state causing or triggering a variety of real physical symptoms is called stress.

    • The causes related to computer work may include:

      • working environment.

      • lack of cooperation.

      • lighting, noise etc.

      • computer phobia.

      • problems with changing to a computerized system.

      • deskilling.

      • less control over work.

        Continued…

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    • poor job design, repetitive work.

    • inadequate training.

    • bad system.

    • poor interface design.

    • wrong specification.

    • too many breakdowns.

    • work monitoring (real or imagined).

    • worry about computers causing stress and other health problems

  • The cures from stress are to:

    • fix the above problems;

    • take regular frequent breaks from VDU work.

      Continued…

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    Chapter 6 Ergonomics

    • Pregnancy problems

    • some evidence showing a link between miscarriage and VDU work.

    • cause unclear:

      • radiation.

      • posture/lack of mobility.

      • stress.

      • in some situations pregnant workers have a right to be moved to other work.

        Eye strain and headaches

  • It can be caused by:

    • high brightness, contrast and color combination.

    • poor VDU image.

    • sitting too close.

    • restricted range of focusing.

    • overwork.

      Continued….

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    Chapter 6 Ergonomics

    Photosensitive epilepsy

    • Attacks can be triggered by VDU use in susceptible individuals.

    • With adjustments to lighting and equipment, affected people can work with VDUs.

      Posture problems

    • It may be caused by bad furniture.

      Repetitive Strain Injuries

    • collective name for a group of specific conditions affecting upper limbs

      • effects include stiffness and pain

    • caused mainly by repetitive actions e.g. typing

    • other contributory factors may include

      • posture.

      • stress.

      • bad design of workstation.

      • bad training in equipment use.

    • If not tackled quickly effects can be permanent and disabling.

      Continued….

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    Chapter 6 Ergonomics

    Skin rashes

    • linked with regular VDU use.

    • cause unknown.

      • radiation.

      • low humidity.

      • electrostatic effects.

      • stress.

        Sick Building Syndrome

    • Many workers in the same building become ill with various symptoms:

      • cause unclear.

      • virus.

      • stress.

        Continued….

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    Chapter 6 Ergonomics

    Human Factors Vs. Ergonomics

    A human factor is a term used mainly in the United States. In Europe and the rest of the world, the term ergonomics is more prevalent. Human factors is a profession that focuses on how people interact with products, tools, procedures, and any processes likely to be encountered in the modern world.

    Simply put, human factors involves work to make the environment work in a way that seems natural to people. This involves research in human performance and capabilities, anthropometrics, usability, and design. Although the terms human factors and ergonomic have only been widely known in recent times, the field's origin is in the design and use of aircraft during World War II.

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