Term
|
Definition
Lifting
Lowering
Carrying
Pushing
Pulling
Holding |
|
|
Term
|
Definition
Finger Pressing
Gripping and Squeezing
Pinching and Squeezing
Torquing |
|
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Term
MMH
Lifting effects
(Factors effecting lifting?) |
|
Definition
Lower back injuries and lower back pain
$30 billion costs to industry per year
degeneration and herniation of L5/S1 and L4/L5 spinal discs |
|
|
Term
MMH
Factors affecting lifting ability?
Task: AND Personal: |
|
Definition
Task: weight, height of lift; frequency of lift; load distance from body; load distance from floor (bending); load position relative to sagittal plane (twisting); C.M. of load;load dimension and characteristics; handles; lifting technique
Personal: strength; body size; experience and knowledge of task; atttitude |
|
|
Term
MMH
Factors affecting lifting ability?
Environmental: Management: Psychosocial: |
|
Definition
Environmental: floor conditions (traction; plane); vibration; illumination; heat and cold
Management: frequency and length of rest breaks;variability of tasks -job rotation or enrichment; overtime
Psychosocial: atttude to work; interaction with co-workers |
|
|
Term
MMH
Classification of Lifts |
|
Definition
Squat: trunk upright and knees sharply flexed
Stoop: trunk flexed at hip and knees fairly straight
Free style |
|
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Term
MMH
Most efficient lift range and weight |
|
Definition
| 40-60 inches off floor and about 40 pounds |
|
|
Term
MMH
Scientific guides for protection from injuries |
|
Definition
The NIOSH lifting equation
The Job Severity Index (Texas Tech) |
|
|
Term
MMH
Scientific guides for protection from injuries |
|
Definition
The NIOSH lifting equation
The Job Severity Index (Texas Tech) |
|
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Term
|
Definition
Estimates the compressive force in the L5/S1 disc of the spine, since the greatest moment (due to external gravity forces) occurs here. Most injuries in the spine occurs at the L5/S1 and L4/L5 discs
Compressive forces over 6400 N at the L5/S1 disc is considered dangerous
3400-6400 N compression is considered a range within which the injury is likely to occur
Below 3400 N is considered safe
This biomechanical criterion is for infrequent, heavy lifts. |
|
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Term
|
Definition
Determines the maximum acceptable lifting weight (MAL) -- the maximum weight a worker is willing to lift and is capable of lifting for a shift, at work
MAL is subjectively determined in the laboratory |
|
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Term
|
Definition
Determines the upper limit of energy expenditure that is considered safe from exhaustion-related problems
This limit corresponds to the 50%-ile female capacity
The limits are
9.5 kcal/min for 8-hr jobs;
50 % of the person’s PWC (VO2 max) for 1-hr; 40 % for 1-2 hours; 33 % for 2-8 hours |
|
|
Term
|
Definition
Computes a recommended weight limit for lifting based on the task conditions
This equation is based on a combination of the biomechanical, metabolic, and psychological criteria in the form of one equation.
The equation gives the RWL (recommended weight limit) based on a constant factor (LC) adjusted for 6 work variables (called multipliers). The variables depend on the lift conditions. The constant factor is for perfect conditions. |
|
|
Term
MMH
NIOSH Equation 6 Variables |
|
Definition
The distance of the person from the load
The height of the object at the start of the lift
The vertical range of the lift
The amount the upper body is twisted (rotated)
The frequency-duration-range of lift combination
How good the hand-handle coupling is
(SEE PAGE 198 FOR EXACT DEFINITIONS)
The equation is:
RWL (kg)
= 23*(25/H)(1-.003|V-75|)(.82+4.5/D)(1-.0032*A)(FM)(CM) |
|
|
Term
MMH
Lifting Index (LI)
How hazardous is the job if a load of weight L is being lifted? |
|
Definition
LI = L/RWL
If LI > 3.0 the work is at great risk to injury |
|
|
Term
MMH
Good Lifting Technique |
|
Definition
-Bring load close to the body
initial position.
-Hold load close to the body
-Avoid twisting the trunk; move the feet instead |
|
|
Term
T6
What hand disorders can result from unnatural wrist and forearm positions? |
|
Definition
| tendinitis; tenosynovitis; CTS; epicondylitis |
|
|
Term
|
Definition
Design for mechanical/electrical power instead of muscular power.
Avoid vibration as much as possible, especially in the range 5-140 Hz. |
|
|
Term
T6
Tissue compression from sharp edges should be avoided |
|
Definition
Tool grip surface should not be sharp
End of tool handle should not rest in the palm of the hand (which is pressure sensitive
Ischemia (obstruction of blood flow)
thrombosis of ulnar artery |
|
|
Term
T6
Methods to avoid large finger forces |
|
Definition
Consider using larger trigger
Consider using more than one finger to reduce force per finger
Consider the position of the trigger |
|
|
Term
T6
How to avoid wrist bending? |
|
Definition
Wrist bending can be avoided
by using a bent handle tool\
Wrist bending can be avoided by bending the tip of the tool also |
|
|
Term
T6
Hand size and Handle size |
|
Definition
| The handle size should allow gripping at the base of thumb and at underside of 2nd finger phalange near knuckles |
|
|
Term
|
Definition
| helps minimize muscular effort |
|
|
Term
T7
How to Maintain proper posture |
|
Definition
avoid sharply bent joints (wrist, elbow, neck, hips, etc.)
avoid extended reaching |
|
|
Term
T7
4 principles of work area design |
|
Definition
| importance; frequency of use; sequence of use; function |
|
|
Term
|
Definition
| Put most important and work items in most visible and accessible areas |
|
|
Term
T7
Sequence-of-use Principle |
|
Definition
| the sequential arrangement of equipment should correspond to the sequence of use |
|
|
Term
|
Definition
| Equipment that are functionally related should be placed near to each other |
|
|
Term
T7
Frequency-of-use Principle |
|
Definition
| Equipment that are most frequently used should be placed in the most accessible areas |
|
|
Term
T7
Identify primary and secondary movement envelopes (regular and extended reaches) on the work table |
|
Definition
| Primary is 16 in (40 cm) for a 5th %-ile woman; secondary is 24 in (60 cm) |
|
|
Term
|
Definition
Sit
Stand
Sit-stand
Kneel
Lying down
Variable |
|
|
Term
|
Definition
To prevent muscular fatigue
To maintain body stability and arm positions
When worker must use foot controls
When fine assembly, writing and precision hand work are required
When the hands will not work at more than 6 in above work surface (desk or table top)
When work period is long |
|
|
Term
T7
Seat and work area should |
|
Definition
accommodate wide range of body sizes
maintain proper work posture
allow change of posture
allow free movements of arms and trunk |
|
|
Term
T7
Bending trunk forward... |
|
Definition
flattens the lumbar curve
increases pressure in the lumbar inverterbral discs
may lead to lower back pain |
|
|
Term
T7
Standing - when and why |
|
Definition
Work periods are not lengthy and muscular fatigue is not a problem
Mobility of the body is required
Great manual forces are required and objects above 10 lb are handles frequently
When fine assembly, writing and precision hand work are required
High, low or extended reaching is frequent
Adequate leg room is not available |
|
|
Term
T7
Consequences of prolonged poor posture (months or years) in VDT (computer) work |
|
Definition
Deterioration of joints, ligaments, and tendons
Lower back pain
Shoulder and neck pain from flexed neck and elevated shoulders
pain in wrist from sharp bending of wrist |
|
|
Term
T7
Sitting Work - Critical Parameters |
|
Definition
Correct work surface height
Correct distance from seat to work surface
Correct eye height
Well- designed chair (seat) for the task
Well-design table or desk for the task
Adequate space for equipment
Good workspace design for equipment |
|
|
Term
T7
Standing Work - Critical Parameters |
|
Definition
Correct eye height
Correct work surface height
Stable standing surface
Adequate space for equipment
Good workspace design for equipment
Workspace free of obstructions
Consider floor pads |
|
|
Term
|
Definition
L.O.S. should be such that
the neck is about 10 deg in flexion
and the eyes rotated downward moderately |
|
|
Term
T7
What is the best angle (range) to the horizontal ? |
|
Definition
Preferred display zone is 15-30 deg. from horizontal l.o.s. (resting l.o.s.)
Acceptable is up to 45 deg. |
|
|
Term
T7
Working Chairs (Seats) - Important Features |
|
Definition
Relevance
Stability
Comfort
Safety
Freedom to adjust posture |
|
|
Term
|
Definition
Chair must suit the task (job)
What different kinds of chairs (seats) are available ? |
|
|
Term
|
Definition
avoid falls and unnecessary movements
when should casters be used ? And on what floor conditions ? |
|
|
Term
|
Definition
adequate workspace prevents cramped postures
consider backrest dimensions and contours
consider backrest adjustability in height and angle with seat
are arm rests necessary ?
are footrests necessary ? |
|
|
Term
|
Definition
| don’t use bar stools unnecessarily; should they ever be used ? |
|
|
Term
T7
Freedom to adjust posture |
|
Definition
| adjustable seat and backrest heights and angles help prevent postural fixity |
|
|
Term
T7
Monitor too high or seat too low
What are the effects on
(a) neck and line of sight ? and
(b) buttocks and lumbar spine ? |
|
Definition
|
|
Term
T7
Keyboard too low
What are the effects on
the body at work ? |
|
Definition
|
|
Term
T7
Desk too low
What are the effects on
the body at work ? |
|
Definition
ANS:Low desk surface forces worker to sit away from work area. Shoulders ? Why
Lower back ? Why ? |
|
|
Term
T7
Seat Too Low
What are the effects on
1. the buttocks ?
2. lumbar spine ? |
|
Definition
|
|
Term
T7
Seat Too High
What are the effects on
1. The popliteal area ?
2. The underside of the thighs ?
3. The ankles ? |
|
Definition
|
|
Term
T7
Advantages of Balans chair |
|
Definition
avoidance of flexed trunk
good arm-trunk geometry |
|
|
Term
T7
Disadvantage of Balans chair |
|
Definition
Pressure on knee
Work duration
Postural fixity |
|
|
Term
T7
Optimal work surface height should be such that.. |
|
Definition
Upper arm is vertical and lower arm at 85-95 deg elbow angle
Trunk and neck bending are slight
work height is adjustable |
|
|
Term
T7
When seated or standing work surface height is a function of... |
|
Definition
elbow height (body size)
type of work (fine, precision, light assembly, coarse manual) |
|
|
Term
T8
Mental Activity - Definition |
|
Definition
A general term for any task where incoming information needs to be processed in some way by the brain
Brain work |
|
|
Term
T8
Response (reaction) time (1) |
|
Definition
interval between the receipt of signal and required response. It is 100 500 ms
It is important where speed of movement is critical
Response time =
actual reaction time (time to initiate response)
+ movement time (time to make response)
An indicator of the level of mental efficiency |
|
|
Term
T8
Response Time (2)
At the neurological level there are many stages |
|
Definition
Conversion of nerve impulse in the sense organ = 1 38 ms
Transmission along a nerve to the cerebral cortex = 2 100 ms
Central processing of signal = 70 300 ms
Transmission along a nerve to muscle = 10 20 ms
Latent time of response of muscle = 30 70 ms |
|
|
Term
|
Definition
governs the effect of having to react to much information. It states that the reaction time (RT) is linearly related to the log (base 2) of the number of alternative pieces of information uncertainty (or entropy or bits)
RT = a + b*log2N
where log2 N is interpreted as the amount of information uncertainty |
|
|
Term
T8
Information Processing Theory |
|
Definition
| If we are sure an event will happen (e.g. the sun rises in the morning), its probability of occurring (pi) = 1.0 and it carries no information uncertainty. For an event which looks almost impossible (pi) = 0 almost and there is a lot of information |
|
|
Term
|
Definition
Information is the reduction of uncertainty
Shannon and Weaver (1949) proposed that information be measured in bits (H).
A bit is the amount of information uncertainty required to decide between two equally likely alternatives
(Hi = log2 (1/pi)
pi = probability of occurrence of event i
Hi = information associated with event i |
|
|
Term
T8
(Hi = log2 (1/pi) CON'T |
|
Definition
e.g. For 2 equally likely alternatives H = 1
For 4 …………………………….H = 2
For 16 ……………………………H = 4
i.e. the greater the number of alternatives to choose from, the greater is the information uncertainty (number of bits) |
|
|
Term
T8
Information Processing Theory |
|
Definition
We can apply Hick’s law to compare alternative designs, realizing that the more information given, the longer is the reaction time.
The theory is valid only for simple situations which can be split into units of information and coded signals |
|
|
Term
T8
Information Processing Theory |
|
Definition
For N events, the average amount of information HAv is
HAV = piHi = pi (log2 1/pi)
When all the pi are equal, HAv is at a maximum, H, where H = log2 N
Redundancy is the reduction from maximum HAv owing to unequal pi ’s
% Redundancy =(1-(Hav/Hmax))x 100 |
|
|
Term
T8
Computation of H max and H ave - 1 |
|
Definition
Given: 4 alternatives events with probability (pi ’s), p1 = 0.5, p2 = 0.25, p3 = p4 = 0.125
Then Have = pi log2 = 0.5(log2 ) +
0.25(log2 )+0.125(log2 )+
0.125(log2 )
= .5(1)+.25(2)+.125(3)+.125(3) =
= .5+.5+.375+.375 = 1.75 BITS |
|
|
Term
T8
Computation of Hmax and Have - 2 |
|
Definition
Hmax is the amount of information conveyed, had the 4 alternatives (N=4) been equally probable
Hmax = 0.25 *log2 (1/0.25)+0.25*log2 (1/0.25)
+ 0.25 *log2 (1/0.25) + 0.25 *log2 (1/0.25)
= 4 (.25log2 4) =4( .25*2) = 2.0 BITS
Have=Hmax for equally likely alternatives |
|
|
Term
T8
Channel Capacity Theory - 1 |
|
Definition
Concerns transfer of information
Compares information uptake with capacity of a channel.
Sense-organs are visualized as delivering a certain quantity of information to the input end of a channel and what comes out at other end depends on ‘capacity’ of channel |
|
|
Term
T8
Channel Capacity Theory - 2 |
|
Definition
| People have large channel capacity for verbal information. A vocabulary of 2500 words required a channel capacity of 34 42 bits/s |
|
|
Term
T8
Channel Capacity Theory - 3 |
|
Definition
A telephone cable can handle up to 50,000 bits/s
In everyday life incoming information exceeds channel capacity of CNS, so a reduction process must be carried out with the following results |
|
|
Term
T8
Channel Capacity Theory - 4 |
|
Definition
Results of reduction process
Process Information stream in bits/s
Registration in sense 1109
At nerve junction 3106
Conscious awareness 16
Lasting impression 0.7 |
|
|
Term
|
Definition
A CHUNK of information is a familiar unit, regardless of size, which can be recalled as an entity.
Most people can recall 7(+/-)2 chunks.
The more meaningful the CHUNK, the more easily it can be recalled; e.g. IBM JFK better than IBMJFK
Practical Applications
Avoid presenting greater than 7(+/-)2 chunks for people to remember
Provide training on how to recall info by chunking |
|
|
Term
|
Definition
Perception is awareness of the elements of the environment via the senses. Includes interpretation in cerebral cortex of brain
Our impressions are a subjective modification of what we perceive
Environmental Sense Bioelectric Cerebral Awareness
Energy Organs Impulses Activity
Perception involves prior experiences and learned associations
(slide 28) |
|
|
Term
|
Definition
Signal is stimulus to be detected
Noise is stimulus which interferes with signal and prevents accurate sensing of signal
The intensity of both noise and signal may have a distribution (overtime) which may be assumed to be normal (from low to high)
Signal detection theory (SDT) is concerned with the probabilities of detecting or not detecting a signal in the presence of a noise |
|
|
Term
|
Definition
| Determining whether a signal or target is present |
|
|
Term
T8
Identification and recognition of signal |
|
Definition
| Determination of class to which signal belongs |
|
|
Term
T8
Factors Influencing Reception and Processing of Information |
|
Definition
Noise
Load stress & speed stress
Time sharing
Use of redundant sensory channels
(AV > A > V)
Compatibility relationships |
|
|
Term
T8
Load or speed stress... |
|
Definition
| has been defined as the reaction by the person which has the effect of worsening performance relative to what would be expected from a situation the person should be able to handle. Note that engineers call this reaction a strain and call the cause the stress; e.g. anxiety=strain; fast pace of work=stress. |
|
|
Term
|
Definition
| – refers to the number of stimuli attended to per unit time, measured in time/stimulus. |
|
|
Term
|
Definition
| – refers to the number and type of stimuli to be attended to |
|
|
Term
|
Definition
– performing two or more activities simultaneously or in rapid succession.
Strategies vary according individuals; e.g. giving primary attention to one task.
Tasks that involve uncertainty or short term memory produce more errors. |
|
|
Term
T8
Example of performance effects of time sharing of auditory inputs |
|
Definition
| – Two verbal messages arrive simultaneously; only one gets through. If a lag occurs the 1st is more accurately identified, unless the second is much more intense. The more similar a competing (irrelevant) message is to the relevant one, the more it interferes with the latter, and vice-versa. |
|
|
Term
T8
Signal Detection Theory - 1 |
|
Definition
According to SDT there are 2 possible states in any situation – there is a signal or there is no signal
Neither state can be easily discriminated. The signal intensity may masked by extraneous background energy, called ‘noise.’ We must decide if the sensory input is only noise or noise plus signal.
Possible outcomes: hit, false alarm, miss or correct rejection according to SDT
See page 87-89 for examples of application of SDT. |
|
|
Term
T8
Signal Detection Theory - 2 |
|
Definition
| To interpret SDT, you must consider the signal and noise values having distributions that overlap, as shown (page 88). Decisions are made so as to maximize hits and minimize misses. The operator is said to have set his/her decision criterion at a certain level β |
|
|
Term
T8
Signal Detection Theory - 3 |
|
Definition
A conservative operator has β more to the right, where the miss rate in mimimized and hits are maximized. However, this means that false alarms are increased. This is a risky decision.
Consider a surgeon who doesn’t want to miss a case for surgery. He/she will end up performing more surgeries unnecessarily (increase in false alarms) |
|
|
Term
T8
Signal Detection Theory - 4 |
|
Definition
The separation of the means of the noise and signal distributions (called the sensitivity, d/) influences the probability of a hit, miss, etc. Experienced operators have large d/ (high sensitivity) . Note that complete separation of the distributions means high sensitivity, 100% hits, 0% miss, etc. This situation is not common.
When separation cannot be achieved we must decide on placement of criterion level and so on the type of error to tolerate. |
|
|
Term
|
Definition
Watching a display to detect a signal – often over a prolonged period of time.
The steady state of vigilance is called Vigilance Level
Vigilance level decreases sharply, non-linearly, with time.
The loss of vigilance level is called vigilance decrement. It increases if
-signal has low strength
-there is spatial or temporal uncertainty
-if only a few events occur in the background |
|
|
Term
T8
Methods to reduce vigilance decrements |
|
Definition
Increase mental availability – increase examples of targets on the screen
Increase target salience – e.g. increase the size
Remove social isolation
Add irrelevant tasks to raise physiological activation level, e.g. playing games
Provide trial testing using signal detection theory
Use job rotation and schedule rest breaks to reduce fatigue
Present signal in two modes (e.g. auditory and visual) |
|
|
Term
|
Definition
| Human error is an inappropriate or undesirable human decision or behavior that reduces or has potential for reducing effectiveness on safety of system performance |
|
|
Term
T8
Classification of human errors |
|
Definition
1. Engineering Classification – assumes that errors are from discrete action
Error of omission
Error of commission
Sequence error
Timing error
Extraneous act |
|
|
Term
T8
2. Information processing classification (or model) |
|
Definition
Human error may be viewed as a break in the stimulus organism response (S-O-R) chain (as input, mediation, or output error)
Failure to perceive stimulus
Inability to discriminate among various stimuli
Misinterpret of meaning of stimulus
Not knowing correct response to stimulus
Physical inability to make response
Responding out of sequence |
|
|
Term
|
Definition
| Memory is the process of storing incoming information in brain storage capacity of human memory 108 to 1015 bits |
|
|
Term
|
Definition
Trace persistence of stimulus after its presentation; its duration depends on its modality: auditory (echoic)=20 sec; visual (iconic)=1 sec
All senses have storage memory. Duration of trace persistence in in sensory memory depends on modality. For auditory (echoic) memory it is ~ 20 seconds after stimulus vanishes. Verbal items left trace in visual system of ~ 200 ms. |
|
|
Term
|
Definition
1. Sensory Storage
2. Working (short term)
3. Long Term |
|
|
Term
T8
Sensory Storage (or Memory) |
|
Definition
Prolongs stimulus for a short period after cessation of presentation. There are 2 types
1. Iconic Storage _ Visual system (1 sec)
2. Echoic Storage – Auditory (a few sec)
Information in S.S. is not coded. It is relatively automatic and the …. of presentation cannot be consciously changed.
If information is encoded and transferred to working memory (person must direct attention to process) it can be retained longer. |
|
|
Term
T8
Short-term memory (STM) |
|
Definition
An item can be moved into STM for conscious attention. This use of STM is called working memory (WM).
Comprises immediate recollection of instantaneous happenings up to about a few hours ago. This model postulates that the trace information continues to circulate as a stimulus through the nervous tract and
Can be recalled into conscious sphere by a kind of feedback loop.
Memory span is 7 2 items. |
|
|
Term
|
Definition
Information in WM is coded in 3 types of codes
1.Visual 2. Phonetic 3. Semantic.
All 3 can exist simultaneously for a particular storage.
Visual word DOG is phonetically coded as sound.
Also if you hear the word DOG you could generate visual code (picture).
You can also form visual image from long term memory alone. |
|
|
Term
|
Definition
Information stored for longer than a few hours
Info in Working memory is transferred to LTM by semantically encoding. i.e. by supplying meaning it and relating it to information already stored in LTM.
The use of MNEMONICS to organize information makes retrieval easier. |
|
|
Term
|
Definition
| are abstract representations of the meaning of a stimulus rather than the sight or sound generated by the stimulus. |
|
|
Term
|
Definition
Errors of recall tend to be acoustic rather than visual e.g. E for D but not E for F (E looks like F-phonetically similar).
Subset of letters should be phonetically dissimilar.
Optimum number of items that can be held in working memory = 7(+/-)2. |
|
|
Term
T8
ATTENTION
Three general types |
|
Definition
SELECTIVE A – Monitor several sources of information and determine whether the event has occurred
FOCUSSED A – Attend to one source of information and exclude all others.
DIVIDED A – pay attention to 2 or more tasks, performed simultaneously (multi-tasking; time sharing). |
|
|
Term
|
Definition
As number of information channels (e.g. dials) increases performance decreases, even when overall signal rate remains constant. This is LOAD STRESS.
Load stress is often more important than speed stress in degrading performance (72 signals/min can be processed better than 24 in 3 channels).
When people have to sample multiple channels of information, they tend to sample channels in which signals occur more frequently. |
|
|
Term
T8
Guidelines for Selective Attention tasks |
|
Definition
Use as few channels as possible.
Let subject know relative importance of channels so as to direct attention more effectively.
Reduce overall effect of stress.
Provide preview of information.
Train subject to scan optimally.
Place visual channel close together.
Do not mask auditory channels.
Rate of storage should be controlled. |
|
|
Term
|
Definition
| It is influenced by proximity in physical space of resources, and masking (indistinctness) |
|
|
Term
T8
Guidelines for Focused Attention |
|
Definition
Have distinctions in competing channels.
Separate competing channels.
Red. No. competing channels.
Make channels more conspicuous than. competing channels. |
|
|
Term
|
Definition
| Time sharing is doing more than 1 task at a time, performance decreases because the capacity to process information is overwhelmed. |
|
|
Term
T8
Guidelines for Divided Attention |
|
Definition
Minimize number of potential tasks.
For time sharing let the subject know relative priorities of tasks.
Lower the difficulty level of tasks.
Make tasks as dissimilar as possible.
Use physical as well as mental resources - manual time shared tasks interfere less with sensory or mental tasks. |
|
|
Term
T8
AGE affects information processing because of : |
|
Definition
A slowing of sensory-motor performance. This is due mainly to difficulty in perception of incoming data and choice of responses in incoming data.
Increased disruption of working memory by shift of attention during the time the material is held there.
Difficulty in searching for material in long term memory.
Difficulty in dealing with incompatibility, especially conceptual, spatial and movement compatibilities. |
|
|
Term
T8
Guidelines for Designing Tasks for the Elderly |
|
Definition
Strengthen signals.
Reduce irrelevant details in display layout
Maintain high level in conceptual, movement, or spatial compatibility.
Reduce time sharing demands.
Let person set the pace of the task
Allow more time and practice to learning phase. |
|
|
Term
T8
Human & System Reliability 1
Definition: |
|
Definition
| the reliability of a system (or component) is the probability of its completing its task successfully. In a human-machine system, the human and the machine are separate components, and are assumed to be independent. Components may be in series, in parallel or in a series-parallel arrangement |
|
|
Term
|
Definition
Data Store empirical performance data (times and probability)
Aerojet GMPDB from task analyses and expert systems; predicts reliabilities during checkout and maintenance in TITAN II
THERP task analysis and application of human reliability table estimates
Simulation computer performs task repeatedly from probabilistic distributions of task element success and failure |
|
|
Term
T8
Criticisms of Human Reliability |
|
Definition
Point estimates unrealistic
Not all errors result in failure
Estimates are inappropriate for conscious tasks
Classical engineering reliability modeling not always good for discrete tasks
Four decimal places unrealistic
Expert judgement data are subjective
Personal judgement input by analyst for particular application
Data too scanty |
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Term
T8
Decision making strategies and biases |
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Definition
In general
We give more weight to early information.
We do not extract enough information as we should.
Odds are not assessed as extreme, as they should be.
We increase our confidence, but not necessarily our accuracy, with more information.
We seek more information than we can absorb.
We treat all information equally reliably. |
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Term
T9
Q. When do we display information? |
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Definition
A1. When sensing is inadequate, because stimulus is
Below threshold
Too large
Embedded in excessive noise
Removed or obstructed
Sensed with low precision
To be stored
Convertible (same or different modality)
Inherently of display type |
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Term
T9
Q. When do we display information?
(2) |
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Definition
A2. When stimuli are outside range of human sensitivity, for example
A sound meter can be used as a display for sounds below the threshold of human hearing
An EKG is a display of the electrical activity of heart muscles |
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Term
T9
Absolute judgements along single dimension |
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Definition
Identifying without actually comparing, except in memory; e.g. identifying an aircraft as a military one
Number of discriminations that can be made on absolute basis is much less than on a relative basis
People can make about 7 2 identifications on absolute basis
Limits based on memory and can be increased with practice |
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Term
T9
Absolute judgements along multiple dimensions (of a single stimulus) |
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Definition
| Coding of dimensions may be orthogonal or redundant. |
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Term
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Definition
| Value of one dimension independent of another; e.g. if color and shape are combined orthogonally then a red square would signify something different from a green square or red circle |
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Term
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Definition
Knowing the value of one dimension helps predict the value of the other dimension; e.g. we may have shapes such that all circles are red, all squares are green, all triangles are amber, etc.
The number of stimuli that can be identified on absolute basis increases when dimensions are combined orthogonally or redundantly |
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Term
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Definition
| Compare stimuli and judge positions along a dimension; e.g. compare two sounds to determine the louder one |
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Term
T9
Multiple Dimensions - 1 |
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Definition
Used for identifying a wide variety of stimuli that differ in dimensions, e.g. frequency of sound, shape of a visual symbol, etc.
Two kinds -- orthogonal and redundant |
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Term
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Definition
value of one dimension independent of another. All combinations equally likely.
For example, if shape and color are orthogonal then red circle and red square would signify two different coding schemes.
Combinations increase number of stimuli that can be identified, but produces less than product of the separate numbers. So redundant combinations of 4 colors and 3 shapes yield more than 4 but less than 12 size-color combinations. |
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Term
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Definition
Not independent; if shape and color are redundant then all circles would be red, all squares green, etc.
Knowing the value of one dimension completely determines the value of the other.
Combinations increase number of identifiable signals to more than the number for a single dimension but yields less combinations than orthogonal dimensions |
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Term
T9
Types of Information on Displays - 1 |
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Definition
Static or Dynamic
Quantitative or Qualitative
Status information
e.g. speeding zone on a speedometer; closed/open sign; etc.
Warnings and signals
Representational information
e.g. photos; maps; graphs; etc. |
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Term
T9
Identification displays |
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Definition
| e.g. color-codes pipes; slippery road sign; etc. |
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Term
T9
Alphanumeric and symbolic |
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Definition
| e.g. textbook material; braille; etc. |
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Term
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Definition
| e.g. morse code; blinker lights; etc. |
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Term
T9
What are the 5 main Display Modality's? |
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Definition
Visual
Auditory
Tactual (or Tactile)
Olefactory (Smell)
Taste |
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Term
T9
Use auditory mode instead of visual when the message is |
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Definition
Simple
Short
Not to be referred to later
Time sequenced
Of emergency type
Or when
Vision is overburdened
Brightness and glare present visual problems
Movement (of person) is necessary |
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Term
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Definition
The ability of the eyes to differentiate between the detailed features of what we see
Indicators and Measures of Visual Acuity -- accomodation, hypermetropia, myopia, minimum separate acuity; visual angle (VA)
VA =(3438H)/D Acuity = 1/VA |
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Term
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Definition
the ability of the 2 eyes to position the object (being viewed) at corresponding positions so that the 2 images are fused
defect = phorias |
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Term
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Definition
cone cells in retina are responsible
R&G and B&Y often confuse
From light to dark (30 mins) |
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Term
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Definition
| the adjustment of the lens of the eyes to focus images sharply on the retina |
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Term
T9
Minimum separate acuity |
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Definition
| the smallest feature, or smallest space between parts of a target, that the eyes can detect |
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Term
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Definition
measures the detail that can be seen as the angle (in minutes of arc) the target makes with the eye. One minute of arc is used as a reference
VA =(3438H)/D Acuity = 1/VA
If visual angle = 2 minutes, say, then acuity score of 1/2 or 0.5 |
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Term
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Definition
- ability to adapt to different levels of light intensity so that eye retina is not overexposed or underexposed
Time for adapting from light to dark is about 30 minutes or more
Time for dark to light varies from a few seconds to about 2 minutes |
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Term
T9
Myopia (hyperopia or short-sightedness) |
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Definition
Difficulty in seeing sharply at far distances but not close up
What is the physiological cause ? |
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Term
T9
Hypermetropia (or hyperopia or far-sightedness) |
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Definition
| Difficulty in seeing close up but not at far distances |
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Term
T9
Convergence: defect = phorias |
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Definition
| Phorias is the inability to converge properly (may be too much or too little) resulting in double vision |
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Term
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Definition
- inability of some people to discriminate between some colors
Red and green are often confused
Blue and yellow are often confused |
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Term
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Definition
The ratio of the amount of light reflected (luminance) by a surface to the amount striking the surface (illuminance) is called the reflectance of the surface
Reflectance =
luminance (cd/sq-m)/illuminance (lux) |
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Term
T9
Conditions that affect visual discrimination or acuity |
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Definition
Luminance contrast (brightness contrast or contrast) is the difference in luminance of the features of the object being displayed – object vs background
B2 is the brighter of the two contrasting areas
Paper has a reflectance of 80 % and print 10 %; therefore contrast = 88 %. For low contrast enlarge the target |
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Term
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Definition
– depends on task; should not vary more than about 5:1 in adjacent areas; very hig levels may ‘wash’ away different gradients.
Public areas – 20-50 lx
Offices – 400-500 lx
Surgical procedures – 10,000-20,000 lx. |
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Term
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Definition
| discriminability increases with viewing time |
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Term
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Definition
| - 3:1 for task and surrounding area in office |
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Term
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Definition
- direct and reflected (specular)
- Discomfort glare; disability glare; blinding glare |
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Term
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Definition
| – decreases the threshold of visual acuity. The ability to make visual discriminations is called dynamic visual acuity (deg/sec). Acuity decreases rapidly beyond 60 deg/sec. |
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Term
T9
Personal factors e.g. age |
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Definition
| Presbyopia occurs. Lens becomes discolored and less flexible, so light intensity must increase and more time must be allowed for refocusing. |
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Term
T9
Perception (meaning vs. seeing). |
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Definition
| A design should help people perceive what they sense. Training may be needed. |
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Term
T9
Cont’d
Adaptation
Color discrimination |
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Definition
| Cones are responsible. Normal people (trichromats) can distinguish hundreds of colors. Color discrimination occurs for red and green. May be inherited or acquired.; 8 % males and 0.5 % females |
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Term
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Definition
refers to various features of the characters and their arrangements - viewing conditions, information importance, distance, and visual acuity
Stroke width ratio of stroke thickness to character height white on black (1:8 to 1:10); black on white (1:6 to 1:8); illumination level
Width to height ratio: capital letters (1:1); numerals (3:5)
Styles of type (fonts). Which is best for you ?
Typography may affect legibility, visibility or readability. |
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