SST102 HUAT AH
HF IMPLICATIONS OF WM LIMITS (when they ask about which one is a better representation)
Exploit chunking • Physical chunk size: optimal arbitrary string is 3-4 items per chunk • Use meaningful sequence: 555, 4321, or JFK • Superiority of letters over numbers: letters induce better chunking (more meaningful), 1-800-663-5900 vs 1-800-GET-HELP (fewer chunks and more associative meaning) • Keep numbers separate from letters: better kept in WM SFA 5555 K
Fit & Reach percentile
Fit 95% Reach 5%
Sound waves (Freq + Ampli)
Frequency (perceived pitch) measured in Hz Amplitude (perceived loudness) measured in dB
LONG-TERM MEMORY (Mental Models)
Mental Models are a type of schema that describes our understanding of dynamic systems, how a system works, and how to use it - Set of expectancies generated - Mental models that are shared by a large group of people are termed population stereotypes
Sound Masking
Minimum intensity difference necessary to ensure that a sound can be heard is about 15 db (above the mask). Guarantee is 30db
Percentile
• A percentile value of an anthropometric dimension represents the percentage of the population with a body dimension of a certain size or smaller. • Percentiles help to estimate the percentage of the user population that will be accommodated by a specific design.
Factors Influencing Visual Search:
Top-Down Processes - Expectancies • Based on prior knowledge - Radiologist searching x-ray plate for tumor will start search in the area suspected of containing the tumor • Important to arrange structure of the search field to be consistent with user's prior experience and mental model. - Phone book listing to find name
Visual Search - Saccadic Movements
• Abrupt, discrete movements from one location to the next • Characterized by: - Movement time (50msec), - Dwell or fixations (3-4 per second) - Useful Field of View (how large around the center of fixation, is available for info extraction)
Focused attention
allows us to filter out unwanted information.
Selective attention
allows us to process important information
Capacity in WM
• 7 +/- 2 chunks of information (Miller's magic number) • A chunk is a unit (1 bit of info) of working memory space defined by properties that bind items together (remember unitization?) • Extent to which units are "chunked" depends on degree of user familiarity with groupings • Chunking decreases the number of items in working memory and therefore increases the capacity of working memory storage
lordosis
lumbar curvature
HF can save companies...
time, money and ppls lives if applied correctly
Mental Model Principles
6. Principle of pictorial realism - A display should look like or resemble the variable that it represents 7. Principle of the moving part - The moving element should move in a spatial pattern and direction compatible to how the represented actually element moves
Goals of Human Factors Engineering
Increase Safety, Enhance Performance, Increase User Satisfaction
Use Auditory or Visual?
(opp for V) Auditory if: Message is simple and short Message will not be referred to later Message needs immediate action Visual system is overburdened Location is too bright or dark adaptation required Job requires moving abou
• Top-down processing
- Ability to correctly guess what a stimulus is even without clear bottom-up features - Based upon expectations and past experience
Divided Attention
- Ability to perform more than one cognitive task by attending to both at once or by rapidly switching attention. - Time sharing decrement —time sharing between multiple tasks usually causes drop in performance for one or more tasks
Our ability to keep information in working memory is dependent on:
- Capacity (how much information must be kept active) - Attention (how much attention is required to keep the material active) - Time (how long it must be kept active) - Similarity (how similar the to-beremembered material is to other elements in working memory)
• Physiological measures (WL Measure)
- Heart rate - Heart rate variability (consistent and reliable for MW) - Blink rate - EEG - Pupil diameter - Visual scanning and fixations
Task Analysis
- Helps to match the demands of the system to human capabilities. - Used to determine the specific jobs, duties, tasks, and actions that a person will be doing - Helps to develop an information base that includes user goals, major tasks to achieve goals, required information, output, etc
Human Error - Error Classification (Commission) - Operator who does something that should not have been done.
- If intended = mistake (e.g., turning into a one-way street) • Knowledge-based mistakes (lacks knowledge-in-the-head or world) • Rule-based mistakes (e.g., misapplies rule in a situation) - If unintended = Slips (e.g., problem with selection of action)
Mental WL Measures (SecondaryTask)
- Measure the reserve capacity left over after performing the primary task (examples: rhythmic tapping, mental arithmetic, etc) - Increasing primary task difficulty will affect secondary task performance - High face validity - Tasks may be intrusive so can use embedded tasks
• Subjective measures
- Most intuitive measure of MW - Easiest to obtain - Operators rate workload on subjective scale - Multidimensional scales are best - Examples are NASA-TLX, MCH, SWAT, etc
Errors of Omission:
- Operator who fails to do something that should have been done. - Non-intentional error of omission = lapses
2. Confirmation Bias
- People tend to seek out only confirming information and not disconfirming ones in evaluating the hypothesis
• Bottom-up feature analysis
- Starts by analyzing raw features of stimulus
Time Weighted Average
- TWA > 85 decibels = Action Level Employers required to implement hearing protection plan - TWA > 90 decibels = Permissible Exposure Level (PEL) Employers required to take steps toward noise reduction
Decision Complexity (Hick-Hyman Law of RT)
- The speed with which an action can be selected is influenced by the number of possible alternative actions that could be selected (complexity of the decision) - User can select more rapidly from menu with two items than from menu with eight
Alerting Displays (In terms of severity of consequences)
- Warnings (most critical) : Should be signaled by salient auditory alerts - Cautions : Can have less salient auditory alerts - Advisories : Can be purely visual
How to Perform a Task Analysis
1. Define the purpose of the analysis and determine the types of data required. 2. Collect task data. 3. Summarize the data. 4. Analyze the data.
Principles of Response Selection
1) Decision Complexity (HH Law) 2) Response Expectancy 3) Compatibility 4) Speed-Accuracy Tradeoff 5) Feedback
Rods & Cones Properties
1) Location - Fovea 2º visual angle (only cones) - Periphery (rods and cones) 2) Acuity - Fine detail resolved on closely spaced cones - Drops rapidly towards periphery (but not motion sensitivity) 3) Sensitivity - Greater for rods (try looking directly at light at night) - Photopic vs scotopic vision 4) Color Sensitivity - Rods are color-blind - affects daytime periphery and night vision 5) Adaptation - Rods lose sensitivity with light stimulation - Half hour for dark adaptation 6) Differential Wavelength Sensitivity - Rods particularly insensitive to long wavelengths (red) - Red object appears black at night - Red light does not destroy rods dark adaptation
cognitive limitations (hypothesis brought to WM)
1. Cognitive Tunneling - 2. Confirmation Bias
Hypothesis Generation, Evaluation and Selection
1. Generation of a limited number of hypotheses - People generate only a small subset of hypotheses (1-4) due to WM constraints and never consider all relevant ones 2. Availability heuristic - People more easily retrieve hypotheses that have been considered recently or frequently 3. Representativeness heuristic - Diagnose a situation because the pattern of cues 'look like' a typical example of this situation 4. Overconfidence - People believe that they are more correct in the hypotheses brought into WM than they actually are; less likely to seek out evidence for alternative hypotheses
5 Perceptual Principles (Principles of Display Design)
1. Make displays legible (or audible) - Contrast, visual angle, illumination, viewing distance, noise, masking 2. Avoid absolute judgment limits - Do not require judging of level from more than 5 levels of single sensory variable 3. Top-down processing - We perceive and interpret based on expectations (past experience) 4. Redundancy gain - When the same message is presented more than once, particularly if the presentation is in alternative physical forms 5. Discriminability: Similarity causes confusion - Remove similar features and highlight disimilar ones
Memory Principles
11. Replace memory with visual information: Knowledge in the world - Place information of 'what to do' in the world - Don't require to retain in WM or retrieve from LTM - E.g. Caller ID, checklist, etc 12. Principle of predictive aiding - Cut down cognitive task and WM load - Becomes a simpler perceptual task 13. Principle of consistency - Standardize and make consistent with other displays encountere
Six guidelines for display layout:
1Frequency of use Most frequently used displays should be adjacent to the human operator's primary visual area. 2Display relatedness or sequence of use Related or sequentially used displays should be close together. 3ConsistencyDisplays should always consistently be laid out with the same item positioned in the same spatial location. 4Organisational grouping All displays within a group should be functionally related. 5Stimulus-response compatibility Displays should be close to their associated controls. 6Clutter avoidance There should be a minimum visual angle between all pairs of displays.
Receiving and Using Cues
2. Cue primacy and anchoring - First impressions last 4. Cue salience - Loudest, brightest, top row cues are more likely to attract attention and are given more weight. The most salient cues aren't always the most diagnostic ones 1. Attention to a limited number of cues - Limited by constraints on working memory 3. Inattention to later cues - Cues occurring later in time or ones that change over time are ignored; attributable to attentional factors 5. Overweighting of unreliable cues - Due to treating all cues as equally reliable
Labels (4 key design criterias)
4 key design criteria a) Visibility/Legibility : Words and shapes should be discerned under poor viewing conditions b) Discriminability : Highlight features that help discriminate label from a possibly inferred alternative c) Meaningfulness : Even if a word or icon is legible and not confusing, no guarantee the person will know what it means : Labels based solely on icons or abbreviations should be avoided where possible : Icons useful for non-native speakers d) Location : Should be physically close to and unambiguously associated with the entity that they label
Principles Based on Attention
8. Minimizing information access cost - There is time and effort to move selective attention from one display location to another to access information - Minimize this by keeping frequently accessed sources of information close 9. Proximity compatibility principle - Two or more sources of information related to the same task must be mentally integrated (graph and legend) - Mental proximity (line, colour, pattern) vs Display proximity (info access cost) - Divided attention vs focused attention 10. Principle of multiple resources - Processing of displayed information should be facilitated by dividing information across resources (visual and auditory concurrently)
guidelines for optimizing monitoring displays (Analog vs Digital)
: Analog superior for representing continuously changing quantities : More easily read at a glance : Easier to estimate rate and direction of change : Digital superior if very precise readings or setting of exact value is required
Analog Form and Direction (read only)
: The orientation of display scale should be in a form and direction congruent with the operator's mental model of the displayed quantity : Dynamic displays should move in a direction consistent with user's expectations
Voice Alarms
Advantages • Compared to "symbolic" alarm sounds, voice alarms are not dependent on learning (e.g., "Engine Fire" or "Pull Up!"). Disadvantages • Can be confused with and are less discriminable from background of other voice communications. • May be more susceptible to frequency-specific masking noise. • Problematic for "non-native" speakers. * Advisable to use redundant system that combines distinctive features of the non-speech alarm sound with more informative features of synthetic voice (redundancy gain).
Height, BReadth and Depth
Anthropometry Terms • Height - A straight-line, point-to-point vertical measurement • Breadth - A straight-line, point-to-point horizontal measurement running across the body or segment • Depth - A straight-line, point-to-point horizontal measurement running fore-aft the body
5 approaches to implement solution
Equipment design Changes the nature of the physical system with which humans work. Task design Changes what humans do with the system. Environment design Changes the aspects of the environment in which the work is carried out. Training Better equips the humans for the task with the necessary skills. Selection Recognises individual differences across humans that are relevant for good system performance.
Influences on Contrast Sensitivity
Contrast - High contrast is easily discerned. - Low contrast (e.g., "black on black" raised printing instruction) is difficult to see.
POV: System =
Device / Device + Human / D + H + Task + Environment
Characteristics of User Centred Design
Early focus on the user and tasks Empirical measurement Iterative design using prototypes Participatory design
HF in product design lifecycle
Front-end analysis The purpose of front-end analysis is to understand the users, their needs, and the demands of the work situation. Activities carried out during this stage include a user analysis, environmental analysis, function and task analysis. Much of the front-end analysis involves understanding and spelling out goals, functions, and tasks. A goal is an end condition or reason for performing the tasks, functions represent general transformations needed to achieve the goal, and tasks represent the specific activities of the person needed to carry out the function. Iterative design and test Once the front-end analysis has been performed and the required information has been gathered, system specifications and conceptual design solutions can be written. System specifications include performance requirements and features. Usability requirements are also included and functional allocation is carried out as well in this stage. Implementation and evaluation This process involves users and is concerned with any aspects of the system that affect human performance, safety, or the performance of the entire human-machine system. To properly evaluate a product or system, it should be tested under conditions as close as possible to those under which it will ultimately be used.
User Analysis
Identify potential users, create complete description of potential user ppln Eg of characteristics age, gender, education level, reading & physical ability, physical size
Response Expectancy
Information Expectations: We perceive information that we expect more rapidly than information we do not expect Response Expectations: We select actions we expect to carry out more rapidly and accurately than actions that surprise us
Iterative Design and Testing
Key Activities - Using information obtained from front-end analysis to develop initial system specifications • QFD, Tradeoff Analysis, Human Factors Criteria Specification, Functional Allocation, Support Materials Development - Creating initial system prototypes - Conducting usability testing - Carrying out multiple interactions of evaluation and re-design
Describe Visual Receptor system
Light first passes through the cornea (protective surface; absorbs some light energy), then through the pupil, before reaching the lens
Stat Analysis (MEan + SD)
Mean (measure of central tendency). Standard deviation (degree of dispersion in a group of measured scores).
TWA is > 85 dB
Noise Remediation: Noise Reduction Source (Equipment and Tool Selection) - Ventilation, fans and tools vary in sound that they produce (important point to consider before buying) - Many sources of noise can be alleviated through the use of damping materials. - Irritating effects of noise greater in high frequency areas. Environmental Noise - Change environment near source - Sound absorbing walls/ceilings & floors can be effective in decreasing sound from reverberations - Reposition workers relative to noise source
TWA is < 85 dB
Noise Remediation: Signal Enhancement Bottom-up Solutions: • Analyze spectral content of the masking noise; then use signal spectra that has least overlap with noise content. • Use lower frequency sounds or earphones to bring the sound closer to the operator's ear. Top-down Solutions: • Use Redundancy. - Face to face mode provides redundant cues (lip movement) that are not provided when the listener cannot see the speaker. - Use of the phonetic alphabet ("alpha, bravo, charlie ...) - Use common words or standardized communications procedures to decrease the chances of error.
Motion Sickness
Normally, visual and vestibular senses convey compatible and redundant information Visual and vestibular channels may become decoupled so that one channel tells the brain one thing and the other tells it something else.
Top-Down: Depth Perception
Object centered cues: Psychological depth perception • Linear Perspective - Converging of parallel lines toward more distant points • Relative Size - If 2 objects are the same size, the object that occupies the smaller visual angle is farther away • Interposition - Nearer objects tend to obscure contours of objects that are farther away • Light & Shading - 3D objects tend to cast shadows and reveal shadows & reflections on themselves from illuminating light • Textural Gradients - Textured surfaces, viewed at an angle, will show gradient or change in texture density across visual field • Relative Motion (Motion Parallax) - More distant objects will show relatively smaller movement across the visual field as the observer moves
Bottom-up: Depth Perception
Observer centered cues: Physiological depth perception - Accommodation • focusing images through changes in shape of the lens - Binocular convergence • inward rotation of eyes - Binocular disparity • stereopsis; disparate view from each eyeball
1. Cognitive Tunneling -
People tend to adopt and fixate on a single hypothesis, assume that it is true, and then proceed with a solution consistent with the hypothesis - Fail to utilize subsequent cues
NIOSH Lifting Equation
RWL = LC x HM x VM x DM x AM x FM x CM
SELECTIVE ATTENTION
Selective attention focuses on some information and not on other information - necessary for perception Selection of what to attend to is driven by four factors: 1) Salience - bottom-up process - attentional capture vs attentional blindness 2) Expectancy - Top-down process - Where would you look at to find the information? 3) Value - Top-down process - How long do we attend to a signal? - How valuable is it to look at somewhere for info? 4) Effort - We scan short rather than longer distances for info
• Unitization
Sets of features occurring together or co-occurrence familiar (rapid and automatic)
SRK
Skill, Rule, Knowledge
Some characteristics of human-machine systems:
Systems have a purpose, goal, or objective. Systems can be hierarchical and be composed of various subsystems. Systems operate in an environment that can impose certain constraints. System components serve various functions (sensing, information storage, information processing and decision, and action) to achieve the system goals. System components interact to achieve system goals. Systems, subsystems, and components have inputs and outputs. System reliability is usually expressed as the probability of successful performance. A system with various human and machine components will have a reliability depending on how the components are combined. Components can be combined in series, parallel, or both. As humans can be the weak link in some systems, human-machine systems can be designed to provide parallel redundancy for some of the human functions. A systems design process effectively brings information on human capabilities, limitations, and principles to bear on the design of systems. Human factors play a vital role in this process, taking a systems approach to designing which involves the following: The purpose and objectives of the system are defined and system performance specifications are listed. The functions that the system has to perform to meet the objectives and performance specifications are defined. The basic design takes shape where functions are allocated, human performance requirements are spelt out, and task analysis conducted. Testing and evaluation is carried out.
Measuring Workload: The Timeline Model Equation
TR/TA (time required for the task/time available for the task) or time-ratio should be 0.8 allowing for spare capacity of about 20% Ratio=1.0 and above causes performancce decrement
Function Analysis
Used to determine the basic functions performed by different parts of the system - Goal (to get money from ATM) - Function (transfer money from account to self) - Tasks (steps at ATM to fulfill above function)
Other benefits of human factor engineering
increase sales, productivity, decrease cost of training, cost of support costs, maintainence cost, user errors, training, sick leaves, expenses
Heuristic Evaluation (Does not involve users)
• Analytically considering the characteristics of a product or system design to determine whether they meet human factors criteria. • In usability engineering, heuristic evaluation means making sure that it meets usability standards. • Ideally should be performed by 5 different evaluators (because most people will only find a small percentage of the potential problems).
- Descriptive Decision Models
• Attempt to describe and model actual human decision-making. • Developed because human decision-making frequently violates key assumptions of normative models. • Descriptive models attempt to capture how humans actually make decisions. - People tend to rely on simpler and lesscomplete means of selecting among choices - They rely on 'heuristics'
Auditory Alarms: Advantages
• Auditory design system is omnidirectional • a person doesn't have to be looking in order to benefit from the warning (harder to close ears than it is to close eyes). • under certain circumstances, auditory alarms induce a greater level of compliance than visual alarms • redundancy across visual and/or tactile modalities can enhance effectiveness of alarms. • If the volume of the auditory warning is set appropriately, it is almost guaranteed to get the attention of the operator whereas visual signals may be missed (especially in high workload environments). • Sound can be used when sight may be degraded, (e.g. night time, bright sunlight, glare, impaired vision). • Auditory perception is not affected as much as visual perception during periods of high g-forces or anoxia.
Auditory Alarms: Disadvantages
• Can cause a panicked reaction. Additionally it can make it hard for the crew to communicate. This can result in the crew directing their efforts to cancelling the alarm rather than the problem that caused the alarm. • There are too many warning sounds for the pilot to comprehend (as many as 15 on a Boeing Aircraft). • Warning sounds may not be conceived of as a set and hence different alarms may sound very similar if not sufficiently different. • The sounds may be too loud (levels over 100db at the pilot's ear) and they start sounding at their full intensity to overcome ambient noise. • If two warning sounds come on at the same time it can be difficult to identify either one of them because of the combined sound. • High frequency tones are often used which are not localizable by the human ear.
Visual Search - Pursuit Movements
• Constant velocity; tracking moving targets
Determine the percentage of the population to be accommodated.
• Design for extremes • Design for adjustable range • Design for the average
Hazard Control
• Design out a hazard (source) • Guard out a hazard (path) • Warning or training (person) • Administrative controls (legislation)
Remediation of Psychological Stress
• Emergency instructions should be easy to locate and salient • Have written instructions (do not rely on working memory) • Extensive practice for emergencies (overlearning) - We tend to perform the dominant behavior (turning action on slippery ice surface) • Emergency stress management: : Avoid tendency to "do something now" - Take time to take a deep breath and plan a strategy
Environmental Analysis
• Identify the context in which products will be used. • ATMs? Grocery stores? At home? Automobiles? Hospitals?
• Knowledge-based behavior
• Knowledge-based behavior - When situation is novel, information is processed at the knowledge-based level (Analytical processing using conceptual information)
Design Criteria for Usable Software
• Learnability • Efficiency • Memorability • Errors (Accuracy) • Satisfaction
Factors Contributing to Brightness
• Luminous intensity (luminous flux): - the actual light energy of the source. - measured in units termed candela. • Illuminance: - the energy reaching the surface of a to-be-seen object or workspace - measured in units of Lux • Luminance: - the amount of light reflected off objects • Reflectance of a surface (Formula) (luminance / illuminance)
GUIDELINES TO SUPPORT PERCEPTION
• Maximize bottom-up processing - legibility, audibility • Maximize automaticity and unitization by using familiar perceptual representations - familiar fonts, words than abbreviations • Maximize top-down processing Use smaller vocabulary Create context: "your fuel is low" vs "fuel low" Exploit redundancy: repeat content in different format Avoid negation in sentences: "do not turn off" becomes "turn off" as default is positive when degraded
Reading print
• Maximize contrast: Employ black on white rather than less readable combinations (e.g., gray on white). - Dark text on light backgrounds—negative contrast (usually better) - Light text on dark backgrounds—positive contrast • Irradiation—disruptive tendency for white letters to spread out over a black background • Font Choice - Use familiar fonts rather than non-standardized shapes • sans serif usually best - Use lowercase or mixed case lettering for sentences and uppercase for label printed serif, non printed san serif
Criteria for Alarms
• Must be heard above background ambient noise. - Should be a minimum of 15 db above the threshold of hearing above the noise level. This typically requires about 30 db difference to guarantee detection. • Should not be above danger levels for hearing whenever possible. - Danger level begins at 85-90 db. Careful selection of frequencies can often be used to accomplish this and the criteria for 15 db above noise alarm. • Should not be overly startling - Trade-off between "too loud" and "too soft." - Can be addressed by tuning the rise time of the alarm pulse. • Should be informative - Signal the nature of the emergency - Signal the appropriate action to be taken (ideally) - Too many types of alarms can produce confusion. • Should not disrupt the processing of other signals or any background speech communications that may be essential to deal with the alarm - Aircraft, Medical equipment, alarm systems.
Level of Arousal
• Performance increases as arousal increases up to a certain point of Optimum Level of Arousal (trying harder or threat of loss providing higher motivation). • Performance decreases with overarousal (overload). • OLA is higher for simpler tasks than complex ones (or for experts)
ESSAY QN Mental WL Measures (Primary Task)
• Primary task measures - Measures of performance on the task itself - Examples are speed, accuracy, error rate - Not really a workload measure but assumed to reflect workload (however, not always the case)
- Normative (or rational) Decision Models
• Revolve around the concept of utility, or the overall value of a choice to the decision-maker. • Specify what people ideally should do. • Do not describe how people actually perform decision making tasks
• Rule-based behavior
• Rule-based behavior - If familiar with task but do not have extensive experience, information is processed at the rule-based level (Meaningful cues (signs) can trigger rules accumulated from past experience) ('If-then' associations between cue sets and the appropriate actions)
Vestibular Senses
• Semicircular canals and vestibular sacs are receptors located deep within the inner-ear. • Head can rotate on three axes—three semicircular canals are aligned to each axis.
MODEL OF HUMAN INFORMATION PROCESSING
• Sensory Register - Short-term sensory store - iconic/visual sensory information (held for less than 1 sec) - echoic/auditory sensory information (held longer for 2-3 sec)
Heuristics and Biases
• Shortcuts or Rules-of-Thumbs (easy ways of making decisions • Very powerful and efficient, but don't guarantee the best solution • Because they are simplifications, heuristics occasionally lead to systematic flaws and errors (deviations from normative model called Biases
Transfer of Training
• Simulators - safer in most cases - cheaper operating cost in some cases - can optimize learning conditions - can be paused to provide feedback • However, issue of fidelity (realism) of simulator - high fidelity expensive but may be irrelevant to target task • Most training produce some positive transfer (to be worthwhile) • Should never produce negative transfer - changing layout of controls
Skill based behaviour
• Skill-based behavior - If extremely experienced with task, information is processed at the skill-based level (React to perceptual elements at automatic or subconscious level)
Methods for Enhancing Training
• Some methods for enhancing training: - Practice and Overlearning - Encouraging Deep, Active, and Meaningful Processing - Offering Feedback - Considering Individual Differences - Paying Attention to Attention - Training in Parts - Simplifying, Guiding, and Adapting Training - Using Training Media
WORKING MEMORY
• Sometimes termed Short-Term Memory • Relatively transient and limited in size • Temporary store that keeps info active while we are using it or until we use • Holds 2 different types of information - Verbal & Spatia
Features that determine ease of later retrieval: (LTM) (S.A.R)
• Strength - Determined by frequency and recency of use (password) • Associations - Retrieval of information in LTM dependent on the number and richness of associations with other items • Rote Memory - Repetition or rehearsal without meaning (pure phonetic loop)
Time
• Strength of information decays over time unless it's actively rehearsed (reactivated) • Maintenance rehearsal is essentially a serial process of sub-vocally articulating each item • The more chunks, the longer it will take to cycle through items in maintenance rehearsal
Usability Testing (involves users)
• The degree to which the system is easy to use or "user friendly." • Important indices of usability: - Learnability - system should be easy to learn. - Efficiency - high level of productivity is possible. - Memorability - easy to remember so that casual users can successfully operate the system after a period of inactivity. - Errors - should have low error rate and errors should be easy to recover from. - Satisfaction - system should be pleasant to use.
Learnability
• The system should be easy to learn so that the user can rapidly start getting work done. • Measure of the degree to which a user interface can be learned quickly and effectively. • Learning time is the typical measure. User interfaces are typically easier to learn when they are designed to be easy to use based on core human factors principles, and when they are familiar.
Absolute Judgment
• Very limited human capability to judge the absolute value of a variable signaled by a coded stimulus • Recommended that no more than 5 colors be used if precise accuracy in judgment is required