mec325

Dual objectives of Human Factors and Ergonomics (IEA)

To simultaneously optimize human well-being (health, safety, and comfort) and overall system performance (productivity, efficiency, and quality).

Universal Design

An engineering and design philosophy focused on creating products, environments, and systems usable by all people to the greatest extent possible, without requiring adaptation or specialized redesign.

Three primary operational phases of product lifecycle interaction

1. Set-up (assembly, installation, adjustment)

2. Use (operational task execution)

3. Put away (cleaning, maintenance, storage, and decommissioning)

Primary goals of system design in ergonomics hierarchy

1. Safety (first priority to prevent harm)
2. Performance (productivity, quality, and reliability)
3. Operator satisfaction (well-being, comfort, and acceptance)

Speed-Accuracy Trade-Off (SATO)

The operational principle establishing that increasing task execution speed impairs movement precision, requiring slower, deliberate motions when high accuracy is mandatory.

Human Factors perspective on human error

Errors are not individual character deficiencies but the predictable consequence of flawed system design, mismatched interfaces, and excessive physical or cognitive workload demands.

Ease of change versus cost of change across development phases

During early conceptual phases, ease of change is highest and cost is lowest; as projects advance into manufacturing and field operation, ease of change plummets while modification costs multiply up to tenfold ($10\times$).

Three system design perspectives in organizational ergonomics

1. Product/Service Design (focusing on end-user physical and cognitive interaction)
2. Operations Design (focusing on workplace process flow, tooling, and workstation layout)
3. Organizational Design (focusing on work structure, psychosocial climate, and management policies)

Two competitive business strategies supported by Human Factors

1. Cost Strategy (reducing overhead, scrap rates, assembly cycle times, and injury claims)
2. Differentiation Strategy (distinguishing products via superior usability, comfort, and ethical production practices)

ErgoBRAND

A commercial differentiation strategy where products establish brand equity and command market premiums by demonstrating healthy working conditions and human-centered design.

Phantom profit

Apparent financial savings achieved by cutting ergonomic investments or overworking personnel that are subsequently neutralized by hidden losses, including scrap, rework, absenteeism, turnover, and injuries.

Primary human factor linking poor ergonomics to manufacturing quality defects (Kolus et al.)

Fatigue (both physical muscular exhaustion and visual/cognitive overload), identified in over half of empirical studies as the root cause of assembly errors.

SSAB ladle-handling economic intervention outcome

An $11\,\text{million}\,\text{SEK}$ ergonomic modernization yielded an annual return of $5\,\text{million}\,\text{SEK}$, driven primarily by quality improvements ($59\%$) and productivity increases ($39\%$), rather than direct sick-leave reductions ($2\%$).

Ergo-Index

A quantitative evaluation tool that weighs physical workload and required physiological recovery times directly against production costs ($\text{currency/unit}$) to justify ergonomic interventions.

Breakdown of software maintenance costs (unforeseen requirements vs. bugs)

Roughly $80\%$ of total software maintenance expenditure stems from unforeseen user requirements and interface deficiencies, whereas only $20\%$ arises from programming bugs.

Return on Investment (ROI) for early user-centered design efforts

Integrating usability engineering into conceptual development typically yields a tenfold return ($10:1$) compared to retrofitting interfaces post-release.

Three classes of human factors investigations (Helander)

1. Descriptive studies (characterizing user population traits and anthropometry)
2. Experimental studies (testing causal relationships between design variables and performance)
3. Evaluation studies (assessing total system performance in operational settings)

Subjective vs. objective data sources in human factors research

Subjective data originates from the human sensory system and conscious perception (e.g., discomfort ratings, interviews); objective data is captured directly through instruments and hardware (e.g., timers, electromyography).

Qualitative vs. quantitative data forms

Quantitative data is expressed numerically (e.g., reaction times, error frequencies); qualitative data is expressed descriptively via language, categories, or visual impressions.

Designing for the margins

An inclusive user-research sampling strategy that intentionally oversamples edge-case users (such as the $5^{\text{th}}$ and $95^{\text{th}}$ percentiles) rather than relying on random sampling clustered around the population mean.

Double-barrelled question

A flawed survey or interview prompt that combines two distinct concepts into one query, forcing a single answer to multiple issues and invalidating the response data.

Borg Rating of Perceived Exertion (RPE) scale

A psychophysical scaling instrument combining numerical ranks with standardized verbal anchors to quantify subjective perceptions of physical effort, fatigue, and pain.

Method triangulation

The deployment of multiple independent qualitative and quantitative evaluation methods to achieve a rigorous, balanced understanding of complex ergonomic constructs.

Construct validity

The degree to which an empirical metric or testing protocol accurately reflects the specific theoretical concept it was designed to measure.

Primary operational liabilities of design checklists

They encourage passive stimulus-response checking, restrict innovative conceptual thinking, rely on non-numerical or ambiguous terms, and contain systematic blind spots.

Major operational assets of design checklists

They require minimal specialized ergonomic training, enforce a structured inspection sequence, standardize data gathering, and ensure critical operating criteria are not omitted.

Relative refractive power of the cornea vs. crystalline lens

The cornea accounts for roughly $70\% \text{ to } 80\%$ of total ocular refraction (fixed coarse focusing), whereas the lens provides the remaining $20\%$ via dynamic accommodation for fine tuning.

Structural and functional specialization of the fovea centralis

Packed exclusively with high-density cone photoreceptors possessing dedicated $1:1$ neural wiring to ganglion cells, delivering maximum visual acuity and color vision in photopic light.

Structural and functional specialization of the peripheral retina

Dominated by rod photoreceptors characterized by many-to-one neural convergence, maximizing light detection and peripheral motion sensitivity at the expense of resolution and color vision.

Photopic vs. scotopic dark adaptation phases

In sudden darkness, initial cone adaptation occurs within the first $10\,\text{minutes}$ (photopic phase), after which rods take over in the scotopic phase, reaching maximal light sensitivity after $30 \text{ to } 40\,\text{minutes}$ ($1000\times$ increase).

Visual target sizing adjustment for low-illumination environments

Because rods possess poor spatial acuity and cones require substantial light, physical target details and display typography must be made significantly larger under low ambient illumination.

Spectral sensitivity limitation of rod photoreceptors

Rods are insensitive to long-wavelength red light ($\approx 700\,\text{nm}$), enabling operators to read illuminated displays using red ambient light without resetting dark adaptation.

Illuminance

The measure of total luminous flux incident per unit surface area, expressed in lux ($\text{lumen/m}^2$) or foot-candles ($1\,\text{fc} \approx 10\,\text{lux}$).

Luminance

The luminous intensity emitted or reflected per unit area of a surface in a given direction, expressed in candela per square meter ($\text{cd/m}^2$) or foot-Lamberts ($1\,\text{fL} = 3.4\,\text{cd/m}^2$).

Direct glare vs. indirect glare

Direct glare results from intense light sources positioned straight within the visual field; indirect glare arises from specular reflections bouncing off shiny surfaces, consoles, or screens.

Presbyopia

The age-related hardening of the crystalline lens and decline of ciliary muscle flexibility, progressively restricting visual accommodation and pushing outward the near point of vision.

Visual Image Store (iconic memory) parameters

A sensory memory stage holding raw physical visual input with an effective half-life ($HT$) of roughly $200\,\text{ms}$ and a storage capacity of roughly $17\,\text{letters}$.

Auditory Store (echoic memory) parameters

A sensory memory buffer that preserves acoustic stimuli in physical waveform format with a half-life ($HT$) of roughly $1500\,\text{ms}$ and a capacity of approximately $5\,\text{letters}$.

Working Memory (short-term memory) capacity and decay

An active cognitive processing workspace limited to $7 \pm 2\,\text{chunks}$ (dropping to $3 \text{ to } 5\,\text{chunks}$ without active rehearsal) with a half-life decay of roughly $7\,\text{seconds}$ for $3\,\text{chunks}$.

Hick's Law

A mathematical relationship establishing that choice reaction time increases logarithmically with the number of alternatives: $RT = a + b \log_{2}(N)$, where $N$ is the number of equiprobable choices.

Skill-Based Behavior (Rasmussen's SRK framework)

Highly automated, subconscious sensory-motor performance governed by pre-programmed motor routines that execute smoothly without deliberate conscious control.

Rule-Based Behavior (Rasmussen's SRK framework)

Conscious task execution driven by familiar procedural rules, flowcharts, or structured "if-then" logic triggered by recognized environmental cues.

Knowledge-Based Behavior (Rasmussen's SRK framework)

High-level conscious problem-solving and diagnostic planning deployed in novel, unexpected, or unfamiliar operational situations where standard rules do not exist.

Three hierarchical levels of Situation Awareness (Endsley/Helander)

1. Level 1: Perception (detecting sensory cues in the environment)
2. Level 2: Comprehension (synthesizing cues to understand current operational meaning)
3. Level 3: Projection (forecasting future system states and trends)

Signal Detection Theory four-quadrant response matrix

1. Hit (signal present, operator confirms "Yes")
2. False Alarm (signal absent, operator confirms "Yes")
3. Miss (signal present, operator confirms "No")
4. Correct Rejection (signal absent, operator confirms "No")

Sensitivity index ($d'$) in Signal Detection Theory

The statistical separation between the means of the noise and signal-plus-noise perceptual distributions, defining an observer's sensory capacity to resolve signal from noise.

Vigilance decrement

The substantial drop in sustained attention and target detection reliability typically observed within $20 \text{ to } 30\,\text{minutes}$ of monotonous monitoring tasks.

Confirmation bias in diagnostic decision making

The cognitive bias where operators seek, prioritize, and over-weight data consistent with their active hypothesis while systematically dismissing disconfirming indicators.

Salience bias

The cognitive tendency for human attention to be captured predominantly by physically striking, brightly lit, loud, or prominent cues rather than by diagnostically critical information.

Three human factors stages of control operation

1. Perceive controls and displays through sensory modalities
2. Understand control mechanics and system mappings
3. Manipulate controls accurately while receiving timely display feedback

Negative transfer of training

A motor or procedural error occurring when automated habits learned on an older layout are mistakenly applied to a redesigned machine that uses conflicting control actions.

Control coding

The deliberate application of sensory characteristics (such as location, color, size, shape, and tactile feedback) to make control identity and function immediately intuitive.

Six primary dimensions of control coding

1. Location
2. Color
3. Size
4. Shape
5. Labeling
6. Mode of operation (tactile and kinesthetic feedback)

Common control movement stereotypes for rotary and toggle switches

Clockwise rotation, upward toggle movement, rightward slide, or forward displacement are population-stereotyped to mean On, Increase, or Raise.

Control-Response Compatibility (spatial mapping)

The spatial and geometric alignment between the layout of physical controls and the layout of their corresponding displays or operational elements (e.g., stovetop burners).

Human Factors design requirements for emergency controls

They must be physically isolated from regular controls to prevent accidental activation, placed in natural reaching pathways, oversized (e.g., mushroom pushbuttons), and colored bright red.

Four essential structural components of a warning sign

1. Signal word (e.g., "Danger", "Caution")
2. Hazard identity (specific nature of the hazard)
3. Consequences (potential harm, e.g., "Can cause death")
4. Instructions (clear, affirmative avoidance behavior)

Four cognitive stages of warning sign information processing (Helander)

1. Exposure and attention (salience and visibility)
2. Active processing and reading (legibility and clarity)
3. Comprehension and agreement (understanding severity and relevance)
4. Response selection and execution (performing the intended safe action)

Primary design defect of the 2000 Palm Beach County butterfly ballot

A broken spatial mapping where candidate party names spanned two outer columns while punch holes sat in a single center column, causing the second punch hole to select the third-listed party.

Four levels of control hierarchy in high-performance cockpits (Gkikas)

1. Strategy (infrequent macroscopic planning adjustments)
2. Tactics (adapting to known changing conditions, e.g., weather settings)
3. Operations (routine sub-system configurations, e.g., pit-lane limiters)
4. Execution (continuous, second-by-second steering and acceleration)

ISO 9241 definition of Usability (1995)

The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.

Five standard dimensions of usability (usability.gov)

1. Learnability
2. Efficiency
3. Memorability
4. Error frequency and severity
5. Subjective satisfaction

Formative vs. summative usability evaluation

Formative evaluation is conducted iteratively during early design (using wireframes and prototypes) to shape development; summative evaluation tests the finished system against formal benchmark criteria.

Three core principles of Direct Manipulation interfaces (Shneiderman)

1. Directness through visibility (continuous visual presentation of system objects)
2. Semantic directness (intuitive, task-relevant icons and metaphors)
3. Directness through fluid action (rapid, reversible, physical actions such as drag-and-drop)

GOMS modeling framework

An analytical cognitive framework modeling human performance through Goals, Operators, Methods, and Selection rules.

Gulf of Execution vs. Gulf of Evaluation

The Gulf of Execution represents the barrier between a user's intent and the physical actions required to command the system; the Gulf of Evaluation represents the difficulty in perceiving and deciphering whether the system's updated state fulfills that intent.

Nielsen Usability Heuristic: Visibility of system status

The design principle that systems must always keep operators informed about operational states through timely, appropriate sensory feedback.

Conductive hearing loss vs. neural hearing loss

Conductive hearing loss results from mechanical obstruction in the outer or middle ear and attenuates sound uniformly; neural hearing loss stems from cochlear hair cell or nerve destruction, producing permanent deficits typically centered at $4000\,\text{Hz}$.

The $3\,\text{dBA}$ exchange rate rule

The occupational safety regulation requiring allowable daily noise exposure durations to be cut in half for every $3\,\text{dBA}$ increase in ambient sound pressure level (e.g., $85\,\text{dBA}$ for $8\,\text{hours}$, $88\,\text{dBA}$ for $4\,\text{hours}$).

Whole Body Vibration (WBV) seated human resonant frequencies

Under vertical vibration, the seated human torso exhibits critical resonance at $3 \text{ to } 5\,\text{Hz}$, the heart at $7\,\text{Hz}$, and the eyeballs/head at $10 \text{ to } 25\,\text{Hz}$.