Glossary

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Age-related Differences(also: Age Effects, Generational Differences)

The systematic variations in technology use, learning strategies, and task performance that occur across different age groups. Research consistently shows older adults take 1.5 to 2 times longer than younger adults on technology tasks even when achieving equal accuracy, due to…

Attention Tunneling(also: Visual Tunneling, Attentional Tunneling, Cognitive Tunneling)

A phenomenon in which a user concentrates so narrowly on a primary information source - typically a visual overlay, head-up display, or instrument - that they fail to notice relevant events, objects, or hazards in their surrounding environment. In augmented and mixed reality,…

Background Noise(also: Ambient noise, Environmental noise)

The sum of unwanted or competing sound in an environment — traffic, construction, conversation, HVAC systems, weather — that is present alongside a signal of interest. Background noise is characterized by sound level (dB), spectral content, duration, and steadiness versus…

Cognitive Cycle(also: Cognitive Processing Time, Cognitive Response Time)

In the Model Human Processor framework, the cognitive cycle represents the time required for a person to process perceived information and make a decision about how to respond. A single cognitive cycle is approximately 70-110 milliseconds. Research with motion-impaired users has…

Computer Literacy(also: Digital Literacy, Technology Literacy, ICT Literacy)

A person's knowledge and ability to use computers and digital technology effectively. In accessibility research, computer literacy is an important variable when studying how different user groups interact with technology, as prior experience significantly affects task…

Ergonomics(also: Human factors engineering)

The scientific discipline concerned with understanding interactions between humans and other elements of a system, and the profession that applies theory, principles, data, and methods to design in order to optimize human well-being and overall system performance (IEA…

Feedforward(also: Anticipatory Feedback)

Design information that tells users what to expect before they take an action, guiding them toward intended functionality by communicating expected results. Unlike feedback (which confirms what happened after an action), feedforward helps users form correct expectations and make…

Fovea(also: Foveal Vision, Fovea Centralis)

The small, central area of the retina responsible for sharp, detailed vision, covering approximately 1 degree of visual angle. The fovea contains the highest density of cone photoreceptors and provides the clearest visual acuity, which is why people move their eyes to point the…

Gorilla Arm(also: Gorilla-arm effect, Gorilla arm syndrome)

A well-documented ergonomic phenomenon in which sustained unsupported arm elevation — typical of mid-air touchscreen, vertical display, or extended reality (XR) gesture interaction — produces rapid shoulder fatigue, pain, and performance decline. The term captures the ache and…

Hierarchical Task Analysis(also: HTA)

A structured method for describing and analyzing tasks by breaking them down into goals, sub-goals, and operations in a hierarchical tree structure. Originally developed for industrial and safety-critical domains, HTA has been adopted in accessibility research to identify where…

Human Failure Modes and Effects Analysis(also: HFMEA, Human FMEA)

An adaptation of Failure Modes and Effects Analysis (FMEA) that focuses specifically on human performance and error. HFMEA systematically examines each step in a process to identify how humans might fail, why they might fail, and what effects those failures would have. In…

Kinesthetics(also: Kinaesthetics, Kinesthesia, Kinesthetic sense)

The sense of body position, movement, and muscular effort derived from receptors in muscles, tendons, and joints. Kinesthetics is closely related to — and often used interchangeably with — proprioception, though kinesthesia typically emphasizes awareness of active movement while…

Mental Workload(also: Cognitive Load, Cognitive Workload)

The amount of cognitive effort and mental resources required to complete a task. In accessibility contexts, mental workload is an important measure of how demanding an interface is to use — an interface may be technically functional but impose excessive cognitive burden on users…

Model Human Processor(also: MHP, Human Processor Model)

A cognitive architecture developed by Card, Moran, and Newell (1983) that models human information processing as three interconnected subsystems: perceptual, cognitive, and motor processors, each with characteristic cycle times. The perceptual processor (~100ms) handles sensory…

Motor Function Time(also: Motor Response Time, Motor Cycle Time)

The time required to execute a physical action such as pressing or releasing a key, clicking a mouse button, or moving a pointing device. In the Model Human Processor, motor function time for able-bodied users averages approximately 70 milliseconds per action. For motor-impaired…

Motor Skills(also: Motor Abilities, Motor Function)

The learned abilities to perform movements with accuracy, speed, and coordination. Motor skills are typically divided into gross motor skills (large muscle movements like walking, jumping, balance) and fine motor skills (small muscle movements like writing, grasping, buttoning).…

Multiple Resource Theory(also: Wickens Multiple Resource Model)

A cognitive psychology theory proposed by Christopher Wickens that explains how humans allocate attention across concurrent tasks. The theory posits that humans have separate pools of cognitive resources for different modalities (visual vs. auditory), processing stages…

Muscle Fatigue(also: Motor fatigue)

A decline in the capacity of a muscle or muscle group to generate force or sustain activity after prolonged or repeated exertion. In human-computer interaction, muscle fatigue is a central concern for input modalities requiring sustained or repetitive motion — notably mid-air…

Occlusion(also: Hand Occlusion, Finger Occlusion, Visual Occlusion)

In the context of touchscreen and pen-based interaction, occlusion refers to the user's hand or finger blocking their view of content on the screen while interacting with it. Occlusion is a significant accessibility barrier, particularly for older adults and users with motor…

Overshoot(also: Cursor Overshoot, Target Overshoot)

In pointing device interaction, the phenomenon where the cursor travels beyond the intended target before the user can stop it, requiring corrective movements back toward the target. Overshoot is measured as the maximum distance traveled beyond the target as a percentage of the…

Perceived Urgency(also: Alert urgency, Urgency perception)

The subjective sense of immediacy or threat conveyed by an alert, shaped by parameters such as pulse rate, inter-pulse interval, pitch, loudness, and — for tactile signals — vibration intensity and pattern duration. Research on aircraft alarms, hospital alarms, and driver…

Perceptual Cycle(also: Perceptual Response Time, Perceptual Processing)

In the Model Human Processor framework, the perceptual cycle is the time required for a person to perceive and register a stimulus from their environment, such as seeing a visual change on screen. The perceptual cycle time for both able-bodied and motor-impaired users is…

Prior Knowledge(also: Background Knowledge, Existing Knowledge)

Information and experience a user brings to a technology interaction before it begins, including technical knowledge of how devices work, functional knowledge of task goals, strategic knowledge of problem-solving approaches, and self-knowledge of personal abilities and…

Psychophysics

Psychophysics is the scientific study of the quantitative relationship between physical stimuli and the sensations and perceptions they produce. Founded in the 19th century, it uses rigorous experimental methods to measure how humans detect, discriminate, and scale sensory…

Response Time(also: Reaction Time, Tact)

The time elapsed between the presentation of a stimulus and the user's physical response, typically measured in milliseconds. In scanning-based AAC, response time (often called Tact) is the interval between when an item is highlighted and when the user activates the switch.…

Satisficing

A decision-making strategy where users select the first option that appears "good enough" rather than evaluating all possibilities to find the optimal choice. Coined by Herbert Simon, satisficing is common in web navigation, especially among older adults and users with cognitive…

Sensory Adaptation(also: Habituation, Olfactory Fatigue)

Sensory adaptation is the diminishing response of a sensory system to a constant or repeated stimulus over time. Classic examples include no longer noticing a steady smell, becoming accustomed to ambient noise, or losing awareness of clothing pressed against the skin. In…

Sensory-Motor Processing(also: Sensorimotor Processing, Sensorimotor Integration)

Sensory-motor processing refers to the brain's ability to receive sensory input (visual, auditory, tactile, proprioceptive) and coordinate appropriate motor responses. This includes fine motor control for tasks like typing and mouse manipulation, as well as the integration of…

Situation Awareness(also: SA, Situational Awareness)

The perception and understanding of one's current environment, including the identification of relevant elements, comprehension of their meaning, and projection of their future status. In accessibility and assistive technology contexts, situation awareness refers to systems that…

Situationally-Induced Impairments and Disabilities(also: SIIDs, Situationally Induced Impairments and Disabilities, Situation-Induced Disabilities)

An accessibility framework, introduced by Sears et al., that describes how everyday environments and tasks can temporarily impose the same kinds of barriers on non-disabled users that permanent impairments create for disabled users. Examples include reading a phone in bright sun…

Slips(also: Slip Errors, Selection Slips)

Errors that occur when a user intends to click on a target but the cursor moves off the target before the mouse button is released, resulting in a missed selection. Slips are particularly common among older adults and people with motor impairments due to difficulties with fine…

Social Acceptance(also: Public acceptance, Bystander acceptance)

In assistive technology research, the degree to which bystanders and the broader public accept the presence and use of a device in shared spaces — and the degree to which the user feels comfortable using it in public. Low social acceptance can drive device abandonment even when…

Submovement(also: Movement Component, Movement Segment)

A discrete component of a larger aimed movement, separated from other submovements by pauses or changes in velocity. According to the Optimized Submovement Model from motor performance theory, a rapid aimed movement such as moving a cursor to a target consists of an initial…

Trust in Automation(also: Automation trust, TiA)

A human factors construct describing the extent to which a person believes an automated system — a car, aircraft, medical device, AI assistant, or robot — will perform reliably and behave in their interest, typically measured via validated questionnaires such as the Trust in…

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