abduction : a form of reasoning in which hypotheses are generated to explain some observed phenomena, and the best explanation is the one that is accepted
absolute threshold : the minimum amount of physical energy in a stimulus necessary for a person to detect that stimulus
accommodation : the process by which the lens changes shape to keep images focused on the retina
acoustic reflex : the muscular reflex within the middle ear that restricts the movement of the bones of the middle ear, protecting the inner ear from loud sounds
active touch : the perception of an object through manipulation of the object
acuity : the ability to perceive fine detail
additive-factors logic : the notion that, if the effect of two variables on reaction time is additive (i.e., the effect of both variables together is equal to the sum of the effects of both variables alone), then the variables must influence different stages of information processing. Systematic application of additive-factors logic can give some idea of the stages of processing required for a task and how these stages are arranged
analogy : a problem-solving heuristic that relies on a comparison between an unfamiliar problem and a well-known problem
anchoring heuristic : an inductive heuristic from which the estimated frequency of an event is determined by the initial evidence presented about the event
anthropometrics : the measurement of human bodily characteristics
apparent motion : perceived motion produced by discrete changes in location of stimulation
archival data : preexisting data that have been collected for some other purpose, such as medical records
arithmetic mean : the sum of all values of a dependent variable divided by the number of such values
articulation index : a measure of speech intelligibility, used especially for situations with background noise
assembly error : see manufacturing error
associative phase : the intermediate phase of skill acquisition in which associations between task elements are being formed
astigmatism : irregularities in the shape of the cornea that blur contours of the image that are in certain orientations
auditory canal : the canal of the outer ear that is located between the pinna and the tympanic membrane
autonomous phase : the final phase of skill acquisition in which task execution becomes automatic
availability heuristic : an inductive heuristic used to estimate probabilities of events according to the ease with which the events can be remembered
backlash : insensitivity to control movement that is present at any control position
basilar membrane : an organ in the inner ear that contains the auditory sensory receptors
behavioral variables : aspects of human action, such as time to respond, that can be measured
binocular depth cues : cues to the distance of an object in an image based on slight differences in the two images that each eye receives
binocular disparity : the retinal distance between corresponding points in the images received by each eye
biomechanics : the mechanical properties of the moving body, including the forces applied by muscles
blind spot : the location on the retina where the optic nerve leaves the eye and, hence, there are no sensory receptors
breach of express warranty : the failure of a product to function as its manufacturer stated or implied that it would
brightness : the sensation corresponding mainly to the intensity of light waves
carpal tunnel syndrome : a cumulative trauma disorder characterized by pain and tingling of the fingers and hand, caused by compression of the median nerve in the carpal tunnel of the wrist
carryover effects : a problem that arises in a within-subject experimental design where performance in one treatment condition is affected by previously received treatments
categorical perception : the tendency to perceive stimuli in discrete categories, rather than as varying along continua
central tendency : a value around which a distribution of numbers (scores or measurements, for example) tends to cluster
certainty effect : gambles with highly probable outcomes tend to be selected over gambles with improbable outcomes of higher value
change blindness : a salient change in a display often goes unnoticed
check reading : a systematic inspection of each of several dials to verify that all register normal operating values
choice reaction time : the amount of time required to select an appropriate response to the onset of a stimulus from two or more alternative responses
circadian rhythms : biological oscillations of the body with periods of approximately 24 hours
closed-loop systems : systems that make use of feedback
cochlea : a bony, fluid-filled coiled cavity in the inner ear that contains the basilar membrane
cognitive architecture : a relatively completely specified information-processing system intended to provide a basis for developing computational models of performance in a range of specific tasks
cognitive phase : the initial phase of skill acquisition, in which performance of a task relies on rules and instructions
color circle : the color appearance system created by connecting the short- and long-wavelength ends of the visual spectrum with nonspectral purple
comfort zone : the temperature and humidity combinations that are comfortable for most people
communication error : inaccurate transmission of information between members of a team
computational method : a method of human reliability analysis that calculates the probability of system success from tabled data giving the probabilities of relevant human and machine errors
cones : the sensory receptors responsible for color vision and perception of detail
connectionist models : models of cognitive function that store information as connections between “ nodes” which represent cognitive or neural structures that may be found in the brain
conspicuity : the ability of a display to attract attention, or how conspicuous it is
contextual interference : difficulty in remembering an item due to the context in which it is presented
continuous controls : controls that can be set to any value along a continuum
contrast sensitivity function : a graph expressing sensitivity to contrast as a function of the spatial frequency of a sine-wave grating
control– display ratio : the ratio of the magnitude of control adjustment to the magnitude of the change in a display indicator
control knowledge : knowledge of how to structure and coordinate a problem to achieve a solution
control order : the relationship between the position of a control and the position, velocity, or acceleration of a display or system
control procedures : systematic methods used to reduce the influence of extraneous variables in a study. Control procedures help ensure that the effects observed on the dependent variables are due to the independent variables and nothing else
control structure : the collection of programs that drive a knowledge-based software system
cooperative principle : the assumption that a speaker is being cooperative and sincere to further the purpose of a conversation
correct rejection : correctly responding that a signal is not present
cost-benefit analysis : calculating the costs associated with some implementation, such as a usability study, relative to the benefits that would be obtained
cost of concurrence : the difference between the performance level on a task when it is performed alone versus when it is performed with another task to which no attentional resources are devoted
counterbalancing procedures : procedures used in within-subjects designs to minimize the effects of practice and fatigue, involving the presentation of treatment conditions in different orders
critical bandwidth : the range of frequencies contained in a complex tone outside which inclusion of additional frequencies increases the loudness
critical flicker frequency : the highest rate of flicker at which a stimulus can still be perceived as flickering. Flicker frequencies higher than this critical frequency result in the perception of a continuous stimulus
crowding : a psychological experience associated with a high population density
cumulative trauma disorders : a family of syndromes arising from repeated physical stress on a joint
dark adaptation : the process of improvement in sensitivity to light energy under conditions of low illumination
data-limited processing : limitations of human information processing attributable to impoverished input
deadspace : the amount of control movement around a neutral position that can occur with no effect on the system
decision analysis : the reduction of a complex decision problem into a series of smaller, simpler component problems
decision-support system : a computer program that guides the decision-making process
declarative knowledge : knowledge that is available for verbalization
deduction : reasoning about the solution to a problem based on formal logic applied to conditions of the problem
dependent variable : a variable representing the phenomenon of interest that is measured as a function of the independent variables
depth of field : the extent of the area before and beyond a fixated object in which other objects are also in focus
descriptive models : models of decision making that capture the ways that people think and decide
descriptive statistics : methods of condensing data to allow the description or summary of research results
design error : an error in machine design that makes operation difficult or error-prone
detail design : the third phase of system development, in which the initial preliminary design is developed further and plans are made for production
detectability : the degree to which the presence or absence of a stimulus can be determined
dichromatic vision : color blindness in which one of the three types of cone photopigments is missing
difference threshold : the minimum amount of difference between the physical energies in two stimuli necessary to detect a difference between the stimuli
differential research : experiments that use subject variables as independent variables to evaluate the effects of individual differences on other variables of interest
digital human models : software design tools that allow a designer to create a virtual human with specific physical attributes who can be inserted into environments with various dimensions and properties
disability glare : glare that reduces the detectability, legibility, and readability of display characters, which in turn impairs performance
discomfort glare : glare that causes visual discomfort when a work surface is viewed for a period of time
discrete controls : controls that can be set to one of a fixed number of states
discriminability : the degree to which a difference between two stimuli can be detected
distinctiveness : the degree to which one remembered item stands apart from other remembered items
distributed practice : performance of a task for periods interspersed with periods of rest
divided attention : the act of focusing attention on several sources of input at once
dorsal stream : visual pathway in the brain that processes information about where objects are located and how to respond to them
dynamic acuity : the ability to resolve detail for moving stimuli
dynamic displays : displays that change over time, such as altimeters
echoic memory : the sensory store for the auditory system
ecological interface design : an approach to interface design that is based on a description of the work domain at different levels of abstraction and on the skills-rule-knowledge framework (see glossary):
ecological validity : the extent to which the effects observed in a research setting can be applied to a real-world setting
elaborative rehearsal : constructing relationships among items in short-term memory to enhance long-term retention
elastic resistance : the resistance felt in a spring-loaded control, which causes the control to return to a neutral position when released
elimination by aspects : a descriptive decision-making heuristic by which the decision-making process occurs through a systematic elimination of features for comparison
empiricism : evaluating scientific hypotheses through the collection of data based on controlled observations
encoding specificity principle : the ability to remember an item will depend on the match between the context in which it is retrieved and the context in which it is encoded
engineering anthropometry : the use of anthropometric data in the design of equipment
engineering models of human performance : models intended to produce quick, approximate predictions of human functioning that can be used to make design decisions
engineering psychology : see human factors
episodic memory : memory for specific events
equal loudness contours : the intensity levels across tones of varying frequencies that result in equal perceived loudness
equal pitch contours : the frequencies across tones of varying intensity levels that result in equal perceived pitch
ergonomics : see human factors
error of commission : the performance of an incorrect action
error of omission : the failure to perform a necessary action
ethnographic methods : research methods that provide qualitative descriptions of human behavioral and social phenomena based on field observations
executive control : processes involved in the coordination of more basic cognitive functions such as direction of attention, rehearsal of information, and so on
expected-utility theory : a normative theory of decision making in which choices are based on the average utility of different objects or outcomes
expert system : a knowledge-based software system intended to perform as an expert consultant
external validity : the extent to which the results obtained in a study generalize to other situations
fact base : the data base and models used by a knowledge-based software system
false alarm : incorrectly responding that a signal was present when it was not
far point : the point beyond which increasing the distance of a fixated object requires no further change in accommodation to keep its image in focus
fatigue effects : decrements in performance attributable only to the amount of time spent at a task
feature-comparison models : models of memory that assume concepts are stored as lists of features
Fechner’ s law : the magnitude of a sensation is proportional to the logarithm of the physical intensity of a stimulus
figure– ground organization : the segregation of parts of an image into objects against a background
filter-attenuation model : a model of attention similar to filter theory that presumes that several sources of input are differentially weighted, which allows some information from unattended sources to enter the central processing channel
filter theory : a model of attention that presumes the existence of a central processing channel that can act on input from only a single source at one time
fine adjust time : after the travel time, the time required to adjust the position of a control precisely
Fitts’ s law : movement time is a linear function of the index of difficulty
focus group : a small group of people selected from a larger population to discuss opinions and views on a topic or product
Fourier analysis : a method of decomposing a complex waveform into its component sinusoids
fovea : that region on the retina containing only cone receptors. Acuity is highest in this region
framing : how a decision-making problem is presented
frequency distribution : a plot of the number of times each value of a dependent variable was observed
frequency of use : a design principle that the most frequently used and important displays or controls should be located in the central visual field
frequency theory : a theory of pitch perception suggesting that the frequency of vibration of the basilar membrane is represented by a pattern of neural firing that occurs at the same frequency
frictional resistance : resistance encountered at any point during the movement of a control due to the mechanical properties of the control
functional equivalence : the extent to which the tasks performed in a simulated environment mimic those of the real world
gain : a measure of the responsiveness of a control, inversely related to the control– display ratio
gaze-contingent multiresolution display : a display for which a region of the image around fixation is of higher resolution than the remainder of the display. The high-resolution region shifts along with shifts in fixation
general adaptation syndrome : a physiological response to stress characterized by swollen adrenal glands, atrophied thymus glands, and stomach ulcers when exposure to stress has been prolonged and severe
gestalt grouping : the tendency for individual elements to be grouped into a larger whole on the basis of principles of proximity, similarity, and so on
given-new strategy : the fact that sentences in a meaningful conversation contain both old and new information
glare : a high-intensity light that interferes with the perception of objects of lower intensity
go-no go reaction time : the amount of time required to execute a single response to the onset of a particular subset of the possible stimuli
gross negligence : reckless and wanton disregard by the manufacturer of a product of the manufacturer’ s legal responsibilities
groupware : computer software developed to support interactions among group and team members on projects
harmonics : integer multiples of the fundamental frequency of a complex tone
Hawthorne effect : changes in performance or productivity that can be traced to any alteration of the workplace environment and not to any specific variable that was manipulated to effect the alteration
head-up display : a display on the windshield of an aircraft, automobile, or other vehicle that allows the operator to read the display without having to direct his gaze away from the outside world
helmet-mounted display : a display mounted on a helmet worn by a person that enables the display to be visible regardless of the direction in which the person is looking
Hick– Hyman law : choice reaction time is a linear function of the amount of information transmitted
hit : correctly responding that a signal is present
human– computer interaction : that area of human factors concerned with the design of computer workstations and software interfaces to optimize performance of computer-based tasks
human– computer interaction (1): the subfield of human factors and ergonomics concerned with designing usable interfaces for people to interact with computerized systems
human error : a decision or action made by a person that has undesirable consequences for the operation of a system or use of a product
human factors : the study of human cognitive, behavioral, and biological characteristics that influence the efficiency with which a human can interact with the inanimate components of a human– machine system
human information processing : the view that human perception, cognition, and action are based on a systematic processing of information from the environment
human– machine system : an entity consisting of a human operator and a machine that work together to achieve some goal
human reliability : the probability that an operator makes no errors while interacting as part of a human– machine system
human–systems integration : a term that refers to the consideration and integration of human issues across an entire system. It is a somewhat broader term than human factors, because human issues might encompass, in addition to engineering psychology or ergonomics/human factors, sociological, economic, political, and psychological concerns
hyperopia : farsightedness, or the inability to see close objects
hypervigilance : a state of panic in which thinking becomes overly simplistic, resulting in hasty, poor decision making
hypothesis : a tentative and testable statement about the cause of some phenomenon
iconic memory : the sensory store for the visual system
identification acuity : acuity as measured by a Snellen eye chart; the distance at which an observer could identify letters that an observer with normal vision could identify at a standard distance
illuminance : the amount of light falling on a surface
independence point : the point in the performance operating characteristic space indicated by the performance level of each task when performed alone
independent variable : a variable that is overtly changed in an experiment to determine whether it affects a dependent variable
index of accessibility : a measure of the ease with which frequently used controls on a panel can be reached
index of difficulty : a measure of the difficulty of an aimed movement, given by the logarithm to the base 2 of the ratio of twice the distance to the target divided by the target width
induced motion : perceived movement of a stationary element induced by motion of its frame of reference
induction : reasoning in which a general solution to a problem is generated from the particular conditions of the problem
inertial resistance : a control resistance that decreases as control acceleration increases
information theory : quantifying the information in a set of events by the average minimum number of binary questions required to determine the identity of an item in the set
input error : an error that occurs during the perception of a stimulus
installation error : an error in the installation of a machine that leads to system failure
interaural intensity differences : differences in the intensity of a sound at each ear, due to a sound shadow created by the head, that provide cues to position
interaural time differences : differences in the time at which a tone reaches each ear that provide cues to positions
internal validity : the degree to which effects observed in a study can be attributed to the variables of interest
inverse square law : the intensity of an auditory signal is inversely related to the squared distance of the sound source
isolation effect : more attention is focused on features that are unique to different choices rather than on features that the choices have in common
isometric control : a fixed control that responds according to the amount of force exerted on it
isotonic control : a movable control that responds according to its amount of displacement
iterative corrections model : a theory of movement control that assumes that an aimed movement is composed of a series of discrete submovements, each traversing a fixed proportion of the distance to the target
job analysis : an analysis of a position (job): to determine the tasks and responsibilities of a worker in that position, the conditions under which that worker must perform, and the skills and training that the position requires
job design : the act of structuring tasks and assigning them to positions
kinesthesis : sensory information about the location of the limbs during movement
knowledge-based behavior : a mode of behavior in which the person must solve problems for which they are not trained and have not learned rules for action
knowledge elicitation : methods for drawing out the knowledge that an expert or user possesses about a domain or task
knowledge of performance : detailed feedback concerning the performance of a movement
knowledge of results : feedback concerning the success or failure of a movement
latent semantic analysis : an analysis that, when applied to a sample of text, produces a semantic space that depicts the relationships between concepts
lateral inhibition : the inhibition of a cell’ s firing rate due to the activity of neighboring cells
late-selection model : a model of attention that presumes that information from all input channels is identified, but that only the information from the attended input source is acted on
legibility : the ease with which symbols and letters can be discerned
level of processing : the degree of elaborative or semantic processing performed on information in short-term memory
lightness : the perceived reflectance of an object, or how dark or light the object appears on a scale from black to white
lightness constancy : maintenance of perceived relative lightness under different levels of illumination
lightness contrast : changes in the lightness of an object with changes in the intensity of the surrounding area
likelihood alarm : a warning, caution, or advisory signal that also presents information about the likelihood of an event
link analysis : an analysis of display panel design based on connections between displays, defined in terms of frequency and sequence of use. Link analysis can also be used to analyze control panels and to aid in the design of workstations
loading task paradigm : a method of measuring mental workload in a dual-task situation in which the emphasis is placed on the secondary task, and mental workload is estimated from performance on the primary task
long-term store : an unlimited-capacity memory system that retains information for an indefinite period of time
luminance : the amount of light generated by a surface
macroergonomics : an approach to human factors that stresses the organizational and social environment in which the human– machine system functions
maintenance error : an error during routine maintenance of a machine that leads to system failure
maintenance rehearsal : covert repetition of material held in short-term memory
manufacturing error : an error in the fabrication of a machine that leads to system failure
masked threshold : the amount of physical energy in a stimulus necessary to detect that stimulus when it is presented in a noisy background
masking : the interference between the presentation of one stimulus and the perception of another presented in close spatial and/or temporal proximity
massed practice : continuous performance of a task for an extended period of time
median : that value of a dependent variable below which and above which 50% of all values fall; the value with a percentile rank of 50%
mediation error : an error that occurs during cognition that is not attributable to misperception of a stimulus or incorrect execution of an intended action
mental effort : the amount of cognitive work required to perform a task
mental model : a dynamic representation or simulation of a problem held in working memory
mental workload : an estimate of the attentional demands of a task
method of constant stimuli : a method to determine a threshold that presents a large number of stimulus intensities in random order
method of limits : a method to determine a threshold that presents stimulus intensities in increasing or decreasing increments
miss : incorrectly responding that a signal was not present
mistakes : errors that arise in the planning of an action
mnemonics : mental strategies used to organize and aid memory for information
mode : the most frequently occurring value of a dependent variable
monochromatic vision : a kind of color blindness in which an individual has either no cones or only one type of cone
monocular depth cues : cues to the depth of an object in an image that are available to a monocular viewer. Stationary monocular cues are those used to portray depth in still paintings. Additional monocular cues are provided when an observer moves
Monte Carlo method : a method of human reliability analysis in which system performance is predicted by simulating a model system
motion contrast : apparent motion of a stationary texture induced by motion of a surrounding texture
motor program : an abstract plan thought to control specific classes of movements
motor unit : a small group of muscle fibers innervated by a single motor neuron
multiple-resource model : a model of attention that presumes the existence of several pools of mental resources, each appropriate to different kinds of stimuli, processing, and response modalities
myopia : nearsightedness, or the inability to see distant objects
naturalistic research : the observation of behavior in real-world settings without manipulation of any independent variables
near point : the point at which moving an object closer produces no further accommodation
negligence : the failure of a manufacturer to engage in reasonable actions to meet his or her legal responsibilities
network models : models of memory in which concepts are represented as connections between functionally related neural units
neuron : a cell that transmits an electrochemical signal within the nervous system
normative models : models of decision making that predict the choices that would be made by an optimal decision maker
null hypothesis : the proposal that a treatment had no effect on the dependent variable
observational learning : learning to perform a task by watching another performer
occupational ergonomics program : a plan for redesigning the work environment and practices to conform to ergonomic principles
occupational stress : stress that arises from the work environment
oculomotor depth cues : cues to the depth of an object in an image based on proprioceptive feedback from the muscles in the eye
olfactory cilia : the likely sensory receptors for olfaction
olfactory epithelium : that area of the nasal cavity that contains the olfactory sensory receptors
open-loop systems : systems that do not make use of feedback
operating error : an inappropriate use or operation of a machine
operational definition : the definition of a concept in terms of the methods by which it is measured
opponent process theory : a theory of color vision that proposes that neural mechanisms code blue and yellow together and red and green together so that one color of a pair can be signaled, but not both
optimized initial impulse model : a model of movement control that combines elements of the iterative corrections and impulse variability models
organizational development : changes in the structure and goals of an organization, designed to improve organizational effectiveness
ossicles : the three small bones in the inner ear that transmit pressure changes from the tympanic membrane to the oval window
output error : the selection and execution of an inappropriate action
oval window : a membrane that receives vibrations from the ossicles and produces waves in the fluid around the basilar membrane
parallel components : system components that receive input and commence operation simultaneously
part-whole transfer : the extent to which practice with the components of a task improves performance of the entire task
passive touch : the perception of a texture pressed against the skin
pay for performance : a pay schedule in which salary depends on a worker’ s level of productivity
percentile rank : a measurement given to a particular value of a dependent variable that specifies the percentage of scores that fall below it
perceptual organization : the way that relationships are formed among the different elements of an image to produce a percept
performance appraisal : the formal evaluation of an employee’ s performance
performance efficiency : a measure of how efficiently two tasks can be performed together, defined as the smallest distance between the performance operating characteristic curve and the independence point
performance operating characteristic : a plot of performance for a divided-attention situation, by which the performance of one task is plotted as a function of the performance on another task under several levels of relative task emphasis
personal space : the area immediately surrounding one’ s body
personnel selection : choosing employees for a job on the basis of the match between their characteristics or qualifications and the job requirements
phoneme : the smallest unit of speech that, when changed, changes the meaning of an utterance
photometry : measurement of the functional amount of light energy for human vision
photopic vision : vision under conditions of bright light, controlled primarily by cones
pinna : the outer, visible part of the ear
place theory : a theory of pitch perception that proposes that the perception of pitch is determined by the location of the active receptors on the basilar membrane and the neurons that they innervate
population stereotype : an intuitive association between a control motion and its associated effect
positive misaccommodation : a problem that arises in the use of head-up displays in which an observer’ s eyes accommodate for a distance closer than the far point. This results in poor size and depth perception
power law of practice : the empirical finding that performance (as measured by response time or accuracy) improves as a power function of the amount of time spent practicing a task
practice effects : improvements in performance attributable only to the amount of time spent performing a task
preference reversals : a change in the most preferred object under changes in the context in which the choice is presented
preferred noise criterion : a level of background noise intensity and frequency that is optimal for a given task environment
preliminary design : the second phase of system development, in which alternative designs are considered, resulting in an initial, tentative design
presbyopia : a loss of accommodative ability that comes with age
proactive interference : forgetting of information that occurs because of the memory of previously presented information
probability : a number from 0 to 1 that indicates the likelihood of a random event. Usually, the number of times that an event of interest is observed divided by the total number of observations made
probability density function : the continuous analogue to the probability distribution; used to assign probabilities to continuous events (e.g., time)
probability distribution : a relative frequency distribution over an entire set of discrete events, describing the proportion of times that each event occurs relative to all other events
problem space hypothesis : a conception of problem solving as a mental space in which the problem solver must move along a solution path from a start state to a goal state
procedural knowledge : knowledge of how tasks are performed that is not available for verbalization
production and development phase : the final phase of system development, in which the system is actually built, tested, and evaluated
production system : a data base, control system, and set of if-then rules that can be used to solve simple or complex problems
proprioception : sensory information about the position of the limbs
proxemics : the way that people manage the space around them and their distances from other people
psychological refractory period effect : increases in response time for the second response when two tasks must be performed in rapid succession
psychophysical scaling : a mathematical expression relating the physical intensity of a stimulus to its perceived magnitude
psychophysics : the study of the relation between physical stimulus properties and psychological experience
pupillometry : the measurement of the diameter of the pupil
Purkinje shift : the relatively greater perceived brightness of objects of short wavelength under scotopic viewing conditions
quantitative error : an action that fails by being either insufficient or excessive
radiometry : measurement of light energy
random walk : a continuous model of information processing that assumes that evidence is accumulated over time toward alternative responses
reach envelope : an area in which controls and other objects should be located to ensure that some large percentage of the population will be able to reach them
reactivity : changes in a mental process due to concurrent verbalization of that process
readability : the degree to which a display of letters or characters allows fast and accurate recognition of information
receiver operating characteristic : a plot of the proportion of hits as a function of the proportion of false alarms under several levels of response bias
receptive field : the area of sensory receptors that, when stimulated, affects the firing rate of a particular neuron
recommended weight limit : the weight of a load that a healthy individual can lift for as much as 8 hours per day without increased risk of lower back pain
reflection effect : when expected utilities are positive, the high probability outcomes are preferred even when their expected utility is low. When expected utilities are negative, low-probability outcomes are preferred
relative frequency distribution : a plot of the proportion of times that a value of a dependent variable was observed
reliability : the probability that a system, subsystem, or component does not fail
representativeness heuristic : an inductive heuristic used to assign probabilities to events according to their perceived similarity between some representative outcome
resolution acuity : the ability to distinguish between a field of varying contrast and a field of uniform intensity
resource-limited processing : limitations in human information processing attributable to a lack of cognitive resources; for example, attention or working memory
response bias : a tendency to prefer one response over others, regardless of the stimulus conditions
retina : a two-dimensional grid of sensory receptors and associated neurons lining the back wall of the eye
risk analysis : a comprehensive analysis of the costs of system failure, taking into account system and human reliability and the risks that accompany specific failures
rods : the sensory receptors responsible for vision under conditions of low illumination
rule-based behavior a mode of behavior in which a person’ s skills are not applicable and she must retrieve previous learned rules from memory
scenario-based design : narratives are developed that depict ways that a person might use a software tool or product, and these narratives are used to guide the design process
schema : an abstract mental representation, similar to a mental model, for organizing sequences of events
schema theory : a theory of motor skill that assumes the existence of a generalized motor program, the parameters of which are determined by schemas acquired through practice
scientific method : the process by which alternative hypotheses concerning the cause of some phenomenon are evaluated. This evaluation is based on the outcomes of controlled observations
scotopic vision : vision under conditions of low illumination, primarily controlled by the rods
selection error : an action performed with the wrong control
selective attention : the act of focusing on one source of information and ignoring all others
semantic context : the effect of the meaning of a context on the perception of a stimulus
semantic memory : long-term memory for general knowledge
sensory receptors : specialized cells in a sensory system that convert physical energy into nervous impulses
sensory store : a buffer that retains sensory information briefly
sequence error : the performance of an action at the wrong position within a sequence of actions
sequence of use : a design principle that states that, if displays must be scanned in a fixed sequence, the displays should be arranged in that sequence
serial components : an arrangement of system components in which each component receives as input the output of a previous component and delivers its output as input to the following component
shape constancy : the tendency to perceive an object as having the same shape regardless of its slant or tilt
short-term store : a limited-capacity memory system in which information is retained through rehearsal
sick building syndrome : a condition in which many occupants of a building experience chronic respiratory symptoms, headaches, and eye irritation
signal-detection theory : a theory that assumes that binary decisions concerning the presence or absence of a signal are based on discriminability of the signal and a response criterion
simple reaction time : the amount of time required to react with a single response to the onset of any stimulus event
situation awareness : consciousness of the objects in the environment, what they mean, and their future status
size constancy : the tendency to perceive an object as having the same size regardless of its visual angle
skill-based behavior : a mode of behavior in which the person is engaged in highly overlearned activities for which she has been trained
skill-rule-knowledge framework : a framework of cognitive behavior in which behaviors are classified according to the level of skill involved
slips : errors arising in the execution of an action
sociotechnical system : an organizational system comprised of a technical subsystem and a personnel subsystem
somesthetic senses : those senses associated with skin, joints, muscles, and tendons, including touch, pressure, temperature, pain, vibration, and proprioception
span of apprehension : the number of briefly displayed visual stimuli that can be reported without error
speech spectrogram : a plot of the frequencies that appear in a speech signal over time
speed– accuracy tradeoff : for performance of tasks, a person can respond faster and less accurately or slower and more accurately
spinal reflex : simple actions controlled by the spinal cord
standard deviation : the square root of the variance of a dependent variable
static displays : displays that do not change over time, such as road signs
Stevens’ s law : the magnitude of sensation provided by a stimulus is directly proportional to some power of the physical intensity of the stimulus when sensation is scaled using magnitude estimation procedures
stimulus-response compatibility : the ease with which a response to a stimulus can be selected based on the assignment of stimuli to responses
stimulus variables : environmental factors that affect behavior
strict liability : a manufacturer’ s responsibility for any product defect
stroboscopic motion : the perception of movement arising from the sequential illumination of two or more spatially separated lights in close succession
strong methods : methods of problem solving based on an expert’ s knowledge of a domain
structurally limited processing : limitations in human information processing that arise when one structure is called on to perform more than one task
subject variables : individual differences such as physical characteristics, mental abilities, and training
subjective assessment techniques : measurements obtained through an operator’ s evaluation of some aspect of a task or procedure. These techniques are commonly used to measure mental workload
subsidiary task paradigm : a method of measuring mental workload using a dual-task situation in which emphasis is placed on the primary task and mental workload is estimated from performance on the secondary task
subtractive logic the notion that the time to perform a mental event can be found by measuring the reaction time in a task that requires that event and in a task that requires everything except that event and then subtracting one from the other
syllogism : a list of premises and a conclusion drawn from them
syntactic context : the effect of grammatical context on the perception of a stimulus
system : a collection of components that act together to achieve a goal that could not be achieved by any single component alone
system planning : the first phase of system development, in which the need for a system is identified
systems engineering : an interdisciplinary approach to the design of complex systems that bases design decisions on achieving system goals
task analysis : the analysis of a task in terms of its perceptual, cognitive, and motor components
task environment : the objects and allowable actions that may be used to achieve a solution to a problem
taste buds : groups of sensory receptors on the tongue
team performance : study of the actions of functioning of two or more people as a team rather than the functioning of a single person
teleoperators : general-purpose, dextrous human– machine systems that augment the physical skills of the operator by allowing him to pick up and manipulate objects from a remote location
territoriality : behavior patterns oriented toward occupying and controlling physical spaces
theory : an organized framework of causal statements that allows the understanding, prediction, and control of some phenomena
threshold shift : a decrease in auditory sensitivity due to exposure to high noise levels
timbre : the texture of a complex tone, which is determined by such factors as the relative intensities of its harmonics
time-and-motion study : an analysis of the movements required to perform a job and the time required for each movement
timing error : the performance of an action at the wrong time
tracking task : a task that requires matching a dynamic stimulus signal with an identical output signal
transfer-appropriate processing : the ability to remember an item encoded in a particular way depends on the way in which the item is tested
transmitted information : the amount of information (in bits) passing through a communication channel, as derived from the amount of information in the input and the amount of information in the output
travel time : the time required to move a control into the vicinity of a desired position
trichromatic color theory : a theory of color vision that proposes that color is perceived as a function of the relative activity in the blue, green, and red color systems
two-point thresholds : the minimum distance between two points of stimulation on the skin that allows the perception of two distinct stimuli
tympanic membrane : a delicate membrane that vibrates with changes in air pressure created by an auditory stimulus. It is also called the eardrum
unitary-resource model : a model of attention that views attention as a single pool of resources reserved for mental activities
user interface : the component of a software system responsible for presenting output to and receiving input from the user
utility : the subjective worth of an object or event
validity : the degree to which a test or some other measurement device measures what it is supposed to measure
variability : a measure that indicates the degree of “ spread” in a distribution of numbers from a central point. Usually, the variance
variability of practice : the extent to which the specific movements executed during practice of a motor skill differ from each other
variables : critical events or objects that change or can be changed
variance : the sum of all squared differences between the values of a dependent variable and their mean, divided by the total number of such values minus 1
ventral stream : visual pathway in the brain that processes information about what an object is
verbal protocol analysis : a method for organizing verbal reports obtained as a person describes what she is thinking of while performing a task
vergence : rotations of the eyes inward or outward with changes in the point of fixation
vernier acuity : the ability to discriminate between a broken and unbroken line
vestibular sense : the sense associated with the perception of bodily motion and balance
vigilance decrement : a decline in the hit rate over time in the performance of a vigilance task
vigilance task : a task characterized by the requirement of detecting small, infrequent changes in the environment over long periods of time
virtual reality environments : computerized “ worlds” intended to provide the experience of moving about and interacting with objects in a three-dimensional space
viscous resistance : control resistance that increases with control velocity
visibility : how well a display can be seen, or how visible it is
visual angle : a measure of the size of the retinal image of an object
visual cortex : the primary receiving area of the cortex in which visual signals are processed and recombined
visual dominance : the priority that visual information receives when information arrives from the visual and other systems simultaneously
Warrick’ s principle : the pointer of a display should move in the same direction as the side of the control nearest the display
weak methods : methods of problem solving of broad applicability used to solve unfamiliar problems when the correct way to proceed is unknown
Weber’ s law : the smallest detectable change in the magnitude of a stimulus is a constant proportion of the magnitude of the original stimulus
work tolerance : the ability of an operator to perform well while maintaining physical and emotional health
working memory : another name for short-term memory that emphasizes the operations that occur on information in short-term memory
Yerkes– Dodson law : performance is an inverted U-shaped function of arousal, with best performance at intermediate levels of arousal