Human Factors Quiz 1

What are the goals of human factors?
Improving the safety, efficiency, and well being of workers through careful design of equipment and environments.

How is human factors different from engineering psychology or experimental psychology?
Human factors relies more on data from other disciplines and is less concerned with theoretical concepts.

What is the current approach of human factors?
Fitting the task to the man.

What was the old approach of human factors?
Identifying the best man for the task.

How many blind spots do you have in each eye at night?

How many blind spots do you have in each eye during the day?

Why are eye movements necessary?
Because only the fovea can resolve small visual details in the environment.

Human factors is concerned with the ______?
Luminous energy.

Which visual system is mediated by the cone photoreceptors?
Photopic visual system.

Which visual system is mediated by the rod photoreceptors?
Scotopic visual system.

Which visual system is responsible for our good visual acuity?
Photopic visual system.

Which visual system is responsible for our good night vision?
Scotopic visual system.

Which visual system is responsible for our good color vision?
Photopic visual system.

Which visual system adapts rapidly to lower illumination?
Photopic visual system.

Which visual system takes 30 minutes to fully dark adapt?
Scotopic visual system.

Photoreceptors of this visual system are not found in the fovea.
Scotopic visual system.

The most numerous type of photoreceptor in the eye.
Scotopic visual system.

Describe the early history of human factors.
Human factors originally tried to find the best man or woman for a job, but now it tries to fit the job or task to the user.

What are some of the themes of this course?
Human factors is not the application of common sense, although common sense may be helpful. Human factors is not the use of lists and guidelines. Never use yourself as the model user.

Why do we need human factors experts?
The user is no longer the designer of the tools they use. It is necessary to evaluate the design and its features on a population of users. There is a need for more systematic ways of evaluating the system, its goals, and distribution of tasks before giving it to the end user. Changes in physical parameters and in the nature of tasks.

What is supervisory control?
Division of tasks between automation and the human operator, feedback to the operator of system functions and states, human ability to maintain vigilance and sustained attention.

How does human factors differ from ergonomics?
Human factors is traditionally based in psychology and ergonomics is traditionally based in industrial engineering. Human factors focuses on the perceptual, psychomotor, and cognitive limitations of the individual. Ergonomics focuses on the physical limitations of the individual, reducing work related injuries.

Define human factors.
Human factors applies knowledge of human physical, biomechanical, sensory, and psychological capabilities and limitations in the design of tools and environments. They design tools and environments which enhance the safety and productivity of works.

What values does a human factors expert bring to the design team?
Experimental design and statistical skills, and understanding of the perceptual and cognitive limitations of the user.

Why is human factors not the application of common sense?
Common sense assumes a shared set of expectations derived from common experience.

What are some of the benefits of having human factors input in the design of a system or tool?
Human factors reduces cost and improves efficiency and safety. It is costly to redesign equipment later in the design cycle, and it costly to retrain users if there is a significant change in a tool.

Explain the difference between relative and absolute judgment.
Absolute judgment is made without comparison to a reference and relative judgment is made by comparison.

What is signal detection theory?
It assumes that “the world” (as it is relevant to the operator’s task) can be modeled as either one in which the “signal” to be detected is present or absent. Whether the signal is present or absent, the world is assumed to contain noise.

Why is it important to distinguish between criterion and sensitivity?
It allows the human factors practitioner to understand the consequences of different kinds of job interventions that may be intended to improve detection performance in a variety of circumstances.

What happens to the number of hits and false alarms if you have a liberal criterion?
There will be a greater number of hits and false alarms.

What happens to the number of hits and false alarms if you have a conservative criterion?
There will be a fewer number of hits and false alarms.

What is focused attention?
The inability to monitor a single source of information. Represents an inability to monitor a single source despite effort to ignore other sources (e.g. reading web page while ignoring moving banners).

What is selective attention?
The monitoring of an inappropriate source of information. Represents an intentional but erroneous choice of a source (e.g. watching road but not monitoring speed).

What is divided attention?
Failure to attend to several things at the same time. Represents failure to divide attention among different tasks (e.g. read and listening to music).

What is sustained attention?
Inability to maintain attentional effort. Represents variation in sustaining attentional effort resulting in missed cues or failure to detect changes (e.g. air traffic controller looking at radar screen, doctor scanning X-rays).

What is the vigilance decrement?
Sustained attention (inability to maintain attentional effort).

What is object versus spaced based attention?
It depends on the task. Supervisory control is the monitoring of displays (cockpit, control panels). Target search is scanning the region of the visual world for a target (hunting, search and rescue, checking X-rays).

How is attention influenced by experience, expectancies and the conspicuity of objects?
Cognitive factors such as where a target is likely to be can influence where attention is directed (expectancies). Attention is likely to be drawn by large, bright, colorful, and changing or moving stimuli (conspicuity). There does not appear to be a consistent scanning pattern when searching for a target.

Explain the effects of the number of distracters on parallel and serial search.
The number of items to be searched has the dominant effect on search time. Search is serial and self terminating. When target is defined along a salient dimension search time is little affected by the number of items. Search proceeds in parallel.

Describe rod or scotopic vision.
Only one type, very sensitive to light, 120 million rods, poor acuity, poor sensitivity to flicker, none found in the fovea, no color vision.

Describe cone or photopic vision.
3 types (L (red), M (green), S (blue)), do not function under dim illumination, only 6 million cones, very good acuity in foveal region, very good sensitivity to flicker, highest concentration in the fovea, responsible for color vision.

What is the dark adaptation curve?
Reveals shift from cone to rod mediated vision. Reveals rate of adaptation and maximum sensitivity.

Which system dark adapts more rapidly?

Which system (rod or cone) has greatest sensitivity?

How long does it take to fully dark adapt?
30 minutes.

How does acuity change with illumination level, with retinal eccentricity?
Higher illumination results in greater acuity. Acuity declines as retinal eccentricity increases.

What is visual acuity?
The ability to resolve fine detail, often expressed as the inverse of the smallest visual angle (in minutes of arc) that can just be detected.

Where is acuity best?
In the fovea.

What is accommodation?
When an out-of-focus image triggers a change in lens shape to accommodate, or bring the image into focus on the retina.

What is the cornea?
A protective surface that absorbs some of the light energy and is also the place where the light rays first pass.

What is the lens?
It is responsible for adjusting its shape, or accommodating, to bring the image to a precise focus on the back surface of the eyeball.

What is the pupil?
It opens or dilates (in darkness) and closes or constricts (in brightness) to admit adaptively more light when illumination is low and less when illumination is high.

What is the retina?
The back surface of the eyeball, where the image is brought to a precise focus.

What is contrast?
Contrast sensitivity can be defined as the reciprocal of the minimum contrast between a lighter and darker spatial area that can just be detected; that is, with a level of contrast below this minimum, the two areas appear homogeneous.

How do you calculate contrast sensitivity?
The contrast of a given visual pattern is expressed as the ratio of the difference between the luminance of light, L, and dark, D, areas to the sum of these two luminance values: c = (L – D)/(L + D).

What does it mean to have good contrast sensitivity?
When the contrast is greater, sensitivity is greater across all spatial frequencies.

What is the contrast sensitivity function?
The ability to detect contrast is necessary to detect and recognize shapes.

How does contrast change with illumination level?
Lower illumination reduces the sensitivity and does so more severely for sensing high spatial frequencies (which depend on cones) than for low frequencies.

What percentage of the population is color limited?
Approximately 7 percent of the male population is color deficient.

What is the range of human hearing?
20 – 20,000 HZ. Children may be capable of hearing up to 40,000 HZ. We are maximally sensitive to sound in the frequency range of 1,000 – 3,000 HZ.

What are the parts and function of the outer ear?
Pinna, auditory canal, and tempanic membrane. The function of the outer ear is to collect sound, enhance sound in the range of 2,000 – 5,000 HZ by resonating, thus increasing sound pressure level by up to 12 dB.

What is the function of the middle ear bones?
Transmit sound energy from the tympanic membrane to the oval window. The three bones form a mechanical lever amplifying the displacement (22x) produced on the tympanic membrane and transmitting it to the oval window. Concentrate the vibration produced in the larger tympanic membrane on to the smaller oval window.

What are the parts and function of the inner ear?
Cochlea, basilar membrane, and organ of Corti. The cochlea forms a snail shaped spiral filled with fluid. Sound waves in the external ear are transferred to the inner ear fluids and to the basilar membrane (organ of Corti).

What are the effects of masking?
Masking studies measure thresholds for different frequency sounds in the presence of a noise stimulus. The findings show effects of noise are asymmetric. A masking noise raises thresholds more effectively for sounds equal or higher in frequency than the mask. Masking effects decrease with increasing disparity in frequency. However, the louder the masking tone, the broader its masking effect on frequencies greater than it.

What cues are used to localize sound?
Stereophony is the ability to localize the point of origin in space of a sound. The two primary cues used in sound localization are sound intensity and phase shifts between sounds.

What problems exist in sound localization?
There is no phase shifts for sounds in front or behind the head. The localization of midrange frequencies, 1,500 to 3,000 Hz is difficult because they generate minimal phase shift or intensity differences.

What are phonemes?
The shortest speech segment which if changed would change the meaning of a word.

What are phoneme confusions?
Groups of letters tend to be confused with each other. E.g. DVPBGCET, FXSH, KJA, MN. Pattern of phoneme confusion is greater in noise.

What is speech intelligibility?
Accuracy in recognizing a list of spoken words or sentences. Intelligibility is worse for nonsense words < words < sentence. Intelligibility is very dependent on context.

What is the McGurk effect?
Visual “Gah” + Auditory “Bah” = “Dah” perception.

What is reverberation?
The time it takes for a sound to decrease by 60 dB (1 million). It degrades intelligibility. Intelligibility is linear function of reverberation time. Older persons (>50) find reverberation troublesome. Some reverberation is good because it gives it acoustical warmth. Without reverberation the room sounds dead.

When are the use of filters effective?
Use of filters are effective where filters can improve the signal to noise ratio by reducing the strength of noise in bands outside that of the signal.

How can you increase the detectability of signals?
Reduce noise in signal frequency band, increase signal intensity, make use of brain’s ability to cancel noise common two ears, more complex sounds are harder to mask with noise (for frequencies between 1,000 – 4,000 Hz), use longer duration signal.

What are the discrimination of frequency differences?
Frequency judgments are better for pure tones that are 60 – 70 dB above threshold and for frequencies between 100 and 1,000 Hz.

Why do listeners have more difficulty in monaural conditions?
It is more difficult to attend to a single source and deleterious effect on speech understanding in informationally complex and noisy conditions.

What is binaural unmasking?
Improved ability to detect a signal in noise when an interaural difference (phase or intensity) is present. E.g.: The signal and noise original from different locations, and the use of only one ear or signal and noise originate from the same location. Demonstrates the auditory systems ability to cancel the input of noise present in both ears. Benefits are greater for younger than older subjects.

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