Unit -4

Work Counter Behavior and Perception

Environmental issues - Physical work capacity (204) - Factors affecting work capacity (205) - Communication and cognitive issues - Information processing and perception (329) - Interaction with machines - mental workload.(436)

COGNITIVE ERGONOMICS

• Study of the capabilities and limitations of the human brain and sensory system while performing activities that have a significant information processing content
• Why cognitive ergonomics is important

–Growth in the service industry sector in which work has high content of information processing and communication

–More use of mechanization and automation

–Increased use of technologically sophisticated equipment

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HUMAN SENSORY SYSTEM

• Humans receive stimuli from sources of energy both external and internal to the body
• Receptors - the body’s sensory organs:
• Vision ~ 80% of human information input
• Hearing ~ 15% to 19% of information input
• Touch
• Smell
• Taste

VISION

• Light - electromagnetic radiant energy that lies within the visible spectrum

–Wavelengths between ~ 400 nm (blue-violet) and ~ 700 nm (red)

• Human eye is stimulated by light

–Light passes through the cornea (the eyeball’s window) and is focused by the lens onto the retina at the back of the eyeball

–The retina consists of millions of light receptors

–The optic nerve transmits the image focused on the retina to the brain for interpretation

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ANATOMY OF THE HUMAN EYEBALL

VISUAL PERFORMANCE

Do not use text consisting entirely of�capitals

• The letters with ascenders (b, d, f, h, k, 1, t) and those with descenders (g, j, p, q, y) stand out and contribute to the image of a word.
• The reader can see at a glance what is written and need not read letter by letter

Avoid confusion between characters

• Some characters are difficult to distinguish from each other, which can lead to confusion.
• The smaller the number of points forming the character, the greater the risk of confusion.
• In a normal text this will not lead to many difficulties, but in abbreviations and for letters, numbers and code numbers, this could well be confusing.

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Make sure that the characters are�properly sized

• The required dimensions of characters depend on the reading distance.
• A rule of thumb is that the height of capital letters should be at least 1/200th of the reading distance.
• Letters presented in a conference room 20 meters long should be at least 10 centimeters high on the screen.

The longer the line, the greater the�required line spacing

• A guideline here is that the line spacing should be at least 1/30th of the line length.
• If the lines are too closely spaced, it is difficult for the eye to follow from the end of one line to the beginning of the next line.

The longer the line, the greater the�required line spacing

• A guideline here is that the line spacing should be at least 1/30th of the line length.
• If the lines are too closely spaced, it is difficult for the eye to follow from the end of one line to the beginning of the next line.

HEARING

• Process of perceiving sound

–The sensation is stimulated by acoustic waves - air pressure oscillations

• A simple sound-generating source produces a pure tone, which is characterized by two physical attributes:

Frequency (Hz) - perceived as pitch

Intensity (dB) - perceived as loudness

SOUND: A PURE TONE

• Sinusoidal pressure oscillations of a simple sound-generating source

SOUND INTENSITY

• Measured as pressure, e.g., N/m2 or Pa
• However, range of sound pressures is very large (0.00002 N/m2 to 20 N/m2)
• Thus, intensity is converted to logarithmic scale, called sound pressure level (SPL) with units of decibel (dB): SPL = 20 log10(ps / pr)
• where ps = sound pressure from source, N/m2 , and pr = reference sound pressure, N/m2 (the usual reference pressure is 0.00002 N/m2)

• Sound intensity is measured from the listener’s perspective

–It is not a power measurement of the sound source

• Intensity of a sound wave varies inversely as the square of the distance from the source
• Example: a person listening to someone talk at a distance of 15 cm (6 in) hears an intensity level of ~ 80 dB, while the same listener hears only ~ 65 dB at a distance of 100 cm (40 in)

DB LEVEL OF VARIOUS SOUNDS

Threshold of hearing 0 dB

Soft whispering at 1 m (3 ft) 20 dB

Library environment 40 dB

Room air conditioner at 3 m (10 ft) 60 dB

Talking at 15 cm (6 in) 80 dB

Powered lawnmower at 1 m (3 ft) 100 dB

Jet engine at 60 m (200 ft) 120 dB

Jet engine at 30 m (100 ft) 140 dB

THE EAR

• It’s a transducer - it transforms mechanical energy of sound waves into electrical nerve signals that are transmitted to the brain for interpretation
• The ear consists of:

–Outer ear - eardrum mechanically transmits sound vibration to middle ear

–Middle ear - transmits and amplifies (20 times) vibrations to the inner ear

–Inner ear - converts vibrations to neural impulses that are transmitted to brain

ANATOMY OF THE HUMAN EAR

AUDITORY PERFORMANCE

• •Humans with normal hearing can perceive sound frequencies in the approximate range 20 Hz to 20,000 Hz when young
• •Low frequencies (below ~ 300 Hz) are not heard as well as high frequencies (in the range 1000 Hz to 5000 Hz)
• •The aging process takes its toll
• –Perception of high frequencies decreases with age
• –Normal hearing loss due to aging is called presbycusis

Environmental Factors

• Noise
• Vibration
• Lighting
• Climate
• Chemical Substance

Noise

• The presence of high noise levels during a task can be annoying and, in time, result in impaired hearing.
• The first symptom of impaired hearing is a perceived difficulty in understanding speech in a noisy environment (party, pub, etc.).
• Annoyance, such as interference in communication or reduction of concentration, can occur even at relatively low noise levels.

Guidelines on Noise

• Keep the noise level below 80 decibels

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�Avoid annoyance�

• An excess of noise will prove annoying even though the limit for damage to hearing has not yet been reached. It is mainly noise produce

• Rooms should not be too quiet
• Noise Reduction at Source

-Choose a low-noise working method

-Use quiet machines

-Maintain machines regularly

-Enclose noisy machines

• Noise Reduction through Workplace

-Separate noisy work from quiet work

-Keep an adequate distance from the source of noise

-Use the ceiling to absorb noise

-Use acoustic screens

• Hearing Conservation

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VIBRATION

• Whole body vibration
• Via Feet/ Seat
• Hand Arm Vibration
• Factors consider for analysing the vibration
• Level (expressed in m/s),
• frequency (expressed in Hz)
• exposure duration.
• Low-frequency
• body vibrations (<1 Hz) can produce a feeling of seasickness
• Body vibrations between 1 and 100Hz, especially between 4 and 8 Hz, can lead to chest pains, difficulties in breathing, low back pain and impaired vision.
• Most common frequency range for handheld motorized tools is between 25 and 150 Hz.

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Guidelines on Vibration

• Avoid heath and safety risks from vibration
• below 0.5 m/s for whole-body vibration and below 2.5 m/s for hand–arm vibration.
• Prevent shocks and jolts
• Tackle vibration at source
• Maintain machines regularly
• Prevent the transmission of vibration
• If necessary, direct the measures at the individual

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Illumination

• The light intensity, which is the amount of light that falls on the work surface, must be sufficiently high whenever visual tasks have to be carried out rapidly and with precision and ease.
• Luminance is the amount of light reflected back to the eyes from the surface of objects in the visual field.
• Light intensity is expressed in lux, and luminance (brightness) in candela per m2 (cd/m2). Color temperature is in Kelvin.
• The color of the light and the presence of daylight can affect a person’s mood and therefore performance.

Guidelines on Light Intensity

• Select a light intensity of 20–200 lux for orientation tasks
• Select a light intensity of 200–750 lux for normal activities
• Select a light intensity of 750–5000 lux for special applications
• Avoid excessive differences in brightness in the visual field
• Limit the brightness differences between the task area itself, the close surroundings and the wider surroundings

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• Avoid too cold and too warm colors for indoor lighting
• Ensure good legibility of information
• Combine ambient and localized lighting
• Daylight can also be used for ambient lighting
• Screen sources of direct light
• Prevent reflections and shadows
• Use diffuse lighting

Climate

• Air temperature
• Radiant temperature of surfaces
• Air velocity
• Relative humidity

Guidelines on Thermal Comfort

• Allow people to control the climate themselves
• Adjust air temperature to the physical demands of the task
• Avoid too humid and too dry air
• Avoid radiating surfaces
• Prevent drafts
• Avoid exposure to extremely hot or cold environments
• Materials, which must be touched, should be neither too cold nor too hot
• Locate equally heavy tasks together in a room
• Adjust the physical demands of the task to the external climate
• Optimize air velocity
• Prevent unwanted radiation
• Limit the time spent in hot or cold environments
• Use special clothing when working for long periods in hot or cold environments

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Chemical Substances

• Chemical substances occur in the environment as liquids, gases, vapours, dusts or solids.
• Some substances can cause discomfort or present a health hazard if inhaled or ingested or if they come into contact with the skin or eyes.

Guidelines on Chemical Substances

• Apply TLVs or other limits as maxima for chemical substances in ambient air
• Avoid carcinogenic substances
• Avoid peak exposures
• Exposure to mixtures of substances should be avoided
• Always aim to remain as far below the TL Vs as possible
• Packages of chemicals should be labeled appropriately
• Remove the source
• Reduce the releases from the source
• Isolate the source of chemicals
• Chemical substances must be extracted directly at source
• Provide an efficient exhaust system
• Pay attention to the effect on climate when designing air extraction and ventilation
• Provide sufficient air changes

Physical Work Capacity

• The basal metabolic rate (BMR) is the rate of energy consumption necessary to maintain life.
• Individuals differ in their BMR. The relative BMR of a child is about twice that of an adult.
• Physical work capacity refers to a worker’s capacity for energy output.
• This will depend primarily on the energy available to the worker in the form of food and oxygen and the sum of the energy provided by oxygen-dependent and oxygen independent processes.
• The rate of energy consumption during physical work is the sum of the basal energy consumption and the metabolic cost of the work in terms of energy consumption.

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• For continuous work at moderate intensities, oxygen-dependent processes usually make the major contribution to energy output.
• For each liter of oxygen consumed about 20 kilojoules of energy is released. Work capacity depends on the ability to take up oxygen and deliver it to the cells for use in the oxidation of foodstuffs.
• The ability to work at a high rate is associated with a high oxygen uptake.
• Exercise physiologists and sports scientists have used the term ‘VO2 max’ to describe an individual’s capacity to utilize oxygen (aerobic capacity).
• Individuals can work continuously over an 8-hour shift at a rate of 30–50% of their maximum capacity, depending on the frequency and length of rest periods.

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Factors affecting work capacity

• Body weight
• Age
• Gender
• Alcohol
• Tobacco smoking
• Training
• Nutritional status and general health
• Food intake and food supplements
• Motivation
• Air pollution
• Climatic factors
• Noise
• Altitude
• Protective clothing and equipment
• Pacing/time pressure

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HUMAN INFORMATION PROCESSING MODEL

• Information can be defined as the absorption of interpreted data, directly or indirectly, through human sensory functions.
• Perception is the process of attaining awareness or understanding of how sensory information or sensation occurs.
• Perceptuel processing has two important features. First, it generally proceeds automatically and rapidly, requiring little attention. Second, it is driven both by sensory input, as the senses receive
• Short-term memory is associated with a temporary storage of information in the brain

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MENTAL WORKLOAD MEASUREMENT

• Physical workload can be measured objectively at the level of both physics and physiology.
• The most direct and obvious approach would be to ask an operator or user how difficult it is to carry out a task.
• Techniques to measure mental workload
• Psychological measures of mental workload
• GSR (galvanic skin response).
• Heart rate.
• EMG (electromyography
• EEG (electroencephalogram).
• Eye movements and blinking.
• Speech pattern analysis.

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• Performance of the main task
• Psychological aspects of human error
• Error categorisation
• Error production
• Error detection, particularly self-detection
• Error identification
• Error recovery
• Error prevention