9.2 Human Performance and Limitations

Question 1

What is the eye similar to?

Answer 1

A simple camera with an aperture (iris)

Question 2

What is the function of the cornea?

Answer 2

It lets light enter and provides 70–80% of the eye’s focusing ability by bending light.

Question 3

What does the iris do?

Answer 3

Controls the amount of light entering the eye by adjusting pupil size.

Question 4

What is the light adjustment ability of the pupil?

Answer 4

It can change light intake by a factor of 5:1.

Question 5

What is accommodation?

Answer 5

The lens changing shape to focus; thickening for close objects and flattening for distant ones.

Question 6

What reduces accommodation?

Answer 6

Fatigue and ageing

Question 7

What are cones responsible for?

Answer 7

Colour vision

Question 8

What are rods responsible for?

Answer 8

Low-light vision

Question 9

Why do we see in greyscale in low light?

Answer 9

Rods take over as cones stop functioning well.

Question 10

Where is visual acuity highest?

Answer 10

At the fovea

Question 11

What creates the blind spot?

Answer 11

The point where the optic nerve joins the retina

Question 12

Why are blind spots not normally noticeable?

Answer 12

Binocular vision and rapid eye movement (saccades) prevent images falling on the spot continuously.

Question 13

How sensitive is the eye compared to the ear?

Answer 13

The eye has about 1.2 million nerve cells vs. 50

Question 14

What does 20/20 or 6/6 vision mean?

Answer 14

Normal visual acuity—seeing clearly at 20 feet (or 6 metres).

Question 15

What causes hypermetropia?

Answer 15

A short eyeball causing images to form behind the retina (difficulty focusing on close objects).

Question 16

What causes myopia?

Answer 16

A long eyeball causing images to form in front of the retina (distant objects appear blurred).

Question 17

What is a cataract?

Answer 17

Clouding of the lens

Question 18

What is astigmatism?

Answer 18

A misshapen cornea causing distorted vision.

Question 19

What is glaucoma?

Answer 19

Increased eye pressure damaging the optic nerve.

Question 20

What is presbyopia?

Answer 20

Age-related loss of lens flexibility

Question 21

Can fatigue affect vision?

Answer 21

Yes

Question 22

What substances impair vision?

Answer 22

Drugs

Question 23

How does lighting affect vision?

Answer 23

Better lighting improves vision up to a point; too much causes glare.

Question 24

What is dark adaptation?

Answer 24

Eyes adjusting to darkness—cones take ~7 mins

Question 25

Why look slightly to the side in low light?

Answer 25

To place images on rod-rich areas instead of the cone-only fovea.

Question 26

What environmental factors impair vision?

Answer 26

Dust

Question 27

What object factors affect vision?

Answer 27

Contrast

Question 28

Why is colour vision important for engineers?

Answer 28

Identifying components

Question 29

What causes colour vision deficiency?

Answer 29

Defects in cone cells

Question 30

What is the most common colour vision issue?

Answer 30

Difficulty distinguishing red and green.

Question 31

How does ageing affect colour vision?

Answer 31

Lens yellowing reduces blue-yellow colour discrimination.

Question 32

Does colour deficiency always prevent engineering work?

Answer 32

No

Question 33

Why is eyesight testing required for engineers?

Answer 33

Vision changes gradually and affects inspection tasks and fine detail work.

Question 34

Is wearing glasses or contacts acceptable for engineers?

Answer 34

Yes

Question 35

What does CAP 562 say about eyesight?

Answer 35

Engineers must have adequate distance and near vision

Question 36

Who is responsible for recognising impaired vision?

Answer 36

The individual engineer must recognise and act on any vision problems.

Question 37

What are the two main functions of the ear?

Answer 37

Detecting sound vibrations and monitoring balance/acceleration.

Question 38

What are the three divisions of the ear?

Answer 38

Outer ear

Question 39

What does the outer ear do?

Answer 39

Directs sound waves to the eardrum

Question 40

What does the middle ear do?

Answer 40

Uses ossicles to transmit vibrations to the inner ear and provides limited protection through the aural reflex.

Question 41

What are the ossicles?

Answer 41

The hammer

Question 42

What is the aural reflex?

Answer 42

A protective mechanism reducing loud sounds by up to 20 dB for about 15 minutes.

Question 43

Why does the middle ear contain the eustachian tube?

Answer 43

To equalise pressure and refresh air

Question 44

What does the inner ear contain?

Answer 44

The cochlea filled with fluid and hair-like cells detecting vibrations.

Question 45

How is sound transmitted to the brain?

Answer 45

Hair cells in the cochlea send neural impulses through the auditory nerve.

Question 46

What affects the vibration size detected in the cochlea?

Answer 46

The pitch and volume of the sound.

Question 47

What is the typical hearing frequency range?

Answer 47

20 Hz to 20

Question 48

What are some negative effects of workplace noise?

Answer 48

Annoyance

Question 49

What are employers required to do under noise regulations?

Answer 49

Provide hearing protection

Question 50

When must hearing protection be provided?

Answer 50

When normal speech cannot be heard clearly at 1 metre.

Question 51

When must employers assess noise risk?

Answer 51

When normal speech cannot be heard clearly at 2 metres.

Question 52

What is the maximum level at which hearing protection must always be used?

Answer 52

Above 115 dB

Question 53

How much noise reduction do ear plugs provide?

Answer 53

Up to 20 dB.

Question 54

How much noise reduction do ear defenders provide?

Answer 54

Up to 40 dB.

Question 55

What is Noise Induced Hearing Loss (NIHL)?

Answer 55

Hearing damage caused by exposure to loud noise

Question 56

What causes temporary hearing loss?

Answer 56

Short exposure to loud noise that temporarily overloads hair cells in the cochlea.

Question 57

What causes permanent hearing loss?

Answer 57

Repeated or long-term exposure damaging the hair cells beyond recovery.

Question 58

Name a sign you may be at risk from noise.

Answer 58

Needing to raise your voice to talk at 2 metres.

Question 59

Another sign you may be at risk from noise.

Answer 59

Using loud powered tools for more than 30 minutes per day.

Question 60

Workplace types with high noise risk?

Answer 60

Forging

Question 61

What is a common early symptom of hearing loss?

Answer 61

Difficulty following conversations.

Question 62

What is tinnitus?

Answer 62

Ringing

Question 63

Why must hearing loss be prevented early?

Answer 63

It develops gradually and is often irreversible by the time it is noticed.

Question 64

What is presbycusis?

Answer 64

Age-related hearing deterioration