Visual Ergonomics Flashcards
1
Q
What are the 14 key points for a Visual Task Analysis?
A
- Adaptation effects – light/dark/glare
- Time taken to respond to particular stimulus
- Flicker (strobe effect) – depends on (nature of) task
- Position in VF
- Viewing distance – how much of a) and b) is required:
a) Accommodation
b) Convergence - Visual subtense of task detail (size/acuity)
- Motion of task
- Contrast of task detail
o How much dark or light there is to clarify task detail – to make more visible - Colour of task
o E.g. if painter/decorator -> need to know shades/hues so need colour vision
o Therefore, colour of task in front of person being analysed for visual efficiency needs taken into account - Clarity of task detail
- Stereopsis requirements
- VF requirements big VF (pilot) or small VF (watchmaker)
- Hazards
o Welding – FBs – light may burn hole in retina need appropriate protection that ↓ hazard but allows for a good VF - Training Requirements
2
Q
Describe Dark Adaptation?
A
- Eye operates over large range of light
- Difference between a starry night & sunny night = ~10” fold change in light intensity – we can see clearly in this range
- Dark adaptation curve reflects activity of cone and rod pathways
- Cones – 6-7million, small Receptive Field detail
o ‘Red’ – 64%
o ‘Green’ – 32%
o ‘Blue’ – 2% - Rods – 120million, not sensitive to colour, large RF
- RF of neuron is retinal region where presence of stimulus alters firing of that neuron
- Pupil diameter determines amount of light that illuminates retina
- Age ↓ pupil diameter under all conditions – senile miosis
- ↓ overall level of light for elderly people and ↓ their ability to cope w/ different levels of light
o E.g. driving at night is a struggle - As age, transmission of light through ocular media ↓ and lens yellows
- Retinal changes e.g. AMD occur w/ age
- Dark adaptation curves for young & old adults differ by factor of 100- 1000
3
Q
Who is Dark Adaptation important for?
A
Process of dark adaptation important for sailors, military, drivers -> can be adversely affected by factors such as retinitis pigmentosa (can only see through centre of retina) or Vitamin A deficiencies (malnutrition)
4
Q
Describe Light Adaptation?
A
- Quick adaptation of eye to background illumination in order to distinguish objects in background
- When first enter extremely bright environment – apparent contrast of object is low
o In <1min contrast appears normal
5
Q
Describe the time taken for visual response (space scotoma)?
A
- Space scotoma: area of partial alteration in VF where there’s degradation of VA but surrounded by normal acuity e.g. blind spot
- Eyes take ~0.1 seconds to ‘see’ image and project to brain to initiate visual sensation
6
Q
Describe flicker?
A
- Critical Flicker Fusion Frequency (CFF) is highest temporal frequency (at high contrast modulation) that can be resolved
- Ferry-Porter law: CFF is proportional to logarithm of luminance of flickering stimulus
- Produced while driving by sunlight incident through a regular array of trees
- Elderly people, w/ smaller pupils, less prone to suffer from flicker (getting less light on retina)
- Rotation of machinery at >CFF can blur rotating blades into invisibility
- Stroboscopic effects between light and machinery may occur
- Neutral density filters may ↓ apparent flicker
7
Q
Desccribe Position in VF?
A
- Normal human VF:
o 60° nasally to 100° temporally from vertical meridian
o 60° above and 75° below horizontal meridian - Minimum driving requirement: 50° either side of vertical, & 20° either side of horizontal
- Macula: central 13° of VF
- Fovea: central 3°
- Scan VF to put fovea on object – require excellent oculomotor co-ordination
o Like join the dots -> sent to visual cortex -> image produced
8
Q
Describe Viewing Distance, accommodation and Weston 1962 experiment?
A
- Demands on observer’s accommodation and convergence
- Accommodation amplitude ↓ with age
- Accommodation response is slow and gets slower with age
- Weston 1962 experiment:
o Teloramic: distance of task >2m —> accommodation <0.5D
o Mesoramic: 2>distance>0.25 —> accommodation 0.5<D<4
o Ancoramic: d<0.25 —> accommodation >4
9
Q
Describe Visual Subtense of Task Detail?
A
- VA depends on image luminance
- Large - >12’ -> 6/72
- Medium small - 4’-2’ -> 6/12 to 6/24
- Small – 2’-1’ -> 6/6 to 6/12
- V small – 1’ -> 6/6 magnification
10
Q
Describe Contrast (Weber contrast)?
A
- Weber contrast:
o (Lmax-Lmin)/Lmax
o Lmax & Lmin = luminances of detail or surround, depending on which is brighter
o Object contrast is ↓ in foggy weather, snowy conditions and rain or at night - Sinusoidal luminance gratings: L to R = low to high
- Spatial frequency
11
Q
Describe Clarity?
A
- Related to image sharpness
- Poor lighting impairs perception of small details
- Inclement weather e.g. fog or rain can severely restrict visual abilities of drivers
12
Q
Describe Task Surround?
A
- Layer light area surrounding task gives better visual efficiency than a small surround
13
Q
Describe Colour of Task?
A
- Colour vision important for recognition of traffic lights and road signs
- Accurate matching of colours in paints/fabrics/vegetables – good colour discrimination required
- Observer should have good colour vision and appropriate lighting (>1000 lux) & colour rendering properties (artificial daylight tubes) should be provided
o Metamerism: abnormal/adequate lighting can cause colours to appear v differently - Rod monochromat has no cones – lacks acuity (& colour vision)
- Trichromat – normal viewer – sees lots of colours
- Protanope – cannot see red
14
Q
Describe Motion?
A
- Dynamic VA:
o Ability to perceive lateral motion & motion in depth
o As critical detail (mins of arc) ↑ & motion ↑, lose acuity - Dynamic VA is lower than static VA
- High demand in cricket or baseball – small ball travelling v fast
o Low demand in golf, medium demand in football
15
Q
Describe Steropsis Requirements?
A
- Stereoacuity required to discriminate 2 objects in depth at distance w/ separation of depth
- Monocular vision – problems: pouring coffee – likely to spill it
- Binocular vision – positioning large objects w/ crane
