ELEMENT 3
The Human Body
3.5 The Senses
3.6 The Eye and Vision
3.7 The Ear and Hearing
3.8 The Inner Ear and Balance
3.9 Sensory Inputs and Spatial Disorientation
AIM & END STATE
• Aim:
– To discuss the senses and how they relate to
human performance limitations
• End state:
– A greater understanding of the human body’s
strengths and weaknesses
• References: In the CRM Reference
Manual.
3.0
SENSES
• How many senses do we have?
– Classic senses are five but perhaps up to 21
– Nine senses are commonly agreed upon and
are tested in aircrew medicals
• A sense is an ability to
interpret information about
our environment that has
been detected through
a sensor, eg chemorecptors in the nose.
3.5
SENSES
• The extra senses we shall investigate:
– Equilibrioception – balance
– Thermoception – ability to detect heat/cold
– Proprioception – ability to tell where the body is
in relation to the environment
– Nocioception – ability to detect pain.
• Equilibrioception and Proprioception are
tested by aviation physicians during aircrew
medicals.
3.5.1.2
SENSES
• Sensory Thresholds
– The limit of the ability to detect a change in a
stimulus: Absolute, Recognition, Differential,
Terminal.
• Sensory Sensitivity
– Detection ability (1st meaning) or a disorder
where a person experiences a debilitating
sensory overload from everyday experiences,
eg touching fabric or a bad smell.
3.5.2
SENSORECEPTORS
• Stimuli detected through SensoReceptors:
3.5.4
THE EYE
• Most important
sensor for humans
• More than 80% of
our sensory
information about
our environment
comes through our
eyes.
3.6
THE EYE
• Light passes through the cornea and lens
and falls upon the
retina, focussing in
particular on the
fovea centralis
• Accommodation is
the way the lens is
bent by ciliary muscles
to focus light.
3.6.2.1
THE EYE
• Rods and Cones are photoreceptors that
detect light
– Cones detect colour and
detail – day/central vision
– Rods detect low light
levels and movement
night/peripheral vision
• Rhodopsin and Iodopsin
are two chemicals that
help in light detection.
3.6.2.2
THE EYE
• Visual Acuity (VA) is the ability to
discriminate the fine details of an object
thus is a requirement of depth perception
• VA is measured as a fraction (20/20 imp 6/6
metric)
– 20/40 or 6/12 is half as good as the average
• VA can be affected by disorders such as
– Myopia (shortsightedness)
– Hyperopia (long sightedness).
3.6.3
THE EYE
• Presbyopia
– Loss of VA due to age
– Becomes very noticeable in a person’s 40s
– Reduction in suppleness of the lens and
weakness in the ciliary muscles causes a
reduction in accommodation
– Hard to read fine print; things are a little blurry;
hard to focus between distances; eye strain
after reading for a long time.
3.6.3.2
THE EYE
• Visual Field
– What a person can see. Depends on light falling
on the retina (central and peripheral vision)
• Binocular Vision
– FOV 200 deg both eyes;
160 deg one eye
– Uses parallax error for
depth perception to approx 12m
– Provide Visual Summation: two eyes are 41%
more effective at detecting stimuli than one eye.
3.6.4
THE EYE
• Depth Perception: the ability to estimate
distances without measuring them
– Relative Size
– Interposition
– Linear Perspective
– Aerial Perspective
– Light and Shade
– Monocular
Movement Parallax
3.6.4.2
THE EYE
• Blind Spots: areas on the retina that do not
receive light information
– Day Blind Spot:
• Optic Disc
• No cones
– Night Blind Spot
• Fovea Centralis
• No rods
• Offset vision
by 10-20 deg.
3.6.5
THE EYE
• Glaucoma: Pressure build up in the corneal
area (anterior and posterior chambers)
causes damage to
the fovea
– Usually gradual
– Can easily be
checked
– Easily fixed if
caught early
before damage to retina is done.
3.6.6
THE EYE
• Hypoxia and Colour Vision: Vision affected
by loss of oxygen, especially at night
– 10% at 5,000’ and 28%
at 10,000’ PA especially
during mesopic
(dawn/dusk) periods
– Breathing oxygen
increases visual
acuity and colour
discrimination.
3.6.7
THE EAR
• The Ear: Primary organ of audition; second
most important organ for
humans
– Detects sounds
– Inner ear detects balance
– Pressure waves in the air
(sound waves) are caught
by the pinna, funnelled into
the auditory canal to the
eardrum which vibrates.
3.7
THE EAR
– The vibrations are transmitted through the
ossicles to the cochlea
where they are
detected by
mechanoreceptors
that induce a signal
to the brain
– Semi-Circular Canals
detect movement
by detecting radial
and linear accelerations.
3.7.1
THE EAR
• Hearing Loss: Two main categories:
– Conductive
• Damage or blockage
due to injury or disease
to the outer and/or
middle ear
– Sensorineural
• Usually caused by
damage to the inner
ear’s stereocilia cells
due to exposure to loud noise.
3.7.3
THE EAR
• Noise Induced Hearing Loss:
– Part of the speech range in the audible range is
first to go.
3.7.3
THE EAR
• Balance: Equilibrioception is through the
organs of the inner ear
– Semi-Circular Canals
arranged in x,y,z axes
– Otoliths arranged in
x,y axes in utricle
– Detects movement by
relative movement of
endolymph fluid in SCC
or by small crystals in gelatinous mix in utricle.
3.7.3
DISORIENTATION
• Spatial Disorientation (SD) is the inability of
the operator (eg pilot) to understand where
the apparatus (eg aircraft) is in relation to
the earth.
• Usually due to poor interpretation of, or
weak sensory stimuli, especially:
– Vision, Equilibrioception and Proprioception
• ATSB says that the career incidence of SD
occurs to 90 to 100% of pilots… (it will happen to you)
3.9
DISORIENTATION
• Types of SD:
– Type 1: SD is not recognised by individual
• Acft usually remains under control but is flown into a
dangerous situation (eg terrain)
– Type 2: SD is confusing but not incapacitating
• Operator knows something is wrong. Information
does not correlate with what the body/mind is saying
– Type 3: SD is incapacitating, potentially fatal
• Operator is physically/psychologically overwhelmed
and is usually unable to recover from the situation.
3.9.1
DISORIENTATION
• Vertigo – usually associated with an
abnormality in the vestibular organ. Similar
effect to SD
– Flicker vertigo: caused by flashing light
1 Hz to 20 Hz
– Often in helicopter ops:
• Front seats occupants
or patients lying in rear
where the sun can
flicker through
rotor blades.
3.9.2
DISORIENTATION
• Pressure Vertigo – due to imbalance in
pressure between middle ears – often due
to imbalanced valsalva attempt
• Medical Vertigo – usually due to temporary
problem in middle ear
• All types of vertigo will cause dizziness,
nausea and disorientation to some degree
• Can happen to anyone at anytime.
3.9.2
DISORIENTATION
• Categories of SD:
– Somatogyral: Dark Night Take Offs
– Somatogravic: Graveyard spiral
– Visual:
Illusions
causing
SD
3.9.3
DISORIENTATION
• Black Hole Approach: Illusion of excessive
altitude when there are no lights below the
aircraft during an approach
– Often leads to incorrect control inputs
• Boeing study found that 52% of
accidents/fatalities occur during the last 4%
of flight (approach/landing phase)
– Most of those were due to pilot error when no
precision approach aid (glidepath) was used.
3.9.3