People: The Sensory Perspective
People in Design
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Sensory - Senses
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Now we could spend a whole semester just
looking at the senses, they are very rich and
detailed, but we have a lot of exciting things to
cover in this module, so we’ll curtail it by just
looking at one sense in detail (Vision) and cover
the others in less detail.
People: Sensory
- Sight
People in Design
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Sensory - Sight
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The eye is a ball filled with fluid with light sensitive
cells coated on the back of the eyeball
It has a small hole in the front to let in light, with a
lens to help focus the light on the cells on the
back of the eye.
The cells on the back of the eye transmit
information through the optic nerve to the brain.
People in Design
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Sensory - Sight
People in Design
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To help understand what an incredibly
sophisticated job the eye does, in terms of
getting input from the external environment
and processing the light waves, it is useful to
look at the evolution of the eye.
People in Design
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At some point in
history the creatures
that evolved to
become human
developed cells on
their body that were
sensitive to light
(photosensitive cells)
These were very
useful for telling the
difference between
day and night.
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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These cells evolved
into a concavity, to
protect the cells from
casual damage, e.g.
scrapes and
scratches.
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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The concavity further
contacts so that there
is a very small
opening, this
improvement helps to
discriminate the
direction of the
brightness.
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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Eventually a slowly
specialize a
transparent humour, in
the eye to allow for
colour filtering,
blocking of ultraviolet
radiation, and the
ability to operate in
and out of water
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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The eye evolved
lenses to improve the
amount of light that
reached the retina,
and to focus the light
exactly on the back of
the eye.
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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Finally a cornea and
iris developed, this
increases refractive
power, eases
circulatory problems,
and can help control
the amount of light
entering the eye.
[Source: Wikipedia –
File: Diagram_of_eye_evolution.svg]
People in Design
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Sensory - Sight
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The eye is like a digital camera in the sense that it
has a lens in the front to focus the incoming light
on the photosensitive cells that coat the rear of
the eye.
The digital camera does some processing on the
images in terms of removing shake and balancing
out the brightness, the human brain does a similar
job, but significantly more processing.
Visual Acuity
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Visual acuity clearness of vision, which depends on
the sharpness of the retinal focus within the eye and
the sensitivity of the interpretative faculty of the
brain.
It is a measure of the spatial resolution of the visual
processing system and is usually tested in a manner
to optimise and standardise the conditions.
To this end, black symbols on a white background
are used (for maximum contrast) and a sufficient
distance allowed to approximate infinity in the way
the lens attempts to focus.
Visual Acuity
Visual Acuity
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In the term "20/20 vision", the numerator refers to the distance
in feet between the subject and the chart. The denominator
indicates the size of the letters, specifically it denotes the
separation at which the lines that make up those letters would
be separated by a visual angle of 1 arc minute, which for the
lowest line that is read by an eye with no refractive error (or the
errors corrected) is usually 20 feet (6.1 m).
The 20/x number does not directly relate to the eyeglass
prescription required to correct vision, because it does not
specify the nature of the problem corrected by the lens, only the
resulting performance.
Visual Impairment Classification
Classification
Description
Partially Sighted
20/30 to 20/60
Low Vision
20/70 to 20/160
Legally Blind
20/200 to 20/1000
Totally Blind
No light perception
Contrast Sensitivity
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Contrast sensitivity is a measure of the ability to
discern between luminances of different levels in a
static image. Contrast sensitivity varies between
individuals, reaching a maximum at approximately
20 years of age.
This text is easier to read, than this text.
According to Dr Daphne Bavelier, University of
Rochester, playing video games may improve a
person’s contrast sensitivity
Interesting illustration of the
complex relationship between
vision and the brain.
The Bucha effect
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The effect is named after a Dr. Bucha who
identified the phenomenon in the 1950s
when he investigated a series of unexplained
helicopter crashes.
The Bucha effect
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The pilots who had survived reported sudden
onset of dizziness and confusion, causing
them to lose control of their aircraft.
The Bucha effect
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Dr. Bucha found that helicopter rotor blades, when
turning at certain speeds, could cause flashes of
sunlight at frequencies coinciding with the electrical
frequencies of the central nervous system
(brainwaves), inducing disorientation.
The Bucha effect
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The problem was solved by a few different
solutions:
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Tinting the window screen of the helicopter
Tinted visors on the pilot’s helmet
People: Sensory
- Hearing
- Taste
- Smell
- Touch
People in Design
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Sensory - Hearing
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The main organ of hearing is the ear.
People in Design
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Sensory - Hearing
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The outer part of the ear collects sounds, which is
focused and amplified in the middle part of the
ear.
When the sound reaches the ear drum (or
tympanic membrane) and passes into the inner
ear, which is coated with hair cells (whose job is
convert the sounds in nerve impulses that the
brain can understand).
People in Design
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Sensory - Hearing
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The frequencies that humans are capable of
being heard are called audio or sonic.
The range is typically considered to be between
20 Hz and 20,000 Hz.
Frequencies higher than audio are referred to as
ultrasonic, while frequencies below audio are
referred to as infrasonic.
People in Design
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Sensory - Hearing
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An important notion when considering hearing is
“Loudness”, which is a quality of sound that is
primarily a psychological interpretation of the
physical signal strength of a sound (amplitude).
The loudness that humans are capable of being
heard are typically 15 dB and 140 dB.
Hearing Impairment Classification
Classification
Who?
decibels of hearing loss, or dB HL
Mild
For Children
between 20 and 40 dB HL
Mild
For Adults
between 26 and 40 dB HL
Moderate
For All
between 41 and 55 dB HL
Moderately Severe
For All
between 56 and 70 dB HL
Severe
For All
between 71 and 90 dB HL
Profound
For All
91 dB HL or greater
People in Design
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Sensory - Taste
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The main organ of taste is the tongue.
People in Design
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Sensory - Taste
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Tastes is sensed through taste cells (called taste
buds).
There are about 100,000 taste buds that are
located on the back and front of the tongue.
Others are located on the roof, sides and back of
the mouth, and in the throat.
People in Design
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Sensory - Taste
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The tongue has different regions to detect
different flavours.
People in Design
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Sensory - Taste
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The tongue has different regions to detect
different flavours.
People in Design
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Sensory - Taste
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The idea that the tongue has different regions that
specialize in different flavours is a common
misconception.
This mistake is as a result of confusion in the
translation of a 1901 German psychology paper
into English.
It actuality all taste sensations come from all
regions of the tongue
Taste Impairment Classification
Classification
Description
Hypergeusia
Abnormally heightened sense of taste
Dysgeusia
Distorted sense of taste
Hypogeusia
Decrease in taste sensitivity
Ageusia
Complete lack of taste
People in Design
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Sensory - Smell
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The main organ of smell is the nose.
People in Design
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Sensory - Smell
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Smell is achieved by specialized neurons at the
top of your nasal passage.
These neurons have hair-like projections called
cilia that capture molecules coming off the object
emitting the smell
When the cilia capture these molecules this
causes neurons to fire, and signals are sent to the
brain.
People in Design
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Sensory - Smell
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Olfactory fatigue (or adaptation) refers to the
fact that after prolonged exposure to a particular
smell, a person will no longer be able to detect it.
For example, when entering a restaurant initially
the smell of food is very strong, but after time the
awareness of the smell fades to the point where
the smell is not perceptible or is much weaker.
After leaving the restaurant, the sensitivity is
restored with time.
People in Design
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Sensory - Smell
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Humans can distinguish more than 10,000
different smells.
Research suggests that humans can detect
individuals that are blood-related kin (mothers
and children but not husbands and wives) from
olfaction.
Smell Impairment Classification
Classification
Description
Hyperosmia
Increased sensitivity to smell
Dysosmia
Distorted sense of smell
Hyposmia
Diminished sense of smell
Anosmia
Loss of the sense of smell
People in Design
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Sensory - Touch
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The main organ of touch is the skin.
People in Design
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Sensory - Touch
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The sense of touch is a very complex and diverse
sensory system composed of the receptors which
detect not only touch, but also temperature, body
position, and pain.
People in Design
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Sensory - Touch
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At its simplest, the system works when activity in
a sensory neuron is triggered by a specific
stimulus such as heat; and this signal is passed to
an area in the brain uniquely attributed to that
area on the body—this allows the processed
stimulus to be felt at the correct location.
People in Design
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Sensory - Touch
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Phantom Limb Syndrome: Approximately 60 to
80% of individuals who have had a limb
amputated experience phantom sensations in
their amputated limb, and the majority of the
sensations are painful.
People in Design
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Sensory - Touch
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A number of treatments have been used to
combat the sensation, include drugs, electrical
stimulation, and Ramachandran’s Mirror Box
treatment.