Good/Bad Examples?

Understanding Users:
Physiology and Psychology
What are our users’ characteristics?
 Terms of Discourse
• Physiology
– The science of the body
• Ergonomics
– From Greek: erg (work) and nomos (study of)
• Anthropometry
– The measure of human dimensions
• Psychology
– The science of the mind
• Psychophysics
– The study of the relationship between physical stimuli and perception
• Culture
– the attitudes and behavior that are characteristic of a particular social
group
 Restriction of Scope
• For the purposes of this course, we’ll focus
primarily on those aspects of humans central to
the use of interactive software
– While anthropometry and ergonomics are important,
we’ll mostly pass them by
• This leaves us largely in the domain of
Cognitive Psychology
 Cognitive Psychology
• Loosely, describes the mental capabilities of
the human
– Sensation and perception
– Attention
– Memory
– Learning
– Reasoning
 Sensation and Perception
• Sensation
– What the sensory organs and processing system
can detect and record
– Of the senses, we will primarily be concerned with
• Visual
• Auditory
• Haptic
• Perception
– What the human brain can do with sensations
– The pathway between sensed stimuli and thought
• Physical stimuli map to perceptual responses
– Objective → subjective
 A Word about Models
• The field of cognitive psychology is dominated
by models
– Models of human function are compared to observed
behavior
– The purpose is to figure out how it works
– Note: a model is not the truth, but an approximation
• A common modeling approach is to consider the
human being an information processing system
– There are problems with this model ...
– …but it will suffice for our purposes
 Information Processing Model
• The IP model considers
Cognition the human to work
something like a computer
system, i.e. with layered
Perception processing
• But there is evidence to
the contrary, e.g.:
Sensation Tachistoscopic detection of
text
Stimulus
 The Human Visual System

Retina
Light
Eye

Striate Cortex
(Cerebrum) Optic Nerves
Anatomy of the Eye
 Physiological Elements of Vision
• The retina (which receives the image from the
lens) consists of two kinds of receptor cells:
– Rods
• Sensitive to luminance (not frequency)
• Wide dynamic range (very dim to very bright)
• Widely distributed on retina
– Cones
• Sensitive to frequency (color)
• Narrow dynamic range (don’t work in low light)
• Concentrated around the fovea
• Denser than rods in fovea
Rods

Cones
 Two Modes of Vision
• Scotopic Vision:
– The contribution of the rods – so no color
– Wide dynamic range means this is effective from
very low light to very bright light
– Good coverage of periphery
• Photopic Vision:
– The contribution of the cones – so color
– Fine resolution due to density of cones
– Not effective in low light
– Poor peripheral coverage
 Binocular Vision
• Not so important as commonly thought
– Indeed, 2% of population have “uncooperative”
eyes, yet suffer little or no deficit
– Listen to the story of one person:
http://www.npr.org/templates/story/story.php?storyId=5536894

• Helps with depth perception (stereopsis),

though head movement can also support this
• Also expands field of peripheral vision
 Dynamics of Vision
• Rods and cones actually respond to changes of
light
• If you could actually hold your eye still, the
image would fade (can be done in a clinic/lab)
• Abrupt onset detection (a combined sensory/
perceptual phenomenon) causes visual
attention to be drawn to motion in an otherwise
static visual field
 Color Perception
• The modern field of psychology was started
by…
Isaac Newton!
• He developed a theory of color vision before
writing his book on optics
• Many theories of color vision have been
developed since
• Color blindness exists in many forms, and
probably effects about 10% of humans
– Red-Green (“hetergeneous dichromacy”) is the
most common
 Visual Stimuli
• Stimuli → perception is loosely as follows:
– Luminance of light → perceived brightness
– Frequency of light → perceived hue
– Spectral shape → perceived saturation
• But these are not “clean”!
– e.g. Hue perception is also impacted by luminance
 Contextual Effects
• Environment impacts
perception
– e.g. Mach bands

Notice that it’s darker here…

…than here?

Well it’s not!

From your colleague…
 Semantic Effects
• What we “see” is also
influenced by so-called
higher-order cognitive
process
– e.g. we complete scenes
based on expectation
– Visual illusions result
from this, as do eye-
witness disparities
The Human Auditory System

Sound wave

Auditory Nerves
Anatomy of the human ear (cont’d)
 How Do You Hear?
• Sound Waves
• Ear Drum Vibrates
• Cochlea
• Mechanical Action to Electrical Action
• Auditory Nerve to the Brain
 Hearing
• First sound waves enter the auditory canal
and strike the ear drum.
• The ear drum vibrates.
• Then the malleus vibrates and passes the
vibrations onto the incus which in turn passes
them onto the stapes. The ossicles multiply
the pressure exerted by the ear drum 20
times.
 Hearing (Cont’d)
• The stapes strikes the oval window causing it to
vibrate and this causes the fluid within the cochlea to
vibrate.
• The vibrations of the fluid in the cochlea cause the
basilar membrane to go up and down
• This causes the hairs of the hair cells (receptors) to
bend
• This in turn initiates impulses that travel along the
fibers of the auditory nerve to the auditory area in the
brain where the impulses are interpreted as sound.
 Hearing (Cont’d)
• The pitch sensation depends on which region
of the basilar membrane vibrates and which
area of the auditory region of the brain is
stimulated.
• The volume depends on the amplitude of
sound waves. Loud noises cause the fluid of
the cochlea to vibrate more which causes the
basilar membrane to move up and down to a
greater extent.
• Hearing loud noises may damage the hair cells
and result in loss of hearing
 Intensity of Sound
• Amplitude of the sound wave entering our ear
(loudness)
• Measured in decibels
• Loudness is also influenced by frequency.
– At high frequencies the same amount of sound
energy is perceived as louder.
– The ear is more sensitive to high frequencies.
 Psychophysics of Sound
• We have a non-linear perceptual response to sound
pressure waves
• Intensity Level [Bels]: IL = log10(I/Iref), where Iref is
least audible (usually use 10-12 W)
• But this is too large, so we use decibels (dB): 10
log10(I/Iref)
• Since I = P2, Sound Pressure Level in dB is SPL =
20log10(P/Pref)
• Pref generally 0.00002 N/m2 (threshold of hearing)
 Frequency Components
• Sound is made up of a combination of
frequency components (Fourier Theorem)
• Pitch is perceptual response to frequency
• Human hearing is not uniformly responsive to
all frequencies
 Loudness
• Noise measured in terms of “equal loudness”
• Compared to a reference of 1000 Hz tone:
– If 65 dB SPL tone at 50 Hz is equally loud as 40
dB 1000 Hz tone, then it has loudness level of 40
phons
• Can draw equal loudness contours as f(ν)
Equal Loudness Contours
 Frequency (pitch)
• Number of cycles per second
• We can discriminate frequencies best between
2000 and 5000 Hz.
• Most communication is between 500-2000 Hz.
• Sensitivity to sound depends on frequency.
The higher the frequency the louder the sound
appears given the same sound energy.
 Digital Telephony
• Nyquist’s Theorem
• Acceptable voice transmission quality
 Sound in the HCI
• Early use: signals and alarms
• This gave way to “Earcons”
– e.g. the sound of the trash being emptied on the
desktop
• Auditory Data Representation
– The use of sound to represent quantitative data
– Example: DRI Economic indicators, 1948-1980
 Attention
• Automatic/Unintentional
– Ecological – e.g. eye “drawn” to movement (so-
called “abrupt onset” detection)
• Intentional
– “What will I read here?”
– “Which conversation am I listening to?”
 Memory
• Three basic types
– Sensory buffer (Iconic/Echoic/Haptic)
– Short-term memory (a.k.a. “working store”)
– Long-term
• George Miller’s “Magical Number 7 +/- 2”
• George Sperling’s Partial Reporting technique
• Recall vs. Recognition
 Gestalt Psychology
• Some general principles
– Closure
– Good form
– Good continuation
– Symmetry
• Has been used to explain illusions:
 Mental Models
• The “mind’s eye”
• Visual vs. Representational
• Can supplement memory, or replace the need
for visual detail with descriptive
representations
– Eye witness issues here!
• Patterns of expectation, especially with respect
to behaviour
 The Differently Abled
• All of the previous describes so-called “normal”
humans
– Good luck finding one!
• “Normal” is a statistical concept, and the term usually
describes a range of capabilities describing most
people
• But we often need to include users outside of this
range
• We address this under the heading of “Universal
Design”
 Elements of Human Differences
• System designs often need to accommodate
people who
– Have different personal capabilities
– Are in different operational surroundings
– Have different social and cultural expectations
• While interaction design often addresses the
“normal”…
– What is normal, and how many does it exclude?
– How can we design for most or all?
 The Goal
• The goal of universal design is to design
products so that “they can be used by as many
people as possible in as many situations as
possible.”
 Different personal capabilities
• Visual impairment
– Far-sightedness
– Color-blindness
– Total blindness
• Haptic impairment
– Tremors
– Missing or non-functional digits/limbs
• Cognitive impairment
– Limited reading skills
– Dyslexia
Different Operational Surroundings
• Harsh environments
– Construction site
– Battlefield conditions
• Inconvenient settings
– Classroom
– Handheld devices
– Police car
And I know what I’m talking about!
 Different Social and Cultural
Expectations
• Language issues
– Other than primary language
– Dialect
– Jargon
• Education
– Knowledge/experience with computing
– Intimidation
 NC State’s 7 Principles
• Equitable Use
– Useful to a wide range of people
– Note: not necessarily identical experience for all
• Flexible in Use
– Allows for a range of ability and preference
• Simplicity and Intuitiveness
– Support expectations and accommodate language
and literacy skills
 NC State’s 7 Principles (cont’d)
• Perceptible Information
– Effective communication in spite of conditions
• Tolerance for Error
– Minimize likelihood of user error
– Minimize error consequences
• Low Physical Effort
– Minimize physical demands on users
• Size and Space for Approach and Use
– Easily reached and controlled (anthropometry)
Multimodality Research Examples
• Stephen Brewster’s group:
– http://www.dcs.gla.ac.uk/~stephen/
• Stephen Barrass’ work:
– http://www.canberra.edu.au/schools/creative-
communication/staff-profiles/docs/stephen-barrass