Understanding Users - Physiology and Psychology

What are our users’ capabilities?

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 the human to work something like a computer system, i.e. with layered processingPerception

Cognition

Sensation

Stimulus

• But there is contrary evidence e.g.:Tachistoscopic detection of text

The Human Visual System

Eye

Retina

Optic NervesStriate Cortex(Cerebrum)

Light

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• 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=5507789

• 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!

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

Auditory Nerves

Sound

Anatomy of the human ear (cont’d)

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

Demo!

Frame of Data

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

– Partial or 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

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-com

munication/staff-profiles/docs/stephen-barrass