The user (human) is the one whom computer systems are designed to assist.
Information is received and responses are given via a number of input and output channels:
Visual channel
Auditory channel
Haptic channel (Touch)
Movement
Causes
Not specified in notes
Goals / Objectives
To design something for someone, we need to understand the capabilities and limitations of that person.
We need to know user (human) capabilities and limitations to design computer systems to assist them 103].
Importance
Understanding human capabilities and limitations is important because humans are limited in their capacity to process information, which has important implications for design.
Procedures
Not specified in notes
Benefits
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Advantages & Disadvantages
Advantages:
Not specified in notes
Disadvantages:
Humans are limited in their capacity to process information.
Impact / Effect
Not specified in notes
Examples
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Vision
Definition
Vision is the mechanism for receiving light and transforming it into electrical energy.
Light reflects from objects.
Images are focused upside-down on the retina.
Cones are concentrated at the front of the retina.
Rods are concentrated at the sides of the retina.
Periphery vision is the vision within the area where the eye is not sensitive to colour (the periphery).
Causes
Light reflects from objects, and images are focused on the retina to create vision.
Goals / Objectives
Not specified in notes
Importance
Colour detection is good when images are placed in front of the eye due to the concentration of cones.
The eye is not sensitive to colour at the periphery.
Peripheral vision is far better at perceiving movement, which is needed to identify potential risks quickly.
Procedures
Light reflects from objects.
Light is received and transformed into electrical energy.
Images are focused upside-down on the retina.
The eye components involved include: Lens, Iris, Cornea, Pupil, Liquid, Ligaments, Cilliary Muscle, Retina, and Optical nerve.
Benefits
Not specified in notes
Advantages & Disadvantages
Advantages:
Colour detection is good for images placed in front of the eye.
Peripheral vision is motion sensitive.
Disadvantages:
The eye is not sensitive to colour at the periphery.
Peripheral vision is insensitive to detail and colour.
Peripheral animation is distracting (e.g., animating sidebars zooming in and out).
Impact / Effect
Elements out of central vision do not require detailed colour.
If an urgent update is needed on a sidebar, use motion instead of colour.
Examples
Peripheral field of view includes a 3∘ area of direct vision.
The total peripheral field of view is about 180∘ (or 130∘ depending on the context/diagram).
Visual Processing and Reading
Definition
Visual processing involves interpreting the signal (light transformed into electrical energy).
Reading involves several stages: visual pattern perceived, decoded using internal representation of language, and interpreted using knowledge of syntax (operating on phrases or sentences).
Law of size constancy states that familiar objects are perceived as constant in size.
Causes
Ambiguity in the visual signal is resolved using context.
Optical illusions sometimes occur due to overcompensation.
Goals / Objectives
Not specified in notes
Importance
Perception of size relies on factors other than the visual angle.
Familiar words are recognized quickly using word shape.
Removing word shape clues (like capitalizing words) will slow down reading speed and accuracy.
Text in all caps reduces the shape contrast for each word.
Procedures
Context is used to resolve ambiguity in the signal.
Cues like overlapping help with the perception of size and depth.
In reading:
The visual pattern is perceived.
The pattern is decoded using an internal representation of language.
The information is interpreted using knowledge of syntax, operating on phrases or sentences.
Benefits
Words can be recognized as quickly as single characters.
Advantages & Disadvantages
Advantages:
Not specified in notes
Disadvantages:
A small percentage of people are colour blind (8% male, 1% female, per Faulkner, 1998).
The most common colour blindness is red-green.
A very small percentage of people have no colour vision at all.
Optical illusions can occur due to over compensation.
Impact / Effect
Builders of interfaces need to take the fact of colour blindness into account.
Examples
Colour Illusions.
The ability to read a jumbled sentence like “The qcuik borwn fox jmup oevr the lzay dog”.
Optical Illusions include the Muller-Lyer illusion and the Ponzo illusion.
Context resolving ambiguity examples (interpreting a line segment as part of a ‘13’ or a ‘B’, or as part of ‘ABC’ or ‘1234’).
Hearing
Definition
Auditory system refers to the system that filters sounds.
The cocktail party phenomenon is the ability to focus on a single conversation in a noisy room.
Causes
Not specified in notes
Goals / Objectives
Not specified in notes
Importance
Not specified in notes
Procedures
The auditory system filters sounds, which allows a person to attend to sounds over background noise.
Benefits
Humans can hear frequencies from 20Hz to 15kHz.
Advantages & Disadvantages
Advantages:
Ability to attend to sounds over background noise (cocktail party phenomenon).
Sound can be used for feedback and/or attracting attention when:
The information is short and simple.
An immediate response is needed (for alerts and warnings).
The visual system is already overburdened.
The user is moving about from place to place.
Poor illumination makes vision unreliable.
Disadvantages:
The ability to detect the lower and upper frequency ranges deteriorates with age and is also affected by health.
Sound can be a source of annoyance & distraction.
Impact / Effect
Sounds are commonly used:
As a means to locate things.
As a means to provide feedback.
As a means to attract attention.
Examples
Common usage of sounds is seen in ATMs, telephones, washing machines, and air conditioners.
The McGurk effect is an auditory illusion where what we see conflicts with what we hear.
Haptic (Touch)
Definition
Haptic refers to the sense of Touch.
Tactile feedback is the feedback given to the user (e.g., from a keyboard).
Causes
Not specified in notes
Goals / Objectives
Not specified in notes
Importance
Provides important feedback about the environment.
May be the key sense for someone who is visually impaired.
Affects comfort and performance.
Procedures
Not specified in notes
Benefits
Not specified in notes
Advantages & Disadvantages
Advantages:
Some areas (e.g., fingers) are more sensitive than others.
Disadvantages:
Not specified in notes
Impact / Effect
Keyboard design should give adequate tactile feedback to the user.
Examples
A watch designed to let blind people feel time using touch.
Movement and Response Time
Definition
Movement refers to how we move and how it affects our interaction with computers.
Time taken to respond to stimulus is the amount of time that takes place between when a person perceives something and responds to it.
Total response time is calculated as reaction time + movement time.
Reaction time is the time taken to detect and process a stimulus.
Causes
Movement time is dependent on age, fitness, etc..
Reaction time is dependent on the stimulus type.
Goals / Objectives
Not specified in notes
Importance
We need to consider motor control in design.
Procedures
The process of responding to a stimulus is: detect > process > respond.
Benefits
Not specified in notes
Advantages & Disadvantages
Advantages:
Not specified in notes
Disadvantages:
User still feels in control when the system delay is noticed (up to 1 sec).
User feels the computer is slow when the response time limit is reached (10 sec).
Impact / Effect
System Response Time Limits (Nielsen 1993):
0.1 sec: The system feels like it’s reacting immediately.
1 sec: The user notices the system delay but still feels being in control.
10 sec: This is the limit for keeping the user’s attention with the system; the user feels the computer respond slowly.
Reaction Times (dependent on stimulus type):
Visual ∼200 ms.
Auditory ∼150 ms.
Examples
Not specified in notes
Movement: Fitts’ Law
Definition
Fitts’ Law is a movement time prediction model.
T is the movement time.
a and b are empirically determined constants that are device dependent.
D is the distance of movement from the start to the target center.
W is the width of the target, which corresponds to accuracy.
The formula is: T=a+blog2(2WD).
Causes
Not specified in notes
Goals / Objectives
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Importance
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Procedures
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Benefits
Corners are the easiest places to reach because they have infinite dimensions.
Edge/corners can be considered to have an “infinite” width.
Advantages & Disadvantages
Advantages:
Not specified in notes
Disadvantages:
Not specified in notes
Impact / Effect
Not specified in notes
Examples
Fitts’ reciprocal tapping paradigm involved subjects moving a stylus back and forth between two plates as quickly as possible and tapping the plates at their centers.
The law applies to interfaces, such as the design of wheel menus and list menus.
Corners and edges of a screen (e.g., the Windows Taskbar or macOS menu bar) have an infinite target width, making them easy to target.