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• The chapter concentrates on human aspects considered in interface design.
• It is about the vision, hearing, touch, and movement of humans.
• Also discussed is the memory of the human, thinking style, errors, mental models, and emotions

The Human Factors

• Information is received through visual, auditory, haptic, and movement I/O channels
• Memory stores information in sensory, short-term, and long-term forms
• How information is processed and applied considers reasoning, problem-solving, skill, and error
• Emotion greatly influences human capabilities
• Each person has different capabilities

Vision

• Vision occurs in two stages: physical reception of stimulus, and processing and interpretation of stimulus

The Eye – Physical Reception

• Is a mechanism for receiving light and turning it into electrical energy
• Images are focused upside-down on the retina
• The retina contains rods for low light vision and cones for color perception
• Ganglion cells help in detecting pattern and movement

Interpreting the Signal

• Visual angle indicates how much of the view an object occupies which relates to size and distance from the eye
• Visual acuity is an ability to perceive detail
• Familiar objects are perceived as constant size despite changes in visual angle when far away
• Overlapping cues help with perception of size and depth
• Brightness: Is a subjective reaction to levels of light, is affected by the luminance of the object and is measured by just noticeable difference
• Colour is determined by hue, intensity, and saturation
• Cones are sensitive to color wavelengths, blue acuity is the lowest.

Compensations

• The visual system compensates for movement and luminance changes
• Context helps resolve ambiguity
• Optical illusions occur from overcompensation

Reading

• The stages include perceiving a visual pattern, decoding patterns internally to language, and interpreting the language to knowledge of syntax, semantics, and pragmatics
• Reading involves saccades and fixations whereby perception occurs during fixations
• Word shape is important for recognition
• Negative contrast improves reading on computer screens

Hearing

• The hearing provides information about environment distances, directions, and objects
• The outer ear protects and amplifies sound.
• The middle ear transmits the sound waves through vibrations to the inner ear.
• The inner ear releases chemical transmitters which cause impulses in the auditory nerve
• Sound is determined by its pitch, loudness and timbre parameters
• The pitch is the sound frequency
• The loudness is the amplitude
• The timbre is the sound's type or quality.
• A human hears frequencies between 20Hz to 15kHz
• It filters background noise to focus on relevant sounds like in the "cocktail setting" phenomenon

Touch

• It provides feedback about environment and is key for visually impaired people because stimulus is received through skin receptors
• Thermoreceptors react to heat and cold
• Nociceptors react to pain
• Mechanoreceptors react to pressure
• Some body areas, like fingers, are more sensitive
• Kinethesis is awareness of body position that affects comfort and performance

Movement

• Responding to stimulus is the sum of reaction time + movement time
• Movement time depends on age and fitness
• Reaction time depends on stimulus type namely:
• Visual ~ 200ms
• Auditory ~ 150 ms
• Pain ~ 700ms
• Increased reaction time decreases accuracy for unskilled not skilled operators
• Fitts' Law describes the time taken to hit a screen target: Mt = a + b log2 (D/S + 1)
• a and b are empirically determined constants
• Mt is movement time
• D is the Distance
• S is the Size of target
• Targets are as large as possible, and distances are as small as possible

Memory

• There are three types of memory: sensory, short-term, and long-term
• Stimuli selection is dictated by arousal

Sensory Memory

• Buffers stimuli received through senses
• Iconic memory processes visual stimuli
• Echoic memory processes aural stimuli
• Haptic memory processes tactile stimuli
• Continuously overwritten

Short-Term Memory (STM)

• It is a scratch-pad for temporary recall
• Rapid access happens ~ 70ms and decay roughly 200ms
• Capacity is limited to 7± 2 chunks

Long-Term Memory (LTM)

• It is the repository for knowledge which has a slow access of ~ 1/10 second
• A slow decay that has huge or unlimited capacity

Types of LTM

• Episodic: Serial memory of events
• Semantic is structured memory of facts, concepts, and skills
• Semantic LTM is derived from episodic LTM

Semantic Memory Structure

• It provides access to information and represents relationships between bits of information and support inference

Model: Semantic Network

• An inheritance model meaning that child nodes inherit the properties of parent nodes and it supports explicit relationships and support inference

Models of LTM - Frames

• Information is organized in data structures
• Slots in the structure instantiate values of data types
• With type-subtype relationships

Models of LTM - Scripts

• Model of stereotypical information is required to interpret situation
• Script elements can be instantiated with values for context

Models of LTM – Production Rules

• Representation of procedural knowledge
• Condition/action rules are used
• This means that if a condition is matched then use the rule to determine action

LTM - Storage of Information

• Storage of information is done through rehearsal as it moves information from STM to LTM
• Total time hypothesis: the amount retained is proportional to rehearsal time
• Distribution of practice effect is optimized by spreading learning over time
• Information is easier to remember if it is meaningfully structured and familiar

LTM – Forgetting

• Decay happens as information is lost gradually but very slowly
• Interference happens as new information replaces it; proactive inhibition

LTM - Retrieval

• Recall- information reproduced can be assisted by cues like categories and imagery
• In recognition, information gives knowledge that it has been seen before, which is less complex than recall

Thinking

• Includes reasoning and problem-solving

Deductive Reasoning

• Derives logically a necessary conclusion of premises, however a logical conclusion is not necessarily true
• People apply world knowledge

Inductive Reasoning

• Generalizes from seen cases to unseen cases
• It can only prove something false not true

Abductive Reasoning

• Infers from an event to its cause
• Leads to false explanations

Problem-Solving

• The process of finding a solution to an unfamiliar task using knowledge.
• Gestalt theory dictates
• Productive vs reproductive problem solving
• Insight and restructuring can facilitate the problem-solving

Problem Space Theory

• Problem space comprises problem states
• Problem-solving involves generating states using legal operators
• Heuristics may be employed to select operators

Problem-Solving - Analogy

• A novel problems occur in a new domain
• Knowledge of a similar problem from similar domain is used to solve it
• Analogical mapping becomes difficult if domains are semantically different

Problem-Solving– Skill Acquisition

• Skilled activity is characterized by chunking - More information is chunked to optimize STM
• Conceptual vs superficial grouping of problems
• Information is structured more effectively

Errors and Mental Models

• Types of error include slips and mistakes
• Slips are characterized as having the right intention but are unable to do it right
• Mistakes are when the wrong intention is chosen

Emotion

• Theories state that :
• Emotion is our physiological response to a stimulus.
• Emotion is a psychological response to the stimuli.
• Emotion is the result of our evaluation of our physiological responses in light of the situation
• Emotion is cognitive and physical responses to stimuli

Emotion–Affect

• The biological response to physical stimuli is called affect
• Has influences on how we respond to situations
• Positive effects are creative in problem-solving - "Negative affect can make it harder to do even easy tasks, positive affect can make it easier to do difficult tasks" by Donald Norman
• Negative effects narrows thinking and can increase stress Stress will increase the problem-solving difficulty
• Relaxed users are forgiving of shortcomings in design
• Aesthetically pleasing and rewarding interfaces will increase positive affect

Individual Differences

• Differences range from long-term abilities like sex, physical and intellectual strength to short-term differences, like stress and fatigue
• Age related long term changes occur as well
• Design decisions must not exclude sections of the user population

Psychology and the Design of Interactive systems

• Avoid using blue for important details because perception is poor
• Correct application requires understanding of context in psychology, and conditions
• There has been distillation of knowledge and guidelines - Guidelines - chapter 7 - Cognitive models - chapter 12 - Experiment and analytic evaluation techniques - chapter 9