The Human In order to design something for some one, we need to understand the capabilities and limitations of that person. This chapter covers how humans perceive the world around them, how they store and process info and solve probs & how they physically manipulate objects Information i/o via visual auditory Haptic-touch movement channels e.g. fingers Speech Information is stored in memory (short and long term memory) Information is processed and applied in problem solving How do you think a human being inputs & outputs info?

The Human Modality: It is a general class of A sense – through which the human can receive the output of the computer A Sensor or device through which the computer can receive the input from the human. A path of communication between the human and the computer. Major modalities: Seeing or vision modality, Hearing or audition modality, Touch, tactile modality - the sense of pressure Other Modalities: Taste or gustation modality, Smell or olfaction modality, thermoception modality – the sense of heat or the cold How do you think a human being inputs & outputs info?

Vision size and depth Two stages in vision physical reception of stimulus: Mechanism for receiving light and transforming it into electrical energy which in turn reflects (mirrors) object processing and interpretation of stimulus size and depth -visual angle indicates how much view object occupies (relates to size and distance from eye) e.g. view of a tree thru window different from view when outside -visual acuity is ability to perceive detail. Size of visual angle affects acuity -Familiar objects perceived as constant size (in spite of changes in visual angle when far away) Visual angle is a line drawn from the top of the object to a central point on the front of the eye and another drawn from the bottom of the object to the same point.

Interpreting the signal (cont) Brightness subjective reaction to levels of light affected by luminance (amount of light emitted by an object) of object measured by just noticeable difference. Contrast (difference) related to luminance of an object & that of its background visual acuity increases with luminance Color Perception comprises of hue (shade), intensity (brightness), saturation (amount of whiteness) Eye perceives color b’se cones are sensitive to light of different wavelengths (blue has shortest, green medium & red long) blue acuity is lowest 8% males and 1% females color blind-can’t distinguish btn green & red What is color blindness?

Reading Concerned with processing text Stages: visual pattern perceived e.g. of the word Study decoded using internal representation of language (English) i.e. knowledge of syntax, semantics, pragmatics (sensible) During reading, eye moves back and forth-regressions. If text is complex, there’ll be more regressions Speed of reading depends on legibility (9-12 points), line spacing & line length(2.3-5.2 inches) Reading from comp slower than bk hence fewer words on a page, dark characters on a light screen (negative contrast) increases acuity

Hearing Provides information about environment: distances, directions, objects etc. E.g. “There is a man behind the house” identify the distance, direction and object components in this statement? Physical apparatus: outer ear - protects inner and amplifies sound middle ear - transmits sound waves as vibrations to inner ear inner ear - chemical transmitters are released and cause impulses in auditory nerve. Sound pitch - sound frequency loudness - amplitude timbre - type or quality

Hearing (cont) Humans can hear frequencies from 20Hz to 15kHz less accurate distinguishing high frequencies than low. Auditory system filters sounds can attend to sounds over background noise. e.g. cocktail party phenomenon.

Touch Provides important feedback about environment. May be key sense for someone who is visually impaired e.g feeling button depress is vital. Stimulus received via receptors in the skin: thermoreceptors - heat and cold nociceptors - pain mechanoreceptors – pressure-what we’re concerned with in HCI Some areas more sensitive than others e.g. fingers What is the touch stimulus of interest in Hci?

Movement e.g using a mouse, hitting a button Time taken to respond to stimulus: reaction time + movement time Movement time - dependent on age, fitness etc. Reaction time - dependent on stimulus type: visual ~ 200ms (millisecond) auditory ~ 150 ms pain ~ 700ms

Memory There are three types of memory function: Sensory memories or sensory storage (buffer for stimuli: Holds info from the eyes (iconic storage) and ears (echoic storage). This information is stored for a brief time. MUST ENTER WORKING MEMORY OR BE LOST.   Short-term memory or working memory Long-term memory Selection of stimuli governed by level of arousal. Attention Rehearsal What is iconic/echoic storage

Short-term memory (STM) Scratch-pad for temporary recall e.g. names of some people at a party rapid access ~ 70ms rapid decay ~ 200ms limited capacity - 7± 2 chunks The capacity of short-term memory is small -- info will disappear within 20 seconds unless it is repeated or practiced.  Chunking: grouping and organizing information to fit into meaningful units. The size of chunks does affect ability to remember.

Long-term memory (LTM) Repository for all our knowledge slow access ~ 1/10 second slow decay, if any huge or unlimited capacity Once information is transferred to long term memory, it is there forever - the problem is accessibility or retrieval.  - the basic debate is how info is located and retrieved, and how many long term memory subsystems exist. Two types episodic - serial memory of events like memories of key events in one’s life semantic - structured memory of facts, concepts, skills

Long-term memory (cont.) Semantic memory structure provides access to information Represents relationships between bits of information Supports inference Model: semantic network inheritance - child nodes inherit properties of parent nodes relationships between bits of information explicit (clear) supports inference through inheritance

Long-term memory - semantic network

Models of LTM - Frames Information organized in data structures Slots in structure instantiated with values for instance of data Type-subtype relationships DOG Fixed legs: 4 Default diet: carniverous sound: bark Variable size: colour COLLIE Fixed breed of: DOG type: sheepdog Default size: 65 cm Variable colour

Script for a visit to the vet Models of LTM - Scripts Model of stereotypical information required to interpret situation Script has elements that can be instantiated with values for context Script for a visit to the vet Entry conditions: dog ill vet open owner has money Result: dog better owner poorer vet richer Props: examination table medicine instruments Roles: vet examines diagnoses treats owner brings dog in pays takes dog out Scenes: arriving at reception waiting in room examination paying Tracks: dog needs medicine dog needs operation

Models of LTM - Production rules Representation of procedural (routine) knowledge. Condition/action rules if condition is matched then use rule to determine action. IF dog is wagging tail THEN pat dog IF dog is growling THEN run away Another good example is illness. Most people can tell when they’ve malaria

LTM - Forgetting decay information is lost gradually but very slowly interference (info gets mixed up with other info) new information replaces old: retroactive interference old may interfere with new: proactive interference affected by emotion - can subconsciously `choose' to forget e.g???

LTM - retrieval recall information reproduced from memory can be assisted by cues e.g. categories recognition information given based on what has been seen before less complex than recall due to cues e.g. metaphors used in computing .

Thinking: reasoning and problem solving Deductive: derive logically necessary conclusion from given premises. e.g. If it is Friday then she will go to work It is Friday Therefore she will go to work. Logical conclusion not necessarily true what if she’s sick this friday?

Inductive Reasoning Inductive: generalize from cases seen to cases unseen e.g. all elephants we have seen have trunks therefore all elephants have trunks.

Abductive reasoning reasoning from event to cause e.g. Sam drives fast when drunk. If you see Sam driving fast, assume drunk. Unreliable: can lead to false explanations. Distinguish btn inductive and abductive reasoning?

Problem solving Process of finding solution to unfamiliar task using knowledge. Several theories. Gestalt problem solving both productive (insight) and reproductive (using existing knowledge)

Problem solving (cont.) Problem space theory problem space comprises problem states (initial state and goal state ) & p’ple use operators to move from former to latter heuristics may be employed to select appropriate operators e.g. means-ends analysis-initial state compared with goal state & operators chosen to reach goal e.g. moving desk in your office largely applied to problem solving in well-defined areas e.g. puzzles rather than knowledge intensive areas

Problem solving (cont.) Analogy analogical mapping: novel problems in new domain? use knowledge of similar problem from similar domain e.g. containing the ebola outbreak in W. Africa using the experience of Uganda analogical mapping difficult if domains are semantically different Skill acquisition skilled activity characterized by chunking - lot of information is chunked to optimize STM conceptual (meaningful) rather than superficial grouping of problems e.g. disease diagnosis process by doctors - information is structured more effectively

Errors and mental models Types of error - humans create mental models to explain behaviour. if wrong (different from actual system) errors can occur. slips right intention, but failed to do it right causes: poor physical skill e.g. car parking, inattention etc. change to aspect of skilled behavior can cause slip. They happen by accident, such as making “typos” by pressing the wrong key or selecting wrong menu item. The most frequent errors are slips, especially in well-learned behavior. mistakes (An incorrect action is taken based on an incorrect decision.) wrong intention cause: incorrect understanding List and briefly explain two types of errors common with human actions. Give an example for each

Individual differences long term - sex, physical and intellectual abilities short term - effect of stress or fatigue changing - age Qestion: will design decision exclude section of user population e.g. for the mobile money service, URA online tax payment portal?

Cognitive Psychology and Interactive System Design Some direct applications e.g. blue acuity is poor  blue should not be used for important detail. However, correct application generally requires understanding of context in psychology A lot of knowledge has been distilled in guidelines - see Chapters 4 and 5 experimental and analytic evaluation techniques - see Chapter 11 of main reference for this course

References & Additional Reading Alan Dix, Janet Finlay, Gregory Abowd & Russell Beale (2004). Human-Computer Interaction. Hillsdale, NJ: Prentice Hall, 2004. ISBN 0-13-458266-7 (hardback); 0-13-437211-5 (paperback) only outside USA. 1998 (Second Edition) ISBN 0-13-239864-8. Chap. 1 Revision question “To design a good system for users it is needed to understand the capabilities and limitations of those different people.” a) Explain the term Universality. b) Explain the following barriers together with the corresponding personal assistive technologies. Sensory Physical Cognitive and Age Associated Barrier