Human Computer Interaction

Lecture 2

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are we human or are we....Aims

◦To explore the human as Input Output Processor

◦To highlight key theories and knowledge for HCI

◦Understand some general characteristics of humans

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The HumanSensesBodyThinkingMemory

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The Human as an Input device

SensesHow we

make ‘sense’ of the world around us…

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Each sense has…A tool – Eye, skin, ear etcA process – Nerves, electricity etcLimitations – Pitch, brightness etc

◦….. and there is the added complexity of individual differences in sensory perception

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http://www.hagenstoons.com

Capturing Images

Sight: = physical reception of stimulus

The eye – ◦mechanism for receiving light and

transforming it into electrical energy - light reflects from objects

◦Images are focused upside-down on retina - retina contains rods for low light vision and cones for colour vision

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Interpreting Images (1)Size and Depth

◦visual angle indicates how much of view object occupies

(relates to size and distance from eye)

◦visual acuity is ability to perceive detail (limited)

◦familiar objects perceived as constant size

(in spite of changes in visual angle when far away)

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Interpreting images (2) Brightness

◦ Subjective reaction to levels of light◦ Affected by luminance of object (brightness)◦ Measured by just noticeable difference◦ Visual acuity (detail) increases with luminance as

does flicker

Colour◦ Made up of hue, intensity, saturation◦ Cones sensitive to colour wavelengths◦ Blue acuity is lowest◦ 8% males and 1% females colour blind

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Interpreting images (3)

The visual system compensates for:◦Movement.◦Changes in luminance.

Context is used to resolve ambiguity.

Optical illusions sometimes occur due to over compensation.

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Optical Illusions

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the Ponzo illusion the Muller Lyer illusion

Hearing Provides information about environment:

distances, directions, objects etc. Physical apparatus:

◦ Outer ear – protects inner and amplifies sound.

◦ Middle ear – transmits sound waves asvibrations 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.

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Hearing (cont)Humans can hear frequencies

from 20hz to 20khz.◦Less accurate distinguishing high

frequencies than low.

Auditory system filters sounds.◦Can attend to sounds over

background noise.◦For example, the cocktail party

phenomenon.

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Touch

Provides important feedback about environment.

May be key sense for someone who is visually impaired.

Stimulus received via receptors in the skin:

◦ Thermo receptors – heat and cold.

◦ Nociceptors – pain.◦ Mechanoreceptors – pressure

. Some areas more sensitive than others

e.g. Fingers. Kinethesis - awareness of body position.

◦ Affects comfort and performance.CO2702 + CO2751 Lecture 2 - 20011/12 13

Smell and TasteTools – nose, tongueNot much used in computer

interfaces but olfactory interfaces using smell are currently being developed… as we will not use these senses we are not discussing them here!

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The Human in Control

As a machine interacting with computers – humans can use whole body interaction or, more commonly interaction with arms and fingers

Kinect

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http://www.stelarc.va.com.au

The Unpredictable Human

Humans are more than machines – there are aspects that vary.

Increasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.

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http://www.cartoonstock.com

Emotion

Various theories of how emotion works◦James-Lange: emotion is our interpretation of a physiological response to a stimuli e.g. See axe-wielding maniac, pulse raises, begin to sweat (interpreted as fear) then we run.

◦Schacter-singer: emotion is the result of our evaluation of our physiological responses, in the light of the whole situation we are in

Emotion clearly involves both cognitive and physical responses to stimuli

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Emotion (cont.)

The biological response to physical stimuli is called affect

Affect influences how we respond to situations

◦ Positive creative problem solving◦ Negative narrow thinking

“Negative affect can make it harder to do even easy tasks; Positive affect can make it easier to do difficult tasks”

(Donald Norman)

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Emotion (cont.)Implications for interface

design◦stress will increase the difficulty of

problem solving◦relaxed users will be more forgiving

of shortcomings in design◦aesthetically pleasing and rewarding

interfaces will increase positive affect

There is a genre of study called affective computing

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Example from researchATM machineTwo machines identical in

function – number of buttons etc..One designed attractively the

other notAttractive one perceived to be

easier to use

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Kurosu, M. & Kashimura, K. (1995) Apparent usability vs. inherent usability: experimental analysis on the determinants of the apparent usability. Denver, Colorado. 292-293.

How humans solve problems

Deductive InductiveAbductive

◦reasoning

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Deductive ReasoningDeduction:

◦ derive logically necessary conclusion from given premises.e.g. If it is Friday then she will go to work

It is FridayTherefore she will go to work.

Logical conclusion not necessarily true:

e.g. If it is raining then the ground is dryIt is rainingTherefore the ground is dry

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Inductive Reasoning Induction:

◦Generalize from cases seen to cases unseen.

E.g.. All elephants we have seen have trunks

therefore all elephants have trunks.

Unreliable:◦Can only prove false not true.

… But useful!

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Abductive reasoningReasoning from event to cause

e.g. Sam drives fast when drunk.

If I see Sam driving fast, assume drunk.

Unreliable:◦can lead to false explanations

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The Human as a Store

Humans have the capacity to remember and retrieve information… this affects the way they use technology CO2702 + CO2751 Lecture 2 -

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http://www.cooperativeindividualism.org

Three different ‘stores’Sensory buffers: momentary stores

for stimuli received by the senses. This information, unless encoded in the short-term memory, is quickly lost.

Short-term memory (or working memory): short-term memory acts as a store for information required fleetingly.

Long-term memory: this forms the main resource for memory.

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Short Term MemoryAn example of this would be recalling a

telephone number long enough to write it down. Short-term memory degrades quickly, and has a limited capacity.

Quick access time – 70ms.Short term storage – 200ms (10 – 20 second

decay time).Limited capacity.

◦ Length of sequence remembered in order = 7 ± 2 (Miller, 1956).chunks of data are similar.recency effect.

Maintained and increased with rehearsal.Nowadays referred to as ‘Working memory.’

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Chunking and STMShort-term memory holds information

that is actively being used (thought about, reasoned with).

A chunk can be thought of as a single object that conveys a larger amount of information (like a chinese ideogram).

Examples of these include words, shapes and colours. However, the information decays in seconds as items are displaced by new items coming in.

Icons are an example of chunked information on a desktop which allows users to distinguish between the various programs available to them.CO2702 + CO2751 Lecture 2 -

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LTM – Networked chunksHere we store everything we ‘know’. Long-term

memory is characterised by huge capacity, slow access time and relative accuracy over time.

It is organised in an Episodic way.events and experiences in sequential order.

And a Semantic way.facts, concepts and skills that we have acquired.

Storage.◦ Structure, familiarity and concreteness

Forgetting.◦ Decay, interference.

Retrieval.◦ Recall - reproduced.◦ Recognition – clue given.

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Impact on HCI

Understanding the limits of human abilities and the scope of their abilities is essential for good design – we will revisit these aspects later in the course

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http://www.offthemarkcartoons.com

Next WeekMore on humans….

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