Humans

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Humans Humans form an important part of

human-computer interaction The limitations of humans influence how

computers must be designed to work well with humans

We will turn our attention to the human senses and brain to become familiar with the capabilities and limitations of each

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Input-Output Channels Humans interact with the world via

Senses Sight, hearing, touch, taste, & smell

Effectors Limbs, fingers, eyes, head, & vocal system

The senses allow us to receive information from the computer while the effectors send information to the computer

The important senses from an HCI perspective are sight, hearing, and touch

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Vision The human visual system depends

on The eye

Receiving the light and converting it into signals

Ganglia in the retina Responsible for edge and shape detection

Visual cortex Part of the brain Responsible for understanding of scene

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The Eye

* Human Computer Interaction, Dix et al, Prentice-Hall, 2004

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The Eye Cornea & lens

Focus light onto the retina Retina

Light sensitive part containing rods & cones Rods

Highly sensitive to light Cannot resolve fine detail ~ 120 million around periphery of retina Dominate low-light & peripheral vision

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The Eye Cones

Less sensitive to light 3 types corresponding to different colors that

permit color vision ~ 6 million, concentrated in the fovea

Blind spot Where optic nerve exits eye where there are

no rods or cones Ganglion Cells

X-cells – in fovea for pattern detection Y-cells – throughout retina for motion

detection

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Edge Detection

Original Image Detected Edges

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Visual Perception Much of vision depends on visual angle

Objects with a large visual angle are closer Visual angle is used to determine distance Overlap helps to determine distance Known object size also determines distance

The visual angle determines the detail which can be resolved A line can be seen at 0.5 seconds of arc Spaces between lines can be detected at

30-60 seconds of arc

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Visual Angle

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Perceiving Brightness Brightness is determined by the

luminance of objects Contrast is the difference in brightness

of objects The visual system compensates for

brightness so that most scenes look the same

As light decreases, the rods dominate and we lose color vision

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Perceiving Brightness

Visual acuity increases with brightness

On computer displays, flicker increases with brightness

Flicker is perceived is the screen is updated less than 50 Hz

Flicker is most often perceived in peripheral vision

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Perceiving Color Color is made up of

Hue Intensity Saturation

We can perceive about 150 hues We can vary the intensity & saturation

to increase this to 7 million colors Untrained individuals might be able to

identify as few as 10 colors

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Perceiving Color

Approximately 8% of males and 1% of females suffer from some form of color blindness

Red / green color blindness is the most common

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Color Blindness

25, 645, 856, 29

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Visual Limitations

The eye compensates for changes in Luminance Location

It also makes interpretations based on what it expects to see, not what is actually there

This can lead to optical illusions

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The Muller-Lyer Illusion

Which line is longer?* Dix, et al

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The Ponzo Illusion

Are the blue rectanglesthe same size?

* Dix, et al

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Text Illusions

Is this text correct?

* Dix, et al

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Reading Reading is performed at about 250

words per minute People recognize words in about the

same time it takes to recognize a character

Fonts between 9 – 12 point are equally legible

Lines between 2.3 – 5.2 inches are easily read

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Reading There is evidence to suggest that it is

slower to read from a computer display Line length too long or short Unfamiliarity with the medium Insufficient contrast

Dark characters on a light background provide higher luminance and higher acuity, but is more prone to flicker

In practice white letters on black is preferred and increases reading accuracy

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Reading Contrast

This is low contrastWith the backgroundAnd can be difficult To read

This is preferred byMost people due to

The high contrast and The lack of flickerIn the background

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Eye Fatigue

Eye fatigue results from letters with too low resolution Professional printers use 1200 DPI

since 600 DPI will cause fatigue Displays have ~100 DPI Scalable fonts should be used Flicker increases fatigue

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Hearing The ear drum vibrates in response to

changes in air pressure The vibration is transmitted via bones to

the liquid-filled cochlea where it is detected by cilia

Humans can detect sound from 20 Hz to 15 KHz

Humans can detect subtle changes in pitch

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Sound in Interfaces

Sound is usually used for warnings It could be used far more

extensively Music and speech can

Enrich the user’s experience Provide the user with more

information Help people with poor vision

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Touch

Although touch, or haptic perception, is viewed as less important that sight and sound, it is vital in daily life

The skin has 3 types of receptors Thermoreceptors for temperature Nociceptors respond to intense pressure Mechanoreceptors respond to lower

pressure

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Touch

Different areas of the body have different numbers of receptors

Exercise Touch various parts of the body with

1 and two objects What parts of the body can tell

whether they are being touched by one or two objects?

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Touch in the Interface

We use touch for a variety of feedback in real life

We can use it in interfaces A click so we can feel a key press Force feedback on a joy stick Force feedback on keys of electronic

musical instruments

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Novint Falcon A device to let users feel

weight, texture, motion, and force

The ball is held in the hand and moved

As it enters different parts of the virtual world, it provides tactile feedback to the user

Technology like this could be used to enhance e-shopping by letting you feel the goods

* Novint Technologies, www.novint.com

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Movement A user can respond to a

Sound – 150 ms Visual signal – 200 ms Pain – 700 ms

To respond the user has to quickly and accurately plan motion of a hand, finger, and arm

Requiring faster responses is often what is done to make levels in games more difficult

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Movement In general, when the user gets a

signal, they must respond and hit a button

This response depends on How far they have to move How big the target is

This is summarized by Fitt’s Law movementTime = a + b log2(distance/size + 1) Where a & b are empirically determined

constants

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Movement

In terms of UI design this means Place controls close to one another to

minimize movement Make controls large enough so that

they can be accurately hit with little effort

Place frequently used menu items near to one another

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Memory

Humans have several forms of memory Sensory memory

Retains input from senses for a brief period Short-term memory

Allows us to retain what we are working on for a few seconds

Long term memory Long term memories of events and facts

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Sensory Memory There are 3 types

Iconic memory Visual images retained for 0.5 s

Echoic memory Aural stimuli retained for a few seconds

Haptic memory Memory of touch

Sensory memory is continually overwritten as new input is received

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Short-term Memory Acts as a scratch pad for

temporary information Used when we perform mental

arithmetic Can be accessed quickly, ~70 ms Decays rapidly Has limited capacity

7 ± 2 items in short term memory

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Short-term Memory

Short term memory stores chunks of information

We can increase the amount retianed by grouping data into chunks 265397620853

Individual digits – hard to remember 44 113 245 8920

Chunks – easier to remember

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Long-term Memory Stores information for years, possibly

forever Two types

Episodic – stores events Semantic – stores facts

Episodic memory is processed to derive new facts to store in semantic memory

There are several models of how long-term memory works

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Semantic Network

A popular model to view memory as interconnected facts.

* Dix, et al

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Closure When a task is completed, the mind

often flushes short-term memory to make way for the next task

Early ATMs gave the money before returning the bank card

This caused many people to take the money, wipe their memories, and forget their card

Newer ATMs return the card before giving the money

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Memorable or Secure?

Random strings make the best passwords

Random strings are the hardest to remember

Therefore, people choose poor passwords that are easy to remember and use them for multiple sites

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Reasoning

Reasoning is the process we use to draw conclusions form the facts we know

There are three types of reasoning Deductive Inductive Abductive

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Deductive Reasoning Derives a logical conclusion from

the facts I go to work on Mondays Today is Monday Therefore, I go to work today

Common problems with deductive reasoning are that people can make mistakes of logic

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Inductive Reasoning This allows us to generalize from what

we have seen to infer what we have not seen Every elephant I have seen has a trunk Therefore, all elephants have trunks

This is not a proven fact and cannot be proven unless we see every elephant

It can be disproven by finding one trunkless elephant

People still rely on this type of logic

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Abductive Reasoning

This reasons from a fact to the action which caused it Sam always drives fast when he drinks We see Sam driving fast and assume

he has been drinking Sam could be in a hurry for other

reasons, but our first thought is that it is because he was drinking

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Problem Solving

Problem solving involves inferring new information from what is already known

There are different theories as to how people solve problems Gestalt Theory Problem Space Theory

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Gestalt Theory Early explanations of problem solving

said that it involved trial and error Gestalt theorists felt it was more

complex than this and had two parts Reproductive problem solving drawing

on previous knowledge Productive problem solving in which the

problem is restructured to yield a new insight

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Maier’s Pendulum A group of subjects is placed in a room

with two strings hanging from the ceiling

The task is to tie the strings together There are pliers and poles in the room No one thinks to use the pliers as a

weight to make one of the strings swing The researcher brushes against a string,

setting it in motion, and soon they come up with the idea

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Problem Space Theory Newell & Simon created this as an

alternative to Gestalt theory Problems can exist in several

states and solving them involves applying operators to move the problem from one state to another

Consider the problem of moving your desk

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Problem Space Theory

You can push it or carry it You can only carry it if it is light

but carrying is faster than pushing Therefore, you try to solve how to

lighten the desk If you solve that, you solve the

whole problem

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Mental Models Whenever we deal with any complex

system we create a mental model of how it works

Consider a car It has an engine which makes it go The engine needs gas to run We push the accelerator to go faster and the

brake to go slower As long as the car performs according to

our model, we can drive safely

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Mental Models Consider the table editor in MS Word

I believed I was editing a table and had operations to

add and delete rows and columns Join rows or columns together

This was reinforced by the buttons on the interface

I tried for three days to edit a simple table !

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Mental Models I thought about the problem and

realized I was not editing a table I was editing a tree data structure in

memory and my operations were tree operations

I finished editing the table in minutes

Many problems are caused by incorrect mental models

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Emotion People are not pure logic machines They have emotions which affect their

behaviour In stressful situations, people have

poorer problem solving abilities Therefore, we should give people

positive responses so that they will feel better about what they are doing and perform better