chapter 1

The human

The human

• The human are limited in their capacity to process information. This has important implications for design.

• Information is received and responses given via number of impute and output channels: visual, auditory, haptic, movement.

• Information stored in memory– sensory, short-term, long-term

• Information processed and applied– reasoning, problem solving, skill, error

• Emotion influences human capabilities• Each person is different

I/O channels

• Input in the human occurs mainly through the sense and output through the motor control of effectors.

• There are five major senses: sight, hearing, touch, taste and smell.

• There are a number of effectors: limbs, finger, eyes, head and vocal system

Vision

Two stages in vision

1. physical reception of stimulus

2. processing and interpretation of stimulus.

• We need to understand both stages as both influence what cannot be perceived visually by a human being, which in turn directly affects the way that we design computer systems.

1.The Eye - physical reception

• Mechanism for receiving light and transforming it into electrical energy

• light reflects from objects

• images are focused upside-down on retina

2.Interpreting the signal (cont)• The signal could be interpreted through the perception of the following issues:

• Size and depth- if the visual angle of an object is too small we will be unable to perceive it at all.-In fact, our perception of an object’s size remains constant even if its visual angle changes.-Law of size constancy indicates that our perception of size relies on factors other than the visual angle such as ( depth, size, height and familiarity that provide cue to the object's distance and).

• Brightness– subjective reaction to levels of light– affected by luminance of object– visual acuity increases with luminance as does flicker.– Using higher display luminance leads to increase visual acuity.

• Colour– made up of hue (spectral wavelength of the light), intensity (the brightness of the colour), saturation (the

amount of whiteness in the colour) – cones sensitive to colour wavelengths– 3-4% of the fovea is occupied by cones which are sensitive to blue light , making blue acuity lower.– 8% males and 1% females colour blind and most commonly unable to discriminate between red and

green.

Optical Illusions

the Ponzo illusion the Muller Lyer illusion

In the optical Illusions, the human expectation disambiguate the interpretation of the object

Reading

• There are several stages in reading process:1. Perceive the word visually.2. Decode with reference to an internal representation

of language3. Syntactic and semantic analysis and operate on

phrase or sentences.

• Adults read 250 words/Minute• Familiar words are recognized by word shape.• Font Size 9-12 points, line length of between

2.3 and 5.2 are equally legible.

Hearing

• Provides information about environment:distances, directions, objects etc.

• 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. – In interface design usually the sound is being

confined to warning sounds and notification.– This suggests that sound could be used more

extensively in interface design to convey information about the system state.

Touch

• Provides important feedback about environment.

• May be key sense for someone who is visually impaired.

• Stimulus received via receptors in the skin

• Some areas more sensitive than others e.g. fingers.

Movement• 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– auditory ~ 150 ms– pain ~ 700ms

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

• Accuracy and speed of movement are important consideration in the design of interactive systems, primary in term of the time taken to move to a particular target or screen. This effects the type of target we design. Thus target should generally be large as possible and the distance to be moved as small as possible.

Memory

There are three types of memory function:

Sensory memories

Short-term memory or working memory

Long-term memory

Selection of stimuli governed by level of arousal.

1.Sensory memory

• Acts as buffers for stimuli received through the sense.• A sensory memory exists for each sensory channel:

– Iconic memory for visual stimuli in which information remains very briefing in the order of 0.5 seconds

– Echoic memory for aural stimuli.

– haptic memory for touch.

2.Short-term memory

• Acts as” scratch-pad” for temporary recall of information.• It has limited capacity.• 72 rule (indicates that we can remember 7 2 chunk of

information. Therefore chunking information can increase the short-term memory.

• Evidence shows that recall of the last words presented is better than recall of those in the middle (recency effect).

• In fact, short-term memory is not a unitary system but is made up of a number of components including a visual channel and articulatory channel.

• Interference only occur if tasks utilize the same channel.

- +-+

Examples

•Chunking Example:212348278493202

0121 414 2626•Pattern Example:

HEC ATR ANU PTH ETR EET)by moving T to the first position we could

create pattern( THE CAT RAN UP THE TREE

3.Long-term memory (LTM)

• Repository for all our knowledge– slow access ~ 1/10 second– slow decay, if any– huge or unlimited capacity

• Two types– episodic – serial memory of events.

– semantic – structured memory of facts,concepts, skills

semantic LTM derived from episodic LTM

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– supports inference through inheritance

LTM - 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

LTM - Storage of information

• Rehearsal– information moves from STM to LTM

• Total time hypothesis– amount retained proportional to rehearsal time

• Distribution of practice effect– optimized by spreading learning over time

• Structure, meaning and familiarity– information easier to remember

LTM - ForgettingDecay

– information is lost gradually but very slowly

Interference– new information replaces old: retroactive interference

(e.g if you change telephone numbers, learning your new number makes it more difficult to remember your old one)

– old may interfere with new: proactive inhibition.(e.g when you find yourself driving to your old jouse rather than your new one)

so may not forget at all memory is selective …

… affected by emotion – can subconsciously `choose' to forget. We tend to remember positive information rather than mundane

LTM - retrieval

Recall – information reproduced from memory can be assisted

by cues, e.g. categories, imagery

Recognition– information gives knowledge that it has been seen

before– less complex than recall - information is cue

Thinking

Reasoning (deduction, induction, abduction)

Problem solving

Deductive Reasoning

• Deduction:– derive logically necessary conclusion from given premises.

e.g. If it is Friday then she will go to workIt is FridayTherefore she will go to work.

• Logical conclusion not necessarily true:e.g. some people are babies.

some babies cry– many people infer that ‘some people cry’ which is incorrect

since we are not told that all babies are people.

Inductive Reasoning

• Induction is generalizing from cases we have seen to infer information about cases we have not see.

• This inference is unreliable and cannot proved to be true in all situations.

• (e.g. if every elephant we have seen has a trunk, we infer that all elephants have truck. However, the next one we see may be trunkless)

Abductive reasoning

• reasoning 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

Problem solving

• Process of finding solution to unfamiliar task using knowledge.• Gestalt Theory claimed that problem solving is both productive

(involves insights and restructuring of the problem) and reproductive ( draw on previous experience).

• Problem space theory proposed that problem space centres on the problem space that comprises problem states , and problem solving involves generating these states using legal state transition operators. The problem has an initial state and a goal state and people use the operators to move from the former to the latter.

• This theory operates within the constraints of the human processing systems, so searching the problem space is limited by the capacity of short-term memory, and the speed at which information can be retrieved.

Skills acquisition

Human can acquire skills through:• Proceduralization: is a mechanism to move from

the first to the second. • Generalization: is a mechanism to move the

second level to the third.( see example in page 48).

Error and Mental models

• There are several different types of errors:-From changes in the context of skilled behavior.

-From an incorrect understanding, or model, of a situation or system. People build their own theories to understand the casual behavior of system (Metal models).

Emotion

• In situation of stress, people will be less able to cope with complex problem solving or managing difficult interface, whereas if people are relaxed they will be more forgiving of limitation of design.

• Building interface that promotes positive responses by using aesthetics or rewards for example make the system more successful

Individual differences

• We should aware of the Individual differences so that we ca account for them as far as possible within our intellectual capabilities.

• Differences may be long-term (sex, physical and intellectual capabilities) or short-term (effect of stress or fatigue on the user). Still other changes through time, such as age.