chapter 1 the human

Intro…. We start with the human, the central character in any discussion of interactive systems. human, the user, is, after all, the one whom computer systems are designed to assist. The requirements of the user should therefore be our first priority

this chapter, we will first look at the human’s input–output channels, the senses and responders or effectors. Secondly, we will consider human memory and how it works. We will then think about how humans perform complex problem solving, how they learn and acquire skills, and why they make mistakes. Finally, we will discuss how these things can help us in the design of computer systems.

There are five major senses: sight, hearing, touch, taste and smell There are five major senses: sight, hearing, touch, taste and smell. The first three are the most important to HCI. Taste and smell do not currently play a significant role in HCI, and it is not clear whether they could be exploited at all in general computer systems, although they could have a role to play in more specialized systems (smells to give warning of malfunction, for example) or in reality systems. However, vision, hearing and touch are central.

Similarly there are a number of effectors, including the limbs, fingers, eyes, head and vocal system. In the interaction with the computer, the fingers play the primary role, through typing or mouse control, with some use of voice, and eye, head and body position. Effector: an organ or cell that acts in response to a stimulus

Imagine using a personal computer (PC) with a mouse and a keyboard Imagine using a personal computer (PC) with a mouse and a keyboard. The application you are using has a graphical interface, with menus, icons and windows. In your interaction with this system you receive information primarily by sight, from what appears on the screen. However, you may also receive information by ear: for example, the computer may ‘beep’ at you if you make a mistake or to draw attention to something, or there may be a voice commentary in a multimedia presentation.

Touch plays a part too in that you will feel the keys moving (also hearing the ‘click’) or the orientation of the mouse, which provides vital feedback about what you have done. You yourself send information to the computer using your hands, either by hitting keys or moving the mouse.

Sight and hearing do not play a direct role in sending information in this example, although they may be used to receive information from a third source (for example, a book, or the words of another person) which is then transmitted to the computer

In this section we will look at the main elements of such an interaction, first considering the role and limitations of the three primary senses and going on to consider motor control.

1. Vision Two stages in vision • physical reception of stimulus from the out side world • processing and interpretation of that stimulus. We need to understand the two as both influence what can and can’t be perceived visually which in turn directly affects the way that we design interfaces.

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 retina contains rods for low light vision and cones for colour vision ganglion cells (brain!) detect pattern and movement

Visual perception The information received by the visual eye must be filtered and passed to processing elements which allow us to recognize coherent scenes, disambiguate relative distances and differentiate colour. we will look at how we perceive size and depth, brightness and colour, each of which is crucial to the design of effective visual interfaces.

Visual perception: perceiving Size and depth Imagine you are standing on HILL top. Beside you on the summit, one can see rocks, sheep and a small tree. On the hill side is a farm house without buildings and a farm vehicles. Some one is on the track walking towards the summit. Below in the valley, is a small market town.

Even in describing such a scene the notions of size and distance predominate. Our visual system is easily able to interpret the images which it receives to take account of these things.

We can identify similar objects regardless of the fact that they appear to us to be of vastly different sizes. In fact, we can use this information to judge distances. Reflected light from the object forms an upside-down image on the retina. The size of that image is specified as a visual angle.

So how doe the eye perceive size, depth and relative distance? visual angle- indicates how much of view the object occupies (relates to size and distance from eye) visual acuity- is ability to perceive fine detail/clarity of vision . Ability to distinguish details and shapes of objects familiar objects perceived as constant size (in spite of changes in visual angle when far away) So how does an object’s visual angle affect our perception of its size? If the visual angle is too small, we wil be unable to perceive it at all The figure below illustrates how the visual angle is calculated

law of size constancy

Perceiving brightness and colour Brightness is subjective reaction to levels of light affected by luminance of object(amount of light emitted by an object) Contrast is related to luminance. It’s a function of the luminance of an object and luminance of its background visual acuity(sharpness) increases with luminance as does flicker-the eye will perceive a light switched on and off rapidly as constantly on

color The eye perceives colour because the cones are sensitive to light of different wave length. The primary colours of blue, green and red have different wave lengths. The eye perceives color because the cones are sensitive to light of different wavelength (Blues have short wavelengths, greens medium and reds long.) We should remember that 8% of males and 1% of males are colour blind, mostly, unable to differentiate between red and green

Capabilities and limitations of visual process Visual processing involves the transformation and interpretation of a complete image Consider the following images:

Optical Illusions the Ponzo illusion: are these the same size?

Muller-lyer illusion the Muller Lyer illusion-which line is longer? these illusions demonstrate that our perception of size is not completely reliable

Reading Several stages: visual pattern perceived decoded using internal representation of language interpreted using knowledge of syntax, semantics, pragmatics Reading involves saccades(jerky movements of the eye) and fixations Perception occurs during fixations Word shape and size are important to recognition Negative contrast(dark characters on a light screen) improves reading from computer screen

2. 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( level of intensity) loudness (amplitude) Timbre(tone quality)

Hearing (cont) Humans can hear different frequencies but it has a limitation less accurate distinguishing high frequencies than low. Auditory system filters sounds can attend to sounds over background noise. for example, the cocktail party phenomenon. If u close you eyes right now, what can u hear? Where are the sounds coming from? Whats making them? How far away are they?

Touch Provides important feedback about environment. May be key sense for someone who is visually impaired. Stimulus received via receptors in the skin: thermoreceptors – heat and cold nociceptors – pain mechanoreceptors – pressure (some instant, some continuous) Some areas more sensitive than others e.g. fingers. Kinethesis - awareness of body position affects comfort and performance.

Movement Time taken to respond to stimulus: reaction time + movement time Movement time dependent on age, fitness etc. Reaction time - dependent on stimulus type: Increasing reaction time decreases accuracy in the unskilled operator but not in the skilled operator.

Speed and accuracy of movement are important considerations in the design of interactive systems, primarily in terms of the time taken to move to a particular target on a screen. The target may be a button, a menu item or an icon, for example

3. 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. Attention Rehearsal

Short-term memory (STM) Scratch-pad for temporary recall It is used to store information which is only required frequently. For example, calculate the multiplication 35 × 6 in your head. The chances are that you will have done this calculation in stages, perhaps 5 × 6 and then 30 × 6 and added the results;

or you may have used the fact that 6 = 2 × 3 and calculated 2 × 35 = 70 followed by 3 × 70. To perform calculations such as this we need to store the intermediate stages for use later. Short-term memory also has a limited capacity

Examples try to recall the following 265397620853 44 113 245 8920 How many digits do you remember?(btn5&9?) HEC ATR ANU PTH ETR EET

Here we store factual information, experiential knowledge, procedural rules of behavior – in fact, everything that we ‘know’. It differs from short-term memory in a number of significant ways. First, it has a huge, if not unlimited, capacity. Secondly, it has a relatively slow access time of approximately a tenth of a second.

Thirdly, forgetting occurs more slowly in long-term memory, if at all. These distinctions provide further evidence of a memory structure with several parts.

Long-term memory (LTM) Two types episodic – Episodic memory represents our memory of events and experiences in a serial form semantic – structured memory of facts,concepts, skills that we have acquired. structured in some way to allow access to information, representation of relationships between pieces of information, and inference semantic LTM derived from episodic LTM

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 - Forgetting decay interference information is lost gradually but very slowly interference new information replaces old: retroactive interference old may interfere with new: proactive inhibition so may not forget at all memory is selective … … affected by emotion – can subconsciously `choose' to forget

LTM - retrieval recall recognition 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

Reasoning deduction, induction, abduction Problem solving 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 work It is Friday Therefore she will go to work. Logical conclusion not necessarily true: e.g. If it is raining then the ground is dry It is raining Therefore the ground is dry

Deduction (cont.) When truth and logical validity clash … Correct? e.g. Some people are babies Some babies cry Inference - Some people cry Correct? all men are mortal, Socrates is a man, therefore Socrates is mortal.

Inductive Reasoning Induction: Unreliable: … but useful! 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!

Jennifer leaves for school at 7:00 a.m. Jennifer is always on time. Jennifer assumes, then, that she will always be on time if she leaves at 7:00 a.m. The chair in the living room is red. The chair in the dining room is red. The chair in the bedroom is red. All chairs in the house are red.

Abductive reasoning reasoning from event to cause Unreliable: e.g. Sam drives fast when drunk. If I see Sam driving fast, assume drunk. Unreliable: can lead to false explanations Can be used for causal reasoning(cause and effect)

Errors and mental models Types of error slips right intention, but failed to do it right causes: poor physical skill,inattention etc. change to aspect of skilled behaviour can cause slip mistakes wrong intention cause: incorrect understanding humans create mental models to explain behaviour. if wrong (different from actual system) errors can occur

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)

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