Chapter Two Human in HCI 1 Human in

Chapter Two Human in HCI 1

Human in HCI � Cognitive psychology � how humans perceive the world around them, � how they store and process information and solve problems, and � how they physically manipulate objects � basic overview of the capabilities and limitations that affect our ability to use computer systems 2

�When we try to understand something, particularly new, we use a combination of �What our senses (sight, hearing, touch, smell, taste) are telling � Past experience � Our expectations 3

Factors to be considered for interaction. �Information input/output �Information stored in memory �sensory, short-term, long-term �Information processed and applied �Emotion influences human capabilities �Each person is different 4

� Humans are limited in their capacity to process information. �Limitedfactors, concentration � Human or limitations, include �Changes in mood �The need for motivation �Biases �Fears �Make errors �Misjudgment �Prefer speech 5

Information input and output �Interaction with the outside world occurs through information being received and sent: input and output. �the human input is the data output by the computer and vice versa. �Input in humans occurs mainly through the senses and output through the motor controls of the effectors. �Vision, hearing and touch are the most important senses in HCI. �The fingers, voice, eyes, head and body position are the primary effectors. 6

Vision � The two stages in vision are: 1. Physical reception of stimulus 2. Processing and interpretation of stimulus � both influence what can and cannot be perceived visually by a human being, 7

The Eye - physical reception � Is the mechanism for receiving light and transforming it into electrical energy �The process: � Light reflects from objects � Images are focused upside-down on retina � Retina contains rods for low light vision and cones for colour vision � receptors in the eye transform it into electrical signals which are passed to the brain � Ganglion cells (in brain) detect pattern and movement 8

The Eye Cont.

Interpreting the signal �Size and depth �Visual angle indicates how much of view object occupies. That is, the eye perceive size and distance. E. g. If two small and large objects have the same distance from the eye the larger have the higher visual angle �The visual angle measurement is given in either degrees or minutes of arc, �Visual acuity is the ability of a person to perceive fine detail � law of size constancy � � � 10 perception of depth size and height of the object in our field of view familiarity

Interpreting Cont. �Brightness � Subjective reaction to levels of light � Affected by luminance (level of light emitted by an object) of object � Measured by just noticeable difference � Visual acuity increases with luminance �Colour � Made up of hue, intensity, saturation � Cones sensitive to colour wavelengths � 8% males and 1% females colour blind 11

Interpreting Cont. �A theory about vision is constructivism: � Our brains do not create pixel-by-pixel images � Our minds create, or construct, models that summarize what comes from our senses � These models are what we perceive � When we see something, we do not remember all the details, only those that have meaning for us � Design implication: � 12 Do not expect people “see” all the details of an interface because people filter out irrelevant information and save only the important ones

Constructivism Cont. � Constructivist theory states that context plays a major role in what we see in an image � Are these letters the same? 13

Constructivism Cont. � With context, the answer will be different � Design implication: � Context can help in resolving ambiguity 14

Reading �Several stages: � Visual pattern of the word is perceived � Decoded using internal representation of language � The word is processed as part of the sentence or phrase using knowledge of syntax and semantics. � During the first two stages (influence perception), the eye makes saccades (jerky movements), followed by fixations (the time where perception occurs). � The eye moves both forwards and backwards over the text called, regression. � Increased �Word shape when the text is more complex. is important to recognition - familiar words are recognized using word shape 15

Hearing � Provides information about environment: factors to be considered are: distances, directions, objects etc affect hearing. � Physical apparatus of ear: � � � Outer ear Middle ear Inner ear � Sound � � � 16 and cause impulses in auditory nerve (vibrations) characteristics: Pitch: sound frequency Loudness: amplitude Timbre: type of the sound � Humans � – Protects inner and amplifies sound – Transmits sound waves as vibrations to inner ear – Chemical transmitters are released can hear frequencies from 20 Hz to 15 k. Hz Less accurate in distinguishing high frequencies than low frequencies.

Touch � Also called haptic perception, stimuli received through skin. � Provides important feedback about environment. � May be key sense for someone who is visually impaired. � Stimulus received via receptors in the skin: Thermoreceptors: for heat and cold perception Nociceptors: for pain perception Mechanoreceptors: for pressure perception: (some instant, some continuous) �If continuous pressure is applied, they stop to respond. � � Some 17 areas more sensitive /acuite than others e. g. fingers.

Movement � Time taken to respond to stimulus: reaction time + movement time � Movement � Reaction � � � time dependent on age, fitness etc. time - dependent on stimulus type: visual auditory pain � Increasing ~ 200 ms ~ 150 ms ~ 700 ms reaction time decreases accuracy in the unskilled operator but not in the skilled operator. 18

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. 19

Sensory memory � Buffers for stimuli received through senses, continuously overwritten � Iconic memory: visual stimuli � Echoic memory: aural stimuli � Haptic memory: tactile stimuli � Information is passed from the sensory memory to the short term memory by: � Attention � Filtering 20 stimuli at that moment of interest

Short-term memory (STM) � Store information which is only required fleetingly. � STM is scratch - pad for temporary recall � STM is accessed and decayed rapidly � Rapid access ~ 70 ms � Rapid decay ~ 200 ms � STM is limited in capacity � STM can store 5 -9 chunks of information � Chunks � STM 21 can be items or groups (like 2 digit number in telephone numbers) recall is damaged by other information interference.

Long-term Memory (LTM) � Repository for all our knowledge Slow access ~ 1/10 second � Slow decay, if any � � LTM has huge or unlimited capacity � Two types of LTM � Episodic: represents our memory of events and experiences in a serial form �Semantic: structured record of facts, concepts and skills that we have acquired, derived from the episodic LTM 22

LTM � Semantic memory structure �Provides access to information � Represents relationships between bits of information � Supports inference � LTM can be modelled using: � Semantic network � Frames � Scripts � Production 23 rule

LTM Model: semantic network � According to the semantic network model, the semantic memory is structured as a network � Inheritance – child nodes inherit properties of parent nodes � Relationships between bits of information is shown explicitly � Supports inference through inheritance � The more general the information is, the higher is the level on which it is stored. This allows us to generalize about specific cases. � The connections in the network are made using associations. 24

LTM - semantic network 25

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 26 COLLIE Fixed breed of: DOG type: sheepdog Default size: 65 cm Variable colour

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 27 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 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 28

LTM � There are 3 main activities related to LTM: �Storage of information �Forgetting �Information retrieval 29

LTM � Storage � The rehearsal of a piece of information from the STM stores it in the LTM. � If the total learning time is increased, information is remembered better - total time hypothesis. � However, the learning time should be well spread-distribution of practice effect. �Spreading � But learning over time repetition alone is not enough, that is: �Information should be meaningful and familiar, so it can be related to existing structures and more easily incorporated into memory. 30

LTM � � � 31 Forgetting � There are 2 main theories of forgetting: �Decay �Interference. Decay � Suggests that information held in LTM may eventually be forgotten. Interference � Information can also be lost through interference: if we acquire new information, it causes the loss of old information: retroactive interference. � It is also possible that the older information interferes with the newly acquired information: proactive inhibition. � Forgetting is affected by emotional factors too.

LTM-Information Retrieval Recall Information reproduced from memory can be assisted by clues, e. g. categories, Imagery � Recognition Information gives knowledge that it has been seen before � less complex than recall - information is clue � 32

Thinking can require different amounts of knowledge. • Some thinking activities are very directed and the knowledge required is constrained. • Others require vast amounts of knowledge from different domains. Thinking can be divided in: � Reasoning • Deduction, � Induction, � � Problem solving � Skill acquisition � Errors 33 and mental models

Deductive reasoning: � 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 Inductive reasoning: � Generalize from cases seen to cases unseen e. g. 34 All birds we have seen fly therefore all birds fly.

Problem solving is the process of finding a solution to an unfamiliar task, using (adapting) the knowledge we have. Different types of theories: Gestalt � Based on insight and restructuring of problem Analogy � Analogical mapping: Uses knowledge of similar problem from similar domain � Analogical mapping is difficult if domains are semantically different Skill acquisition Skilled activity characterized by chunking: Lot of information is chunked to optimize STM Problem space theory Analysing means-ends Largely applied to problem solving in well-defined areas E. g. puzzles rather than knowledge intensive areas 35

Skill acquisition � Experts often have a better encoding of knowledge: information structures are fine tuned at a deep level to enable efficient and accurate retrieval. �These skills are acquired through 3 levels: � The learner uses general-purpose rules which interpret facts about a problem. (slow, memory-demanding) � The learner develops rules specific to the task, using procedures. � The rules are tuned to speed up performance, using generalization. 36

Errors and mental models Types of error right intention, but failed to do it right � � slips causes: poor physical skill, inattention etc. � change to aspect of skilled behaviour can � cause slip mistake wrong intention � s � cause: incorrect understanding humans create mental models to explain behaviour. if wrong (different from actual system) errors can occur � 37

Emotion � Emotion is a psychological response to a stimuli � Various theories of how emotion works � � � James-Lange: emotion is our interpretation of a physiological response to a stimuli Cannon: emotion is a psychological response to a stimuli Schacter-Singer: emotion is the result of our evaluation of our physiological responses, in the light of the whole situation we are in � Emotion stimuli 38 clearly involves both cognitive and physical responses to

Emotion � 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” � Implications � Stress for interface design 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 39

Individual differences � The principles and properties discussed apply to the majority of people, but humans are not all the same. � Differences should be taken into account in the designs � � 3 Divide the users in target groups and ask yourself: will design decision exclude section of user population? causes for individual difference: � Long term – Sex, physical and intellectual abilities � Short term – Effect of stress or fatigue � Changing – Age 40

Individual differences Psychology and the Design of Interactive System �Some have 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, and an understanding of particular experimental conditions 41

Summary 42