Human Computer Interaction

1. Chapter-1 The Human Human Computer Interaction

2. Human Computer Interaction • HCI is the study and the practice of usability. • Usability means easy to learn, effective to use and provide an enjoyable experience. • It is about understanding and creating software and other technology that people will want to use, will be able to use, and will find effective when used.

3. The human • Consider human as information processor • Receiving inputs from the world, storing and using information • Information receive through the senses, particularly, in case of computer use, through sight, hearing and touch • It is stored in memory, either temporarily in sensory or permanently in LTM • It can then be used in reasoning and problem solving

4. The human • Humans are limited in their capacity to process information • Human perception and cognition are complex but they are not without their limitations • An understanding of the capabilities and limitations of the human as information processor can help us to design interactive system • Each person is different • Five major senses: sight, hearing, touch, taste & smell

5. Vision • Human vision is a highly complex activity but it is primary source of information. • Two stages in vision • physical reception of stimulus from the outside world • processing and interpretation of stimulus

6. The Human Eye • mechanism for receiving light and transforming it into electrical energy • 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

7. Interpreting the signal • Size and depth • visual angle indicates how much of view object occupies(relates to size and distance from eye)

8. Interpreting the signal • Brightness • subjective reaction to levels of light • measured by just noticeable difference • Colour • 8% males and 1% females colour blind

9. Optical Illusions

10. Reading • During reading, the eye makes jerky movements • The speed at which text can be read is a measure of its legibility • Experiments shown that standard font size of 9 to 12 points equal legible • Word shape is important to recognition • Negative contrast improves reading fromcomputer screen • Reading from a computer screen is slower than a book

11. Hearing • Provides information about environment:distances, directions, objects etc. • Auditory system filters sounds • can attend tosounds over background noise.

12. Touch or haptic perception • Provides important feedback about environment. • May be key sense for someone who is visuallyimpaired. • Stimulus received via receptors in the skin: • The skin contains three types of sensory receptor: • thermoreceptors – respond to heat and cold • nociceptors – respond to heat and pain • mechanoreceptors – respond to pressure, vibrations • Some areas more sensitive than others e.g.fingers.

13. Movement • Speed and accuracy of movement are important considerations in design of interactive system • Primarily in terms of time taken to move to a particular target on a screen • Time taken to respond to stimulus: reaction time+ movement time • Movement time - dependent on age, fitness etc. • Reaction time - dependent on stimulus type:

14. Memory • There are three types of memory function: • Sensory memories (visual  iconic,auditory echoic, touchhaptic) • Short-term memory or working memory • Long-term memory Attention Rehearsal

15. Short-term memory (STM) • STM acts as a scratch-pad for temporary recall of information • It is used to store information which is only required fleetingly • Has a limited capacity

16. Examples • 212348278493202 • 0121 414 2626 • HEC ATR ANU PTH ETR EET • ATM

17. Long-term memory (LTM) • Repository for all our knowledge • slow access • slow decay, if any • huge or unlimited capacity

18. Long-term memory - semantic network

19. 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

20. Script for a visit to the vet Entry conditions: dog ill vet open owner has money 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 - Scripts • Script has elements that can be instantiated with values for context

21. Models of LTM - Production rules • Representation of proceduralknowledge. • 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

22. LTM - Forgetting • decay information is lost gradually butvery slowly • interference new information replacesold: retroactive interference old may interfere with new: proactiveinhibition

23. Thinking: reasoning and problem solving • Animals receive and store information, there is little evidence to suggest that they can use it in quite same way as humans. • Similarly AI produced machines which can see and store information. • Humans are able to use information to reason and solve problems • Thinking can require different amounts of knowledge • Some thinking activities are very directed and the knowledge required is constrained.

24. Reasoning Reasoning is the process by which we use the knowledge we have to draw conclusions or infer something new about the domain of interest. Deductive: derive logically necessary conclusionfrom 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: (it conflicts with our knowledge of what is true in the world) e.g. If it is raining then the ground is dry It is raining Therefore the ground is dry

25. Deduction • Human deduction poor when truth and validityclash e.g. Some people are babies Some babies cry Inference - Some people cry • People bring world knowledge into the reasoning process.

26. Problem solving • Problem solving is the process of finding a solution to unfamiliar task,using knowledge. • Several theories. • problem solving both productive andreproductive • reproductive problem solving draws on previous experience • productive problem solving involves insight and restructuring of problem

27. Errors and mental models • Human capability for interpreting and manipulating information is quite impressive. • However, we do make mistakes. Some are trivial, resulting in no more than temp inconvenience. • Some are serious, requiring more effort to correct. • Types of error slips right intention, but failed to do it right causes: poor physical skill, inattention etc. change to aspect of skilledbehavior can cause slip

28. Errors and mental models mistakes wrong intention cause: incorrect understanding - humans createmental models to explain behavior. ifwrong (different from actual system) errorscan occur.

29. Individual differences • Our assumption that everyone has similar capabilities & limitations that we can make generalizations. • We should be aware of individual differences so that we can account for them as far as possible within our design • These differences should taken into account in our design.