An Overview of the “H” in HCI

1. An Overview of the “H” in HCI laura leventhal

2. Reference • Chapter 14

3. Overview • This lecture is a whirlwind tour of some of the important psychological characteristics of people that impacts HCI.

4. Psycholgy and UI Design • Goal of UI design is to improve efficiency and effectiveness of user performance • Improving usability • Accommodating user characteristics • Support user tasks

5. What Can We Learn (quickly) from Psychology? • We need a cognitive model of the user that will help us predict the way that a user will react to an interface or situation • The model will help us to explain why a user reacted the way they did.

6. Example • Psychological Fact: • Humans are limited in their capacity to process information • We say that cognitive resources are limited

7. HCI Consequence • Want to limit resources that users spend on operational tasks. • Want users to focus on functional tasks.

8. Simple Model of a Cognition • Thinking about what we know about (computers) can help us organize our model of cognition. • Computers have structures for and support • Input and Output • Memory (storage) • Processing • Now can we apply the idea of a computer as an analogy to think about humans??

9. Our Cognitive Model - Three Aspects • Physiological structures and processes • (i/o) • Cognitive structures • (storage) • Cognitive processes • (data processing)

10. A Model of a Human Information Processor

11. Sensation/Perception: IO Channels • Input Channels • Sensors: • eyes, ears, touch, taste, smell, balance (proprioceptors) • Output Channels • Effectors: • limbs, fingers, eyes(where looking), head, vocal system

12. Perception is often Parallel, Generation is Serial • We are often able to take in multiple inputs and recognize them. • Driving, talking on cell phone, recognizing instructions from street signs. • Reading screen and hearing alarm sounds • Generation of output tends to be more serial. • Hear alarm, push button • HCI Consequences • We take in a number of inputs at once, even when some of the inputs are unrelated to the task at hand. So when we build an interface with lots of "extras", such as sounds and videos, we take those in, even as we are taking the task-related input in. It is very difficult to selectively close out some of these inputs, even if they are unrelated to the task. And, just like computer inputs, even the input from the "extras" requires processing. • Because generation is more serial, we tend to produce (generate) activities more in sequence.

13. Sensation/Perception: Vision • Vision is our most important input device. • Brain structures reflect the importance of vision in cognition. • For example, our brain structures would be different if we had monocular vision. • Humans are drawn to looking at vistas. This preference pattern and others are “built-in”

14. Sensation/Perception: Vision • Human visual perception is attuned to movement. • HCI Consequence. • Our vision is drawn to moving objects in a user interface.

15. Sensation/Perception: Vision • Visual system is like a camera, different in some critical ways (from simple camera!): • Eye is in a fixed position and the shape is distorted by various muscles. • Light sensitivity varies across the retina. It is best in the center and worst at the edges. • Two eyes permit depth perception. • HCI Consequence. • People can become fatigued when they receive visual input from a user interface. When it is likely that your user will become fatigued from visual input, consider having an alternative presentation modality, such as audio.

16. Sensation/Perception: Vision • Color is increasingly important in HCI. • Color perceptions are subject to fatigue. • We are sensitive to flickering lights

17. Sensation/Perception: Vision • Visual Ability Declines with Age • Vision is an ability that declines with age, despite the common belief that most human abilities do not decline with age. • For example, a person’s perception of color may change. Disorders such as macular degeneration and glaucoma severely limit what a person is able to see. • HCI Consequence. • When designing for users who include persons of all ages, be sure to accommodate some of the specific changes which come with age

18. Sensation/Perception: Vision • Visual processing involves transformation and interpretation • What we "see" is affected by what we know and what we expect and the context • Overhead A

19. Sensation/Perception: Vision • “Gestalt Principles” guide our vision system to make images whole: • proximity • similarity • continuation • Closure • HCI consequence. • We tend to "fill in" or "finish" a pattern even if it is incomplete.

20. Sensation/Perception: Vision • Reading • We see a visual pattern: • whole words or phrases, morphemes, syntax, semantics • Overhead B • HCI Consequence • If we disrupt "normal" patterns of words, with strange combinations of font types and sizes for example, it is difficult to read because we see individual characters rather than patterns of characters.

21. Sensation/Perception: Hearing • We are constantly bombarded with sound • We use selective attention to filter through the sounds. • Cocktail party phenomena - • We can hear our name across a room • HCI Consequence. • Use alarms sparingly and when appropriate.

22. Sensation/Perception:Touch • Use touch to provide feedback • 3 types of touch receptors: • heat/cold • intense pressure, heat, pain • Pressure

23. A little bit about output • Next two slides overview the relationship between hand movements and performance as predicted by Fitts Law

24. Fitt’s Law • Moving hand is a series of small discrete movements and corrections • Each small movement takes 240 msec • Time T to move hand to target of size S which is distance D away • T = 100 msec * log2(D/S + .5) • Time to move hand depends on the relative precision needed (D/S) • Fitt’s law used to demonstrate for a small number of choices (low precision) a pie menu is faster than a linear menu.