Sunyoung Kim, PhD

Human-Computer Interaction8. Understanding Users – Human Models

Sunyoung�Kim,�PhD�

Recap: Interview•  Structured

•  Pre-determined questions to ask in a set way

•  Semi-structured

•  Start with set topics for discussion and follow up based on the

answers

•  Useful for gathering requirements and understanding users’

opinions

Recap: Use Interviews to find out•  Current behavior patterns •  Opinions of currently used products/services •  Complaints about poor or missing functionality •  Comparisons of two or more known options

-  What they do -  How they do things -  Their opinions about their current activities -  Their complaints about their current activities -  How much they like one thing that they know compared with

another thing that they know

But before all of these, you should have a clear definition of who “they” are!

Recap: Interviews: do’s and dont’s

Recap: Create interview questions1.  Know what you want answered: Write down a problem statement

2.  Reframe your problem statements: think of different perspectives to express the

same problem statements.

3.  Build a list of questions based on your reframed problem statements

4.  Paraphrase each question 2–3 times

5.  Give the whole list of questions a structure

1)  Introduction

2)  Warm up questions

3)  Main body questions

4)  Wrap up

Recap: Guidelines for surveys1.  Identify the scale and the significance of the unit

•  Use the most intuitive order

•  You can use positive or negative scales or a combination

2.  Use odd numbers when you want to allow neutral responses

3.  Use even numbers when you want to force a choice: positive or

negative

4.  Provide a not applicable (N/A) when appropriate

5.  Do not use too many degrees within the scale; seven is considered a

general limit

6.  Test your questionnaires before use

Recap: Questionnaire & SurveyTypes of survey questions •  Mutually exclusive choices (radio buttons)

•  Non-mutually exclusive choice (checkboxes)

•  Ranges (overlapping, open-ended)

•  Scales (Likert scales, semantic differential

scales)

•  Short answer fill-ins

•  Comments

Likert Scale Example

Recap: Interview or Survey?Interviews •  Explore a domain •  Probe & follow-up •  Capture multiple data sources •  Rapport-building à Can ask

about sensitive issues But: •  Expensive •  Requires coding to interpret data •  Difficult to make comparisons

Surveys •  Defined sample from larger

population ➔ Generalizable •  Comparatively low cost •  Ask multiple questions efficiently •  Standardized data allows

comparisons •  Quantitative results

But poor for: •  Starting research •  Determining questions to ask •  Clarifying questions for respondent •  Following up unexpected comments

Today’s agenda

Human models

Human models

Freezer is too cold but fresh food is just right. How would you adjust the control?

.

I'm fat because my metabolism is slow, hormone and gland

problems and too much stress. Health professionals should help

me lose weight. I am most worried about difficulties getting

to work.

Obesity is due to eating too much and not enough

exercise. The patient is to blame, so solutions must start with the patient. The biggest

concern is diabetes.

“The models people have of themselves, others, the environment and the

things with which they interact. People form mental models through

experience, training and instruction”

•  An explanation of someone's thought process about how something

works in the real world

•  Enable people to reason about a system

•  Affect the way we see and interpret reality

•  When users approach an unfamiliar system, they subconsciously refer

to their mental model, User’s model

“To break a mental model is harder than splitting the atom.”

--Albert Einstein

Mental models

User vs. designer model

the conceptual model of the system to be built

the way the user interprets the System Image

Gulfs of Execution & Evaluation The gaps between the user and the interface, pointing to how to better design an interface so that the user can cope with it •  Gulf of execution: the distance between the user's goals and the

means of achieving them through the system

•  Gulf of evaluation: the amount of effort required to determine the system state

The Model Human Processor

•  Published by Card, Moran & Newell, 1983, in the book “The

Psychology of Human-Computer Interaction”

•  Consider humans as information processing systems

•  Core cognitive aspects •  Attention

•  Perception and recognition

•  Memory

•  Reading, speaking, and listening

•  Problem-solving, planning, reasoning and decision-making, learning

•  Describes how a user interacts with a computer system

Processors: •  Perceptual •  Cognitive •  Motor Memory: •  Working memory •  Long-term memory

Why model human performance?

•  To predict impact of new technology/interface

•  Apply model to predict effectiveness

•  We could build a simulator to evaluate user interface designs

Human performance modeling

(1) Perceptual processor

Physical store from our senses: sight, sound, touch,… •  Code directly based on sense used •  Visual, audio, haptic, … features Selective •  Spatial •  Pre-attentive: color, direction… Decay time for working memory: 200ms

Pre-attentive •  A limited set of visual properties that are detected very rapidly and

accurately by the low-level visual system

•  Typically, tasks that can be performed on large multi-element displays

in less than 200 to 250 milliseconds are considered pre-attentive.

How many 3’s?

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Visual pop-out: color (hue)

Resources from : https://www.csc2.ncsu.edu/faculty/healey/PP/index.html

Visual pop-out: shape (curvature)


Feature conjunctions


Change blindness

Change blindness A perceptual phenomenon that occurs when a change in a visual

stimulus is introduced and the observer does not notice it

Our visual intelligence can only detect changes in those parts of the

image to which we explicitly attend.

Selective attention

Selective attention The act of focusing on a particular object for a period of time while

simultaneously ignoring irrelevant information that is also occurring

This occurs on a daily basis and can be seen in basically any of your

interactions. Because it is impossible to give attention to every

stimulus in our environment, we use selective attention to select what

stimuli are important as events occur.

The problem with the classic ‘7±2’ •  George Miller’s theory of how much information people can remember

•  People’s immediate memory capacity is very limited

•  The number of objects an average human can hold in working memory

(short-term) is 7 ±2

•  Example: DECIBMGMC vs. DEC IBM GMC 6174591765 vs. 617‐459‐1765

The problem with the classic ‘7±2’ •  Wrong application of ‘7 ± 2’ theory: Designers present only 7 options/

menus/icons/tabs. Why?

•  People can scan lists of bullets, tabs, menu items till they see the

one they want

•  They don’t have to recall them from memory having only briefly

heard or see them

•  ‘7 ± 2’ applies to serial presentation of information

Chunking

Chunking Hierarchy

Processors: •  Perceptual •  Cognitive •  Motor Memory: •  Working memory •  Long-term memory

Working memory Working memory is small

•  Temporary storage

•  Decay in 200ms

Recognition over recall •  Recall – information reproduced from memory

•  Recognition

– Presentation of information provides cues that information has been

encountered before

– Easier because of cues (context) for retrieval

Recognition over recall •  Command line interface (recall) vs. GUI (recognition) interface

Cognitive processor Typical matching time

•  Digits: 33ms

•  Colors: 38ms

•  Geometry: 50ms…

Motor processor Receive input from the cognitive processor

Execute motor programs

•  Pianist: up to 16 finger movements per second

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Fitts’s law

Fitts’s law •  Fitts’s law predict the amount of time taken to move to and select a

target

•  It is faster to hit larger targets close to you than smaller targets

further from you

T = a + blog (D / S +1) -  a, b = constants (empirically derived)

-  D = distance

-  S = size

•  T increases as the distance to the target increases

•  T decreases as the size of the target increases

Applying Fitts’s law to UI design •  Bring items closer to the cursor

•  Increase the target size

•  Exploit the edges

Applying Fitts’s law to UI design

Does Fitts’s law apply to mobile devices?

•  Yes! Original experiment by Fitts was on human arm movement,

not mouse pointing!

•  Extension to target acquisition with mouse was a big result of Card

et al. and not obvious.

•  Tablet setting is closer to original experimental setting.

•  No more benefit on device edges

•  How device is held is important

Individual assignments

Individual project: Planning Data Collection

Design a semi-structure interview script/survey questions that you will use

to collect data from potential users. How many questions to ask? At least

2 topic areas/ultimate goals and 3 questions per topic for an interview,

and at least 15 questions for a survey. But, you need to make sure that

you have enough questions to know about the users, their context, and

the task. If I find important topics (based on your proposal) are missing,

you will lose points.

#Disclaimer. Further instruction of this submission can be given verbally during class or through Piazza.

Individual project: Planning Data CollectionFormat

•  Turn-in: a PDF of interview scripts & survey questions

•  Add a title and brief description of the project idea on top

•  List topics/goals and put relevant questions under the topic (Both interview &

survey) •  E.g.,

Topic 1. Identify why people buy things online. Q1. What was the item that you have purchased online most recently?

Q2. xxx

Q3. xxx

Topic 2. xxx Q1. xxx

•  a PDF file, 12 point scale in Times New Roman, 1.5 line spacing


Individual project: Planning Data Collection

Rubric •  Interview (5pt)

o  Structure: intro-main body-closing (2pt) o  Quality of questions

•  Whether you ask relevant questions to your topic/problem (1pt) •  Whether you ask in-depth contextual questions (1pt) •  Whether the answers to questions lead to in-depth, follow-up questions (1pt)

•  Survey (5pt) o  Whether you used proper types of questions (e.g., open ended vs. radio button)

(2pt) o  Whether you ask relevant questions to your topic/problem (2pt) o  Whether you ask appropriate demographic information questions (1pt)

•  You will lose 50% if your submission does not follow the format •  You will lose 20% if it’s a late submission (Not accepting a late

submission submission after that) •  You will lose 10% per missing an important topic Due by Midnight 10/9


By next class Reading 1.  Contextual Design. Ch.9 #discussion paper

q  Submit a group project P2. Part1: Data collection design by 10/5

midnight

q  Submit an individual project P2. Part1: Data collection design by 10/9

midnight

Sunyoung Kim, PhD

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