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Extensive Lecture Notes usability (LIX016B05)
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This document entails extensive notes of all the lectures of the course Usability (LIXo16B05).
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UsabilityLecture Notes
Lecture 1 – Introduction
Usability is the ease of use – the extent to which a product can be used by specified users to achieve
specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
There are several usability goals.
Effectiveness: does the object do what it is supposed to do (it’s goal)?
o E.g., when you press a light switch, does it turn on the light?
Efficiency: how is this goal achieved? Is there an optimal usage?
o E.g., can the switch be pressed easily, with one finger, or should it be pushed with
great power?
Safety: is the object safe to use? Is there a protection from making errors?
Functionality: is there a right functionality? Can a user do much with the object?
Easiness: is the object easy to learn to use?
Rememberable: is the usage of the object easy to remember?
Usability is part of Interaction Design: designing interactive products to support the way people
communicate and interact in their everyday and working lives (- Sharp, Rogers, and Preece).
Usability is also part of User Experience: how do people experience a specific product? Besides
usability, user experience also focusses on enjoyment and satisfaction during use (e.g., looks, how to
hold it, open/close, etc.).
Garrett: “Every product that is used by someone has a user experience: newspapers, ketchup bottles,
reclining armchairs, cardigan sweaters.”
o Example in the lecture: the part where you have to kind of throw the ketchup bottle
(but keep holding it) to get the final bit out of the bottle, is part of its user
experience.
Part of apple’s success of, e.g., the iPad is it’s simple, elegant, and distinctive design, it’s enjoyable
use, and it’s attractive name.
Just like usability, there are also user experience goals, consisting of
wanted aspects, such as meeting requirements, pleasant, fascinating, helpful, motivating,
fun, challenging, surprising, etc.
unwanted aspects, such as boring, frustrating, annoying, childish, etc.
There are some differences between usability and user experience.
A potential conflict, namely: can a product be enjoyable as well as safe?
A difference in goals, which can be differently measured.
Donald A. Norman – The Design of Everyday Things
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,A design can have challenges. There are e.g. daily challenges in the (former) use of the Leitz slide
projector which only has one button at which the next slide is a short click and the previous slide is a
long click, but what happens if you are in a hurry? Another example is the use of a telephone at
which the challenge lies in how to transfer a call, or how to adjust the volume, or how to store a
number (and the instructions that come along with the telephone aren’t always helping to make this
clear).
There are a few usability concepts.
1. Affordance
The quality or property of an object that defines its possible uses or makes clear how it can or should
be used – possibilities that are easy to discover – indication of use without explanation – how you
can perceive how to use a specific object; how to use a specific thing without an explanation. (i.e., if
you’re from the jungle and you find an object, would you know how to use it by its, e.g., design?)
Does the object afford to be used like x?
Visual affordances: observed and present properties of an object that indicate how you use
that object ((part of) the design of the object).
o E.g.: a button affords to be pressed/turned, a door handle affords to be either
pushed (usually a flat surface) or pulled (with a handle on it).
o E.g.: the example of the emergency exits, which usually have bars which you can
press to open the exit. This bar can be (I) across the entire width of the door, where
people push anywhere from left to right (although the doo opens at one of the
sides), or (II) at one side of the door to indicate where the user should push to open
the door in the most efficient way, e.g. a bar on the left side if the door opens on the
left (meaning the hinges are on the right).
Without affordance, one wouldn’t know what to do with an object, or what it is for. Take the
example in the lecture of the glass plate on the wall. Only the glass plate looks strange, but if one
adds white markers, it would explain its usage as a writing board.
Physical vs. virtual affordances: e.g., the handle on coffee mucks for lifting it vs. buttons
which affords to be clicked on.
Norman: “If a simple object like a door needs instructions, then it probably indicates a poor design.”
There are two basic principles by Norman: (1) make the method of use visible (by affordances), and
(2) use a good conceptual model.
2. Conceptual model
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,How people make an internal image of how we can use specific things – people make their own
image of how something works. Understanding its precise operation is not necessary. We all can
have a different conceptual model, as long as it’s working.
o E.g.: we use a laptop and we know how to use it, but most do not know how it is
operating exactly, i.e. how the chips inside the laptop operate.
o E.g.: pedestrian traffic lights: some people think pressing it multiple times will turn
the light on green faster (that is their conceptual model).
3. Visibility
Hidden functions lead to problems. With visible functionality, the user does not have to remember
the use of an object.
o E.g.: when number of functions is greater than number of buttons – having to get
into a menu and further to get to a certain function, that function is hidden and
therefore not visible.
o E.g.: bathroom faucets with the two functions of hot/cold and on/off. Can you see
how it works? Are these two functions clear and independent? (Does the design
makes this clear to you?)
o E.g.: the function of setting the clock at another time, is this easier if you have to
press many buttons (at a digital watch) or if you can see at first sight the button to do
this (the button which you have to pull out at the side and twist, of an analog watch).
4. Mapping
The relationship between the action and the desired result. (The actual place of a certain object (e.g.
the button) – relationship between button and action/result.)
o E.g.: when you place the front window warming button (in the car) next to the rear
window warming button, mapping wise you would say the rear window button
would be behind the front window button.
o E.g.: two light switches in one: which switch controls which light?
o E.g.: a stove, is it clear which button controls which stove burner?
o E.g.: money, at which a larger amount is a larger money bill.
5. Feedback
Letting users know what is happening. This can also be a physical change (e.g., stove flames that are
visible).
o E.g.: a beep when you check in at the bus or train, and another kind of beep when
you check out.
o E.g.: a red dot at the specific stove that’s one at induction cooking plate.
o E.g.: the light on your keyboard that’s on if you’ve pressed Caps Lock.
6. Constraints
Limitation of the number of possible actions to prevent selection of wrong options. Physical objects
often have constraints.
o E.g.: a key can only be used in a certain way in a certain lock, this prevents you from
entering another, e.g., house with your key (preventing a wrong action).
o With the usb it is hard to perceive in which way you should put in the, e.g., laptop.
(so this has no constraints) The new usb-c will make a connection either way, either
putting the usb up or down inside the device.
3
, In addition, there are virtual (online, software) constraints.
o The grayed out options in e.g. a menu in word prevent you from using those options.
7. Consistency
Design interfaces with similar functions and elements for similar tasks – having the same functions
operating in the same way in all types of programs. The benefit of this is that it is easier to use and
remember.
o E.g.: ctrl+s does the same thing in word and in sublime text editor
However, there are consistency limitations: what if several tasks start with the same letter (e.g. ctrl +
s for save or select?)? A solution is maybe to use different combinations (e.g.: ctrl+s or alt+s).
However, this breaks with consistency which increases the learning curve for users and the risk of
making errors.
Internal consistency are the same operations within an application. External consistency means that
you have the same operations in different programs.
o See below for an example of external inconsistency.
8. Conventions
The accepted norms or standards; the things we already are using a lot and know how to use. These
can be culture dependent. It is often not recommended to change conventions, because it can lead
to ambiguity.
o E.g.: driving on the ride side is a convention in some culture, while in other cultures
the convention is driving on the left side.
o E.g.: scrollbar on right side of a screen.
o E.g.: the color red indicating danger or bad. Also: red at, e.g., a restaurant openings /
closing sign indicates often that it is closed: saying it’s closed in green can create
confusion.
Norman: “Use conventions with respect. Violate them only with great risk.”
Execution-Evaluation cycle: physical system gulf of execution / gulf of evaluation user
goals. Goals: what we want to happen – Execution: what we do to the world – Evaluation:
comparing what happened with what we wanted to happen. (A model by Norman)
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