10 Heuristics for an Optimal User Experience - alt.chi 2013

10 Heuristics for an Optimal User Experience - alt.chi 2013

10 Heuristics for an Optimal User Experience - alt.chi 2013


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Luca Colombo<br />

University of Lug<strong>an</strong>o<br />

Via Buffi 13<br />

6900 Lug<strong>an</strong>o<br />

Switzerl<strong>an</strong>d<br />

luca.colombo@usi.ch<br />

Marco Pasch<br />

University of Lug<strong>an</strong>o<br />

Via Buffi 13<br />

6900 Lug<strong>an</strong>o<br />

Switzerl<strong>an</strong>d<br />

marco.pasch@usi.ch<br />

<strong>10</strong> <strong>Heuristics</strong> <strong>for</strong> <strong>an</strong> <strong>Optimal</strong> <strong>User</strong><br />

<strong>Experience</strong><br />

Permission to make digital or hard copies of all or part of this work <strong>for</strong><br />

personal or classroom use is gr<strong>an</strong>ted without fee provided that copies are<br />

not made or distributed <strong>for</strong> profit or commercial adv<strong>an</strong>tage <strong>an</strong>d that<br />

copies bear this notice <strong>an</strong>d the full citation on the first page. To copy<br />

otherwise, or republish, to post on servers or to redistribute to lists,<br />

requires prior specific permission <strong>an</strong>d/or a fee.<br />

CHI’12, May 5–<strong>10</strong>, 2012, Austin, Texas, USA.<br />

Copyright 2012 ACM 978-1-4503-<strong>10</strong>16-1/12/05...$<strong>10</strong>.00.<br />

Abstract<br />

In this paper we present <strong>10</strong> heuristics <strong>for</strong> ensuring a<br />

good user experience, derived from a critical inspection<br />

of flow theory <strong>an</strong>d applying it to the context of hum<strong>an</strong>computer<br />

interaction. The heuristics are intended as<br />

guidelines <strong>for</strong> practitioners when designing <strong>an</strong>d<br />

evaluating interactive products. We show how each<br />

heuristic derives from flow theory, provide design<br />

recommendations based on the heuristic, <strong>an</strong>d give <strong>an</strong><br />

example that illustrates it.<br />

Author Keywords<br />

<strong>Heuristics</strong>, <strong>User</strong> <strong>Experience</strong>, Flow Theory<br />

ACM Classification Keywords<br />

H.5.m. In<strong>for</strong>mation interfaces <strong>an</strong>d presentation (e.g.,<br />

HCI): Miscell<strong>an</strong>eous<br />

General Terms<br />

Hum<strong>an</strong> Factors<br />

Introduction<br />

Interactive products have become ubiquitous<br />

comp<strong>an</strong>ions of all facets of everyday life. In hum<strong>an</strong>computer<br />

interaction research, these ch<strong>an</strong>ges are<br />

reflected in a shift away from investigating how to<br />

make task-related interaction more effective <strong>an</strong>d<br />

efficient towards finding out how interaction c<strong>an</strong>

happen in a more joyous <strong>an</strong>d satisfying way. After a lot<br />

of discussion on competing frameworks <strong>an</strong>d<br />

terminology, the term user experience has emerged <strong>for</strong><br />

this direction of research.<br />

We argue that there is only little consensus on what<br />

user experience is or should be, <strong>an</strong>d <strong>an</strong> abund<strong>an</strong>ce of<br />

possible definitions that while stimulating make it<br />

difficult to come up with a working one. As a<br />

consequence, practitioners are left without guidelines<br />

on what constitutes a good user experience <strong>an</strong>d how<br />

they c<strong>an</strong> design <strong>for</strong> it.<br />

In <strong>an</strong> ef<strong>for</strong>t to build <strong>an</strong> underst<strong>an</strong>ding of enjoyment in<br />

games, Sweetser <strong>an</strong>d Wyeth [20] develop the<br />

GameFlow model. They do so by mapping elements<br />

from game literature to flow theory. The result is a list<br />

of 8 criteria that c<strong>an</strong> be used to evaluate how enjoyable<br />

a particular game is.<br />

In this paper, we follow a similar approach by deriving<br />

general user experience heuristics from flow theory. In<br />

doing so, we pursue two goals. From a theory<br />

perspective, we aim at in<strong>for</strong>ming, exp<strong>an</strong>ding, <strong>an</strong>d<br />

contributing to the ongoing discussion on what good<br />

user experience is or should be. For practitioners, we<br />

provide a list of heuristics that c<strong>an</strong> be used in the<br />

design <strong>an</strong>d evaluation of interactive devices <strong>an</strong>d<br />

applications.<br />

The notion of heuristics is not undisputed in hum<strong>an</strong>computer<br />

interaction research. Under the user-centered<br />

design paradigm that dem<strong>an</strong>ds involvement of users as<br />

early <strong>an</strong>d often as possible in the development process,<br />

the idea of relying on experts inspecting a system<br />

based on a number of heuristics has come under heavy<br />

criticism.<br />

Our motivation <strong>for</strong> proposing user experience heuristics<br />

here comes from our background. Both authors have<br />

worked in small design comp<strong>an</strong>ies <strong>an</strong>d often witnessed<br />

how the requirement of involving users was neglected,<br />

justified with a number of reasons such as time or<br />

money constraints. In consequence we believe there is<br />

still a lot of merit to the discount usability claim that<br />

while it may not be the best usability methodology to<br />

use, it is better th<strong>an</strong> using none. Our list of heuristics is<br />

intended as a resource-friendly way to ensure good<br />

user experience of a product when time <strong>an</strong>d money are<br />

scarce.<br />

Flow Theory<br />

Flow is a well-established <strong>an</strong>d validated psychological<br />

theory developed by Mihaly Csikszentmihalyi, that<br />

describes what <strong>an</strong> optimal experience is.<br />

Csikszentmihalyi [5] defines flow as a mental state of<br />

deep enjoyment <strong>an</strong>d intense engagement in a certain<br />

activity, where most of a person’s attentional resources<br />

are devoted to accomplish that activity. An optimal<br />

experience is what a person experiences when being in<br />

a state of flow <strong>an</strong>d it is characterized by universal<br />

conditions: 1) clear goals; 2) feedback; 3) focused<br />

concentration; 4) loss of self-consciousness;<br />

5) merging of action <strong>an</strong>d awareness; 6) challenging<br />

activity that requires adequate skills; 7) sense of<br />

control; 8) a distorted sense of time; 9) autotelic<br />

activity (motivations).<br />

These 9 major components (in [5], 8 components are<br />

given, but we split “clear goals <strong>an</strong>d feedback” <strong>for</strong><br />

convenience) are the most often mentioned<br />

accomp<strong>an</strong>ying factors of <strong>an</strong> optimal experience<br />

regardless of the activity per<strong>for</strong>med <strong>an</strong>d of one’s<br />

sociocultural characteristics. As stated by the author<br />

there is no need to meet all these conditions to<br />

experience flow.

Flow theory has been already used in HCI studies (<strong>for</strong> a<br />

review see [9] [11], [21]) as a framework <strong>for</strong> modeling<br />

mental states like enjoyment, engagement, <strong>an</strong>d<br />

pleasure.<br />

There are still two main limitations when using flow<br />

theory <strong>for</strong> HCI research. First, there is still a lack of<br />

consistency in the conceptual <strong>an</strong>d methodological<br />

definitions of flow used by different researchers [15]<br />

even though researchers generally agree on the original<br />

conceptual definition of flow as presented by<br />

Csikszentmihalyi in [5].<br />

The second limitation is that flow theory, in its original<br />

<strong>for</strong>m, looked into the optimal experience by considering<br />

solely the person, the activity per<strong>for</strong>med by her <strong>an</strong>d the<br />

interaction between the two. But when this interaction<br />

is mediated by <strong>an</strong> artefact (or system, we use these<br />

two terms interch<strong>an</strong>geably) then it would be better to<br />

re-conceptualize flow in order to consider this third<br />

component as well as its interaction with the person<br />

<strong>an</strong>d the task (or the user <strong>an</strong>d the activity).<br />

Some authors already stressed the import<strong>an</strong>ce to<br />

distinguish task from artefact [8], <strong>an</strong>d consequently,<br />

task flow from artefact flow [17]. But to our best<br />

knowledge there are no works specifically focused on<br />

providing a detailed list of recommendations on how a<br />

system should be designed in order to facilitate <strong>an</strong><br />

optimal user experience. In this paper we try to fill this<br />

gap as much as drawing a clearer link between flow<br />

theory <strong>an</strong>d HCI while enabling researchers to overcome<br />

the above-mentioned limitations. The heuristics we<br />

present are the result of <strong>an</strong> extensive literature review<br />

<strong>an</strong>d of a deductive approach in which we map the flow<br />

components into guidelines <strong>for</strong> providing <strong>an</strong> optimal<br />

user experience.<br />

<strong>User</strong> <strong>Experience</strong> <strong>Heuristics</strong><br />

In the following we present each heuristic, describe<br />

how it derives from flow theory, provide design<br />

recommendations based on the heuristic <strong>an</strong>d give <strong>an</strong><br />

example that illustrates it. The first 9 are directly<br />

mapped from the a<strong>for</strong>ementioned flow components<br />

(following the same order). The tenth heuristic<br />

(conservative innovation), derives from<br />

Csikszentmihalyi’s finding that what all flow activities<br />

have in common is providing a sense of discovery, a<br />

creative feeling of tr<strong>an</strong>sporting the person into a new<br />

reality [5].<br />

1. Clear goals<br />

The purpose of the system should be clear. The system<br />

has to fulfill, or even better exceed, user’s<br />

expectations.<br />

Flow theory states that in order to be engaged in <strong>an</strong><br />

activity, one should define clear goals to be obtained<br />

from the activity itself, <strong>an</strong>d should strive to a<strong>chi</strong>eve<br />

them [5].<br />

When the experience is mediated by a system, users<br />

have some expectations on how the system will support<br />

them in per<strong>for</strong>ming a certain activity. These<br />

expectations depend on the af<strong>for</strong>d<strong>an</strong>ces of the system.<br />

Af<strong>for</strong>d<strong>an</strong>ces make it obvious how <strong>an</strong> object is me<strong>an</strong>t to<br />

be used [8] even though the actual perception of<br />

af<strong>for</strong>d<strong>an</strong>ces will be determined in part by the observer’s<br />

culture, social setting, experience <strong>an</strong>d intentions [<strong>10</strong>].<br />

Obviously designers do not have control over such<br />

variables, but they c<strong>an</strong> determine which af<strong>for</strong>d<strong>an</strong>ces<br />

are present in the system <strong>an</strong>d how users will perceive<br />

them. As such we recommend:

! the system should be designed with the right<br />

af<strong>for</strong>d<strong>an</strong>ces to explicitly tell users its purpose(s):<br />

! the system must be functional, me<strong>an</strong>ing that it<br />

must fulfill the purposes highlighted by the af<strong>for</strong>d<strong>an</strong>ces<br />

<strong>an</strong>d meet users’ expectations;<br />

! additional features (other th<strong>an</strong> the core ones) are<br />

welcome, even better if they <strong>for</strong>esee possible<br />

<strong>alt</strong>ernative uses of the system: a product that is<br />

actually exceeding users’ expectations is often a<br />

predictor of a good user experience [3].<br />

As <strong>an</strong> example consider so-called bridge cameras.<br />

These are often comparable in size, weight <strong>an</strong>d<br />

appear<strong>an</strong>ce to digital single-lens reflex (DSLR)<br />

cameras, but they lack the adv<strong>an</strong>ced functionalities <strong>an</strong>d<br />

image quality of the latter. However their DSLR like<br />

camera-body (af<strong>for</strong>d<strong>an</strong>ce) could create expectations<br />

that are not met by the system.<br />

This discrep<strong>an</strong>cy between users’ expectations <strong>an</strong>d<br />

system purpose could explain (amongst other factors)<br />

the low commercial success of this specific category of<br />

digital cameras. This could also explain the increasing<br />

popularity of mirror-less interch<strong>an</strong>geable-lens camera<br />

(MILC) where the expectations suggested by their<br />

af<strong>for</strong>d<strong>an</strong>ce (they look like compact cameras) are<br />

exceeded by the system.<br />

2. Appropriate feedback<br />

The user-system interaction should be sustained<br />

through steady, prompt <strong>an</strong>d unobtrusive feedback.<br />

Feedback is import<strong>an</strong>t as it increases users’ confidence<br />

in interacting with a system by creating order in<br />

consciousness, <strong>an</strong>d strengthening the structure of the<br />

self. Feedback c<strong>an</strong> increase engagement provided it is<br />

logically related to a goal in which one has invested<br />

mental energy [5].<br />

But feedback alone is not enough; it should be provided<br />

steadily (to sustain user interaction), promptly (to<br />

increase awareness) <strong>an</strong>d unobtrusively (to not interfere<br />

with the experience).<br />

From this we derive as design recommendations that:<br />

! the system should provide steady <strong>an</strong>d prompt<br />

feedback;<br />

! the feedback should be as less obtrusive as<br />

possible;<br />

! the “obtrusiveness” of the feedback should be<br />

proportional to the level of priority (to establish a sort<br />

of hierarchy).<br />

The Web 2.0 paradigm provides a good example on<br />

how feedback c<strong>an</strong> influence user experience. The most<br />

import<strong>an</strong>t technological innovation of Web 2.0 is<br />

Asynchronous JavaScript <strong>an</strong>d XML (AJAX), which made<br />

it possible to provide users with real-time feedback.<br />

Moreover the obtrusiveness of the feedback was<br />

reduced since with AJAX the page content c<strong>an</strong> be<br />

updated without refreshing the page, thus avoiding<br />

interrupting user interaction with the webpage.<br />

3. Focused concentration<br />

The system should be simple <strong>an</strong>d intuitive in its use; it<br />

should facilitate user concentration on the task at h<strong>an</strong>d<br />

by providing me<strong>an</strong>ingful feedback <strong>an</strong>d avoiding nonrelev<strong>an</strong>t<br />

distractions.<br />

A characteristic of optimal experience is that <strong>for</strong> people<br />

to reach this state, they must be able to focus their<br />

attention at length on the task at h<strong>an</strong>d. Concentrating

on the task further enh<strong>an</strong>ces one’s focus, often<br />

enabling them to tune out other input [1].<br />

According to perceptual load theory [4] task-irrelev<strong>an</strong>t<br />

stimuli are perceived in situations of low perceptual<br />

load when the relev<strong>an</strong>t task leaves spare capacity <strong>for</strong><br />

their processing, but not in situations of high perceptual<br />

load where all available capacity is consumed. This<br />

phenomenon is also known as inattentional blindness.<br />

M<strong>an</strong>cero et al. [13] found that that the more relev<strong>an</strong>t<br />

<strong>an</strong>d me<strong>an</strong>ingful the stimuli are the more responsive the<br />

person became.<br />

From this we c<strong>an</strong> obtain the recommendations that:<br />

! the system must be usable;<br />

! the system should provide feedback that is relev<strong>an</strong>t<br />

<strong>an</strong>d me<strong>an</strong>ingful <strong>for</strong> the task at h<strong>an</strong>d;<br />

! the system should avoid distractions, namely<br />

stimuli that are not relev<strong>an</strong>t <strong>for</strong> the task at h<strong>an</strong>d;<br />

Google AdWords provides a good example <strong>for</strong> all this.<br />

When users per<strong>for</strong>m searches on Google they are<br />

provided with the result of the search together with<br />

some advertisements based on their current search<br />

terms. The main reason why these advertisements are<br />

more effective, <strong>an</strong>d users have a better experience,<br />

th<strong>an</strong> disruptive colorful blinking b<strong>an</strong>ners is mainly<br />

because the stimulus provided to users is not<br />

distracting them from their primary task (sear<strong>chi</strong>ng)<br />

<strong>an</strong>d it is relev<strong>an</strong>t <strong>an</strong>d me<strong>an</strong>ingful to the task at h<strong>an</strong>d.<br />

4. Ergonomical tr<strong>an</strong>sparency<br />

The system should almost disappear, be tr<strong>an</strong>sparent,<br />

while used to allow users to focus on the activity <strong>an</strong>d to<br />

engage in the experience.<br />

When <strong>an</strong> activity is thoroughly engrossing, there is not<br />

enough attention left over to allow a person to consider<br />

<strong>an</strong>y temporarily irrelev<strong>an</strong>t stimuli, including selfconsciousness<br />

[5].<br />

More mental energy devoted to the activity me<strong>an</strong>s<br />

more engagement as well as less space in mind to keep<br />

consciousness of the self <strong>an</strong>d, equally import<strong>an</strong>t, of the<br />

system.<br />

The loss of self-consciousness mainly depends on one’s<br />

mental attitude, but the system c<strong>an</strong> be designed to be<br />

as “tr<strong>an</strong>sparent” as possible. A technology that is well<br />

fitted to our skills, our purposes <strong>an</strong>d the activity we are<br />

per<strong>for</strong>ming is almost invisible in use [2].<br />

The aim is to move users’ flow into the realm of the<br />

task <strong>an</strong>d to engage them there (task flow) <strong>an</strong>d to focus<br />

their minds on the experience, rather th<strong>an</strong> on the<br />

system (artifact flow) [17]. To be “tr<strong>an</strong>sparent” the<br />

system should then meet these characteristics:<br />

! the system should be ergonomic, it should fit users’<br />

skills <strong>an</strong>d activity purposes;<br />

! the system behavior should be consistent <strong>an</strong>d<br />

predictable;<br />

! the system should be designed with aesthetical<br />

integrity, in other words the design should be visually<br />

appealing <strong>an</strong>d common principles of good design should<br />

be followed; it should also provide a graceful flow,<br />

namely the interaction between users <strong>an</strong>d the system<br />

should be smooth <strong>an</strong>d graceful.<br />

Loss of self-consciousness <strong>an</strong>d invisibility of the system<br />

are especially import<strong>an</strong>t to a<strong>chi</strong>eve while playing<br />

videogames, indeed they are often referred as<br />

indicators of immersion [20].

We c<strong>an</strong> see how these principles work in practice in one<br />

of the most-popular videogame of the last few years:<br />

Angry Birds.<br />

All the criteria we listed above are met by the system<br />

consisting of the game engine (the gameplay, the<br />

sound, the physic engine, etc. <strong>for</strong> a deeper review see<br />

[14]) <strong>an</strong>d of the device on which it runs (the<br />

touchscreen makes the interaction with the system<br />

more intuitive <strong>an</strong>d tr<strong>an</strong>sparent). No matter which<br />

mobile device we are using, if the battery is running<br />

low or if our train stop is the next one: we must<br />

destroy those loathsome pigs!<br />

5. Technology appropriation<br />

<strong>User</strong>s should be allowed to customize <strong>an</strong>d m<strong>an</strong>ipulate<br />

the system according to their peculiarities <strong>an</strong>d<br />

preferences, to feel familiar with the system, as if the<br />

system was tailored specifically <strong>for</strong> them.<br />

When people are completely absorbed by the activity,<br />

they become so involved in what they are doing that<br />

the activity becomes spont<strong>an</strong>eous, almost automatic;<br />

they stop being aware of themselves as separate from<br />

the actions they are per<strong>for</strong>ming [5].<br />

As a result, the person will then feel part of a whole,<br />

completely merged into a system of interaction<br />

consisting of the person itself, the artifact <strong>an</strong>d the task<br />

[8].<br />

We wrote above that a tr<strong>an</strong>sparent system would<br />

facilitate user engagement, but this feature alone is not<br />

enough. The possibility to appropriate <strong>an</strong>d adapt the<br />

technology c<strong>an</strong> improve the system’s situatedness<br />

(adaptability to the context of use) <strong>an</strong>d dynamicity<br />

(adaptability to ch<strong>an</strong>ges over time) <strong>an</strong>d users’ sense of<br />

ownership [15]. Hence we recommend that:<br />

! the system should be, to a certain extent,<br />

customizable <strong>an</strong>d m<strong>an</strong>ipulable by users in both its<br />

appear<strong>an</strong>ce <strong>an</strong>d its functionality;<br />

! the customization process should be easily<br />

accessible, <strong>an</strong>d with a predictable outcome<br />

! provide users with multiple choices <strong>for</strong> interacting<br />

with the system (doing the same activity in m<strong>an</strong>y<br />

different ways)<br />

An example of this c<strong>an</strong> be found in office software<br />

suites. <strong>User</strong>s c<strong>an</strong> customize toolbars <strong>an</strong>d menus, the<br />

customization is easily accessible <strong>an</strong>d reversible <strong>an</strong>d<br />

they have different options <strong>for</strong> accomplishing the same<br />

activity (e.g. to paste the content of the clipboard one<br />

c<strong>an</strong> use the comm<strong>an</strong>d-v keyboard shortcut, the<br />

edit->paste menu bar item or the clipboard<br />

toolbar button).<br />

6. Challenges/skills bal<strong>an</strong>ce<br />

The system should adapt to the user in that it should<br />

be designed to dynamically provide adequate<br />

challenges <strong>for</strong> both novice, average <strong>an</strong>d experienced<br />

users.<br />

An import<strong>an</strong>t factor in determining flow or frustration is<br />

not the absolute challenges of the activity, nor the<br />

absolute level of users’ skills, but rather the relative<br />

bal<strong>an</strong>ce between the two [16]. Enjoyment comes at a<br />

very specific point: whenever the opportunities <strong>for</strong><br />

action perceived by the individual are equal to his or<br />

her capabilities [5].<br />

It is worth noticing that this bal<strong>an</strong>ce is dynamic. While<br />

we interact with a system we implicitly masters new<br />

skills, skills that need to be bal<strong>an</strong>ced by new adequate<br />


Challenges should not be interpreted as “barriers to<br />

use” but as a bundle of opportunities <strong>for</strong> action,<br />

opportunities <strong>for</strong> a more efficient <strong>an</strong>d fulfilling<br />

interaction. So, to allow a dynamic bal<strong>an</strong>ce between<br />

challenges <strong>an</strong>d skills:<br />

! the system should have a steep learning curve to<br />

help novice users;<br />

! the system should encourage users to explore it<br />

<strong>an</strong>d to discover all the features <strong>an</strong>d opportunities <strong>for</strong><br />

interaction;<br />

! the system should provide adv<strong>an</strong>ced features or<br />

extra functions (e.g. accelerators, macros, adv<strong>an</strong>ced<br />

settings, etc.) <strong>an</strong>d make them accessible <strong>for</strong><br />

intermediate/adv<strong>an</strong>ced users;<br />

This dynamic bal<strong>an</strong>ce c<strong>an</strong> be found in Mac OS X<br />

operating system. The system is intuitive <strong>an</strong>d simple<br />

enough <strong>for</strong> novice users (Have you ever tried to install<br />

a new application both on Windows or OSX?); it is<br />

possible <strong>for</strong> intermediate users to customize <strong>an</strong>d<br />

optimize it (e.g. create macros with Automator <strong>an</strong>d<br />

customize keyboard shortcuts, trackpad gestures or<br />

screen hot corners); while it gives full control to<br />

experienced users (with the UNIX shell you c<strong>an</strong> hack<br />

almost everything).<br />

7. Potential control<br />

The system should make users feel “free” of constraints<br />

<strong>an</strong>d, at the same time, in control of the experience.<br />

The flow experience is typically described as involving a<br />

sense of control or, more precisely, as lacking the<br />

sense of worry about losing control that is typical in<br />

m<strong>an</strong>y situations of normal life [5]. Needless to say that<br />

feeling in control of the system is a precondition <strong>for</strong><br />

feeling in control of the experience.<br />

The adjective “potential” is used intentionally, me<strong>an</strong>ing<br />

that actually users do not have to always be in<br />

complete control of the system: what people enjoy is<br />

not the sense of being in control, but the sense of<br />

exercising control in difficult situations [5].<br />

Or, to use Shneiderm<strong>an</strong>’s words the system should<br />

“support internal locus of control” [17], me<strong>an</strong>ing that<br />

users have to believe that activity outcomes result<br />

primarily from his own behavior <strong>an</strong>d actions. In order<br />

to do so:<br />

! the system should help users to improve their skills<br />

<strong>an</strong>d to reduce the margin of error in per<strong>for</strong>ming the<br />

activity;<br />

! the system should not make users feel trapped.<br />

Avoid (as far as possible) constraining users’ actions,<br />

provide them <strong>an</strong> exit strategy <strong>an</strong>d make the actions<br />

easily reversible;<br />

! users should be always allowed to enable or disable<br />

automatic processes or system aids.<br />

If we look at modern racing simulation videogames<br />

they all provide driving aids (e.g. traction control) in<br />

order to support players in the first phases of the<br />

gaming experience. But each of these features c<strong>an</strong> be<br />

easily disabled by users whenever they w<strong>an</strong>t, in some<br />

videogames even while they are playing: the possibility<br />

of enabling/disabling this kind of aids is crucial <strong>for</strong><br />

supporting internal locus of control.<br />

Finally, players c<strong>an</strong> always restart the race (exit<br />

strategy) <strong>an</strong>d in some games even rewind<br />

(reversibility) if they have committed some mistakes.

8. Follow the rhythm<br />

The pace of the system should adapt to the user <strong>an</strong>d to<br />

the rhythm of the experience.<br />

One of the most common descriptions of optimal<br />

experience is that time no longer seems to pass the<br />

way it ordinarily does. The objective duration of time is<br />

rendered irrelev<strong>an</strong>t by the rhythms dictated by the<br />

activity [5].<br />

Thus to enable <strong>an</strong> optimal user experience it is not<br />

crucial to have a fast <strong>an</strong>d hyper-responsive system, it is<br />

rather crucial that the system pace is appropriate to the<br />

experience <strong>an</strong>d to the user.<br />

This does not me<strong>an</strong> that “fast is bad”: time still has <strong>an</strong><br />

import<strong>an</strong>t role when it comes to user experience, but in<br />

this case the focus should be on the user’s perception<br />

of time rather th<strong>an</strong> on “mere” efficiency. For this<br />

reason:<br />

! the system’s pace should be suitable <strong>for</strong> the<br />

activity <strong>for</strong> which it was designed;<br />

! the experience should not be interrupted by the<br />

system but users should be allowed to suspend the<br />

interaction <strong>an</strong>d to restart it from the point of<br />

a<strong>chi</strong>evement he reached;<br />

! users should be allowed to speed up or slow down<br />

the rhythm of the interaction.<br />

We know that this heuristic could sound odd <strong>for</strong><br />

videogames where speed increase is crucial <strong>for</strong> keeping<br />

the user engaged, like Tetris <strong>for</strong> inst<strong>an</strong>ce. Let us take it<br />

as example.<br />

It is true that users are not allowed to slow down the<br />

game but the purpose of “soft/hard drop” <strong>an</strong>d “pause”<br />

controls is to give users a certain degree of control over<br />

the game speed. This will allow them to adapt the<br />

game speed to their skills thus improving gaming<br />

experience.<br />

By looking at file sharing systems, we c<strong>an</strong> underst<strong>an</strong>d<br />

the import<strong>an</strong>ce of adapting system pace to the user.<br />

Downloading on a dial-up connection a large file is<br />

frustrating. But it is also true that the opposite situation<br />

could be misleading: downloading at high speed a very<br />

small file could result in the users not being aware of<br />

the task being completed. In order to avoid this, the<br />

system should “deceive” users. By showing, <strong>for</strong><br />

inst<strong>an</strong>ce, a progress bar <strong>for</strong> more th<strong>an</strong> the actual time<br />

of download (as it happens on http://ge.tt).<br />

9. Know thy user’s motivations<br />

The system should help users to fulfill the motivations<br />

behind its use <strong>an</strong>d to satisfy basic psychological needs.<br />

Enjoyable events occur when a person has not only met<br />

some prior expectation or satisfied a need or a desire<br />

but also gone beyond what he or she has been<br />

programmed to do <strong>an</strong>d a<strong>chi</strong>eved something<br />

unexpected, perhaps something even unimagined<br />

be<strong>for</strong>e [5].<br />

The system should help users to fulfill their<br />

motivations, then it will be more likely <strong>for</strong> them to<br />

perceive the experience as enjoyable.<br />

Moreover, when applicable, the system could help users<br />

to have “basic psychological needs” [18] (need <strong>for</strong><br />

competence, autonomy <strong>an</strong>d relatedness) satisfied as<br />

well, thus resulting in <strong>an</strong> improvement of enjoyment<br />

[4]. Then to allow <strong>an</strong> optimal user experience:

! the system should be designed by looking at final<br />

users <strong>an</strong>d the activity they seek to accomplish, this<br />

me<strong>an</strong>s that you should know them first;<br />

! but knowing all the possible users <strong>an</strong>d activities is<br />

impossible so, the system should be flexible in order to<br />

adapt to various users <strong>for</strong> various activities <strong>an</strong>d in<br />

different contexts;<br />

! when applicable, the system should help users to<br />

satisfy the three basic psychological needs (in a broad<br />

sense): need <strong>for</strong> competence, autonomy <strong>an</strong>d<br />

relatedness.<br />

Facebook is a perfect example of a system that fulfills<br />

motivations behind its use <strong>an</strong>d satisfies basic<br />

psychological need.<br />

<strong>10</strong>. Conservative innovation<br />

The system should be innovative (<strong>an</strong>d conservative at<br />

the same time).<br />

Though innovation is not among the nine key principles<br />

of Flow, in his studies Csikszentmihalyi found that what<br />

all flow activities have in common is providing a sense<br />

of discovery, a creative feeling of tr<strong>an</strong>sporting the<br />

person into a new reality [5].<br />

The system c<strong>an</strong> enh<strong>an</strong>ce this “sense of discovery” by<br />

actually implementing novelty <strong>an</strong>d variety, by allowing<br />

users to per<strong>for</strong>m the activity in a more fulfilling way or<br />

experiencing “something new”.<br />

But at the same time the system should not be<br />

completely different from existing systems, which serve<br />

the same purpose. We approve of things that comply<br />

with st<strong>an</strong>dards, things we are familiar with, <strong>an</strong>d we<br />

disapprove of things that conflict with st<strong>an</strong>dards [6].<br />

Still according to Desmet et al.: “St<strong>an</strong>dards are our<br />

beliefs, norms or conventions of how we think things<br />

should behave.” [6]. It follows that:<br />

! the system should provide a certain degree of<br />

novelty <strong>an</strong>d variety to users;<br />

! the system’s should be the result of a tradeoff<br />

between innovation <strong>an</strong>d tradition, where tradition is<br />

me<strong>an</strong>t as consistency with familiar systems <strong>an</strong>d<br />

compli<strong>an</strong>ce to st<strong>an</strong>dards;<br />

! the system should ensure interoperability to<br />

seamlessly integrate into the existing context.<br />

Nowadays smartphones provide a good example. Multitouch<br />

has been undoubtedly a breakthrough<br />

innovation, but modern smartphone are “just” a<br />

mixture of existing technologies people were already<br />

familiar with (i.e. touchscreens were already used in<br />

other contexts).<br />

Conclusions<br />

We presented a list of <strong>10</strong> heuristics, which we derive<br />

from flow theory. We described how each flow<br />

component applies to a HCI context <strong>an</strong>d gave design<br />

recommendations based on each heuristic.<br />

We believe these heuristics c<strong>an</strong> help interaction<br />

designers deliver good user experiences. In flow<br />

theory, not all of the flow components have to be met<br />

<strong>for</strong> someone to experience flow. Similarly, not all<br />

heuristics have to be considered in the same way in<br />

order to design good user experiences. It is up to<br />

designers to prioritize heuristics <strong>for</strong> each context in<br />

order to produce the most engaging user experience.

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