Spatial Ability and Visual Navigation: An Empirical Study

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Nov 15, 2013 (3 years and 7 months ago)

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Spatial Ability and Visual Navigation: An Empirical Study

Chaomei Chen
1

and Mary Czerwinski
2


1
Department of Information Systems and Computing, Brunel University, Uxbridge UB8 3PH, UK

2
Microsoft
Research
,
One Microsoft Way, 9N/2290, Redmond, WA 98052,
USA




In this paper, we describe an empirical study of individuals' spatial navigation strategies and a number of
performance and preference measures with regard to the design of a novel 3D visualisation. The underlying
semantic space of the user interface co
nsists of a collection of papers from the three most recent ACM SIGCHI
conference proceedings, visualised as a virtual reality network. This network was automatically constructed
based on semantic similarities derived from latent semantic analysis. We stud
ied the search strategies and
general preferences of eleven subjects who used this system to find papers on various topics. The study has led
to a number of interesting findings, which should be valuable for designers and evaluators of 3D user interfaces.
The results highlight the importance of structural elements in the design of a semantically based user interface,
because search strategies of users relied heavily on these mechanisms in the design. The results of this study also
demonstrate that we are ab
le to characterise and learn from users' search strategies in a visual environment
strongly shaped by semantic relationships of the information content. Implications for user interface design
based on users’ psychological models of a semantic space are des
cribed.


INTRODUCTION

Individual differences are by far the most significant cause of differences in various human
-
computer interaction
activities (14). However, it has also been stated that a well
-
designed interface is effective and crucial in
accommodati
ng individual differences (11). Using visualisation and virtual reality techniques in the design of
new generations of information systems has highlighted the need for a better understanding of a number of
fundamental issues during the design process, incl
uding individual differences and the elements of good design

2

that can accommodate these differences. It is well known that users approach these novel user interfaces with
different domain knowledge, differential depths of computer experience and different
styles of using an
information system, as well.

Navigation is a process whereby people determine where they are in relation to their surrounding environment,
and how to get to particular objects or places given that location in space. Recently, researche
rs have identified a
number of issues with regard to navigating in electronic worlds (15). The mapping between structure and
semantics has been regarded with particular interest, as it is one of the most challenging issues facing designers
of visual user i
nterfaces today. What are the relations between semantic structures and visualisation structures?
What visualisation structures are appropriate to tasks in visual navigation? What is the nature of the interaction
between the inherent structure, the imposed

structure and the user's cognitive model of the space?

There is little data and few criteria for assessing the effectiveness and usability of 3D interfaces and a wide
variety of visualisation techniques (but see 24, 9, 22). In virtual reality
-
based inform
ation systems, it is crucial
for designers to understand the usability of 3D representations and how these visual representations affect
people's ability to handle information systems. The goal of such research efforts is to develop guidelines and
heurist
ics for design that are beneficial to the human
-
computer interaction (HCI) community.

In this paper, we will describe an empirical study in attempt to address some of these problems, and provide
further empirical support for design principles in the realm
of semantic visualisation. The aim of this empirical
study is twofold: 1) to assess the usability of a particular virtual environment for visual navigation and thereby
improve the design of this specific system, and 2) to examine essential aspects of 3D se
mantic visualisation and
develop an integrated methodology for development and evaluation. Specifically, we will attempt to determine
the following:




Is spatial ability and user satisfaction with a 3D navigation structure correlated?



Do users who have hig
her spatial ability search more efficiently in a novel, 3D environment? Do they visit
fewer nodes during search tasks? Will users with higher spatial ability traverse longer distances?



Will distinct, structural patterns be frequently accessed in a 3D vir
tual environment? Will they be
memorable?



What is the role of virtual reality in enhancing 3D semantic visualisation? How should we assess the
usability of such systems?




3

In this study, we visualised 169 papers from the Association for Computing Machinery
’s (ACM) Special Interest
Group in Computer
-
Human Interaction (SIGCHI) according to semantic relatedness in a spatial environment in
virtual reality. The semantic similarities were obtained automatically by Latent Semantic Indexing (12), and a
user interfa
ce was designed to visualise patterns in these similarities. The method of design is described in (6, 7).
The spatial navigation strategies and abilities of users were correlated with several different performance and
preference measures. Implications for
user interface design based on users’ psychological models of a semantic
space are described.

Usability Issues on Visualisation

One basic research question in the context of information visualisation is simply how to assess the effectiveness
of a new visua
lisation tool. The problems with using traditional measures of recall and precision as means of
evaluating interactive information retrieval are now well
-
known, especially the relevance as decided according
to judgements from experts, rather than the searc
hers themselves (25). Veerasamy and Belkin (25) suggested that
one should not take for granted the ease of use of visualisation tools in interactive information retrieval systems.
They found that some topics appeared to be easier than others in terms of th
e extent to which they benefited from
the visualisation tools. They also noted the problems of finding enough subjects to account for inter
-
subject
differences, and of being able to account for inter
-
topic differences.

The influence of spatial ability on
users’ performance with hypertext systems has been investigated in earlier
studies. For example, Vicente and Williges (26) found that users with high spatial ability completed their tasks
quicker than users with lower spatial ability. Campagnoni and Ehrlic
h (5) reported that users with good
visualisation ability used the top
-
level table of contents less frequently than users with lower visualisation
ability, suggesting that a good spatial ability may help one to memorise how the information is organised. On

the
other hand, Leidig (18) only found a marginal main effect of spatial ability on the accuracy of performance,
although there was a significant main effect of spatial ability on users' general satisfaction. More recently,
Czerwinski and Larson (9) stud
ied usability issues of 2.5D visual user interfaces. In their study it was noted that
higher spatial abilities were significantly related to a user’s ability to initially navigate and find search items in
worlds requiring “fly
-
through” with the mouse. Sea
rch time, specifically, was positively related to spatial
ability. It was also observed that users with lower spatial abilities were hesitant to explore large numbers of
categories, as if the mental effort required was higher, when compared to users with
high spatial ability test
scores. These less spatially adept users were also more likely to get lost, and to complete fewer search tasks.
In

4

addition to these findings, a review of the literature informed us that visual scanning abilities, as measured by
c
ognitive battery subtests, have been correlated strongly with certain kinds of computer interaction behaviors,
such as scanning for a document in a menu item search task (17). However, a spatial ability subtest was found to
correlate highly with performan
ce in other kinds of computer tasks, such as navigating a complex hierarchical
user interface structure. So clearly, spatial ability subtests are capable of tapping into something more than a
simple notion of "intelligence" and can differentially predict
performance, depending on the task in question.
We decided, therefore, to monitor this ability in our subjects, in the hope that it might help elucidate
characteristics in subjects’ performance that would otherwise simply add variability to the data.

Wayf
inding in Virtual Environments

Another factor that can influence subjects’ abilities to navigate 3D environments is their preferred navigation
strategy. Darken and Sibert (10) studied whether people use physical world wayfinding strategies in large virtua
l
worlds. They examined a complex searching task in a number of virtual worlds with different environmental
cues. Their study showed that subjects were often disoriented in virtual worlds without any landmarks, paths or
cues. Simply adding cues like borde
rs, boundaries and gridlines significantly improved navigation performance.
Since wayfinding strategies and behaviours were strongly influenced by the environmental cues in the Darken
and Sibert study, the results reflected underlying principles for 3D us
er interface design. In other words, an
organisational metaphor, with landmarks and navigational cues, was of utmost importance in successfully
navigating these virtual worlds.
In fact, cue availability was shown to have a much stronger influence on subje
ct
behaviour than did individual differences in related work on this topic (11).
Darken and Sibert (10) also
investigated their subjects’ spatial memory in connection with using a virtual environment, by asking their
subjects to sketch an overall organisat
ion of the virtual environment for trials in which they searched for ships on
the sea. They found that different organisational cues resulted in significant differences in terms of the recall
accuracy of the spatial layout of the sketch and for individual
targets in the environment.

Method

Subjects

Eleven subjects participated the study, including three females and eight males. Nine of the subjects were
enrolled in a M.Sc. in Information Systems course. On the average, these subjects have used computers fo
r three
years or more and have used the WWW for less than 6 months. They had used the Internet more than 4 times a

5

week prior to their involvement in this study. Email and WWW browsing were the most common activities they
described as performing with their

personal computers. We acknowledge that our user population was an
advanced, computer
-
experienced group. Yet, even in this group we were able to observe a wide range of spatial
abilities and navigational strategies during the study. We are anxious to run

more studies with less experienced
users to further generalise the findings reported in this paper.

Visualisation of the Semantic Space

The underlying semantic space of the user interface used in this study consisted of 169 papers published in the
three m
ost recent ACM SIGCHI conference proceedings, namely CHI'95, CHI'96 and CHI'97 (1, 2, 3). Papers
were structured and visualised according to their semantic similarities, such that papers on similar topics tended
to be grouped near to each other. A virtual
link structure was automatically generated according to patterns of
semantic similarities. Further details on underlying models and algorithms can be found in (6, 7).

In this study, the user interface
1

was based on the Netscape Navigator 3.0 browser and i
ts Live3D VRML 1.0
plug
-
in viewer. The screen was split into two frames. The virtual world was displayed in the left
-
hand side
frame. The right
-
hand side frame was used to display the abstract of a paper selected from the virtual world.
Papers were visuali
sed as coloured spheres in a connected network. The initials of authors of each paper labelled
the node in the user interface. If the user moved the mouse cursor onto a sphere, the title of the paper would pop
up next to the sphere. If the user clicked on
the sphere, the abstract would appear in the right
-
hand side frame.





1

The version used in this study is at
http
://www.brunel.ac.uk/~cssrccc2/vrml/acm/spatial/spatialx.html


6


Figure
1
. The user interface of CHI Proceedings.

Users could manipulate the virtual world in a number of ways. For example, they could
walk

towards the
visualis
ation model by moving their mouse cursor forward. The most important design rationale of the virtual
space was to allow users to have greater control over the amount of information displayed in the frame. If they
wanted to have an overview of the entire sp
ace, they could walk backwards until they could see the entire
structure at a glance. If they wanted to examine local details, they could walk up closer to an area so that they
could see labels clearly in that area.

The actual abstracts of these papers we
re stored on a web server at the Brunel University. The experiment was
conducted on a PC with 233MHz CPU and 32Mb RAM, with a 17
-
inch display monitor. All the movements on
the computer screen were videotaped for subsequent examination and analysis.

Procedu
re

This study included pre
-
test and post
-
test phases. In the pre
-
test, spatial ability scores were collected from a
standard paper folding test (13), in which subjects were asked to answer multiple
-
choice questions about the
consequence of punching a hole
in a paper folded in a particular way. This test is widely included in a battery of

7

tests used for determining overall cognitive ability, but is the specific subtest tapping into spatial ability. An
overall spatial ability score on this test ranged from 0

to 20. The average of the spatial ability scores in our study
was 10 with a standard deviation of 3.91.

A short demonstration was given to subjects on how to use the Live3D VRML viewer. Then subjects were asked
to complete two major tasks (named Task 1 a
nd Task 2) and two minor tasks. Ten minutes were allowed for each
major task. Three minutes were allowed for each minor task. After subjects completed these tasks, they were
asked to complete a post
-
test questionnaire concerning usability and user satisfac
tion.

The two major tasks required subjects to find articles related to specific topics. Once they found a relevant paper,
they were instructed to save the abstract of the paper to a local directory on their PC. In Task 1, subjects were
instructed to find

as many papers as they could about a topic, whereas in Task 2, they were told to find only 5
papers on a different topic.

For scoring user performance on Tasks 1 and 2, a relevance judgement was derived for each subject as follows.
First, we generated a l
ist of papers based on a full
-
text search for a task's topic across the entire collection of 169
papers. Then, irrelevant papers were removed from the list and additional relevant papers were added to the list
based on the first author's own judgement. Thi
s process led to three types of relevancy, depending on the strategy
used. For highly relevant papers, one could retrieve the papers directly from an examination of their titles. For
the intermediately relevant papers, one would have to read the papers’ ab
stracts and keywords. For the difficult
determinations, one would need to explore the paper’s content more deeply. For example, if one looks for papers
on "visualisation", it is likely that one will retrieve papers #1 and #2 below easily just from reading
the titles, but
the relevance of paper #3 is less obvious.

1.

Tilebars: visualization of term distribution information in full text information access

2.

Visualizing complex hypermedia networks through multiple hierarchical views

3.

An organic user interface for se
arching citation links

There were 24 relevant papers for Task 1 and 18 for Task 2 in the semantic space of 169 papers.

After Task 1 was completed, subjects were asked to complete a brief spatial memory test. For this memory test,
subjects were asked to sk
etch the shape of the visualised semantic space as best they could from memory. This
test was designed to find out what subjects could remember after having searched through the semantically
designed user interface. Studies have shown that the more informa
tion processing resources applied to study
materials, the better those materials are recalled (8). It was our hope that subjects were engaged in this
information visualisation deeply enough that memory performance for the structure of the space would be h
igh.

8

Details from these sketches should highlight what subjects learned about the structure of the semantic space, and
how deeply the visualised structure that they worked with was encoded into memory.

Next, subjects performed Task 2, followed by a catego
rization and abstraction exercise. For the latter task,
subjects were asked to name the clusters of papers in the visualised semantic space. We intended to use this task
to find out whether subjects could summarise groups of papers associated with distinct
ive structural patterns and
what naming schemes they might use. If meaningful user patterns emerged from this task, these patterns will be
used in future designs based on these materials, with the hope that the added semantic structure (e.g., labels,
land
marks, and signs) will benefit ease of use with the user interface.

Other task performance measures were calculated by means of determining the number of times a subject
selected to read the abstract of a paper, the number of abstracts saved for each task,

and the number of saved
abstracts relevant to the study topics as per their instructions. These scores were calculated for Tasks 1 and 2
only. The entire session lasted approximately 30 minutes.

Results

As stated above, both qualitative and quantitativ
e performance measures were collected during the test session.
Correlations were computed between some measures of task performance and subjects’ spatial ability scores
from the paper folding exercise. We also analyzed the drawings of the memorized struct
ure of the user interface,
and compared that to the parameters of the actual structure, and correlated this with spatial ability. The
videotapes of the search strategies of subjects who had the highest/lowest performance scores were also
examined, in orde
r to identify usability issues and strategies relevant to future user interface designs of this
genre.

Task Performance

The number of abstracts saved by each individual was positively correlated with spatial ability in both Task 1
and Task 2 (r=0.45 and 0.
27, respectively). In addition, recall was positively correlated with spatial ability in
both Task 1 and Task 2 (r= 0.42 and 0.37, respectively). Precision was considerably higher than recall in both
tasks, which is not surprising given that no keyword
-

or

fulltext
-
search facility was provided. The pattern of
relationships between precision and the total number of abstracts viewed and spatial ability was not as
meaningful, and sometimes went in a direction that was counter
-
intuitive.

Task 1

Mean

S.D.

Corr
elation

9

(r
-
value)

with spatial
ability



Recall

0.13

0.09


0.42


Precision

0.64

0.35

-
0.53


Abstracts viewed

15.30

5.95


0.07


Abstracts saved

5.30

4.00


0.45

Task 2





Recall

0.13

0.07


0.37


Precision

0.79

0.32

-
0.18



Abstracts viewed

14.60

11.26

-
0.43


Abstracts saved

4.20

3.71


0.27

Table
1
. Task performance statistics and their correlations with spatial ability.

Navigation Strategies

In order to analyse navigational patterns in further
detail, we superimposed the frequencies of accessing papers
that were judged relevant in Task 1 over the visualised semantic structure (see
Figure
2
). In the figure, relevant
papers are marked as boxes and the number of dots besid
e each box indicates how many different individuals
successfully found that target in Task 1.

Task performance scores suggested that subjects did reasonably well if relevant papers were located in some
structurally significant areas of the user interface.

However, if task
-
relevant papers were located in outskirts of
the structure in the user interface, results demonstrated that subjects were less successful. In addition, subjects
seemed to be affected by the varying visibility of topical keywords (i.e., w
hether a search word appears in the
title, or was hidden in the abstract, or if there was a complete vocabulary mismatch) across the semantic space.
This was a serious issue for users, especially when they were examining a node in a key position, such as a

gateway or a branching point. (We found that subjects, in their first few moves, typically examined these
positions, or hotspots; if a user failed to recognise a relevant paper at a hotspot, they typically abandoned local
exploration in favour of another
area of the network, potentially missing many local targets). We will discuss this
issue in more detail in later sections.



10


Figure
2
. The locations of search targets in Task 1.

To understand how users actually navigated through t
he semantic space, we reviewed the videotapes of subjects
who have the highest and lowest task performance scores. The findings were informative. First of all, regardless
of task performance, the majority of the subjects regarded the central circle structu
re as a natural starting point.
They tended to aim at the central circle as an initial user interface location and zoom into the virtual world in
order to bring this circular area into focus. Outskirts of the central circle tended to be ignored during the
initial
search. Next subjects would check a number of positions on the circle, especially points connecting to branches.
Over time, subjects would gradually expand their search space outwards to reach nodes farther away from the
central area. An example of

a good strategy observed was when one subject sampled a single node in each
cluster and moved on to other clusters quickly during the initial stage. This strategy maximised the likelihood of
not becoming lost in a local minimum.

It is interesting to no
te that sometimes, even when a subject actually hit a target, she would ignore it initially.
However, when she came back to the same target after saving several other targets, she saved the previously

11

ignored or unrecognised target immediately. This raises

the conjecture of subjects’ raising and lowering their
acceptance thresholds as they gain experience with the information space.

Based on our initial observations, visual navigation strategies can be characterised by high
-

and low
-
level
browsing modes.
In a high
-
level browsing mode, the unit of browsing is a group of objects in the semantic map,
and users jump from one cluster of papers to another. In a low
-
level browsing mode, the unit of browsing is
individual nodes, i.e., users move carefully from one

node to another. In the latter case, their browsing paths
were clearly confined by the visualisation structure. Some subjects hopped from one cluster to another in long
jumps, whereas other subjects carefully examined each node along a path according to t
he virtual semantic
structure. Subjects who made longer jumps apparently realised that they might be able to rely on the global
structural cues to help with their navigation. Navigational patterns observed also verified the special role of
distinctive str
uctural patterns such as circles, stars, and long spikes as we expected from earlier research (6).

It appeared that good performers, as measured by recall rates, tended to have a balance between the two modes
(exploiting global and local structural cues),

whereas less efficient performers tended to exhibit local scanning
earlier and stay there longer. Given that recall was correlated with spatial ability in both Task 1 and 2 (r=0.42
and 0.37, respectively), one may conjecture that subjects with good spatia
l ability scores were able to benefit
from the visualisation structure more than subjects with lower spatial ability scores. This echoes the findings
observed by Vicente and Williges (26) in a 2D user interface environment. They found that subjects with lo
wer
spatial ability scores returned to a hierarchical table of contents more frequently than subjects with higher spatial
ability scores, suggesting that there were significant differences between individuals in learning and using the
abstract structure in

information search tasks. We will be analysing the videotapes of our users more thoroughly
to gather detailed data about navigation strategies and report our findings in the near future.

Search Strategies

The videotapes of our users captured a number of i
nteresting search strategies, although we haven't yet examined
all of the subjects’ interactive sessions. Many subjects directed their initial focus towards the central circle in the
visualisation model. We found that each task session started with a pre
-
s
earch stage. In this stage, subjects would
adjust the visualisation model to a comfortable position to start navigation. It turned out to be a common choice
for many subjects to devote all of the screen real estate to the display of the central circle befo
re they started to
examine titles and/or abstracts of papers. Branching points, where two branches were connected, were also found
to be strategically significant in our initial analyses. Subjects often checked the title of a paper at such positions.

12

The v
ideotapes revealed that subjects were able to jump across a considerable distance from these branching
points. This confirms our speculation that distinctive structural patterns do have a special place in guiding visual
navigation.
Figure
3

shows the first few moves in the virtual environment of a particularly effective subject. The
large shaded area denotes where he had subsequently focused his search in this area for a considerably long time
and was able to retrie
ve several targets successfully. Note that this subject achieved the highest task performance
scores for both tasks, but did not have the highest spatial ability score in the paper folding pre
-
test.

People with lower spatial ability scores may develop good

strategies, if they understand how the structure is
organised, but this may take time. Some people only realised that they could benefit from the structure during the
second half of their session. On the other hand, some subjects thought that the idea was

simple enough to
understand straightaway, but exhibited difficulty manipulating the virtual world in the Live3D viewer.
Therefore, more research needs to be carried out looking at the longitudinal benefits of using these kinds of
visualisations in informa
tion retrieval tasks, as well as examining better user interface controls and 3D input
devices.



Figure
3
. One subject's initial moves while searching the semantic space.

Spatial Memory

The spatial memor
y test provided an alternative viewpoint of the interaction between visualised semantic
structures and users’ understanding of that space. By identifying what subjects learned about the structure and

13

how their remembered details vary from one another, we w
ere able to understand more about how to exploit
various characteristics of visual semantic structures to support navigation.

Figure 4 shows the sketches of the semantic space from four different subjects. These sketches show not only
that these subjects h
ave focused on similar features in the semantic space, but also what level of detail subjects
can remember about the user interface. These figures are directly related to the differences between subjects’
navigation strategies and their emerging cognitive
maps.



Figure 4. Subjects' sketches of the semantic information space searched during the study.

Most subjects clearly remembered the shape of the central circle. In (a), the subject highlighted the central circle
and three sub
-
areas around the circle.

The video analysis confirmed that these areas had been intensively visited
during his search. In (b), the subject was able to remember more details about the branches surrounding the
central circle. In addition, he added some strokes inside the circle, a
lthough they were not as accurate as other
structural patterns in his sketch. In (c), the subject had been focused on the central circle and sub
-
structures
within the circle. He vaguely indicated the existence of some branches outside the circle, but accur
ately outlined

14

the shape of the branch inside the circle. In fact, the video shows that his initial search focused on the circle and
the branch inside the circle, before he switched to a local search mode. Another factor may be also related to his
memorise
d cognitive map. At one point, he found a relevant paper, saved it and adjusted the view to search more
carefully in the local area, keeping the inside
-
circle branch in the centre of the screen for about 2 minutes. In (d),
the sketch becomes more conceptua
l. The subject probably had focused on the outskirts of the semantic space, as
it is more accurately depicted than is the central area. It is also interesting to note that nodes differ in size in (d),
and that there is a sense of symmetry, which is general
ly regarded as a desirable feature in graph drawing. The
subjects who sketched (a) and (b) achieved higher recall in task performance, whereas the subjects who sketched
(c) and (d) had higher precision scores. While this provides an brief hint of how subj
ects’ spatial memory may
be influenced by this information visualisation, as well as their individual differences in ability and strategy, we
will continue to analyse these structures for meaningful implications for 3D user interface design.

We are curren
tly examining the sketches across all the subjects in an attempt to identify structural patterns in
these drawings associated with their spatial ability scores. Preliminary analyses have shown that all subjects
remember the main cycle of the structure very

well. Interestingly, spatial ability can be used to predict how
likely a subject is to more closely remember the correct number of major and minor arteries in the structure
(r=.77 and .75, respectively, for major and minor arteries). Clearly, subjects w
ith higher spatial abilities are
building a fairly veridical representation of the space in as short a period as 30 minutes, and these subjects were
able to incorporate that knowledge in their navigation strategies (longer jumps, using global structural cu
es).
One interesting question that awaits future research is whether all subjects’ maps would begin to converge over
repeated exposures and longer use of the information space.

Categorisation and Abstraction

The categorisation and abstraction task was des
igned to help us understand how individuals would refer to
distinctive structural patterns and what features associated with these patterns are likely to be most useful in
design.

Seven subjects were able to give names to structural patterns without reque
sting further details. However, some
subjects found this task very difficult, and could not complete it. Some wanted to check particular spheres again
before they could confidently provide a name for the given structures. One subject named the central cir
cle a
"General Issues" area and another one as "the M25"


a motorway around the Greater London. These names
could make sense as personal landmarks. For example, the shape of the central circle is similar to a ring

15

motorway in a road atlas. One subject nam
ed a cluster as "Virtual Reality"

apparently because he remembered
some virtual reality papers in that area. (Note that virtual reality was not even a task topic.)

Some clusters in the categorisation and abstract tasks contained items that were relevant t
o the targeted areas for
Task 1 and Task 2. For example, one cluster includes a number of papers on information visualisation


a
search topic in Task 1. The following names were given by some of the subjects to this cluster:



22 point bug;



coral;



informat
ion models;



information access;



interface issues;



searching, data, graphic;



information, hypertext, cscw
2
;

The name
22
-
point bug

was obviously based on the fact that there are 22 objects in the cluster. The majority of
the subjects, however, used a content
-
based naming scheme, which is usually more informative about the
semantic nature of a group of papers from the users' point of view. Content
-
based names should also be useful in
designing a search facility and a query formation user interface. It appears
that subjects with higher performance
scores were able to give more informative names based on semantic characteristics, whereas subjects with lower
performance scores relied more on the physical appearance of a cluster.

There are clearly a number of fund
amental questions we must answer in the future research and development.
For example, based on user requirements that we have gathered from various sources, users apparently would
like to see clearly labelled clusters. How do we achieve this? If individual

domain experts name clusters, will
these names be generally meaningful to a variety of user groups? In terms of distinctive labelling, what is the
upper limit on the number of names that can be practically handled manually? If we choose an automated
label
ling approach, should we develop or adapt a domain
-
specific naming algorithm, and what semantic
attributes should be taken into account? These are some of the research questions that we will be investigating in
our future projects.




2

Computer
-
Supported Cooperative Work (CSCW)


16

User Satisfaction

A stan
dard post
-
test questionnaire was used to assess usability issues and user satisfaction. The questionnaire
consists of three blocks of questions and multiple
-
choice statements about overall satisfaction, usability issues
and user interface design. The quest
ionnaire was developed over two years by Microsoft usability engineers, as
part of an effort to understand what defined an “engaging” user interface for the web. The questionnaire has
been well validated. Details of the validation efforts are described i
n (16, 21).

In general, user satisfaction ratings suggested areas of the user interface that worked well, and areas for
improving the software.

The majority of the subjects liked the system, on average (Mean=3.36, S.D. =1.02Subjects were less likely to
re
commend this system to others or state that they would use it on a regular basis (see
Table
2
).


Global Appeal
(all ratings are on a 1
-
5 Likert
scale, with 1=negative and 5=positive).

Mean

S.D.

I liked it.

3.36

1.02

I would rec
ommend this software to others.

2.82

1.54

I would use this software on a regular basis.

2.27

1.56

Table
2
. Global appeal ratings for the user interface.

Eight of the eleven subjects (73%) liked the visualisation idea for organis
ing papers. Nine subjects (82%)
thought the user interface was imaginative, but 36% felt that it was confusing and 19% thought it lacked
predictability. None of the users rated the user interface as boring.


The design was…

Agree (%)

…imaginative

82

…fun

55

…original

36

…confusing

36

…intuitive

36

…not my type of program

18

…predictable

9

…boring

0


17

Table
3
. Design satisfaction ratings for the user interface.

The following four usability scores were slightly below average.

During the post
-
test interview, a number of
possible reasons for these ratings were identified, such as being unfamiliar with manipulating a VRML world,
the incorporation of unlabelled structures and a lack of understanding of clustering models in general
. These
issues will be discussed further in following sections.


Usability

Mean

S.D.

Right when I started, the purpose of the software was clear.

2.82

1.72

It was easy to get where I wanted to go.

2.45

1.44

Right when I started, I knew what I could do.

2.36

1.63

Each area of the software was clearly marked to indicate my location.

2.18

1.60

Table
4
. Usability satisfaction ratings for the user interface.

Online appeal factor ratings were mixed, although many subjects liked the u
nique user interface design
(Mean=4.45, S.D.=0.52). In particular,
simplicity, ability to zoom and walk around topics,
and

navigating in
topical clusters

were among the named favourite features. On the other hand, average ratings were low in the
areas of c
ustomisability, community and familiarity. Obviously these are areas in which the authors will need to
put serious efforts into redesigning the user interface.


Online Appeal

Mean

S.D.

This software feels unique (or different).

4.45

0.52

This software
is mentally challenging.

3.64

0.92

This software has appealing graphics.

3.45

1.13

This software is responsive (not too slow).

3.36

1.50

This software provides valuable information.

3.27

1.74

This software is easy to use.

2.82

1.72

This software uses
cutting edge technology.

2.73

1.62

This software provides a detailed environment to interact with.

2.64

1.63

This software is timely.

2.55

1.63

This software is personalised or customisable.

2.18

1.72

This software provides a shared experience (or comm
unity).

1.91

1.75


18

This software feels familiar.

1.82

1.54

Table
5
. Satisfaction ratings for the online appeal of the user interface.

When asked "Who would use this software?", a number of possible applications were mentioned, in
cluding
researchers who want to have an overview of topics or people who want to use it as a personalised digital library.

Discussion

This study has produced an interesting but complex set of findings and a large amount of data yet to be fully
analysed. Ba
sed on the initial results of our analyses, we identified some significant implications for system
design, usability evaluation and user behavioural modelling. We intend to incorporate these insights into our next
versions of the system. An in
-
depth observ
ation of individuals' navigation strategies should be of interest to the
design and evaluation of other spatial semantic systems in the HCI community.

Future Design Directions: Index Search and Cluster Labels

An important issue that has been studied in pre
vious studies in hypertext information retrieval is how efficiently
one can locate a primary target in hyperspace, and how that influences subsequent browsing (23). In this study,
subjects heavily relied on popping up title information to assess the releva
nce of papers at least at initial stages of
search in the virtual world. Subjects confirmed in post
-
test interviews that it would have been much more
helpful if they could have had some means of quickly narrowing down their search space. One natural solut
ion to
this problem could be to provide index search facilities that could help users locate a highly probable paper with
which to start their navigation through the space.

We are working on a new prototype of combining this notion with the structural visu
alisation approach. Figure 5
is a screen shot of how the hits of a search could be superimposed on the overall semantic structure as an initial
step in this direction. With this improvement, it is hoped that users will be able to choose their starting poi
nt for
navigating more easily. Cluster labelling is another improvement to the user interface that has been requested by
a number of users. We will be conducting more empirical studies on refined versions of the system in the near
future. It will be very i
nteresting to analyse how the user
-
driven search enhancements will affect how individuals
navigate and search through the virtual environment.



19


Figure 5. An initial prototype that superimposes search hits on the overall semantic structure of the user
int
erface.

In this study, several subjects commented on the need for more accurate user interface controls so that the
manipulation of the VRML world would be easier. For example, some users would have liked to have been able
to specify the degree of zooming

accurately instead of having to use the walk control. A few subjects had
problems of losing control of the VRML world while navigating. Once this occurred, these subjects had to reset
the viewpoint to its initial position. An application
-
specific dashboar
d might be useful in these instances. Some
subjects over
-
shot their targets in the virtual world

the virtual world is then behind the viewpoint. From our
observations, it proved difficult for users to get the appropriate viewpoint back if they were new to
using the
Live3D viewer. It was also disconcerting to the users when this happened. Therefore, a prudent guideline might
be to avoid dramatic shifts in the point of view of a virtual world, at least in this type of system, for novice users.
As reported i
n the Results section, we have observed that an understanding of the organisational principles in the
user interface seemed to be reflected in the search strategies subjects used in this study. For instance, one
successful search strategy was to focus on t
he central ring initially, and then sample documents outward from the
ring. In this way, subjects were able to make optimal use of the clustering organisation inherent in the user
interface, and corroborates previous research (e.g., 10, 11). In addition,
the spatial memory test in this study
underlined the need for reinforcing strategically significant points, or structural hotspots, as well as larger
structural patterns in the virtual environment. Strong cues (e.g., landmarks or signs) should be included
in the
design to reinforce users' cognitive map of the virtual space. For example, an animation of how papers were

20

organised would help users to understand the nature of the organisation. This notion awaits future user interface
design work.

Incremental L
earning

A somewhat surprising behaviour was observed in a few subjects' sessions. On several occasions, especially
when subjects encountered a paper that was indeed judged to be relevant according to our list of correct papers,
subjects carried out their s
earch as if they didn't notice the relevance of a paper. However, when they came back
to the same paper, after successfully finding a few other papers, they saved the paper without hesitation. Reasons
behind this phenomenon are still not clear although it
happened during several subjects’ sessions. One possible
explanation is that these papers only seem relevant to the search at hand after fully investigating the space. Other
related papers that subjects found between their first encounter and the second en
counter with these questionable
items might fill in some conceptual gap. This consideration led us to the triangular inequality assumption in
Pathfinder network scaling. If we use this assumption, we can conjecture a model as follows to explain this
behavi
our. To an individual user, the semantic similarity between the task topic and a subtle paper is not clear
initially. Then if she found another paper obviously related to the topic and somehow related to the first paper as
well, she was able to associate t
he task topic with the first paper. Based on this argument, one would expect that
since the explicit links in the visualisation model were derived as a Pathfinder network, see (7) for details of the
modelling, users would be able to identify such implicit
connections more easily. However, this is a complex
issue that is beyond the scope of this study.

Spatial Ability

Correlation between spatial ability and user behaviour was computed for a number of different tasks, as well as
preference data. Although w
e found that recall was positively correlated with spatial ability, as were a number
of other measures, the overall impact of spatial ability was not straightforward. Sometimes the direction of the
correlation was unexpected. A few aspects of the design of

this study could be improved in future research to
help clarify the impact that spatial ability might have on the usability of such information visualisations. For
example, the entire task session was very limited in terms of time, especially for subjects

who had not used the
VRML viewer prior to the test session. The sample size should be increased to minimise variability in the data
resulting from extreme combinations of spatial ability and experience with computers.


21

On the other hand, the spatial memo
ry test and the categorisation task turned out to be very informative. The
videotape coding provided an additional means of understanding users' navigation strategies. We would
recommend usability studies on visualisation
-
based information systems to inclu
de such exercises.

Conclusion

In this study, users searched through a virtual world of semantically organised HCI papers. They knew little
about the underlying computational model from which the user interface was derived prior to their test session.
For
the most part, the participants were naive with regard to manipulating VRML worlds using an ordinary
mouse.

We predicted that people with higher spatial ability would navigate the virtual world better, more efficiently, and
would be more satisfied with th
e 3D user interface, as had been reported in previous studies. The results with
regard to spatial abilities were not as clear for 3D user interface visualisations, and demonstrated that users faced
two major types of problems when navigating 3D user interf
aces of this type:



Cognitive: the number of explicit navigational cues in the virtual world was suboptimal, and will be a ripe
area for future design research. Being unfamiliar with the similarity
-
based organisation model used to
develop the user interfac
e, users needed to take advantage of user interface landmarks and directional cues
to guide their initial search paths. This study observed different search and navigation strategies, from fast
cluster dipping, to paper mining, depending on the spatial abi
lities and computer expertise of subjects. In
addition, users needed to develop an adequate spatial representation of the user interface for better
wayfinding during their search tasks. Having strong cues in the environment will likely hasten the
developm
ent of such representations so that they can be manipulated during navigation tasks.



Motor: the problems with directly manipulating the user interface in Live3D may have accounted for more
performance variability than did subjects’ different spatial abilit
ies.

No strong correlation was found with consistency between spatial ability and task performance measures as
predicted. Increased understanding from examining videotapes, as well as conducting more experimental studies,
should provide us with useful des
ign directions. We intend to recruit a broader range of user types (i.e., less
experienced computer users) in order to generalise our findings to larger segments of the general population, as
well.



22

What have we learned from this study? We now know severa
l typical search strategies that deploy in a virtual
world, which have not been observed in textual or static graphical user interfaces. Some subjects' strategies
demonstrated that leveraging semantic clustering in the user interface is advantageous

these
subjects were able
to retrieve information within a cluster much faster than between clusters. We now know what information
would be good for users to recognise, including landmarks and directional cues. As presented above, our initial
redesigns have alre
ady incorporated the findings from this research, with the goal of increasing the likelihood
that subjects can memorise special structural patterns within an information visualisation, and thereby maximise
their search performance.



Acknowledgements

This

work was partially supported by EPSRC under the Multimedia and Networking Applications programme,
Research Grant Number GB/L61088. Thanks to all the people who participated in the study as subjects. Thanks
to anonymous reviewers for their helpful comments
.


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