EFFICIENT NAVIGATION ON THE WORLD WIDE WEB FOR THE

PHYSICALLY DISABLED

Leo Spalteholz, Kin Fun Li

Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC, Canada

Nigel Livingston

University of Victoria Assistive Technology Team, University of Victoria, Victoria, BC, Canada

Keywords:

Web accessibility, single switch input, web navigation, physical disability.

Abstract:

One of the major obstacles with current web access solutions for those with physical disabilities is the efﬁcient

selection of links and other web page elements. This is especially so for users of single switches. Current

solutions simply build a list of the selectable web page elements and use a linear scan to iterate through them,

selecting the highlighted link when the user activates an input device. We propose a new method based on

incremental searching of the link text to select elements. This approach, paired with well-established switch

typing solutions, allows a single switch user to select any element on a web page by typing very few (most

often only one) letters.

1 INTRODUCTION AND

MOTIVATION

For many people with limited dexterity or severe

physical disabilities, interaction with a computer re-

quires a specialized input device. The choice of which

input device to use is highly dependent on the users’

level of physical control. For example, for those at

the advanced stage of Amyotrophic Lateral Sclerosis

(ALS), eye muscles are often among the last to de-

teriorate, making the use of an eye tracking system

suitable to control the computer mouse pointer. For

other disabilities, such as muscular dystrophy, one or

more hardware switches, activated by any body part

capable of consistent, voluntary movement, may be

used along with specialized software to control the

computer. For the severely disabled, a single switch –

although it is a low bandwidth input – is a widely used

control device due to its simplicity and economy. A

switch may take the form of a physical button, a relay

activated by a puff of air through a tube, or a switch

activated by the electrical signals produced by muscle

cells as in electromyography (Prinz et al., 2006). The

problem of how to produce text with a single input

has been thoroughly researched, with the ﬁrst typing

devices for single switch users being proposed almost

30 years ago (Rowell et al., 1978).

While typing text is still a key component of com-

puter access, efﬁcient access to the information on

the world wide web is becoming central to the use

of computers. Especially for those with mobility im-

pairments, the world wide web represents an excit-

ing opportunity to move beyond the limitations they

may face when interacting with people in the out-

side world. To that end, it is critical that the world

wide web be accessible for those with physical im-

pairments. Although standards for accessible web

pages are an important component of the overall ef-

fort towards universal accessibility, for example the

W3C Web Accessibility Initiative (w3.org, 2006), the

reality is that the majority of web pages are not devel-

oped with accessibility in mind and this statistic is not

improving (Hackett et al., 2004). The current state of

accessibility support on the world wide web requires

tools that can handle any web site, regardless of its

structure or adherence to standards.

From the authors’ experience with users of low

bandwidth input devices as well as with their aides

(University of Victoria Assistive Technology Team,

UVATT.org), it is apparent that although there are

many people that use their devices for computer con-

trol or text input, the web has remained largely inac-

cessible to them. Judging from requests received for

assistance in accessing the web by users with a wide

321

Spalteholz L., Fun Li K. and Livingston N. (2007).

EFFICIENT NAVIGATION ON THE WORLDWIDEWEB FOR THE PHYSICALLY DISABLED.

In Proceedings of the Third International Conference on Web Information Systems and Technologies - Web Interfaces and Applications, pages 321-327

DOI: 10.5220/0001287703210327

 SciTePress

range of disabilities, we can conclude that an effec-

tive web access method would be useful to many. As

there is no lack of either potential users or demand for

a usable web access system, the fact that it is so rarely

seen in practice may be partially due to the inadequate

efﬁciency of currently available solutions. In our ex-

perience testing various accessible web browsing sys-

tems, the large number of links and the complex lay-

out in modern web pages makes navigation unaccept-

ably slow and cumbersome.

To address this issue, we propose a new technique

for selecting web page elements for bandwidth lim-

ited input devices. This method will be a key com-

ponent in a customized browser designed to be used

with alternative, low bandwidth input devices. Sec-

tion 2 discusses some of the previous work in this

area, with particular emphasis on the linear scanning

selection method (Section 2.1) for selecting elements

as employed by many previous approaches. The ma-

jor components of our proposed system are detailed

in subsections of Section 3, including speciﬁcs of the

implementation.

2 BACKGROUND SURVEY

One of the cornerstones of computer use has always

been, and continues to be entering text into the com-

puter. This has prompted a wealth of work on cre-

ating efﬁcient typing interfaces that can be operated

with a single input signal such as that generated by

an alternative input device. A common approach to

this typing interface has remained relatively constant

from its inception, with letters being selected from a

grid by automatic scanning and typed upon activation

of the input device. The most efﬁcient implemen-

tations use a divide and conquer approach by divid-

ing the available characters into groups and narrowing

down the selection on each switch activation. Com-

monly found in commercial switch scanning prod-

ucts (madentec.com, 2006) is the row-column scan-

ning approach where letters are displayed in a two di-

mensional matrix and scanned through ﬁrst by row,

and then, upon switch activation, by column until the

desired letter is selected (Steriadis and Constantinou,

2003).

Conversely, the primary method for navigating on

the world wide web has traditionally been by “point

and click”. This method is not easily adaptable to sin-

gle input devices that are not capable of accurate two

dimensional input. One approach to solving this prob-

lem is to use several on-screen buttons to move the

mouse pointer on the screen. For single switch users,

this is usually done by presenting a button for each

direction of mouse movement (x and y, as well as di-

agonal) and then scanning through the buttons. While

this method is a valuable fallback for applications that

are not accessible via the keyboard, it is not an ef-

ﬁcient interface for continuous use, and requires pre-

cise timing control in switch activations from the user.

The inefﬁciency of these pointer control schemes has

prompted research into other ways to navigate on the

world wide web.

There are two notable attempts at creating a web

browser speciﬁcally accessible to single switch users,

the AVANTI browser (Stephanidis et al., 1997) and

the MultiWeb browser (Owens and Keller, 2000).

Both of these approaches use a linear scanning ap-

proach to link selection, with some differences in how

the link scanning is presented to the user. In addition,

(Mankoff et al., 2002) developed a web browser ac-

cessible to users capable of operating four separate

switches using a similar linear scanning approach,

with focus being advanced by switch activation in-

stead of automatically on a timeout. The linear scan-

ning technique is discussed more thoroughly in Sec-

tion 2.1. Hanson et al. with their accessibilityWorks

project, while focusing more on adapting the appear-

ance of web pages, also consider the issue of con-

trol by devices with zero or one dimensional input

(Hanson et al., 2005). Similar to other work in the

area, they propose to extract the list of links and place

them in an external list such that they can be selected

by a user incapable of two dimensional cursor con-

trol. The Gnome On Screen Keyboard (gok.ca, 2006)

implements a similar link extraction scheme for web

browsers that can expose web page structure to an ac-

cessibility framework (Zhao et al., 2005).

In more mainstream web browsers, two alternate

approaches to linearly iterating through links on a

web page have emerged: incremental search and au-

tomatic access keys. Mozilla Firefox implements a

feature called “ﬁnd as you type”, which incremen-

tally searches a web page and can highlight match-

ing links as one types a search query (mozilla.org,

2006a). If only one link matches a search, it can be

navigated to by pressing the “enter” button on the key-

board. This allows the user to select text and image

links, but does not allow focusing of text entry boxes,

clicking of form buttons, or selecting other form input

ﬁelds. Another approach is automatic access keys, as

implemented in the Konqueror (konqueror.org, 2006)

web browser on the Linux platform. The automatic

access keys approach assigns a unique alphanumeric

character to each selectable element on a web page,

and shows these characters with a tooltip over each

element. Typing an assigned letter will select the cor-

responding element. Currently, the system only as-

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322

signs the 36 alphanumeric characters, meaning that

any web pages with more than 36 elements will not

be accessible.

2.1 Linear Scanning Selection

The most common approach to web page element se-

lection for switch speciﬁc browsers is to construct a

list of selectable elements in the current web page,

and then linearly scan through this list. There are two

general approaches to scanning through selectable el-

ements: in-place and external scanning. In-place

scanning, as used by the MultiWeb browser, as well

as all major mainstream browsers, scans through the

list of selectable elements on the page by highlighting

them within the original web page layout. The ex-

ternal scanning approach works by extracting all the

selectable elements in the page and displaying them

in a list beside the web page. This list is then scanned

through top to bottom, and a link can be navigated

to by activating the switch when the target is high-

lighted.

While the linear scanning approach is a logical

extension of the scanning used in switch typing in-

terfaces, it has some key disadvantages that limit its

efﬁcacy for navigating the web. In-place scanning

has the advantage of lending context to links with

non-descriptive names. Although it is considered bad

practice in the ﬁeld of web development, many hy-

pertext links are given names such as “link” or “click

here” which are only meaningful in the context of the

surrounding text. If these types of links are extracted

from the web page and scanned through in an exter-

nal list, it becomes very difﬁcult to determine which

link is the desired target. Another disadvantage of the

in-place scanning technique is that the scanning order

can be unpredictable. Since the user must quickly ac-

tivate the switch when his/her element is selected, it

is crucial that the scanning order be predictable. Al-

though scanning elements in a top to bottom order

is logical for simple web pages, sites with a compli-

cated layout can make element scanning very difﬁcult

to follow.

The primary disadvantage of both linear scanning

approaches is their lack of scalability to web pages

with many selectable elements. It is very common for

web pages, especially those of news networks, search

engine results pages, or site maps to contain many

tens or even hundreds of links. Linearly scanning

through large numbers of elements to ﬁnd a desired

target is a very tedious process. The external scanning

approach gives more ﬂexibility in grouping the list of

links and selecting them via a divide and conquer ap-

proach to improve performance, but is still difﬁcult to

present to the user in an intuitive way for large num-

bers of links. The error cost of the linear scanning

approach is also high, as a missed target would, in the

best case, involve having to wait for the scan to loop

around, and in the worst case result in a click on an

incorrect link, necessitating multiple steps to return

to the previous page.

3 PROPOSED SYSTEM

OVERVIEW

Our proposed system is designed as an extension to

the open source Mozilla Firefox web browser (Sec-

tion 3.3), adding a more efﬁcient text based naviga-

tion method for low bandwidth input. This system

will facilitate the activation of selectable elements on

a web page, such as hypertext links, text entry boxes,

form buttons, or image maps. After a web page is

loaded, the label builder (Section 3.2) constructs a

textual label for each selectable element on the page.

To select an element, the user employs a text en-

try interface (Section 4) to type the starting letters

of his/her desired element’s label. After each letter,

the selectable elements on the page are searched and

highlighted according to the algorithm described in

Section 3.1. When only a single element matches the

entered query, the user is prompted to activate (nav-

igate to) the selected element. Figure 1 depicts an

overview of the major components of the system.

3.1 Incremental Search Selection

To address the usability issues found in the linear

scanning approach, we propose an alternate approach

to selecting elements on a web page based on text en-

try instead of direct selection. Using this approach,

we can leverage the research done on efﬁcient text en-

try using alternative input devicessuch as eye tracking

systems or single switch devices.

The incremental search selection method is based

upon selecting a web page element by typing a sub-

section of its user-visible label. For hypertext links or

form buttons, the identifying label is simply the text

of the link or button. For text input boxes and other

selectable elements with no meaningful identiﬁer, the

system will generate a unique label to present to the

user. Our approach to automatic label generation is

discussed further in Section 3.2.

When a new page has completed loading, the sys-

tem extracts all selectable elements from the page and

builds a list of labels from them. This list comprises

the search space for the highlighter module. When the

EFFICIENT NAVIGATION ON THE WORLD WIDE WEB FOR THE PHYSICALLY DISABLED

323

Figure 1: System Overview.

link function is selected, the system waits for text in-

put from an external on-screen keyboard application

designed for alternative input devices. To select an el-

ement on the page, the user starts typing the label of

that element. When the ﬁrst letter is typed, the system

performs a preﬁx search of all the elements and visu-

ally highlights any matches. Every subsequent letter

will narrow this search until only one element is high-

lighted. The system will then prompt the user if that

selected element should be activated. In the case of a

hypertext link, an activation entails navigating to the

linked page, while a text box would be focused, and

a button would be pressed. The goal of the highlight-

ing algorithm is to be as intuitive as possible for the

user while allowing ﬁne grained speciﬁcation of the

desired link. Figure 2 details our algorithm used to

highlight elements on the page.

In Figure 2, the step labeled “Widen Search Field”

requires some additional explanation. When the

user initially activates the link selection function, the

search ﬁeld is comprised of the visible selectable el-

ements on the current screen. Thus, if a web page is

longer vertically than the size of the screen, the al-

gorithm will only match elements that are currently

visible to the user. If no elements start with the let-

ter(s) typed by the user, the search ﬁeld expands to en-

compass all the selectable elements on the web page.

If there are no matching elements at this level, the

search criterion is relaxed to consider any substring

Figure 2: Search Selection Highlighting Algorithm.

of all the elements on the current page. In the vast

majority of cases, the user will be attempting to se-

lect an element that is currently visible to them. This

search fallback method maximizes the efﬁciency for

the common case of a user wishing to select a visible

element, while still allowing a user to select an off-

screen target if he/she has existing knowledge of its

label.

The selective case sensitivity is included to de-

crease the average number of necessary letters to

uniquely identify any given element while not impos-

ing additional constraints on the user. When using an

on-screen keyboard, much like with a physical key-

board, producing a capital letter requires pressing an

extra key. Thus, if a user types a capital letter, it is as-

sumed that it is not accidental. Performing a case sen-

sitive search when the user has typed a capital letter

opens up the set of upper case letters to be populated

with labels. For example, if a page contains multiple

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324

links starting with a lowercase ’b’, and the desired el-

ement label starts with a capital ’B’, then the desired

element can be uniquely selected by typing a capital

B, instead of possibly having to type multiple letters

if the system was not case sensitive. Typing a lower

case letter matches both upper and lower case labels

since the system should not reduce efﬁciency in cases

where there is only a single label starting with that

letter (in upper case).

3.2 Element Labeling

There are several factors to consider for the element

label generation algorithm. The primary goal is to

minimize the number of characters necessary to se-

lect any given element on the web page. A secondary

goal is to present link text intuitively and make as few

modiﬁcations to the visual appearance and layout of

the web page as possible. Initially, the system ex-

tracts the text of every link and every button on the

page and constructs a list based on these labels. For

elements without a user-visible label, the system con-

structs a list of the alphanumeric characters that are

not already used as starting characters in the set of el-

ement labels. For each unlabeled element, a label is

created consisting of an unused alphanumeric charac-

ter preﬁxed to the type of the element. For example,

a text edit box might receive the label “bTextbox” or

“4Textbox” while an image link may receive the la-

bel of “tImage”. It should be noted that these kind

of labels are only constructed if no meaningful infor-

mation about the element can be determined which

could be used instead. For example, some form input

controls (check boxes, text entry boxes, radio buttons,

etc.) are referenced by an external “label” HTML tag

which provides a textual description of its purpose,

and image links may have an alternate textual label

speciﬁed.

The tradeoff to consider when constructing labels

for textual links is whether to provide as much cover-

age of the alphanumeric character set as possible ver-

sus leaving the labels as they appear on the page. Ag-

gressive relabeling ensures maximum efﬁciency but

necessitates more layout modiﬁcations and may re-

duce the intuitiveness of the labels for textual links.

For example, if there are 30 selectable elements on

a web page, it is possible to relabel elements that

have the same starting letter(s) as other elements to

maximize selection efﬁciency. This approach is sim-

ilar to automatic access keys, and thus faces similar

problems in that the relabeling of many elements con-

tributes to visual clutter or causes layout changes. In

our implementation, the aggressiveness of the label

builder will most likely be tunable based on the input

characteristics of the user. If a user has a very dif-

ﬁcult time activating their input device, efﬁciency is

of paramount importance, and elements should be re-

labeled for maximum coverage of the alphanumeric

character set. In other cases, minimizing the changes

to the existing labels may be desired to minimize the

impact on the look of the web page.

3.3 Implementation

One of the reasons that previous attempts at custom

browsers for low bandwidth input have been less use-

ful than theorized is that implementations were often

based around custom written HTML rendering en-

gines. Although this approach gives absolute con-

trol over the presentation of web pages, it limits any

implementation’s usefulness for today’s highly com-

plex web pages. Fortunately for future developers

in this area, two mature open source HTML render-

ing engines are now available for use. Both Webkit

(webkit.org, 2006) (the core of Apple’s Safari Web

Browser) and Gecko (mozilla.org, 2006b) (the foun-

dation of the Mozilla Firefox browser) can be em-

bedded into custom applications or extended in any

fashion. We are in the process of implementing our

navigation technique as an extension to the Mozilla

Firefox browser.

One obstacle for users not able to move the mouse

is determining the location of selectable elements on

the page. For regular textual links, identiﬁcation is

not a problem as these links are usually underlined

and colored blue. However, an image link or the links

within an image map may be difﬁcult to locate with-

out having the visual feedback of the mouse cursor

turning to a hand symbol. To overcome this prob-

lem, our implementation will darken any areas of the

page that are not selectable when the link function

is selected. Figure 4 shows an example page with

non-selectable elements darkened. In the regular view

(Figure 3) it is not possible to determine that the im-

age of the stick ﬁgure is actually a link. This tech-

nique gives users a visual cue to discover selectable

elements without introducing complexity to the user

interface or modifying the page layout.

Additionally,in Figure 4 the label overlays are vis-

ible for the image link and the text entry box. These

two elements normally do not show a user visible tex-

tual description, so our system assigns a label based

on the information available about the element. In the

case of the image, the system has extracted the al-

ternate text speciﬁed in the HTML code and turned it

into a label for the element. If no alternate text is spec-

iﬁed, the system would generate a label consisting of

an unused (as the ﬁrst character in another label) al-

EFFICIENT NAVIGATION ON THE WORLD WIDE WEB FOR THE PHYSICALLY DISABLED

325

Figure 3: Example Page Containing Different Selectable El-

ements.

Figure 4: Example Page Showing Selective Darkening and

Label Overlays.

phanumeric character and the type of the element (im-

age, check box, text box, etc.). The search query box,

for example, has a label that was constructed in this

manner.

4 TYPING INTERFACE

The appropriate typing interface is highly dependent

on the speciﬁc input device and performance char-

acteristics of the user. For single switch users, this

may be a row-column scanning keyboard or Morse

code, while for eye or head tracking users this will be

an on-screen virtual keyboard. Some commercially

available alternative input devices are paired with ap-

propriate software for the user to type into any third

party application. While future developments may re-

quire a more integrated typing interface (Section 6),

initially we intend to leverage existing text entry so-

lutions.

5 DISCUSSION AND

CONCLUSIONS

This paper has presented a new approach to navigat-

ing on the web for people not able to easily use a stan-

dard computer mouse or keyboard. Using text input

to search the labels of selectable elements on a given

page and selecting matching elements, users are able

to acquire and activate their desired element in a pre-

dictable and efﬁcient way. Compared to the scanning

selection technique, our approach improveson perfor-

mance for web pages with many selectable elements,

reduces the time cost of incorrect selections, and in-

creases the system’s predictability for the user. It is

our hope that more efﬁcient tools for web access will

make it feasible for users with severe disabilities to

take full advantage of the world wide web.

Although we believe that the incremental search

selection process will be signiﬁcantly more efﬁcient

than a linear scanning approach for most web pages,

there are certain cases where it is not optimal. The

most common case is when the web page contains

only a small number of selectable elements. In this

case, the system should fall back to a linear scanning

approach. The exact number of selectable elements

where a linear scanning approach is more efﬁcient de-

pends on the distribution of starting letters in the se-

lectable elements and the characteristics of the virtual

keyboard (which letters are fastest to type). This num-

ber may be calculated independently for each page

based on these properties.

It remains to be seen whether users are more or

less comfortable with the search based selection pro-

cess versus the scanning based one. Although speci-

fying one’s desired target by typing part of its name

seems intuitive, it is a departure from the direct se-

lection modes the user may be familiar with such as

“point and click” or automatic scanning. After the

implementation phase is complete, this issue will be

investigated further through user trials.

A beneﬁcial side effect of the search selection

method is that it gives the user more control over the

process of navigation. With previous approaches, the

system controlled the pace of the scanning and the

user was merely reacting to events instead of control-

ling them. Although the scanning pace can be ad-

justed, these systems have long scanning processes

that require the user’s complete attention and cannot

be interrupted. Not being in control of the system’s

operation can cause users to feel “pushed” and anx-

ious about using the software.

6 FUTURE WORK

On many web pages, some elements are more fre-

quently used or more important relative to other el-

ements on the page. Important elements may be the

main links in the navigation bar, the email body text

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326

box in a web based email page, or the submit button

for a form. In addition, in most virtual keyboard in-

terfaces some letters are easier and faster to type than

others. For example, the characters closest to the top

left corner are usually the fastest to type in a row-

column scanning keyboard since the scanning starts in

the topmost row and leftmost column. If typing using

Morse code, symbols with shorter dot/dash combina-

tions (e, t, a, i, m, n, etc.) are faster to type. Which

characters are the most efﬁcient depends on the spe-

ciﬁc typing interface being used.

In future work, we intend to examine matching the

most important elements in a web page to the charac-

ters that are easiest to type in a given interface. This

requires an algorithm to order the selectable elements

based on their estimated importance. A measure for

the importance of an element could be determined

based on a combination of metrics such as text size

of a link label, the actual text of a button, the name

of an input ﬁeld, or even a dynamic measure such as

the PageRank (Page et al., 1998) of a link. In addi-

tion, this approach would require tighter integration

between the typing interface and the web browser to

determine the cost of typing each character in the in-

terface.

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