Reading from paper versus screens: a critical review of the empirical literature.
HUSAT Research Institute
University of Technology
This item is not the definitive copy. Please use the following citation when referencing
this material: Dillon, A. (1992) Reading from paper versus screens: a critical review of
the empirical literature. Ergonomics, 35(10), 1297-1326.
The advent of widespread computer use in general and increasing developments in the
domain of hypertext in particular have increased awareness of the issue of reading
electronic text. To date the literature has been dominated by reference to work on
overcoming speed deficits resulting from poor image quality but an emerging literature
reveals a more complex set of variables at work. The present review considers the
differences between the media in terms of outcomes and processes of reading and
concludes that single variable explanations are insufficient to capture the range of issues
involved in reading from screens.
Published in Ergonomics, 35,10 1297-1326
In simple terms, there exist two schools of thought on the subject of electronic texts. The
first holds that paper is far superior and will never be replaced by screens. The argument
is frequently supported by reference either to the type of reading scenarios that would
currently prove difficult if not impossible to support acceptably with electronic text, e.g.,
reading a newspaper on the beach or a magazine in bed, or the unique tactile qualities of
paper. The latter aspect is summed up neatly in Garland’s (1982) comment that electronic
text may have potential uses:
“but a book is a book is a book. A reassuring, feel-the-weight, take-your-own-time kind
of thing...” (cited in Whaller 1987, p. 261).
The second school favours the use of electronic text, citing ease of storage and retrieval,
flexibility of structure and saving of natural resources as major incentives. According to
this perspective, electronic text will soon replace paper and in a short time (usually ten
years hence) we shall all be reading from screens as a matter of habit. In the words of its
greatest proponent, Ted Nelson (1987):
“the question is not can we do everything on screens, but when will we, how will we and
how can we make it great? This is an article of faith - its simple obviousness defies
Such extremist positions show no signs of abating though it is becoming clear to many
researchers in the domain that neither is particularly satisfactory. Reading from screens is
different from paper and there are many scenarios such as those cited that current
technology would not support well, if at all. However, technology is developing and
electronic text of the future is unlikely to be handicapped by limitations in screen image
and portability that currently seem major obstacles. As Licklider pointed out when
considering the application of computers in libraries as early as 1965:
"our thinking and our planning need not be, and indeed should not be, limited by literal
interpretation of the existing technology” (p.19).
Even so, paper is an information carrier par excellence and possesses an intimacy of
interaction that can never be obtained in a medium that by definition imposes a microchip
interface between the reader and the text. Furthermore, the millions of books that exist
now will not all find their way into electronic form, thus ensuring the existence of paper
documentation for many years yet.
The aim of the present review is not to resolve the issue of whether one or other medium
will dominate but to examine critically the reported differences between them in terms of
use and thereby support reasoned analysis of the paper versus electronic text debate from
the perspective of the reader. In so doing it should highlight the crucial issues underlying
the usability of a medium.
2 The outline of the review
The review will describe the reported differences between the media before examining
the attempts at explaining and overcoming them. At the outset it must be stated that
drawing any firm conclusions from the literature is difficult. Helander et al (1984)
evaluated 82 studies concerning human factors research on VDUs and concluded:
"Lack of scientific rigour has reduced the value of many of these studies. Especially
frequent were flaws in experimental design and subject selection, both of which threaten
the validity of results. In addition, the choice of experimental settings and dependent and
independent variables often made it difficult to generalize the results beyond the
conditions of the particular study." (p. 55.)
Waern and Rollenhagen (1983) point to the frequently narrow scope of experimental
designs in such studies. Important factors are either not properly controlled or are simply
not reported and most studies use unique procedures and equipment, rendering direct
comparison meaningless. The present review is not intended to untangle the
methodological knots of other researchers but rather to make sense of the major findings
in a general way and indicate where the research needs lie.
A detailed literature already exists on typographical issues related to text presentation on
paper (see particularly the work of Tinker) and issues such as line spacing and formatting
are well researched. This work will not be reviewed here as much of it remains
unreplicated on VDUs and evidence suggests that, even when such factors are held
constant, reading differences between the two presentation media remain (see for
example Creed et al, 1987).
In the first instance this review examines the nature of the possible differences between
the media and draws a distinction here between outcome (section 4) and process (section
5) differences. Following this, a brief overview of the type of research that has been
carried out is presented (section 6). This describes the range of issues that have been
covered and presents the intended scope of the subsequent review. Experimental
comparisons of reading from paper and screen are then reviewed; these are grouped
according to the variables they manipulated (sections 7 and 8). A final section highlights
the shortcomings of much of this work and indicates the way forward for research in this
3 Observed differences: outcome versus process measures
Analysing reading is not a simple task and a distinction has been drawn between
assessing reading behaviour in terms of outcome and process measures (Schumacher and
Waller 1985). Outcome measures concentrate on what the reader gets from the text and
considers such variables as amount of information retrieved, accuracy of recall, time
taken to read the text and so forth. Process measures are more concerned with how the
reader uses a text and include such variables as where the reader looks in the text and
how s/he manipulates it.
In the domain of electronic text outcome measures take on a particular relevance as
advocates proclaim increased efficiency and improved performance (i.e., outcomes) with
computer presented material (aspects of direct concern to ergonomists). It is not
surprising therefore to find that the majority of work comparing the two media has
concentrated heavily on such differences. With the emergence of hypertext however,
navigation has become a major issue and process measures are gaining increased
recognition of importance.
In the following sections a summary of the observed differences between the media in
terms of outcomes and processes is presented.
4 Outcome Measures
By far the most common experimental finding is that silent reading from screen is
significantly slower than reading from paper ( Kak,1981; Muter et al, 1982; Wright and
Lickorish,1983; Gould and Grischkowsky, 1984; Smedshammar et al 1989). Figures vary
according to means of calculation and experimental design but the evidence suggests a
performance deficit of between 20% and 30% when reading from screen.
However, despite the apparent similarity of findings, it is not clear whether the same
mechanisms have been responsible for the slower speed in these experiments, given the
great disparity in procedures. For example, in the study by Muter et al (1982), subjects
read white text on a blue background, with the subject being approximately 5 m from the
screen. The characters, displayed in teletext format on a television, were approximately 1
cm high, and time to fill the screen was approximately 9 seconds. Even ignoring the
unnatural character size and distance from the screen, the authors reported that the
experimental room was “well illuminated by an overhead light source”, a factor which by
virtue of the possible reflections caused could account for a slow reading speed.
Additionally, unless the book used was one of the large format books prepared for the
partially sighted, we must assume that the screen text characters were substantially larger
than the printed characters.
In comparison, Gould and Grischkowsky (1984) used greenish text on a dark
background. Characters were 3 mm high and subjects could sit at any distance from the
screen. They were encouraged to adjust the room lighting level and the luminance and
contrast of the screen for their comfort. Printed text used 4 mm characters and was laid
out identically to the screen text. Wright and Lickorish (1983) give no details of text size
other than that it was displayed as white characters on a black 12" screen driven by an
Apple ][ microcomputer with lower case facility. This would suggest that it was closer to
Gould's text than Muter's text in appearance. Printed texts were photocopies of printouts
of the screen displays produced on an Epson MX-80 dot matrix printer, compared with
Gould's 10-point monospace Letter Gothic font.
In contrast to these studies, Switchenko (1984), Askwall (1985) and Cushman (1986)
found that reading speed was unaffected by the presentation medium. Askwall attributes
this difference in findings to the fact that her texts were comparatively short (22
sentences), and the general lack of experimental detail makes alternative interpretations
difficult. Although it is reported that a screen size of 24 rows by 40 columns was used,
with letter size approximately 0.5 x 0.5 cm and viewing distance of approximately 30-50
cm, no details of screen colour or image polarity and none of the physical attributes of the
printed text are given.
Cushman's primary interest was in fatigue but he also measured reading speed and
comprehension using 80-minute reading sessions. Negative and positive image VDU and
microfiche presentations were used and most of the 76 subjects are described as having
had “some previous experience using microfilm readers and VDUs.” On the basis of this
study Cushman concluded that there was no evidence of a performance deficit for the
VDU presentations compared with printed paper.
As this indicates, the evidence surrounding the argument for a speed deficit in reading
from VDUs is less than conclusive. A number of intervening variables, such as the size,
type and quality of the VDU may have contaminated the results. As will be consistently
demonstrated, this criticism applies repeatedly to most of the evidence on reading from
VDUs. However, despite the methodological weaknesses of many of the investigations,
evidence continues to mount supporting the case for a general speed decrement. As
Gould et al (1987a) noted, many of these experiments are open to interpretation but :
“the evidence on balance...indicates that the basic finding is robust-- people do read more
slowly from CRT displays” (p. 269)
Accuracy of reading could refer to any number of everyday activities such as locating
information in a text, recalling the content of certain sections and so forth. In
experimental investigations of reading from screens the term accuracy has several
meanings too though it most commonly refers to an individual's ability to identify errors
in a proofreading exercise. While a number of studies have been carried out which failed
to report accuracy differences between VDUs and paper (e.g., Wright and
Lickorish,1983; Gould and Grischkowsky,1984) recent well controlled experiments by
Creed et al (1987) and Wilkinson and Robinshaw (1987) report significantly poorer
accuracy for such proofreading tasks on screens.
Since evidence for the effects of presentation media on such accuracy measures often
emerges from the same investigations which looked at the speed question, the criticisms
of procedure and methodology outlined above apply equally here. The measures of
accuracy employed also vary. Gould and Grischkowsky (1984) required subjects to
identify misspellings of four types: letter omissions, substitutions, transpositions and
additions, randomly inserted at a rate of one per 150 words. Wilkinson and Robinshaw
(1987) argue that such a task hardly equates to true proofreading but is merely
identification of spelling mistakes. In their study they tried to avoid spelling or contextual
mistakes and used errors of five types : missing or additional spaces, missing or
additional letters, double or triple reversions, misfits or inappropriate characters, and
missing or inappropriate capitals. It is not always clear why some of these error types are
not spelling or contextual mistakes but Wilkinson and Robinshaw suggest their approach
is more relevant to the task demands of proofreading than Gould and Grischkowsky's.
However Creed et al (1987) distinguished between visually similar errors (e.g., "e"
replaced by "c"), visually dissimilar errors (e.g., "e" replaced by "w") and syntactic errors
(e.g., "gave" replaced by "given"). They argue that visually similar and dissimilar errors
require visual discrimination for identification while syntactic errors rely on knowledge
of the grammatical correctness of the passage for detection and are therefore more
cognitively demanding. This error classification was developed in response to what they
saw as the shortcomings of the more typical accuracy measures which provide only gross
information concerning the factors affecting accurate performance. Their findings
indicate that visually dissimilar errors are significantly easier to locate than either visually
similar or syntactic errors.
In a widely reported study Egan et al (1989) compared students’ performance on a set of
tasks involving a statistics text presented on paper or screen. Students used either the
standard textbook or a hypertext version run on SuperBook, a structured browsing
system, to search for specific information in the text and write essays with the text open.
Incidental learning and subjective ratings were also assessed. The search tasks provide an
alternative to, and more realistic measure of reading accuracy than identifying spelling
The authors report that subjects using the hypertext performed significantly more
accurately than those using the paper text. However a closer look at the experiment is
revealing. With respect to the search tasks, the questions posed were varied so that their
wording mentioned terms contained in the body of the text, in the headings, in both of
these or neither. Not surprisingly the largest advantage to electronic text was observed
where the target information was only mentioned in the body of text (i.e. there were no
headings referring to it). Here it is hardly surprising that the search facility of the
computer outperformed humans. When the task was less biased against the paper
condition e.g., searching for information to which there are headings, no significant
difference was observed. Interestingly the poorest performance of all was for SuperBook
users searching for information when the question did not contain specific references to
words used anywhere in the text. In the absence of suitable search parameters or look-up
terms hypertext suddenly seemed less usable.
McKnight et al (1990) compared reading in two versions of hypertext, a word processor
file and a paper copy of a document on winemaking. The measure of accuracy taken was
the number of answers correctly made to a set of questions seeking information to be
found in the document. Interestingly they report no significant difference between paper
and word processor file, but readers in both hypertext conditions were significantly less
accurate than readers of the paper document.
Regardless of the interpretation that is put on the results of any one of these studies, the
fact remains that investigations of reading accuracy from VDU and paper take a variety
of measures as indices of performance. Therefore two studies, both purporting to
investigate reading accuracy may not necessarily measure the same events. In summary it
would seem that for routine spelling checks reading from VDUs is not less accurate than
reading from paper. However, a performance deficit does seem to occur for more visually
or cognitively demanding tasks. Altering the structure of the document as in hypertext
applications introduces another level of complexity to the discussion that requires much
The proliferation of information technology has traditionally brought with it fears of
harmful or negative side-effects for users who spend a lot of time in front of a VDU (see
for example Pearce, 1984). In the area of screen reading this has manifested itself in
speculation of increased visual fatigue and/or eyestrain when reading from screens as
opposed to paper.
In the Muter et al (1982) study subjects were requested to complete a rating scale on a
number of measures of discomfort including fatigue and eyestrain both before and after
exposure to the task. There were no significant differences reported on any of these scales
either as a result of condition or time. Similarly Gould and Grischkowsky (1984)
obtained responses to a 16-item "Feelings Questionnaire" after each of six 45-minute
work periods. This questionnaire required subjects to rate their fatigue, levels of tension,
mental stress and so forth. Furthermore various visual measurements such as flicker and
contrast sensitivity, visual acuity and phoria, were taken at the beginning of the day and
after each work period. Neither questionnaire responses nor visual measures showed a
significant effect for presentation medium. These results led the authors to conclude that
good-quality VDUs in themselves do not produce fatiguing effects, citing Starr et al
(1982) and Sauter et al (1983) as supporting evidence.
In a more specific investigation of fatigue Cushman (1986) investigated reading from
microfiche as well as paper and VDUs with positive and negative image. He
distinguished between visual and general fatigue, assessing the former with the Visual
Fatigue Graphic Rating Scale (VFGRS) which subjects use to rate their ocular
discomfort, and the latter with the Feeling-Tone Checklist (FTC, Pearson and Byars,
1956). With respect to the VDU conditions, the VFGRS was administered before the
session and after 15, 30, 45 and 60 minutes as well as at the end of the trial at 80 minutes.
The FTC was completed before and after the session. The results indicated that reading
from positive presentation VDUs (dark characters on light background) was more
fatiguing than paper and leads to greater ocular discomfort than reading from negative
Cushman explained the apparent conflict of these results with the established literature in
terms of the refresh rate of the VDUs employed (60 Hz) which may not have been
enough to completely eliminate flicker in the case of positive presentation, a suspected
cause of visual fatigue. Wilkinson and Robinshaw (1987) also reported significantly
higher fatigue for VDU reading and while their equipment may also have influenced the
finding they dismiss this as a reasonable explanation on the grounds that no subject
reported lack of clarity or flicker and their monitor was typical of the type of VDU that
users find themselves reading from. They suggest that Gould and Grischkowsky's (1984)
equipment was "too good to show any disadvantage" and that their method of measuring
fatigue was artificial. By gathering information after a task and across a working day
Gould and Grischkowsky missed the effects of fatigue within a task session and allowed
time of day effects to contaminate the results. Wilkinson and Robinshaw liken the
proofreading task used in these studies to vigilance performance and argued that fatigue
is more likely to occur within the single work period where there are no rest pauses
allowing recovery. Their results showed a performance decrement across the 50-minute
task employed, leading them to conclude that reading from typical VDUs at least for
periods longer than 10-minutes is likely to lead to greater fatigue.
It is not clear how comparable conclusions drawn from measures of fatigue such as
subjective ratings of ocular discomfort are with inferences drawn from performance rates.
It would seem safe to conclude that users do not find reading from VDUs intrinsically
fatiguing but that performance levels may be more difficult to sustain over time when
reading from average quality screens. As screen standards increase over time this
problem should be minimised.
Perhaps more important than the questions of speed and accuracy of reading is the effect
of presentation medium on comprehension. Should any causal relationship ever be
identified between reading from VDU and reduced comprehension, the impact of this
technology would be severely limited. The issue of comprehension has not been as fully
researched as one might expect, perhaps in no small way due to the difficulty of devising
a suitable means of quantification i.e., how does one measure a reader’s comprehension?
Post-task questions about content of the reading material are perhaps the simplest method
of assessment, although care must be taken to ensure that the questions do not simply
demand recall skills. Muter et al (1982) required subjects to answer 25 multiple-choice
questions after two 1 hour reading sessions. Due to variations in the amount of material
read by all subjects, analysis was reduced to responses to the first eight questions of each
set. No effect on comprehension was found either for condition or question set. Kak
(1981) presented subjects with a standardised reading test (the Nelson-Denny test) on
paper and VDU. Comprehension questions were answered by hand. No significant effect
for presentation medium was observed. A similar result was found by Cushman (1986) in
his comparison of paper, microfiche and VDUs. Interestingly however, he noted a
negative correlation between reading speed and comprehension, i.e., comprehension
tended to be higher for slower readers.
Belmore (1985) asked subjects to read short passages from screen and paper and
measured reading time and comprehension. An initial examination of the results appeared
to show a considerable disadvantage, in terms of both comprehension and speed, for
screen presented text. However, further analysis showed that the effect was only found
when subjects experienced the screen condition first. Belmore suggested that the
performance decrement was due to the subjects' lack of familiarity with computers and
reading from screens - a factor commonly found in this type of study. Very few of the
studies reported here attempted to use a sample of regular computer users.
Gould et al (1987a) compared subjects reading for comprehension with proofreading for
both media in order to check that typical proofreading tasks did not intrinsically favour a
medium that supported better character discrimination. Though only concerned with
reading speed (i.e., they took no comprehension measures) they found that
comprehension actually exacerbated the differences between paper and screen.
The Egan et al study (1989) described earlier required subjects to write essay type
answers to open book questions using paper or hypertext versions of a statistics book.
Experts rated the essays and it was observed that users of the hypertext version scored
significantly higher marks than users of the paper book. Thus, the authors conclude, the
potential of restructuring the text with current technology can significantly improve
comprehension for certain tasks.
The most recently published study covering this issue is by Muter and Maurutto (1991)
who asked readers to answer questions about a short story read either on paper or screen
immediately after finishing the reading task. They reported no significant comprehension
difference between readers using either medium.
It seems therefore that comprehension of material is not negatively affected by
presentation medium and under some circumstances may even be improved. However, a
strong qualification of this interpretation of the experimental findings is that suitable
comprehension measures for reading material are difficult to devise. The expert rating
used by Egan et al is ecologically valid in that it conforms to the type of assessment
usually employed in schools and colleges but the sensitivity of post-task question and
answer sessions to subtle cognitive differences caused by presentation medium is
debatable. Without evidence to the contrary though, it would seem as if reading from
VDUs does not negatively affect comprehension rates though it may affect the speed with
which readers can attain a given level of comprehension.
Part of the folklore of human factors research is that naive users tend to dislike using
computers and much research aims at encouraging user acceptance of systems through
more usable interface design. Given that much of the evidence cited here is based on
studies of relatively novice users it is possible that the results are contaminated by
subjects' negative predispositions towards reading from screen. On the basis of a study of
800 VDU operators' comparisons of the relative qualities of paper and screen based text,
Cakir et al (1980) report that high quality typewritten hardcopy is generally judged to be
superior. Preference ratings were also recorded in the Muter et al (1982) study and
despite the rather artificial screen reading situation tested, users only expressed a mild
preference for reading from a book. They expressed the main advantage of book reading
to be the ability to turn back pages and re-read previously read material, mistakenly
assuming that the screen condition prevented this.
Starr (1984) concluded that relative subjective evaluations of VDUs and paper are highly
dependent on the quality of the paper document, though one may add that the quality of
the VDU display probably has something to do with it too. Egan et al (1989) found a
preference for hypertext over paper amongst subjects in their study of a statistics text
where the electronic copy was displayed on a very high quality screen. Recent evidence
from Muter and Mauretto (1991) revealed that approximately 50% of subjects in their
comparative studies of reading from paper and current screens expressed a preference for
screen, lending some support to the argument that preferences are shifting as screen
What seems to have been overlooked as far as formal investigation is concerned is the
natural flexibility of books and paper over VDUs, e.g., paper documents are portable,
cheap, apparently "natural" in our culture, personal and easy to use. The extent to which
such "common-sense" variables influence user performance and preferences is not yet
Empirical investigations of the area have suggested five possible outcome differences
between reading from screens and paper. As a result of the variety of methodologies,
procedures and stimulus materials employed in these studies, definitive conclusions
cannot be drawn. It seems certain that reading speeds are reduced on typical VDUs and
accuracy may be lessened for cognitively demanding tasks. Fears of increased visual
fatigue and reduced levels of comprehension as a result of reading from VDUs would
however seem unfounded though the validity of separating accuracy and comprehension
into two discrete outcomes is debatable. With respect to reader preference, top quality
hardcopy seems to be preferred to screen displays, which is not altogether surprising.
5 Process Measures
Without doubt, the main obstacle to obtaining accurate process data is devising a suitable,
non-intrusive observation method. While techniques for measuring eye-movements
during reading now exist, it is not at all clear from eye-movement records what the reader
was thinking or trying to do at any time. Furthermore, use of such equipment is rarely
non-intrusive, often requiring the reader to remain immobile through the use of head
restraints, bite bars etc., or read the text one line at a time from a computer display —
hardly equatable to normal reading conditions!
Less intrusive methods such as the use of light pens in darkened environments to
highlight the portion of the text currently viewed (Whalley and Fleming 1975) or
modified reading stands with semisilvered glass which reflect the readers’ eye
movements in terms of current text position to a video camera (Pugh 1979) are examples
of the lengths researchers have gone to in order to record the reading process. However,
none of these are ideal as they alter the reading environment, sometimes drastically, and
only the staunchest advocate would describe them as non-intrusive.
Verbal protocols of people interacting with texts require no elaborate equipment and can
be elicited wherever a subject normally reads. In this way they are cheap, relatively
naturalistic and physically non-intrusive. However, the techniques have been criticised
for interfering with the normal processing involved in task performance and requiring the
presence of an experimenter to sustain and record the verbal protocol (Nisbett and Wilson
Although a perfect method does not yet exist it is important to understand the relative
merits of those that are available. Eye-movement records have significantly aided
theoretical developments in modeling reading (see e.g., Just and Carpenter 1980) while
use of the light-pen-type techniques have demonstrated their worth in identifying the
effects of various typographic cues on reading behaviour (see e.g., Waller 1984). Verbal
protocols have been effectively used by researchers to gain information on reading
strategies (see e.g., Olshavsky 1977).
Nevertheless, such techniques have rarely been employed with the intention of assessing
the process differences between reading from paper and from screen. Where paper and
hypertext are directly compared, although process measures may be taken with the
computer and or video cameras, the final comparison often rests on outcome measures
(e.g., McKnight et al 1990).
Despite this, it is widely accepted that the reading process with screens is different than
that with paper regardless of any outcome differences. The following sections outline
three of the most commonly cited process differences between the media. In contrast to
the outcome differences it will be noted that, for the reasons outlined above, these
differences are less clearly empirically demonstrated.
5.1 Eye movements
Mills and Weldon (1986) argue that measures of eye movements reflect difficulty,
discriminability and comprehensibility of text and can therefore be used as a method of
assessing the cognitive effort involved in reading text from paper or screen. Indeed
Tinker (1958) reports on how certain text characteristics affect eye movements and
Kolers et al (1981) employed measures of eye movement to investigate the effect of text
density on ocular work and reading efficiency. Obviously if reading from screen is
different than paper then noticeable effects in eye movement patterns might be found
indicating possible causes and means of improvement.
Eye movements during reading are characterised by a series of jumps and fixations. The
latter are of approximately 250 msec. duration and it is during these that word perception
occurs. The 'visual reading field' is the term used to describe that portion of foveal and
parafoveal vision from which visual information can be extracted during a fixation and in
the context of reading this can be expressed in terms of the number of characters
available during a fixation. The visual reading field is subject to interference from text on
adjacent lines, the effect of which seems to be a reduction in the number of characters
available in any given fixation and hence a reduction in reading speed.
Gould et al (1987a) report an investigation of eye movement patterns when reading from
either medium. Using a photoelectric eye movement monitoring system, subjects were
required to read two 10-page articles, one on paper, the other on screen. Eye movements
typically consisted of a series of fixations on a line, with re-fixations and skipped lines
being rare. Movement patterns were classified into four types: fixations, undershoots,
regressions and re-fixations. Analysis revealed that when reading from VDU subjects
made significantly more (15%) forward fixations per line. However this 15% difference
translated into only 1 fixation per line. Generally, eye movement patterns were similar
and no difference in duration was observed. Gould explained the 15% fixation difference
in terms of image quality variables. Interestingly he reports that there was no evidence
that subjects lost their place,"turned-off" or re-fixated more when reading from VDUs.
It seems therefore that gross differences in eye movements do not occur between screen
and paper reading. However, given the known effect of typographic cueing on eye
movements with paper and the oft-stated non-transferability of paper design guidelines to
screens, it is possible that hypertext formats might influence the reading process at this
level in a manner worth investigation.
Perhaps the most obvious difference between reading from paper and from screens is the
ease with which paper can be manipulated and the corresponding difficulty of so doing
with electronic text. Yet manipulation is an intrinsic part of the reading process for most
tasks. Manipulating paper is achieved by manual dexterity, using fingers to turn pages,
keeping one finger in a section as a location aid, or flicking through tens of pages while
browsing the contents of a document, activities difficult or impossible to support
electronically (Kerr 1986).
Such skills are acquired early in a reader's life and the standard physical format of most
documents means these skills are transferable between all document types. With
electronic text this does not hold. Lack of standards means that there is a bewildering
range of interfaces to computer systems and mastery of manipulation in one application is
no guarantee of an ability to use another. Progressing through the electronic document
might involve using a mouse and scroll bar in one application and function keys in
another; one might require menu selection and “page” numbers while another supports
touch-sensitive “buttons”. With hypertext, manipulation of large electronic texts can be
rapid and simple while other systems might take several seconds to refresh the screen
after the execution of a “next page” command.
Such differences will almost certainly affect reading. Waller (1986) suggests that as
readers need to articulate their needs in manipulating electronic texts (i.e., formulate an
input to the computer to move the text rather than directly and automatically performing
the action themselves) a distraction of cognitive resources required for comprehension
could occur. Richardson et al., (1988) report that subjects find text manipulation on
screen awkward compared to paper, stating that the replacement of direct manual
interaction with an input device deprived users of much feedback and control.
It is obvious that manipulation differences exist and that electronic text is usually seen as
the less manipulable medium. Current hypertext applications however, support rapid
movement between various sections of text which suggests that innovative manipulations
might emerge that, once familiar with them, convey advantages to the reader of electronic
texts. This is an area for further work.
When reading a lengthy document the reader will need to find their way through the
information in a manner that has been likened to navigating a physical environment
(Dillon et al 1990a). There is a striking consensus among many researchers in the field
that this process is the single greatest difficulty for readers of electronic text. This is
particularly (but not uniquely) the case with hypertext where frequent reference is made
to “getting lost in hyperspace” (e.g., Conklin 1987, McAleese 1989) which is described,
in the oft-quoted line of Elm and Woods (1985), as:
“the user not having a clear conception of the relationships within the system or knowing
his present location in the system relative to the display structure and finding it difficult
to decide where to look next within the system” (p.927).
With paper documents there tends to be at least some standards in terms of organisation.
With books for example, contents pages are usually at the front, indices at the back and
both offer some information on where items are located in the body of the text. Concepts
of relative position in the text such as ‘before’ and ‘after’ have tangible physical
correlates. No such correlation holds with hypertext and such concepts are greatly
diminished in standard electronic text.
There is some direct empirical evidence in the literature to support the view that
navigation can be a problem. Edwards and Hardman (1989) for example, describe a study
which required subjects to search through a specially designed hypertext. In total, half the
subjects reported feeling lost at some stage (this proportion is inferred from the data
reported). Such feelings were mainly due to “not knowing where to go next” or “not
knowing where they were in relation to the overall structure of the document” rather than
“knowing where to go but not knowing how to get there” (descriptors provided by the
authors). Unfortunately, without direct comparison of ratings from subjects reading a
paper equivalent we cannot be sure such proportions are solely due to using hypertext.
McKnight et al (1990) compared navigation for paper, word processor and two hypertext
documents by examining the number of times readers went to index and contents
pages/sections, inferring that time spent here gave an indication of navigation problems.
They reported significant differences between paper and both hypertext conditions (the
latter proving worse), with word processor users spending about twice as long as paper
readers in these sections (a statistically non-significant difference however).
Indirect evidence comes from the numerous studies which have indicated that users have
difficulties with a hypertext (Monk et al 1988, Gordon et al 1988). Hammond and
Allinson (1989) speak for many when they say:
“Experience with using hypertext systems has revealed a number of problems for
users..... First, users get lost... Second, users may find it difficult to gain an overview of
the material... Third, even if users know specific information is present they may have
difficulty finding it” p294.
There are a few dissenting voices.Brown (1988) argues that:
“although getting lost is often claimed to be a great problem, the evidence is largely
circumstantial and conflicting. In some smallish applications it is not a major problem at
all” (p. 2) .
This quote is telling in several ways. The evidence for navigational difficulties is often
circumstantial, as noted above. The applications in which Brown claims it is not a
problem at all, are, to use his word, “smallish” and this raises a crucial issue with respect
to electronic text research that is taken up later, how much faith can we place in evidence
from studies involving very short texts. However, the evidence that we currently possess
seems to indicate that navigation is a reading process issue worthy of further
The reading process is affected by the medium of presentation though it is extremely
difficult to quantify and demonstrate such differences empirically. The major differences
appear to occur in manipulation which seems more awkward with electronic texts and
navigation which seems to be more difficult with electronic and particularly hypertexts.
Eye movement patterns do not seem to be significantly altered by presentation medium.
Further process issues may emerge as our knowledge and conceptualisation of the
reading process improves.
6 Explaining the differences: A classification of issues
While the precise nature and extent of the differences between reading from either
medium have not been completely defined, attempts to identify possible causes of any
difference have frequently been made. A significant literature exists on issues dealing
with display characteristics such as line length and spacing. It is not the aim of this
review to detail this literature fully except where it relates to possible causes for reading
differences between paper and screen. Experimental investigations which have controlled
such variables have still found performance deficits on VDUs, thus suggesting that the
root cause of observed differences lies elsewhere. For a comprehensive review of these
issues see Mills and Weldon (1985).
Examining the last 15 years of Human Factors research in this area it is possible to
distinguish three types of investigation. Dillon (1990) for example, has loosely
categorised these as levels, depending on their concern with: broad or narrow issues (e.g.,
cognition or perception); size of text (e.g., one page or multi-page document) and
specificity of prediction that can be made from this work (e.g., the nature of the
difference between media or the likely existence of a difference).
Initial (or first level) work concentrated on what could be termed basic ergonomics such
as screen angle, image polarity and so forth. This work continues to some extent today.
Concerned with perceptual or physical rather than mainly cognitive issues, this work has
been carried out mainly on proofreading short texts and has produced detailed results on
the likely performance deficits for certain screen types. As technology developed and
user interfaces afforded more sophisticated interaction with electronic texts, second level
issues to do with document manipulation, such as scrolling versus paging, came to the
fore. These involved work with larger texts and more cognitively demanding tasks than
proofreading. This is still an area of concern for many researchers. The third level in this
scheme has resulted from the explosion of hypertext systems and concerns issues such as
navigation and information models grouped under the heading information structuring.
In a very real sense all these areas are inter-related. Hypertext, by necessity involves
reading from screens and manipulating electronic text and therefore research at the basic
ergonomic level has relevance to the information structuring work, if only as a reminder
of necessary but insufficient preconditions to effective reading reading from screens.
Given the major concern of this review is with empirical literature, a form mainly lacking
in much of the hypertext area, the following sections cover only the issues of basic and
visual ergonomics as well as those of document manipulation. The issues concerned with
information structuring are sufficiently detailed to warrant a paper of their own which
would be different in granularity from the present one by virtue of poor level of
empiricism involved. However a paper dealing with those issues and relating them to the
present areas is currently in preparation by the present author. Readers concerned
primarily with navigation in electronic documents are referred to Dillon et al. (1990a)
7 Basic Ergonomic Issues
An electronic text is physically different from a paper one. Consequently, many
researchers have examined these aspects of the medium in an attempt to explain the
performance differences. An exhaustive programme of work conducted by Gould and his
colleagues at IBM between 1982 and 1987 represents probably the most rigorous and
determined research effort. They tried to isolate a single variable responsible for observed
differences. The following sections review this work and related findings in the search for
an explanation of the observed performance differences between reading from paper and
reading from VDUs.
One of the advantages of paper over VDUs is that it can be picked up and orientated to
suit the reader. VDUs present the reader with text in a relatively fixed vertical orientation,
though thanks to more ergonomic designs some flexibility to alter vertical orientation is
now available in many systems. Gould et al (1987a) investigated the hypothesis that
differences in orientation may account for differences in reading performance. Subjects
were required to read three articles, one on a vertically positioned VDU, one on paper-
horizontal and the other on paper-vertical (paper attached via copy-holder to equivalent
VDU). Both paper conditions were read significantly faster than the VDU and there were
no accuracy differences. While orientation has been shown to affect reading rate of
printed material (Tinker, 1963) it does not explain the observed reading differences in the
comparisons reported here.
7.2 Visual angle
Gould (1986) hypothesised that due to the usually longer line lengths on VDUs the visual
angle subtended by lines in each medium differs and that people have learned to
compensate for the longer lines on VDUs by sitting further away from them when
reading. In an initial crude experiment of reading differences Gould (1986) visited the
offices of 26 people who were reading either from VDU or paper and measured reading
distance from both media with a metre stick. They found significantly greater reading
distances for VDUs. Further work has confirmed that preferred viewing distance for
screens is greater than that for paper (Jaschinski-Kruza 1990).
In a more controlled follow-up study Gould and Grischkowsky (1986) had 18 subjects
read twelve different three-page articles for misspellings. Subjects read two articles at
each of six visual angles: 6.7, 10.6, 16.0, 24.3, 36.4 and 53.4 degrees, varied by
maintaining a constant reading distance while manipulating the image size used. Results
showed that visual angle significantly affected speed and accuracy. However the effects
were only noticeable for extreme angles, and between a range of 16.0 to 36.4 degrees,
which covers typical VDU viewing, no effect for angle was found.
7.3 Aspect ratio
The term aspect ratio refers to the relationship of width to height. Typical paper sizes are
higher than they are wider, while the opposite is true for typical VDU displays. Changing
the aspect ratio of a visual field may affect eye movement patterns sufficiently to account
for some of the performance differences. Gould (1986) had eighteen subjects read three
8-page articles on VDU, paper and paper-rotated (aspect ratio altered to resemble screen
presentation). The results however showed little effect for ratio.
Detailed work has been carried out on screen filling style and rates (e.g., Bevan, 1981;
Kolers et al, 1981; Schwartz et al, 1983) and findings suggest that variables such as rate
and direction of scrolled text do influence performance and subjective ratings. In order to
understand the role of dynamic variables such as scrolling, "jittering" and screen filling in
reading from VDUs, Gould et al (1987a) had subjects read from paper, VDU and good
quality photographs of the VDU material which maintained the screen image but
eliminated any possible dynamics. Results provided little in the way of firm evidence to
support the idea of dynamics causing problems. Subjects again read consistently faster
from paper compared to both other presentation media, which did not differ significantly
from each other. Creed et al (1987) also compared paper, VDU and photos of the screen
display on a proofreading task with thirty subjects. They found that performance was
poorest on VDU but photographs did not differ significantly from either paper or VDU in
terms of speed or accuracy, though examination of the raw data suggested a trend
towards poorer performance on photos than paper. It seems unlikely therefore that much
of the cause for differences between the two media can be attributed to the dynamic
nature of the screen image.
Characters are written on a VDU by an electron beam which scans the phosphor surface
of the screen, causing stimulated sections to glow temporarily. The phosphor is
characterised by its persistence, a high-persistence phosphor glowing for longer than a
low-persistence phosphor. In order to generate a character that is apparently stable it is
necessary to rescan the screen constantly with the requisite pattern of electrons. The
frequency of scanning is referred to as the refresh rate. Since the characters are in effect
repeatedly fading and being regenerated it is possible that they appear to flicker rather
than remain constant. The amount of perceived flicker will obviously depend on both the
refresh rate and the phosphor's persistence; the more frequent the refresh rate and the
longer the persistence, the less perceived flicker. However refresh rate and phosphor
persistence alone are not sufficient to predict whether or not flicker will be perceived by a
user. It is also necessary to consider the luminance of the screen. While a 30 Hz refresh
rate is sufficient to eliminate flicker at low luminance levels, Bauer et al (1983) suggested
that a refresh rate of 93 Hz was necessary in order for 99% of subjects to perceive a
display of dark characters on a light background (i.e., positive presentation, see 7.6.) as
If flicker was responsible for the large differences between reading from paper and VDU
it would be expected that studies such as Creed et al's (1987) which employed
photographs of screen displays would have demonstrated a significant difference between
reading from photos and VDUs. However the extent to which flicker may have been an
important variable in many studies is unknown as details of screen persistence and
refresh rates are often not included in publications. Gould et al (1987a) admit that the
photographs used in their study were of professional quality but appeared less clear than
the actual screen display. It is likely that using photos to control flicker may not be a
suitable method and flicker may play some part in explaining the differences between the
7.6 Image polarity
A display in which dark characters appear on a light background (e.g., black on white) is
referred to as positive image polarity or negative contrast. This will be referred to here as
positive presentation. A display on which light characters appear on a dark background
(e.g., white on black) is referred to as negative image polarity or positive contrast. This
will be referred to here as negative presentation. The traditional computer display
involves negative presentation, typically white on black though light green on dark green
is also common.
Since 1980 there has been a succession of publications concerned with the relative merits
of negative and positive presentation. Several studies suggest that, tradition
notwithstanding, positive presentation may be preferable to negative. For example Radl
(1980) reported increased performance on a data input task for dark characters and Bauer
and Cavonius (1980) reported a superiority of dark characters on various measures of
typing performance and operator preference.
With regards to reading from screens Cushman (1986) reported that reading speed and
comprehension on screens was unaffected by polarity, though there was a non-significant
tendency for faster reading of positive presentation. Gould et al (1987a) specifically
investigated the polarity issue. Fifteen subjects read 5 different 1000 word articles, 2
negatively presented, 2 positively presented and one on paper (standard positive
presentation). Further experimental control was introduced by fixing the display contrast
for one article of each polarity at a contrast ratio of 10:1 and allowing the subject to
adjust the other article to their own liking. This avoided the possibility that contrast ratios
may have been set which favoured one display polarity. Results showed no significant
effect for polarity or contrast settings, though 12 of the 15 subjects did read faster from
positively presented screens, leading the investigators to conclude that display polarity
probably accounted for some of the observed differences in reading from screens and
In a general discussion of display polarity Gould et al (1987b) state that:
"to the extent that polarity makes a difference it favours faster reading from dark
characters on a light background." (p.514)
Furthermore they cite Tinker (1963) who reported that polarity interacted with type size
and font when reading from paper. The findings of Bauer et al (1983) with respect to
flicker certainly indicate how perceived flicker can be related to polarity. Therefore the
contribution of display polarity in reading from screens is probably important through its
interactive effects with other display variables.
7.7 Display characteristics
Issues related to fonts such as character size, line spacing and character spacing have
been subjected to detailed research. However the relationship of much of the findings to
reading continuous text from screens is not clear.
Character size on VDUs is closely related to the dimension of the dot matrix from which
the characters are formed. In the sixties 5x7 matrices were used but they offer little
opportunity for representing lower-case ascenders and descenders, and consequently
produce poor legibility. The dramatic increase in computer processing power now means
that there is little cost in employing larger matrices and Cakir et al (1980) recommend a
minimum of 7x9. Pastoor et al (1983) studied the relative suitability of four different dot-
matrix sizes and found reading speed varied considerably. On the basis of these results
the authors recommended a 9 x13 character size matrix. However their study was
concerned with television screens and their tasks included isolated word reading and
column searching. In short, the optimum character size for reading from screens appears
to be contingent on the task performed.
Considerable experimental evidence exists to favour proportionally rather than non-
proportionally spaced characters (e.g., Beldie et al 1983). Once more though, the findings
must be viewed cautiously. In the Beldie et al study for example, the experimental tasks
did not include reading continuous text. Muter et al (1982) compared reading speeds for
text displayed with proportional or non-proportional spacing and found no effect. In an
experiment intended to identify the possible effect of such font characteristics on the
performance differences between paper and screen reading, Gould et al (1987a) found no
evidence to support the case for proportionally spaced text.
Kolers et al (1981) studied interline spacing and found that with single spacing
significantly more fixations were required per line, fewer lines were read and the total
reading time increased. However the differences were small and were regarded as not
having any practical significance. On the other hand Kruk and Muter (1984) found that
single spacing produced 10.9% slower reading than double spacing, a not inconsiderable
Muter and Maurutto (1991) attempted various “enhancements” to screen presented text to
see if they could improve reading performance. These included double spacing between
lines, proportional spacing within words, left justification only and positive presentation.
“Enhanced” text proved to be read no differently from more typical electronic text (i.e.,
basically similar to paper) which the authors state may be due to one or tow of their
“enhancements” having a negative and therefore neutralising effect on others or some
“enhancements” interacting negatively. Unfortunately, their failure to manipulate such
variables systematically means firm conclusions cannot e drawn.
Obviously much work needs to be done before a full understanding of the relative
advantages and disadvantages of particular formats and types of display is achieved. In a
discussion of the role of display fonts in explaining any of the observed differences
between screen and paper reading Gould et al (1987a) conclude that font has little effect
on reading rate from paper (as long as the fonts tested are reasonable). They add that it is
almost impossible however to discuss fonts without recourse to the physical variables of
the computer screen itself e.g., screen resolution and beam size, once more highlighting
the potential cumulative effect of several interacting factors on reading from screens.
Most computer displays are raster displays typically containing dot matrix characters and
lines which give the appearance of "staircasing" i.e. edges of characters may appear
jagged. This is caused by undersampling the signal that would be required to produce
sharp, continuous characters. The process of anti-aliasing has the effect of perceptually
eliminating this phenomenon on raster displays. A technique for anti-aliasing developed
by IBM accomplishes this by adding variations in grey level to each character.
The advantage of anti-aliasing lies in the fact that it improves the quality of the image on
screen and facilitates the use of fonts more typical of those found on printed paper. To
date the only reported investigation of the effects of this technique on reading from
screens is that of Gould et al (1986). They had 15 subjects read three different 1000 word
articles, one on paper, one on VDU with anti-aliased characters and one on VDU without
anti-aliased characters. Results indicated that reading from anti-aliased characters did not
differ significantly from either paper or aliased characters though the latter two differed
significantly from each other. Although the trend was present the results were not
conclusive and no certain evidence for the effect of anti-aliasing was provided. However
the authors report that 14 of the 15 subjects preferred the anti-aliased characters,
describing them as clearer and easier to read.
7.9 User characteristics
It has been noted that many of the studies reported in this review employed relatively
naive users as subjects. The fact that different types of users interact with computer
systems in different ways has long been recognised and it is possible that the differences
in reading that have been observed in these studies result from particular characteristics
of the user group involved.
Most obviously, it might be assumed that increased experience in reading from
computers would reduce the performance deficits. A direct comparison of experienced
and inexperienced users was incorporated into a study on proofreading from VDUs by
Gould et al (1987a). Experienced users were described as "heavy, daily users.....and had
been so for years". Inexperienced users had no experience of reading from computers. No
significant differences were found between these groups, both reading slower from
Smedshammar et al (1989) report that post-hoc analysis of their data indicate that fast
readers are more adversely affected by VDU presentation than slow readers. However,
their classification of reading speed is based on mean performance over three conditions
in their experiment rather than controlled, pre-trial selection suggesting caution in
drawing conclusions. Smith and Savory (1989) report an interaction effect between
presentation medium, reading strategy and susceptibility to external stress measured by
questionnaire suggesting that working with VDUs may exaggerate some differences in
reading strategy for individuals with high stress levels. Caution in interpretation of these
results is suggested by the authors.
No reported differences for age or sex can be found in the literature. Therefore it seems
reasonable to conclude that basic characteristics of the user are not responsible for the
differences in reading from these presentation media.
7.10 The interaction of display variables: the work of Gould et al.
Despite many of the findings reported thus far, it appears that reading from screens can at
least be as fast and as accurate as reading from paper. Gould et al (1987b) have
empirically demonstrated that under the right conditions such differences between the
two presentation media disappear. In a study employing sixteen subjects, an attempt was
made to produce a screen image that closely resembled the paper image i.e., similar font,
size, colouring, polarity and layout were used. Univers-65 font was positively presented
on a monochrome IBM 5080 display with an addressability of 1024 x1024. No
significant differences were observed between paper and screen reading. This study was
replicated with twelve further subjects using a 5080 display with an improved refresh rate
(60Hz). Again no significant differences were observed though several subjects still
reported some perception of flicker.
On balance it appears that any explanation of these results must be based on the
interactive effects of several of the variables outlined in the previous sections. After a
series of experimental manipulations aimed at identifying those variables responsible for
the improved performance Gould et al (1987b) suggested that the performance deficit
was the product of an interaction between a number of individually non-significant
effects. Specifically, they identified display polarity (dark characters on a light, whitish
background), improved display resolution, and anti-aliasing as major contributions to the
elimination of the paper/screen reading rate difference.
Gould et al (1987b) conclude that the explanation of many of the reported differences
between the media is basically visual rather than cognitive and lies in the fact that reading
requires discrimination of characters and words from a background. The better the image
quality is, the more reading from screen resembles reading from paper and hence the
performance differences disappear. This seems an intuitively sensible conclusion to draw.
It reduces to the level of simplistic any claims that one or other variable such as critical
flicker frequency, font or polarity are responsible for any differences. As technology
improves we can expect to see fewer speed deficits at least for reading from screens.
Recent evidence from Muter and Maurutto (1991) using a commercially available screen
has shown this to be the case, although other differences remain.
Although reading from computer screens may be slower and occasionally less accurate
than reading from paper, no one variable is likely to be responsible for this difference. It
is almost certain that neither inherent problems with the technology nor the reader are
causal factors. Invariably it is the quality of the image presented to the reader which is
crucial. Tinker (1963) reports dramatic interaction effects of image quality variables on
paper and according to Gould et al (1987a) it is likely that these occur on screen too.
Positive presentation combined with a high screen resolution to avoid flicker can produce
good images and with the addition of anti-aliased characters it becomes possible to
provide a screen display that resembles the print image and thereby facilitates reading. It
must be remembered however that typical computer displays present images that are still
of poorer quality than those used by Gould and his associates to overcome the
performance deficit. Until screen standards are raised sufficiently these differences are
likely to remain.
A major shortcoming of the studies by Gould et al is that they only address limited
outcome variables: speed and accuracy. Obviously speed is not always a relevant
criterion in assessing the output of a reading task. Furthermore, the accuracy measures
taken in these studies have been criticised as too limited and further work needs to be
carried out to appreciate the extent to which the explanation offered by Gould is
sufficient. It follows that other observed outcome differences such as fatigue, reader
preference and comprehension should also be subjected to investigation in order to
understand how far the image quality hypothesis can be pushed as an explanation for
reading differences between the two media.
A shortcoming of most work cited in this section is the task employed. Invariably it was
proofreading which hardly constitutes normal reading for most people. Thus the
ecological validity of many of these studies is low. Beyond this, the actual texts
employed were all relatively short (Gould’s for example averaged only 1100 words but
many other researchers used even shorter texts). As a result, it is difficult to generalise
these conclusions beyond the specifics of task and texts employed to the wider class of
activities termed ”reading”. Creed et al (1987) defend the use of proofreading on the
grounds of its amenability to manipulation and control. While this desire for experimental
rigour is laudable one cannot but feel that the major issues involved in using screens for
real-world reading scenarios are not addressed by such work. With this in mind, the
following section considers the literature on research concerned with the manipulation
facilities where of necessity, lengthy texts need to be employed.
8 Manipulation Facilities
It is clear that the search for the specific ergonomic variables responsible for differences
between the media has been insightful. However, few readers of electronic texts would be
satisfied with the statement that the differences between the media are visual rather than
cognitive. This might explain absolute speed and accuracy differences on limited tasks
but hardly accounts for the range of process differences that are found as described
Once the document becomes too large to display on a single screen other factors than
image quality immediately come into play. At this stage readers must start to manipulate
the document and thus be able to relate current to previously-displayed material. In such
a situation other factors such as memory for text and its location, ability to search for
items and speed of movement through the document come into play and the case for
image quality as the major determinant of performance is less easy to sustain. Several
researchers have pinned their hopes on improved manipulation facilities with electronic
texts removing many of the differences between the media. In this section, research into
variables affecting such issues is reviewed.
8.1 Scrolling versus paging
The manner in which a reader moves through a document is distinctly different in either
medium and even within the electronic medium, various techniques are employed for
displaying sections of the text. Scrolling (the facility to move the text up or down on the
screen smoothly by a fixed increment to reveal information currently out of view) and
paging (the facility to move the text up or down in complete screensful - akin to page
turning with paper texts) are two of the most common.
There is evidence to suggest that readers establish a visual memory for the location of
items within a printed text based on their spatial location both on the page and within the
document (Rothkopf, 1971; Lovelace and Southall, 1983). This memory is supported by
the fixed relationship between an item and its position on a given page. A scrolling
facility is therefore liable to weaken these relationships and offers the reader only the
relative positional cues that an item has with its immediate neighbours.
On the basis of a literature review, Mills and Weldon (1986) report that there is no real
performance difference between scrolling and paging though Schwartz et al. (1983)
found that novices tend to prefer paging (probably based on its close adherence to the
book metaphor) and Dillon et al (1990b) report that a scrolling mechanism was the most
frequently cited improvement suggested by subjects assessing their reading interface.
Scrolling has also been investigated in conjunction with direction (vertical or horizontal
—Sekey and Tietz, 1982), rate (self-paced or machine-paced—Kolers et al., 1981) and
display size (Duchnicky and Kolers, 1983). With reference to direction and rate, all seem
to conclude that ideally, lengthy texts should be presented vertically and at the reader’s
choice of rate. Even so, Kolers et al. (1981) report that forcing readers to increase their
rates by 10-20% does not lead to loss of comprehension and actually appears to increase
efficiency of eye-movements as measured by rate and length of fixation.
It seems therefore that scrolling is a popular form of text manipulation with more
experienced users probably due to its speed even if there are theoretical grounds for
doubting its superiority over paging. There is no firm evidence that either facility
significantly affects reading performance compared to paper.
8.2 Display size
Display size is a much discussed but infrequently studied aspect of human-computer
interaction in general and reading electronic text in particular. Popular wisdom suggests
that “bigger is better” but empirical support for this edict is sparse. Duchnicky and Kolers
(1983) investigated the effect of display size on reading constantly scrolling text and
reported that there is little to be gained by increasing display size to more than 4 lines
either in terms of reading speed or comprehension. Elkerton and Williges (1984)
investigated 1,7,13, and 19-line displays and reported that there were few speed or
accuracy advantages between the displays of 7 or more lines. Similarly, Neal and Darnell
(1984) report that there is little advantage in full page over partial page displays for text-
These results seem to suggest that there is some critical point in display size, probably
around 5 lines, above which improvements are slight. Intuitively this seems implausible.
Few readers of paper texts would accept presentations of this format. Experiences with
paper suggest that text should be displayed in larger units than this. Furthermore, loss of
context is all too likely to occur with lengthy texts and the ability to browse and skim
backward and forward is much easier with 30 or so lines of text than with 5 line displays.
Of the experiments cited, only the Duchnicky and Kolers study was concerned with
reading for comprehension and their passages were never longer than 300 words. Thus
their findings on window size seem to bear little relevance to reading of lengthy texts.
Deliberately examining this, Richardson et al (1989) had subjects perform 10 information
location tasks using an electronic book with a display size of 20 or 40 lines. Though they
observed no performance differences between conditions they did report a significant
preference effect favouring the larger display. Similarly Dillon et al (1990b) investigated
screen sizes of 20 and 60 lines for reading an electronic version of an academic article.
Interestingly they found a manipulation effect for screen size that could not be explained
by the fact that to read a complete text on a small screen necessitates more manipulations
than seeing it on a large one. They reported that when such simple manipulations are
discounted and attention is paid only to changes in direction or jumps of 2 or more
“pages”, readers using the small screen still manipulated the text more. They proposed
that the likeliest explanation was that readers like to re-read large parts of texts or jump
about when using articles and that the smaller screen condition required more
manipulations to observe the same amount of text as the bigger screen. As in the
Richardson et al study, the authors report a preference effect favouring the larger display.
As with many variables, the task being performed is likely to be a deciding factor. Small
screens pose problems for readers wishing to browse through lengthy texts but are likely
to be more acceptable for tasks requiring a straight perusal of short material such as a
letter or memo. Significantly, many applications now allow the user to change window
size within the constraints of the overall screen size which may accommodate some
preference differences but does not resolve issues to do with optimum screen size for
It is likely that many of the effects of screen size are too subtle to be assessed by gross
outcome measures such as speed and accuracy. Larger screens might suit better spatial
memory formation or browsing, variables that are not usually measured by investigators.
As concluded in the basic ergonomic research, it is likely that the interaction of size with
other manipulation variables is important.
8.3 Text splitting across screens
A related issue to display size and scrolling/paging is the splitting of paragraphs mid-
sentence across successive screens. In this case, which is more likely to occur in small
displays, the reader must manipulate the document in order to complete the sentence.
This is not a major issue for paper texts such as books or journals because the reader is
usually presented with two pages at a time and access to previous pages is normally easy.
On screen however, access rates are not so fast and the break between screens of text is
likely to be more critical.
Research into reading has clearly demonstrated the complexity of the cognitive
processing that occurs. The reader does not simply scan and recognise every letter in
order to extract the meaning of words and then sentences. Comprehension is thought to
require inference and deduction, and the skilled reader probably achieves much of his/her
smoothness by predicting probable word sequences (Chapman and Hoffman, 1977
though see Mitchell 1982). The basic units of comprehension in reading that have been
proposed are propositions (Kintsch, 1974), sentences (Just and Carpenter, 1980) and
paragraphs (Mandler and Johnson, 1977). Splitting sentences across screens is likely to
disrupt the process of comprehension by placing an extra burden on the limited capacity
of working memory to hold the sense of the current conceptual unit while the screen is
filled. Furthermore, the fact that between 10-20% of eye movements in reading are
regressions to earlier fixated words and that significant eye movement pauses occur at
sentence ends (Ellis, 1983) would suggest that sentence splitting is also likely to disrupt
the reading process and thereby hinder comprehension.
In the Dillon et al (1990b) study cited earlier, the role of text splitting on performance
was also examined. They found that splitting text across screens caused readers to return
to the previous page to re-read text significantly more often than when text was not split.
Though this appeared to have no effect on subsequent comprehension of the material
being read, they concluded that it was remarked upon by the subjects sufficiently often to
suggest that it would be a nuisance to regular users. In this study however the subjects
were reading from a paging rather than scrolling interface where the effect of text
splitting was more likely to cause problems due to screen-fill delays. With scrolling
interfaces text is always going to split across screen boundaries but there is rarely a
perceptible delay in image presentation to disrupt the reader. It would seem therefore that
to the extent to which such effects are likely to be noticeable, text splitting should be
avoided for paging interfaces.
8.4 Window format
It has become increasingly common to present information on computer screen via
windows i.e., sections of screen devoted to specific groupings of material. Current
technology supports the provision of independent processes within windows or the
linking of inputs in one window with the subsequent display in another, the so called “co-
ordinated windows” approach (Shneiderman 1987).
Such techniques have implications for the presentation of text on screen as they provide
alternatives to the straightforward listing of material in “scroll” form or as a set of
“pages”. For example, while one window might present a list of contents in an electronic
text, another might display whole sections of it according to the selection made. In this
way, not only is speed of manipulation increased but the reader can be provided with an
overview of the document’s structure to aid orientation while reading an opened section.
The use of such techniques is now commonplace in hypertext applications. GUIDE for
example, uses windows in one instance to present short notes or diagrams as elaborations
or explanations of points raised in the currently viewed text, rather like sophisticated
footnotes. The concept of hypertext as non-linear text is, in a very real sense, derived
from such presentation facilities.
Tombaugh et al (1987) investigated the value of windowing for readers of lengthy
electronic texts. They had subjects read two texts on single or multi-window formats
before performing 10 information location tasks. They found that novices initially
performed better with a single-window format but subsequently observed that, once
familiar with the manipulation facilities, the benefits of multi-windowing in terms of
aiding spatial memory became apparent. They highlight the importance of readers
acquiring familiarity with a system and the concept of the electronic book in order to
accrue the benefits of such facilities.
Simpson (1989) compared performance with a similar multi-window display, a “tiled”
display (in which the contents of each window were permanently visible) and a
'conventional' stack of windows (in which the windows remained in reverse order of
opening). She reported that performance with the conventional window stack was poorest
but that there was no significant difference between between the “tiled” and multi-
window displays. She concluded that for information location tasks, the ability to see a
window's contents is not as important as being able to identify a permanent location for a
section of text.
Stark (1990) asked people to examine a hypertext document in order to identify
appropriate information for an imaginary client and manipulated the scenario so that
readers had to access information presented either in a ‘pop-up’ window which appeared
in the top right hand corner of the screen or a ‘replacement’ window which overlaid the
information currently being read. Though no significant task performance or navigation
effects were observed, subjects seemed more satisfied with pop-ups than replacements.
Such studies highlight the impact of display format on readers’ performance of a standard
reading task: information location. Spatial memory seems important and paper texts are
good at supporting its use through permanence of format. Windowing, if deployed so as
to retain order can be a useful means of overcoming this inherent weakness of electronic
text. However, studies examining the problems of windowing very long texts (where
more than five or six stacked windows or more frequent window manipulations are
required) need to be performed before any firm conclusions about the benefits of this
technique can be drawn.
8.5 Search facilities
Electronic text supports word or term searches at rapid speed and with total accuracy and
this is clearly an advantage for users in many reading scenarios e.g. checking references,
seeking relevant sections, etc. Indeed it is possible for such facilities to support tasks that
would place unreasonable demands on users of paper texts e.g., searching a large book
for a non-indexed term or several volumes of journals for references to a concept.
Typical search facilities require the user to input a search string and choose several
criteria for the search such as ignoring certain text forms (e.g., all uppercase words) but
sophisticated facilities on some database systems can support specification of a range of
texts to search. The usual form for search specification is Boolean, i.e., users must input
search criteria according to formal rules of logic employing the constructs ‘either’, ‘or’ as
well as ‘and’, which when used in combination support powerful and precise
specifications. Unfortunately most end-users of computer systems are not trained in their
use and while the terms may appear intuitive, they are often difficult to employ
In current electronic text facilities a simple word search is most common but users still
seem to have difficulties. Richardson et al (1988) reported that several subjects in their
experiment displayed a tendency to respond to unsuccessful searches by increasing the
specificity of the search string rather than lessening it. The logic appeared to be that the
computer required precision rather than approximation to search effectively. While it is
likely that such behaviour is reduced with increased experience of computerised
searching, a study by McKnight et al (1989) of information location within text found
other problems. Here, when searching for the term "wormwood" in an article on wine
making, two subjects input the search term "woodworm", displaying the intrusion of a
common sense term for an unusual word of similar sound and shape (a not uncommon
error in reading under pressure due to the predictive nature of this act during sentence
processing). When the system correctly returned a "Not Found" message, both users
concluded that the question was an experimental trick.
Thus it seems as if search facilities are a powerful means of manipulating and locating
information on screen and convey certain advantages impossible to provide in the paper
medium. However, users may have difficulties with them in terms of formulating
accurate search criteria. This is an area where research into the design of search facilities
and increased exposure of users to electronic information can lead to improvements
resulting in a positive advantage of electronic text over paper.
8.6 Input device
Over the last 15 years numerous input devices have been designed and proposed as
optimal for users e.g., trackerball, mouse, function keyboard, joystick, light pen etc. Since
Card et al’s (1978) claim that the speed of text selection via a mouse was constrained
only by the limits of human information processing, this device has assumed the
dominant position in the market.
It has since become clear that, depending on the task and users, other input devices can
significantly outperform the mouse (Milner 1988). For example, when less than ten
targets are displayed on screen and the cursor can be made to jump from one to the next,
cursor keys are faster than a mouse (Shneiderman 1987). In the electronic text domain,
Ewing et al (1986) found this to be case with the HyperTIES application, though there is
reason to doubt their findings as the mouse seems to have been used on less than optimal
Though 'direct manipulation' (Shneiderman 1984) might be a common description of an
interface, it seems that its current manifestations leave much to be desired when it comes
to manipulating text. Obviously practice and experience will play a considerable part
here. Expertise with an input device affords the user a high level of control and breeds a
sense of immediacy between selection and action.
It is important to realise that the whole issue of input device cannot be separated from
other manipulation variables such as scrolling or paging. For example, a mouse that must
be used in conjunction with a menu for paging text will lead to different performance
characteristics than one used with a scroll bar. For the moment however the mouse
appears dominant and as the “point and click” concept becomes integrated with the “look
and feel” of hypertext it will prove difficult to replace, even if convincing experimental
evidence against its use, or an innovative credible alternative should emerge.
8.7 Icon design
In aiding the manipulation of documents electronically, icons have become popular in
many hypertext applications. GUIDE, for example, uses such forms as boxes, arrows and
circles when the cursor moves over an actionable area of the document, while HyperCard
provides numerous “button” shapes that cause different document manipulations to
occur. Used in conjunction with a mouse such facilities can support rapid, easy
manipulations of the text and allow the user to access the document through numerous
routes – giving rise to the notion of non-linearity in hypertext.
Icons are also used to represent a document in situations where the user might be
selecting one of several texts. While it is easy enough to convey an image of book or
other text type iconically few systems attempt to provide the range of cues available with
paper such as size, age, level of usage and so forth.
There are sound theoretical grounds for supporting iconic representation. Being language
independent icons convey information by pictographic means and should thus support
use by individuals unfamiliar with the terminology of operating systems and command
languages. Further advantages of iconic representations are that they utilise little display
space and render syntax errors obsolete (Gittens 1986)
On the negative side, icons can be confusing if their form provides no immediate clue to
their action. Arrows, trashcans and folders might be intuitive but this is not always the
case (the “home” icon on HyperCard is a picture of a little house and naive users have
failed to appreciate the intended reference [McKnight et al 1989]). Designing icons to
convey less obvious actions than “goto” is not a simple task. Some designers even
provide icons with textual descriptors to provide clues to their use which seems to defeat
Stammers et al (1989) reported that icons are most useful when they represent concrete
rather than abstract actions which while intuitively sensible, suggests ultimate limitations
on their use as many computer functions are highly abstract in nature. Brems and Whitten
(1987) found that icons were more appropriate for experienced than novice users which is
ironic given the stated benefits of icons.
Generalising such findings to the electronic text domain is difficult at present. A
reasonable conclusion seems to be that icons have a role, particularly for simple or
repetitive actions such as “go there” or “look at this in more detail” but are less applicable
for conveying information of abstract actions. For manipulation purposes the basic range
of actions is always likely to be limited therefore it is conceivable that standard designs
for such actions might appear soon. Obviously this is an area for further research.
Manipulating electronic text is considered to be more difficult than manipulating paper.
Research suggests that factors such as non-splitting of text, rapid response and increased
display size can improve matters and that facilities such as searching and multi-
windowing might even offer benefits to electronic text over paper.
As with the basic ergonomic issues reviewed earlier the interaction of several of these
variables is likely to be crucial. Small displays limit windowing facilities and may
increase text-splitting causing manipulation differences with paper that might not emerge
with large, multi-windowed displays. Furthermore, as Tombaugh et al (1987) pointed out
familiarity with the facilities is vital. It is not always clear from the literature how this
variable has been controlled in many studies.
The range of tasks used for such investigations is much wider and often more
ecologically valid than those used in the basic ergonomic work reviewed. However, the
increased variability in both text size and task range mean that comparisons between
studies are more difficult than for studies concerned with visual ergonomics. For
example, the Dillon et al (1990b) investigated screen size effects by asking subjects to
read an academic text for comprehension purposes, allowing them to manipulate the text
by a paging mechanism while Duchnicky and Kolers (1983) investigated the same
variable using different window sizes, short test texts, different comprehension
techniques, with subjects using a knob to control scrolling rate. Obviously in such
situations, comparisons are difficult.
As an explanation of the differences between the media, manipulation must be
incomplete. Even if combined with good image quality, optimum manipulation facilities
are unlikely to remove all the problems associated with electronic text. This is becoming
obvious from much of the recent work on hypertext that is concerned with structuring
information and has shown that even with high quality screens and supposedly optimum
input devices such as a mouse, paper may still prove more usable than screen presented
text for some tasks (e.g., McKnight et al 1990). In other words, even by making images
clear, and supporting readers manipulating the text, we are still missing something else.
Unfortunately, empirical data on reading from paper and screen largely stops here and we
enter the realm of conjecture and theorising about “information strucutures”and
“hyperspace” and out of the experimental data domain that is of concern in this review.
9. General Conclusion
At the outset it was stated that reading can be assessed in terms of outcome and process
measures. To date however, most experimental work has concentrated on the former and
in particular, has been driven by a desire to identify a single variable to account for the
significant reading speed differences that have been reported. The present review sought
to examine the experimental literature with a view to identifying all relevant issues and
show how single variable explanations are unlikely to offer a satisfactory answer.
While substantial progress has been made in terms of understanding the impact of image
quality on reading speed, it is clear that ergonomists are still a long way from
understanding fully the effect of presentation medium on reading. While it is now
possible to draw up recommendations on how to ensure no speed deficit for proofreading
short texts on screen, changes in task and text parameters mean such advice has less
One is struck in reviewing this literature by the rather limited and often distorted view of
reading that ergonomists seem to have. Most seem to concern themselves with the control
of so many variables that the resulting experimental task bears little resemblance to the
activities most of us routinely perform under the banner “reading”. It is perhaps no
coincidence that the major stumbling block of reader preference has been so poorly
investigated beyond the quick rating of screens and test documents in post-experimental
The assumption that overcoming speed or accuracy differences in proofreading is
sufficient to claim, as some authors have, that “there is no difference” between the media
(Oborne and Holton 1988) is testimony to the limitations of some ergonomists’ views of
human activities such as reading. Other tasks, such as reading to comprehend, to learn or
for entertainment are less likely to require readers to concern themselves with speed.
These are the sort of tasks people will regularly wish to perform and it is important to
know how electronic text can be designed to support them. Such tasks will also of
necessity involve a wide variety of texts, differing in length, detail, content-type and so
forth¬– issues that have barely been touched upon to date by researchers.
The findings on image quality and the emerging knowledge of manipulation problems
should not be played down however. Knowing what makes for efficient visual processing
and control of electronic text can serve as a basis for future applications. As Muter and
Maurutto (1991) demonstrated, a typical high quality screen with effective manipulation
facilities can provide an environment that holds its own in speed, comprehension and
preference terms with paper, at least over the relatively constrained reading scenarios
found in the researchers’ laboratory. But if our desire is to create systems that improve on
paper rather than just matching it in performance and satisfaction terms (as it should be)
then much more work and a more realistic conceptualisation of human reading is
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