Interface Design and Optimization of Reading of Continuous Text Paul Muter
University of Toronto
In van Oostendorp, H., and de Mul, S. (Eds.) (1996), Cognitive aspects of electronic text processing. Norwood, N.J.: Ablex.
(c) Copyright 1996 Ablex Publishing Corp.
"Reading is the means by which the world does a large part of its work.... The slightest improvement either in the page or in the method of reading means a great service to the human race" (Huey, 1908).
Introduction At present, we do not know how to optimize reading via electronic equipment. In this chapter, some considerations that may help us do this in the future will be raised, and some of the relevant evidence and theory that does exist will be cited and briefly highlighted. The focus of this paper is on reading of continuous text, whether in linear form or hypertext form, and with or without the presence of graphics or other types of information.
Paradoxically, computer technology may lead to an increase in the use of text and an increase in literacy, because we are in a window of time in which it is easy and efficient to produce, store, manipulate, and transmit computerized text files, and comparatively difficult to process graphics, sound, or video. The amount of reading of text from electronic displays is increasing substantially every year.
Computerized presentation of text has some clear advantages over paper media (Egan, Remde, Gomez, Landauer, Eberhardt, & Lochbaum, 1989; Yankelovich, 1985):
- ease of searching for information
- ease of updating
- capability of presenting other media simultaneously
- dynamic text presentation (see below)
- inexpensive customizability
- connectivity; webs of related information
In past research on optimization of reading, the main two dependent variables have been reading time and comprehension, as measured by recall, questionnaires, or error detection. Some other dependent measures of interest are:effective reading rate:
- effective reading rate: reading speed times percent correct on a comprehension test
(Jackson & McClelland, 1979), to avoid problems associated with tradeoffs between
speed and comprehension
- re-reading time
- size of saccades; saccades per unit time (Kolers, Duchnicky, & Ferguson, 1981)
The issue of visual fatigue will not be emphasized in the present paper, but following are some of the dependent measures that have been used:
- accommodation (speed, range, resting focus, fluctuations)
- pupil diameter
- critical flicker frequency (frequency at which flicker is just perceptible)
Harwood & Foley, 1987
- blink rate
- contrast threshold
- saccade speed
- fixation duration
- lacrimation (Yaginuma, Yamada, & Nagai, 1990)
- subjective reports
Paper vs. CRTs (cathode ray tubes) Much of the published research on optimization of reading has been done with paper media. Research on reading from paper media has yielded the following results (Frenckner, 1990):
- Upper case print, italics, and right justification by inserting blanks
result in slower reading.
- Black characters on a white background produces faster reading than the reverse,
and most readers prefer it.
- There is no effect of margins, serifs, or typeface in general, within reasonable limits.
- Effects of type size, line length, and interline spacing interact.
Bever, Jandreau, Burwell, Kaplan, and Zaenen (1990) found that comprehension was facilitated by adding spaces between major phrases, as determined by a simple automatic parser.
It is unknown to what extent findings from paper media can be extended to electronic media. Certainly at least some of the results do not generalize. For example, Wright and Lickorish (1988) found that color cues were effective as location aids for paper texts but not for computerized texts (though in the former case the backgrounds were colored and in the latter case the text itself). Prominent researchers in the field have expressed the opinion that it is risky to generalize from research on paper to electronic media (e.g., Kolers, Duchnicky, & Ferguson, 1981).
Muter, Latremouille, Treurniet, and Beam (1982) compared speed and comprehension in reading from a videotex terminal and a book. Results over two hours of reading indicated that, though extended reading from videotex was feasible, it was 28% slower than reading from paper. There was no significant difference in comprehension. Several other researchers have also found decreased efficiency from CRTs of the 1980s (e.g., Gould & Grischkowsky, 1984; Wilkinson & Robinshaw, 1987), some with reading and some with proofreading. Proofreading and reading share some component processes, but other processes are unique to each skill.
Dillon (1992) complained of the "great disparity in procedures" in studies demonstrating slower reading with CRTs than with paper, but this disparity could be interpreted as a virtue: Seeking "robustness in variation" can be a useful strategy in the face of complex interactions (see Interactions, below).
There are many typical differences between book and computer reading that conceivably could account for the observed slower reading from computer screens of the 1980s (adapted from Muter & Maurutto, 1991):
- edge sharpness
- character shape
- inter-character spacing
- stroke width of characters
- distance between the reading material and the reader
- angle of the reading material
- actual size of characters
- visual angle of characters
- characters per line
- lines per page
- words per page
- inter-line spacing
- polarity (light characters on a dark background vs. the reverse)
- contrast ratio between characters and background
- intermittent vs. continuous light
- emissive vs. reflected light
- stability (potential flicker, jitter, shimmer, or swim; Stewart, 1979)
- interference from reflections
- absence vs. presence of incidental location cues
- aspect ratio
- curvature of screen
- distortion in corners
- system response time
- method for text advancement
- posture of the reader
- reader's familiarity with the medium
It is quite clear that no single variable accounts for the obtained differences in performance between CRTs and paper. Several of the above variables, including resolution, interline spacing, polarity, and edge sharpness contribute to the effect (Gould, Alfaro, Barnes, Finn, Grischkowsky, & Minuto, 1987; Kruk & Muter, 1984; Muter & Maurutto, 1991). With a more modern system, including a large, higher-resolution screen with dark characters on a light background, reading from a computer can be as efficient as reading from a book (Muter & Maurutto, 1991).
Of course, the efficiency of books notwithstanding, electronic text presentation should not simply mimic a book. The strengths and potential of computerized presentation should be pursued and exploited.
Selected Independent Variables It is beyond the scope of the present chapter to comprehensively review the empirical evidence and theory on the effects of all of the independent variables that might affect reading via computers. (For reviews, see Dillon, 1992; Frenckner, 1990: and Mills & Weldon, 1988.) In this section, I will present brief comments on a number of independent variables, and more extensive treatment of one variable: color. In my opinion, the worst sins in the computerized presentation of text are committed with the use of color.
Of course, some of the following variables are inextricably intertwined, and some of them interact with each other.
Color Many disadvantages and potential problems with the use of color in text presentation have been pointed out (Rubin, 1988; Shneiderman, 1987):
- Color displays in effect have lower resolution because three phosphors are required
at each point.
- Edges created by color alone are difficult to resolve.
- Approximately 8% of males are at least partly color-blind, and deficiencies in color vision are sometimes amplified with CRTs because red phosphors have a sharply peaked spectrum.
- The use of color sometimes results in a contrast ratio that is so low that performance is impaired; e.g., the author's name is almost illegible on the cover of Rubin (1988).
- The tendency to overuse color (the "fruit salad" approach) can clutter up the screen
and create confusion.
- Color displays are not universally available, and are "more costly, heavier, less reliable, hotter, and larger" than monochrome displays (Shneiderman, 1987, p. 342).
- Different colors, especially highly saturated ones at opposite ends of the spectrum, sometimes appear to be in different depth planes because of chromatic aberration
and/or color stereoscopy, and this can be fatiguing.
- It is difficult to generalize from experiments on the use of color with computers, because different products, e.g., with different phosphors, produce different colors, and phosphors degrade with age. In many experiments purportedly on color, brightness and contrast are uncontrolled.
Many factors affect the ability to distinguish colors (Silverstein, 1987), including:
- Misconvergence, produced when the red-green-blue electron guns are imperfectly aligned, can disrupt perception (Travis, 1990).
- Some colors have expected meanings which may contradict the intended meaning. For example, in some nuclear power plants, red denotes on and green denotes off (Bailey, 1982).
- Color perception is affected by context: simultaneous color contrast (e.g., a surrounding blue induces a change toward yellow), and color adaptation effects (Jameson & Hurvich, 1964; Laar & Flavell, 1988).
- Small blue objects (< 0.25 degrees of visual angle) are difficult to see (small field tritanopia; Williams, MacLeod, & Hayhoe, 1981).
Of course, people often prefer color, and color can be useful to emphasize format, to highlight, to categorize, and to improve aesthetics (Nes, 1986; Rubin, 1988). Color can also aid in visual search (Smith, 1962). To maximize discriminability of colors, evidence suggests that differences in hue and lightness should be maximized and differences in saturation should be minimized (Laar & Flavell, 1988).
- wavelength separation
- color purity
- stimulus size
- brightness adaptation level
- number of colors
- background (light vs. dark)
- stimulus location (central vs. peripheral)
- type of discrimination (relative vs. absolute)
- individual differences (e.g., age).
Polarity Evidence suggests (Radl, 1983) that a large majority of users prefer positive polarity (dark characters on a light background). In theory, positive polarity reduces optical distortion, and increases visual acuity, contrast sensitivity, speed of accommodation, and depth of field (Bauer & Cavonius, 1983). It also decreases the problem of interfering reflections of external light (Bauer, 1987). However, the effects of polarity are controversial (Pawlak, 1986; Taylor & Rupp, 1987). A definite disadvantage of positive polarity is an increase in the risk of perceived flicker, though this problem can be overcome with a sufficiently high refresh rate.
Variables Affecting Perception of Flicker The probability of perceiving flicker increases (Nylen & Bergqvist, 1987; Pawlak, 1986):
- with increasing luminance (e.g., with dark characters on a light background)
- as phosphor persistence time decreases
- if the screen is seen peripherally
- if the user is talking (vibrations are transmitted from the vocal cords to the eye)
- with line jitter
- with the size of the screen
- with temporal contrast
Pixel Attributes Two goals in display design were suggested by Murch and Beaton (1987):
- The adjacent raster line (or pixel) requirement: the raster lines or pixels should be imperceptible at typical viewing distances; for example, characters should appear to be continuously constructed.
- The alternate raster line (or pixel) requirement: an alternating on-off pattern of adjacent rasterlines or pixels should be perceptible at typical viewing distances.
Resolution One measure of resolution is the resolution/addressability ratio, which is the width of pixels divided by the peak-to-peak distance between pixels (Harpster, Freivalds, Shulman, & Liebowitz, 1989). Harpster et al. found that a high ratio resulted in better visual search performance.
Interline Spacing Evidence of Wilkins and Nimmo-Smith (1987) suggests that increasing spacing between lines and proportionately decreasing horizontal spacing between letters may improve the clarity and comfort of text without affecting the density of the text. Close inter-line spacing may impair reading because of vertical masking, and because return sweeps are more difficult (Kruk & Muter, 1984). Evidence of Lunn and Banks (1986) suggests that interline spacing should be variable to prevent fatigue resulting from adaptation to spatial frequency.
Words per Screen With respect to words per screen, Muter, Latremouille, Treurniet, and Beam (1982) suggested that reading speed tends to decrease as words per page decreases. Findings consistent with this idea have been reported several times (Creed, Dennis, & Newstead, 1988; de Bruijn, de Mul, & van Oostendorp, 1992; Reisel & Shneiderman, 1987).
Screen Size There is both theory (Lansdale, 1988) and data (de Bruijn, de Mul, & van Oostendorp, 1992; Dillon, Richardson, & McKnight, 1990) to support the idea that large screens enhance the processing of text, perhaps partly because the number of words per screen can be larger (see above).
Multiple Windows An experiment on reading of lengthy texts indicated that, after practice with the system, a multi-window display helped readers to relocate information (Tombaugh, Lickorish, & Wright, 1987).
Scrolling vs. Paging Paging is apparently superior to scrolling in terms of both performance and user preference (Kolers, Duchnicky, & Ferguson, 1981; Schwarz, Beldie, & Pastoor, 1983). One advantage of paging is that incidental memory for location within a page (Rothkopf, 1971) may facilitate processing.
Distance Within reasonable limits, the distance between the reader and the reading material has no effect on perceptual span (Morrison & Rayner, 1981) or reading efficiency (Kruk & Muter, 1984). With increasing distance, retinal image size decreases linearly, but so does retinal eccentricity (distance of the image from the fovea), and these two effects offset each other exactly. Acuity is a decreasing linear function of eccentricity (Anstis, 1974).
Size of Characters
Within reasonable limits, size of the characters has no effect on proofreading speed (Gould & Grischkowsky, 1986). The probable reason is analogous to the reason that distance has no effect (see above).
Proportional Spacing Variable letter width (proportional spacing) led to faster reading of lists of isolated words (Beldie, Pastoor, and Schwartz, 1983).
Indentation Huey (1908) recommended three-space indentation of every other line to facilitate return sweeps, but to my knowledge this idea has never been tested directly.
Hyphenation Reading is slower if words are divided (hyphenated) at the ends of lines (Nas, 1988).
Highlighting Techniques for highlighting include (Nes, 1986; Shneiderman, 1987; Tullis, 1988):
The evidence on highlighting suggests that sometimes it helps and sometimes it has a negative effect (Fisher & Tan, 1989). A key variable seems to be highlighting validity: the percentage of time that a target, as opposed to a distractor, is highlighted.
- enclosing in a box
- pointing with an arrow
- adding asterisks
- reversing polarity
- flashing: on-off; fluctuating brightness; or normal and reverse video
- varying size
- varying font
- varying brightness
- adding color or audio
Case Searching for words is faster with uppercase characters, but reading of continuous text is slower (Vartabedian, 1971), perhaps because interline masking is greater with uppercase (Nes, 1986). In addition, lowercase enhances reading efficiency because word shape is helpful in word recognition (Rudnicky & Kolers, 1984).
Integration Ideally, reading from a computer should be easily integrated with other tasks such as decision making, annotating (including unofficial comments), and report writing (Erickson & Salomon, 1991; Wright & Lickorish, 1984). Van Oostendorp (in press) found that performance in annotating text was as good in several computer conditions as in a paper and pencil condition.
Access Devices Following are some potential enhancements of conventional text that can mimic hypertext and enable selective access, and which may affect efficiency of reading (Jones, 1987):
- parenthetical remarks
- verbal references; for example, "see Section ..." or "see Smith ..."
- tables of contents
- section headings
- topic sentences of paragraphs
Dynamic Text Presentation Until this point in the present chapter, it has been assumed that presentation of text is static. In dynamic text presentation, an attempt is made to optimize reading by utilizing some of the special capabilities of the computer. Two methods of dynamic text presentation that have been tested are rapid serial visual presentation (RSVP) and the Times Square format.
With RSVP, text is presented at a fixed location on the screen, one word at a time or a few words at a time. Several researchers have demonstrated that readers can perform approximately as efficiently with RSVP as with normal page-format reading (e.g., Juola, Ward, & McNamara, 1982). There are several potential uses of RSVP:
The optimal conditions for RSVP seem to be the following (Juola, Haugh, Trast, Ferraro, &
- when display space is limited
- scanning and skimming, which constitute a high proportion of cognitive processing of text
- reading by users with impaired peripheral vision, for example, retinitis pigmentosa (Williamson, Muter, & Kruk, 1986)
- studying cognitive processes
- with certain kinds of poor readers, who perform better, after practice, with RSVP than with regular page format (Juola, Haugh, Trast, Ferraro, & Liebhaber, 1987)
- as an efficient way to present continuous text in general, when optimal parameters are established, because there is no need to expend cognitive capacity on controlling eye movements
Giving the user control over RSVP presentation, e.g., over regressions and rate of presentation, sometimes has adverse effects on performance (Chen and Chan, 1990; Muter, Kruk, Buttigieg, & Kang, 1988). But, of course, under many circumstances, people will prefer to have this control.
- about 12 characters per window on average
- two or three words per window
- idea-unit segmentation
- 250-500 msec blank window between sentences
Times Square Format Kang & Muter (1989) found that smooth (pixel-by-pixel) horizontal scrolling with a small window (Times Square format) produced performance at least as good as RSVP, contrary to earlier studies which did not use pixel-by-pixel scrolling. In addition, subjects preferred the Times Square format, which is often used in electronic billboards.
Interactions A major difficulty in research in text presentation, whether static or dynamic, is that the various independent variables often interact, sometimes in extremely complex ways: The effect of one variable depends on the level of other variables. For example, this has been a problem with to respect to typographic variables such as type size, line length, and interline spacing (Frenckner, 1990). Following are some possible approaches for handling the problem of intractable high-order interactions:
- Perform a huge number of factorial experiments. (This is usually not practical.)
- Sample randomly from a large range of several factors.
- Re-construe the problem: "What is sometimes required is not more data or more refined data but a different conception of the problem" (Shepard, 1987, p. 1318).
- Seek "robustness in variation": Try to find evidence for a principle in many relevant settings (Landauer, 1988).
- Prune the alternative space; i.e., somehow reduce the number of possibilities under consideration.
- Use an algorithm such as Simplex (Nelder & Mead, 1965) to determine which values of several independent variables to experimentally test next in order to maximize a dependent variable such as reading rate.
- Use a "kitchen sink" approach for practical problems (Muter & Maurutto, 1991): throw into a single condition every feature that might have a beneficial effect, based on theory or data, and compare it to a control condition.
A second source of problems is individual differences. The use of computers entails huge individual differences, but it also permits extensive individualization (Rich, 1983). It is particularly important to take individual differences into account in human-computer interaction, for several reasons (Bailey, 1982; Egan, 1988):
The effects of age are an important source of individual differences in reading. For example, the following visual functions decline with age (Czaja, 1988):
- As time passes, the group of computer users becomes more and more heterogeneous.
- Individual differences tend to account for more of the variance in performance than do differences in system design or training.
- If individual differences are taken into account in the design of systems, more people
can use them.
- It is now known, to some extent, how to accommodate individual differences (see below).
Various ways of accommodating user differences have been developed:
- acuity, both static and dynamic (for moving objects)
- dark adaptation
- perception of targets of low contrast
- peripheral vision
- color perception
- iconic memory
- Allow user to personalize system (Bournique & Treu, 1985).
- Develop robust interfaces: (Egan & Gomez, 1985): assay user differences; isolate the source of variation; then re-design to accommodate differences among users.
- Develop user prototypes: Produce two or more interfaces, one for each type of user (Morris, 1987), based on: user's self-classification; the answers to a few questions; or dynamic user modeling (user may change).
Concluding Comments Despite the large number of published experiments on reading continuous text from computers, to my knowledge no circumstances have been found in which reading in normal subjects is more efficient, with respect to speed and comprehension, than from a book. Perhaps performance superior to that achieved with the book has not been demonstrated because the new techniques of presentation require that the user have extended practice, and the experiments in the literature last no more than several hours per reader. Bigger experiments with dozens or even hundreds of hours of testing per subject may be necessary.
A more economical strategy is suggested by some work by Coleman and Kim (1961). They found that several formats, in particular a center-justified format with one word per line, had a positive effect on the processing of tachistoscopically presented text, but no effect or a negative effect on reading, probably because of entrenched habits. With extended practice, the effect might emerge in reading. If it could be established that tachistoscopic studies like this are good predictors of results of reading studies with extensive practice, then studies using tachistoscopic presentation - or analogous studies using computers to flash stimuli - could be used as short cuts to determine which presentation techniques optimize performance in reading.
On the other hand, perhaps the reason that no computer condition superior to a book has been found is that the bottleneck is in the central processing in the human brain, rather than in the input channels. Carver (1982) found that the optimal rate of reading and listening tended to be constant under a wide range of conditions. It is possible, though unlikely in my opinion, that tinkering with modes of presentation will do little or no good past a certain point, a point which has been reached by the technology of the book. The book has evolved over several centuries to its present highly efficient form. Of course, the evolution of the human brain has not kept pace with the evolution of technology. However, perhaps co-ordinated developments in computer technology and cognitive science can pave the way toward more efficient reading, and therefore toward the facilitation of work and problem-solving in many areas of endeavor.
Author Note Dept. of Psychology, University of Toronto, Toronto, Ont., Canada, M5S 1A1., email@example.com. I thank Valerie Temple for general assistance, and Boyd Blackburn, Pavel Muresan, Oren Satov, and Herre van Oostendorp for helpful comments.
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