Reading Ebooks Hurts My Eyes Comparison Confound
PLoS One. 2013; eight(12): e83676.
E-Readers and Visual Fatigue
Simone Benedetto
one CHArt/LUTIN, Université Paris 8, Paris, French republic,
Véronique Drai-Zerbib
2 CHArt/LUTIN, Université Paris 6, Paris, France,
Marco Pedrotti
two CHArt/LUTIN, Université Paris half dozen, Paris, France,
Geoffrey Tissier
ane CHArt/LUTIN, Université Paris 8, Paris, French republic,
Thierry Baccino
ane Nautical chart/LUTIN, Université Paris eight, Paris, France,
Kevin Paterson, Editor
Received 2013 Jul three; Accepted 2013 Nov half-dozen.
Abstract
The mass digitization of books is irresolute the way information is created, disseminated and displayed. Electronic book readers (e-readers) generally refer to two main display technologies: the electronic ink (E-ink) and the liquid crystal brandish (LCD). Both technologies have advantages and disadvantages, just the question whether one or the other triggers less visual fatigue is still open up. The aim of the present research was to study the effects of the display technology on visual fatigue. To this stop, participants performed a longitudinal study in which ii final generation e-readers (LCD, Due east-ink) and paper book were tested in three different prolonged reading sessions separated past - on boilerplate - ten days. Results from both objective (Blinks per second) and subjective (Visual Fatigue Scale) measures suggested that reading on the LCD (Kindle Fire HD) triggers higher visual fatigue with respect to both the E-ink (Kindle Paperwhite) and the newspaper volume. The absence of differences betwixt Due east-ink and newspaper suggests that, concerning visual fatigue, the E-ink is indeed very similar to the paper.
Introduction
Reading behavior has been investigated by psychologists for several decades, some of them focusing on depression-level processing of words such as visibility [1] or legibility [2] and others on comprehension levels [iii], [4], [5]. Although researchers generally studied them separately, these three theoretical levels are very practical for delimiting reading [6]. Usually, the visibility processing (i.eastward. distinguishing a visual betoken from the background) is not a matter of involvement in reading since everyone assumes that visual factors are generally fitted in reading experiments. This supposition would exist truthful if any linguistic cloth was presented on the same support. In the existent world this cannot be truthful, and the use of figurer displays for presenting linguistic textile may involve a big variability. For example, it has been shown that the display polarity (negative/positive polarity) [7] or the refresh rate [eight], [9] might bear on vision during reading.
In the era of digitalization, nothing remains untouched and newspaper books are no exception. Electronic books (due east-books) are changing the mode data is created, disseminated and displayed. Although e-books are usually displayed on dedicated e-book readers (e-readers), almost any electronic device equipped with reading software can exist used to read an due east-volume. With respect to traditional books, the advantages as well every bit the disadvantages of digital books are many. E-books are hypertexts that let carrying an entire library within a pocket-sized space, they are cheaper (about l–60% lower than impress), more ecology friendly, and they share college levels of text personalization (east.g. font size, font blazon, color and luminance). At the same time they show issues related to piracy (e-books are easier to re-create) and are less emotionally involving (e.g. lack of tactile and olfactory feedback).
E- readers generally refer to two main display technologies: the electronic ink (E-ink) and the liquid crystal display (LCD). The Eastward-ink (i.e. electronic ink or electronic paper) is designed to reproduce the advent of ink on paper. With respect to LCD, the primary advantages of E-ink display are amend readability of their screens - especially in bright sunlight - and longer battery life. While E-ink readers practice not allow colors and are limited for reading, LCD due east-readers are commonly tablets, which means they are not simply a replacement for a book, rather multifunctional devices, which tin can be used for advice, organization or leisure activities [x]. LCD tablets accept faster screens capable of higher refresh rates and are more suitable for interaction. Some final generation Eastward-ink displays, like the Kindle Paperwhite, offer a reading experience in all lighting conditions, from bright sunlight to bedtime reading, guiding calorie-free towards the surface of the e-ink brandish from above.
In forums well-nigh e-readers there are many statements about the advantages and disadvantages of these displays and their term of comparison is usually the paper, which is yet the most used support for reading. According to Siegenthaler et al. [10], the discussion whether E-ink or LCD is improve for reading is emotional, and scientific evidence is quite sparse. In fact, just few studies are focused on reading behavior and even less deal with visual fatigue. Moreover, the results of these studies are device-dependent, and the rapid technological advancement of these supports turns recent results out of date quite quickly.
Concerning reading beliefs, Shen et al. [11] found East-ink reader (Sony e-reader) to have higher search accurateness with respect to LCD (Kolin e-reader). Siegenthaler et al. [12], found no differences between the aforementioned E-ink device (Sony eastward-reader) and LCD (iPad 1st generation), as confirmed by both subjective (VFS - [thirteen]) and objective measures (eye and reading performance measures). Siegenthaler et al. [10] showed that iPad anest generation, under special artificial light conditions, may even provide better legibility than Sony due east-reader. Siegenthaler et al. [14], comparing five E-ink displays and a paper volume, found that reading behavior on e-readers is very like to the reading behavior on print (i.e. no differences in reading speed and regressive saccades), and that Due east-ink may fifty-fifty provide better legibility than paper. Zambarbieri & Carniglia [15] found no differences in reading behavior between paper book, iPad 1st generation and East-ink (Kindle DX).
The aim of the present inquiry was to study the effects of the display technology on visual fatigue using prolonged reading sessions [16]. According to the International Classification of Diseases (ICD-10) of the World Health System (WHO), visual fatigue - likewise called visual strain - is classified every bit a subjective visual disturbance (H53.one), manifested by a degree of visual discomfort typically occurring after some kind of prolonged visual action, and characterized past fatigue, pain effectually the eyes, blurred vision or headache.
In this framework, the need to empirically evaluate visual fatigue on e-readers and paper is getting more and more important. Yet, only few studies accept focused on visual fatigue [11], [12], [17], [18]. Kang et al. [17] institute LCD (Kolin e-reader) to trigger higher visual fatigue than newspaper volume as well as lower reading operation. Lee et al. [xviii] showed that Sony e-reader triggers shorter search times and higher accurateness with respect to LCD (Kolin e-reader), whereas no differences were found equally to visual strain.
In our experiment, participants performed a longitudinal study in which ii terminal generation e-readers (LCD, E-ink) and paper volume were tested in 3 dissimilar reading sessions separated by - on average - ten days. The experiment consisted of prolonged reading (>1 hr) on each device while eye data were recorded. Subjective and objective visual fatigue measures were collected at the beginning and at the end of each reading session. Variables such as font size, typeface and number of words per page were not manipulated and were kept constant during the whole experiment, as well as beyond the three devices [17], [xix]. If reading on Eastward-ink, LCD, and print is like, then no differences in objective and subjective measures should be found.
Materials and Methods
Participants
Twelve participants (5 males, mean historic period = 27 years, SD = 4) volunteered for the experiment. All of them had no previous experience with eastward-readers, had normal or corrected-to-normal vision, and were naïve as to the aims and the expected outcomes of the experiment. Participants gave written informed consent before participation. The written report was performed in keeping with the declaration of Helsinki. The protocol was canonical by the French National Board of Computer science and Freedom.
Apparatus
Eye data were recorded with a 30 Hz infrared video-based centre tracker (SMI Center Tracking Glasses - ETG). In order to ensure the best tracking quality, scale was fabricated for each participant at the offset of each reading trial and further checked at the stop of each one. Measurements were taken under constant bogus illumination. As assessed by a digital light meter sensor (Extech 403125; Extech Instruments, Nashua, NH) placed on the participants' forehead at 60 cm from the reading device, the amount of light incident on that expanse totaled 54 60. This measurement did not vary among the three reading devices.
Stimuli
Iii different reading devices were chosen: two last generation e-readers (of the same brand) and a paper book (Fig. 1). Concerning e-readers, the selection criteria were a) the display engineering science (both LCD and Due east-ink), and b) the ranking based on users' reviews (http://ebook-reader-review.toptenreviews.com). According to these criteria a Kindle Fire Hard disk drive (LCD display) and a Kindle Paperwhite (Due east-ink display) were employed. Specifications of the iii reading devices are shown in Tabular array 1.
The three reading devices used in this study: the paper book, the Kindle Paperwhite and the Kindle Fire HD (from left to right).
Table one
Device specifications.
| Reading device | Support size | Support blazon | Resolution |
| Kindle Fire Hard disk | seven″ | Hard disk drive LCD | 216 ppi |
| Kindle Paperwhite | 6″ | Paperwhite display | 212 ppi |
| Paper volume | 6″ | Paper | 300 dpi |
Since the text displayed on each support had to be identical across the three devices (same page size, font size, typeface and number of words per folio), regulations were made accordingly. As to the paper book, each single folio was edited using a give-and-take processor, and a screw binding was used to allow pages to lay apartment, improving page turn (encounter Fig. i).
In order to allow comparison among the devices, we tried to find a compromise betwixt the level of luminance of the devices and their readability. To this terminate, the level of luminance emitted by the e-readers' displays was adjusted at the beginning of the experiment. Plainly, since the newspaper reflects only does not emit light directly, the luminance of the paper book could not be manipulated. The Michelson definition of contrast [20] was used to make up one's mind the actual contrast ratios [C = (Lmax − 50min)/(Lmax+Lmin)] where C = dissimilarity, 50max = maximal luminance, 50min = minimal luminance. We measured luminance for black (minimal luminance) and white (maximal luminance) displays for the 2 reading devices. As assessed by a digital luminance meter for contact measurements (Mavo-Monitor; Gossen, Germany), Michelson contrast ratios were equally follows: Kindle Burn Hard disk (LCD): 0,99 (50max: 20 cd/1000two; Lmin: 0,05 cd/thousandtwo); Kindle Paperwhite (Due east-ink): 0,91 (50max: two,10 cd/mtwo; Lmin: 0,ten cd/k2).
Nosotros and so measured the total amount of light (emitted plus reflected) by each device with a digital luminance meter (Konica Minolta LS-110; Tokyo, Japan) placed at 60 cm from the reading device at the exact lighting settings and eye level used during data acquisition. The Michelson ratios were as follows: Kindle Burn Hard disk drive (LCD): 0,96 (Lmax: 27,77 cd/grandtwo; Lmin: 0,58 cd/m2); Kindle Paperwhite (East-ink): 0,77 (Lmax: 11,27 cd/k2; Fiftymin: 1,44 cd/1000two); Paper book: 0,ninety (Fiftymax: 16,42 cd/m2; Lmin: 0,86 cd/m2).
Experimental Design and Procedure
A longitudinal full within-subjects design was employed. Each participant read on each of the iii reading supports. The sequence of the reading devices was randomized to command for order furnishings. The experiment took place in three sessions separated by 10 days on average (Session i, Session 2, Session 3). Reading sessions took identify at the same fourth dimension of the 24-hour interval. Text textile was a novel [21] in French linguistic communication, i.e. the mother tongue of all the participants. For each reading session a different part of the volume was employed (run into Tabular array 2). Since adults - on average - read prose text at 250 to 300 words per minute [22], [23] we expected people to consummate each reading session in about 70 min.
Table 2
Number of characters (without spacing) and number of words for each reading session.
| Readingsession | Capacity | Number ofcharacters | Number ofwords |
| i | I–II–Three | 75341 | 15943 |
| 2 | IV–Five | 78042 | 17037 |
| 3 | VI–Seven | 75473 | 16329 |
The exam was performed in a controlled and standardized room at LUTIN - Paris (www.lutin-userlab.fr). A schematic representation of the process is provided in Figure 2.
Experimental procedure: schematic representation.
VFS = Visual Fatigue Scale; CFF = Critical Flicker Fusion; CT = Comprehension Test.
After giving written consent, participants familiarized themselves with the reading device. Each experimental session started with the subjective visual fatigue scale (VFS - [13]), and was followed by the Disquisitional Flicker Fusion test (CFF). Subsequently that, participants sat on a comfortable chair at a stock-still altitude of approximately lx cm from the reading support (placed on a tailor-made bookrest allowing a 45° reading angle) and the eye tracker was calibrated.
Participants were so required to silently read the selected part of the novel (see Table ii) on one of the randomly assigned supports, while their eye data were recorded. At the end of each reading session, participants underwent the VFS and the CFF for the 2d time. After that, a comprehension examination (CT) was administered in club to verify that participants had effectively read the book, together with a subjective preference scale [v]. The CT consisted of 5 questions for each of the three reading sessions selected from http://colleges.ac-rouen.fr/abaquesne/activites/francais/belam/qcmbelam.htm.
Dependent Variables
CFF (Critical Flicker Frequency)
The flicker fusion is the visual phenomenon in which a repetitively presented stimulus (flickering stimulus) appears as a single continuous stimulus. A fall in CFF values reflects a drop in the sensory perception function, attributable to a subtract in alertness [24]. As to visual fatigue, there are controversies related to the reliability of this measure. Inside similar studies, to the authors' knowledge just ane study [17] was able to observe changes in visual fatigue whereas others were not [xi], [18]. With the aim to verify the soundness of the CFF, a staircase method collecting 3 ascending and iii descending presentations (with 1 Hz steps) in an alternate order was used to detect the thresholds. For the ascending trials, participants were required to indicate when the low-cal appeared to transition from flickering to continuous by pressing a push. Conversely, for the descending trials, they were required to printing the push button when the light appeared to transition from continuous to flickering. The CFF was measured in Hz at the beginning and at the end of each reading session.
Centre blink
The eye blink, the rapid closing and reopening of the eyelid, is well known indicator of visual fatigue [25], [26], [27].
A large body of literature suggests that blinks decrease during reading (eastward.yard. [28]), and even more when reading on backlit video display terminals (VDT) [29], [30], [31], [32], [33], [34]. According to Blehm [30], such a reduction contributes to a poor tear film quality and temporarily stresses the cornea (producing increased corneal exposure), causing dry eye. The dry eye is one of the near common symptoms of the Computer Vision Syndrome (CVS), which is the combination of centre and vision problems associated with the prolonged apply of video terminals [32].
With the aim of verifying the hypothesis that reading on backlit display decreases the number of blinks with respect to hard copy material, the number of heart blinks per second (BPS) was chosen as a dependent variable. BPS was calculated as the quotient of the full amount of eye blinks that occur in each reading session divided past the duration (in seconds) of each reading session.
Visual Fatigue Scale (VFS)
A rating calibration of visual fatigue (VFS - [thirteen]) was administered at the beginning and at the stop of each reading session. It consisted of 6 items: 1) I accept difficulties in seeing; two) I accept a strange feeling around the eyes; three) My eyes feel tired; 4) I experience numb; 5) I take a headache; half-dozen) I experience dizzy looking at the screen. Each item was rated on a 10-point Likert scale.
Subjective preference
Similarly to Siegenthaler et al. [14], subjective preference was judged on a seven-indicate Likert scale for each reading device.
Results
The significance level α was prepare at.05 for all statistical analyses. Primal variables (i.due east. CFF, BPS) were analyzed with a repeated measures analysis of variance (rmANOVA), and p values were adapted following a Greenhouse-Geisser correction [35]. Ordinal variables (i.east. VFS, Subjective preference) were analyzed with a Friedman's ANOVA [36], while the Wilcoxon paired-sample test method [37] was used for planned comparisons (a Bonferroni correction [38] was applied). Means and standard deviations for each of the dependent variables are reported in Table 3.
Table three
Means and standard deviations (italic) for each of the dependent variables.
| Dependent Variable | Reading Device | |||
| LCD | E-ink | Paper | ||
| CFF (Hz) | Before | 41,lx (1,66) | 41,54 (i,65) | 41,82 (1,70) |
| Afterwards | 40,65 (1,48) | 41(one,76) | 41,28 (1,44) | |
| VFS (one–10) | Before | ane,76 (0,62) | 1,85 (0,89) | i,79 (1) |
| Subsequently | 3,36 (1,55) | ii,90 (one,65) | ii,44 (1,58) | |
| BPS (blinks/second) | 0,43 (0,nineteen) | 0,61 (0,25) | 0,61 (0,32) | |
| Subjective Preference(ane–7) | three,55 (i,44) | four,45 (ane,88) | half-dozen,64 (0,64) | |
The first requirement for proceeding further into the analysis was to make sure that participants had effectively read and understood the book. This was validated past the absence of incorrect answers to the CT. The second requirement consisted in verifying that participants spent at least one hour on each reading session: independently from the support, participants read on average 73 min (SD 10 min). For reference only, an analysis on reading speed was conducted and no pregnant differences were found neither between the reading supports nor the reading sessions (all Fdue south due north.s.).
Two variables underwent a measurement earlier and after reading: the CFF and the VFS.
Equally to the CFF, a time issue was found (F(1, 11) = fifteen,91, p<.005 ηii p = .59, Figure 3-left), revealing a significant drop in sensory perception afterward reading, independently from the device. Furthermore, no device result and no interactions between device and fourth dimension were found.
CFF (left) and VFS (correct) before and afterwards reading for each reading device.
Vertical bars denote 95% confidence intervals calculated using Morey' s correction [39], [forty]. N = 12.
With regard to the VFS, a main effect was found (Tentwo r (v, 12) = 30.83, p<.001, Figure 3-right). Higher scores were found later on reading on the LCD (Z = two.93, p<.01, r = .60), whereas no differences were found for the E-ink (Z = 2.12, north.s.), nor for the Paper book (Z = 2, n.s.).
Concerning the number of eye blinks per second (BPS), since the Shapiro-Wilk's exam [41] revealed information to be not normally distributed, a Box-Cox transformation [42] was applied. A principal effect was constitute (F(ii, 22) = 4.17, p<.05, η2 p = .27, Figure 4). Planned contrasts between LCD and Eastward-ink (F(1, 11) = 6.xxx, p<.05, ηtwo p = .36) and between LCD and Paper (F(i, 11) = vi.59, p<.05, η2 p = .38) showed that reading on LCD significantly decreases the number of blinks with respect to other devices. Furthermore, the non-significant planned contrast between Paper and E-ink (F(i, 11) = .06, n.s.), revealed that both the devices generate a very similar blink beliefs.
BPS for each reading device.
Vertical bars denote 95% confidence intervals calculated using Morey' s correction [39], [40]. N = 12.
With the aim of verifying whether our results are attributable to the higher level of luminance emitted by the LCD, an analysis of average pupil size (APS) was carried out. Since the man educatee primarily constricts as luminance increases [43], reduced APS was expected for the LCD. A main effect was found (F(2, 22) = 11.92, p<.001, η2 p = .52). Planned contrasts between LCD and East-ink (F(1, 11) = 27.12, p<.001, η2 p = .71) and betwixt LCD and Paper (F(1, 11) = 9.xv, p<.05, η2 p = .45) showed that the higher level of luminance emitted by the LCD (encounter Materials and Methods) reduces the size of the pupil with respect to the other devices. Furthermore, the non-significant planned dissimilarity between Paper and E-ink (F(1, 11) = 1.88, due north.s.) revealed that reading on these devices leads to similar tonic pupil diameter.
As to Subjective preference, a primary issue was found (X2 r (2,12) = 13.35, p<.005, Effigy five). Planned contrasts between LCD and Newspaper (Z = ii.93, p<.01, r = .60) and between Paper and E-ink (Z = 2.49, p<.05, r = .51), indicated a preference for the paper book. The planned contrast betwixt LCD and E-ink (Z = 1.52, n.s.), revealed no deviation between the ii devices in terms of personal preference.
Subjective preference for each reading device.
Vertical confined denote 95% conviction intervals calculated using Morey' s correction [39], [40]. N = 12.
Word
The aim of the present written report was to compare prolonged reading on iii different supports regarding their effects on visual fatigue. Likewise Kang et al. [17], and Chang et al. [19], variables such as font size, typeface and number of words per page were not manipulated and were kept constant across the three devices for the unabridged reading sessions. Subjective measures (VFS) suggested that prolonged reading on the LCD (Kindle Fire HD) triggers college visual fatigue with respect to the E-ink (Kindle Paperwhite) and the newspaper book. Concerning objective measures (BPS and CFF), contrasting results were found.
As to CFF, results revealed a meaning drop in sensory perception afterwards reading independently from the device, thus failing to show significant differences among the three reading supports. On the one paw, these results are in line with previous studies employing the CFF for similar purposes, which did not succeed in finding differences between paper book, Due east-ink and LCD [11] and betwixt E-ink and LCD [18]. On the other hand, although our experimental plan has some similarities with that of Kang et al. [17], where the task consisted of reading novelettes for xl to 60 min, our results are contrasting. These authors found a significant difference between the newspaper book and the LCD, namely a larger CFF reduction when reading on the LCD. In the present written report, nosotros could non replicate this finding.
With regard to BPS, experimental evidence indicated that reading on the LCD leads to a larger decrease in the number of blinks, with respect to the other supports. This effect is in line with a large number of studies on CVS (for a review see [32]), where the use of backlit displays is usually associated with a decreased frequency of blinking and an increased rate of tear evaporation, each of which contributes to dry eyes. In fact, prolonged display exposure contributes to incomplete blinking provoking tear film instability [44], which is one of the main factors for visual fatigue on VDT [45].
In contrast with previous studies, where no differences in terms of perceived visual fatigue (VFS) were establish betwixt LCD, E-ink and paper book [two] and LCD and E-ink [xviii], our results showed that participants felt visually fatigued only when reading on the LCD. Such a finding might be attributable to the longer reading sessions employed in our study (on average 73 min, SD x min), with respect to previous studies [xi], [18].
Finally, results on Subjective preference suggest that participants with no experience with e-readers prefer paper books. The overall belief that digital reading media reduce the pleasance of reading could exist cultural rather than cerebral [46]. Moreover, since reading habit for paper books is ordinarily fixed in childhood [17], information technology's quite obvious that people prefer paper books rather than eastward-books.
In conclusion, our results might be imputable to the higher level of luminance emitted by the LCD (see Materials and Methods). With respect to the paper book and the E-ink, reading on the LCD reduces the size of the pupil (APS) and the frequency of eye blink (BPS), and increases the perceived visual fatigue (VFS).
Although the Kindle Burn Hard disk adopts a final generation LCD with IPS (in-plane switching) technology, advanced polarizing filter, and anti-glare applied science, the issues related to backlight engineering science are still present. In contrast to LCD-displays, which have been associated with dumb reading performance [xiv] and higher visual fatigue [17], results on Eastward-ink displays are encouraging.
Since visual discomfort and related symptoms occurring in VDT workers have been recognized as a growing health trouble [32], we believe that the growing spread of e-readers should be taken into business relationship besides. Although the aim of this written report was to make an up-to-date comparison of reading devices apropos their furnishings on visual fatigue, information technology should be emphasized that comparisons with previous studies, employing older brandish technologies, take some limits. The use of reading devices as independent variables clearly leads to device-dependent results.
Future studies will include the manipulation of the length of the reading sessions, the luminance levels of the displays, and the study of binocular vision on prolonged reading [47].
Acknowledgments
We would like to thank Andrea Carbone, Damien Paillé, Jean-Luc Perrin, Kaoutar El Ghali and Roland Brémond for their precious assist.
Funding Argument
The authors accept no support or funding to report.
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3873942/
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