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Article
Spectral Overlays for
Reading Difficulties:
Oculomotor Function
and Reading Efficiency
Among Children and
Adolescents With
Visual Stress
Ma
´rcia Reis Guimar~
aes
1,2
,
Douglas de Ara
ujo Vilhena
1,2,3,4
,
Stephen J. Loew
2,5
, and
Ricardo Queiroz Guimar~
aes
1,2
Abstract
This study analyzed the effects of spectral overlays on ocular motility during reading
among a clinical group of children and adolescents experiencing visual–perceptual
distortions of text. We reviewed the records of 323 eye-hospital patients diagnosed
with visual stress and divided this participant sample into two age-based cohorts:
children (n¼184; Mean [M] age ¼10.1, standard deviation [SD]¼1.3 years) and
adolescents (n¼139; Mage ¼14.6, SD ¼1.5 years). We used a Visagraph III Eye-
Movement Recording System to record ocular motor efficiency while reading with
1
NeuroVision Department, Hospital de Olhos Dr. Ricardo Guimar~
aes, Nova Lima, Brazil
2
Laboratory of Applied Research in Neuroscience of Vision, Universidade Federal de Minas Gerais, Nova
Lima, Brazil
3
Graduate Program on Psychology: Cognition and Behavior, Department of Psychology, Universidade
Federal de Minas Gerais, Belo Horizonte, Brazil
4
Faculty of Psychology and Education Sciences, Universidade do Porto, Portugal
5
School of Psychology and Behavioural Science, University of New England, Armidale, Australia
Corresponding Author:
Douglas de Ara
ujo Vilhena, Laboratory of Applied Research in NeuroVision, Universidade Federal de
Minas Gerais, Rua da Paisagem, 220—Vila da Serra, Nova Lima, MG-CEP 30720-600, Brazil.
Email: douglasvilhena@ufmg.br
Perceptual and Motor Skills
0(0) 1–20
!The Author(s) 2019
Article reuse guidelines:
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DOI: 10.1177/0031512519889772
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and without spectral overlays, and we examined the following parameters:
(a) Fixations, (b) Regressions, (c) Span of Recognition, (d) Reading Rate, (e)
Relative Efficiency, and (f) Comprehension. Our results showed that using one or
some combination of 10 participant-selected spectral overlays immediately and sig-
nificantly (p<.001) reduced the number of Fixations and Regressions per 100
words, while there were significant (p<.001) gains in positive factors such as
Span of Recognition, Reading Rate, Relative Efficiency, and Comprehension.
Our findings indicate that spectral filtering can be an effective tool for helping
many young patients who experience visual–perceptual distortions while reading.
Future expanded research employing eye-tracking technology is clearly needed.
Keywords
child motor development, eye-tracking analysis, ocular motor skills, perceptual dis-
orders, reading difficulties, spectral overlays, visual measurement, visual perception,
visual stress
Introduction
Reading is a challenging task, as it not only demands a complex cognitive net-
work to process reading content, but it also requires a refined coordination of
the eyes (and simultaneously compensating for head movements) in order to
efficiently track lines of text. Thus, a growing number of researchers have inves-
tigated reading difficulties beyond those that can be explained by socioeconomic
factors (e.g., poor education), neurocognitive anomalies (e.g., dyslexia), and
optometric or ophthalmological deficits (e.g., refractive errors and visual
acuity) (Gaertner et al., 2013; Nicolson & Fawcett, 2019; Stein, 2019;
Vidyasagar, 2019). As will be detailed here, many studies have reported that
the reading process can also be compromised by inadequate ocular motor skills
or neural-based visual processing anomalies (such as those present in patients
with Meares-Irlen syndrome or visual stress [VS]).
VS is characterized by visual discomfort when reading (e.g., sore or tired eyes,
headaches, photophobia, excessive blinking or squinting) and visual–perceptual
distortions of text (e.g., “halos” or “patterns” around words, or words appear-
ing to “move,” “vibrate,” or “shimmer”). VS symptoms are typically accompa-
nied by a clear and rapid deterioration in oral reading ability, usually occurring
within 5–10 minutes (Evans & Allen, 2016; Evans, Allen, & Wilkins, 2017; Loew
& Watson, 2013). Estimates of the incidence of VS in the general population
have ranged from 5% (Evans & Allen, 2016) to 24% (Jeanes et al., 1997), while a
number of studies have found significant symptoms of VS-related reading dis-
comfort in 12–14% of unselected samples of school and university students
2Perceptual and Motor Skills 0(0)
(Kriss & Evans, 2005; Loew, Marsh, & Watson, 2014; Loew et al., 2015).
However, the levels of VS severity appear to lie on a continuum from mild to
highly symptomatic (Evans & Allen, 2016; Evans & Joseph, 2002).
With respect to underlying biological factors, several studies have identified a
range of biochemical anomalies in people with VS, including abnormal metab-
olism of essential fatty acids (crucial for retinal and visual-pathway functioning;
Robinson, McGregor, Roberts, Dunstan, & Butt, 2001) and significant anom-
alies in urinary amino acids and blood lipids that may indicate immune system
activation (e.g., lower cholesterol levels, including low density lipoprotein [LDL]
cholesterol, and higher heptadecanoic acid levels; Sparkes, Robinson, Dunstan,
& Roberts, 2003). There is also a strong genetic predisposition to VS, as 80% of
VS-diagnosed children have one or both parents with similar symptoms
(Robinson, Foreman, & Dear, 1996, 2000). A higher prevalence of certain var-
iant alleles of the apolipoprotein-B100 gene (coding for a key cholesterol trans-
porter molecule) has also been identified in people with VS symptoms (Loew &
Watson, 2012).
It has been widely reported that VS symptoms can be alleviated by the use of
spectral overlays (colored plastic sheets) placed over a page of text when read-
ing. One variety of these translucent overlays is available from Irlen
International
TM
, and a set of these overlays contains a wide selection of
spectral-filtering colors ranging from those favoring shorter wavelength trans-
missions (e.g., “Aqua,” “Blue-Gray,” and “Turquoise” overlays) to those that
favor longer wavelength light (e.g., “Yellow,” “Goldenrod,” and “Peach” over-
lays). Many studies have reported positive reading effects through the use of
spectral overlays, including improvements in letter or number recognition and in
reading speed and accuracy (Allen, Evans, & Wilkins, 2012; Evans & Joseph,
2002; Kriss & Evans, 2005; Ludlow, Wilkins, & Heaton, 2006, 2008; Nichols,
McLeod, Holder, & McLeod, 2009; Noble, Orton, Irlen, & Robinson, 2004;
Singleton & Henderson, 2007; Wilkins, Lewis, Smith, Rowland, & Tweedie,
2001; Wright, Wilkins, & Zoukos, 2007). A recent study involving Brazilian
elementary school children also found that those presenting with several symp-
toms of reading discomfort were three times more likely (odds ratio ¼3.36) to
experience increased reading speed with spectral filters compared with readers in
a group of children with fewer symptoms (Garcia, Momensohn-Santos, &
Vilhena, 2017). Longitudinal studies have produced analogous results, for exam-
ple, Jeanes et al. (1997) and Wilkins et al. (2001) respectively found that 24%
and 31% of unselected children who volunteered to select an overlay of their
preference continued to read with it eight and 10 months later; thus, novelty or
placebo effects were unlikely to have been primary motivational factors. Noble
et al. (2004) found that reading with overlays helped VS-diagnosed children with
school-documented delayed reading reach expected grade-level reading norms
within three months, while a control group comprising similar children showed
negligible gains.
Guimar~
aes et al. 3
While the use of spectral filters has remained controversial, with some
researchers arguing that no benefits to reading by means of such tools have
been validated through scientifically objective measures (Griffiths, Taylor,
Henderson, & Barrett, 2016; Hyatt, Stephenson, & Carter, 2009; Ritchie,
Della Sala, & McIntosh, 2011, 2012), recent studies employing highly objective
measures (e.g., functional Magnetic Resonance Imaging) have detected hyper-
excitability of the visual cortex in research participants with VS, epilepsy, or
migraines and have produced evidence of marked reductions in excitation when
participants read while using self-selected colored filters (Chouinard, Zhou,
Hrybouski, Kim, & Cummine, 2012; Huang et al., 2011; Kim, Seo, Ha, &
Kim, 2015; Wilkins, Huang, & Cao, 2007). As strong criticisms of spectral
filter use persist, this study hypothesized that eye-tracking technology might
provide a novel, parallel means of objectively testing the validity of reported
benefits of spectral filters for people with VS by providing measurable physical
evidence of any changes or absence of changes in ocular motor skills.
Currently, the two most widely accepted neurological explanations of VS
(and spectral overlays as an assistive tool for VS) are the Cortical
Hyperexcitability and the Transient-on-Sustained Inhibition (ToSI) theories.
The former argues that visual distortions while reading are caused by hyper-
excited or abnormal neuronal firing in the visual cortex due to inadequate sen-
sorial excitation diffusion. Spectral overlays then might allow a greater diffusion
or distribution of reading information to less excited areas (Allen, Gilchrist, &
Hollis, 2008; Wilkins et al., 2001). This theory has been supported by the
reported benefits of spectral filtering for other conditions associated with corti-
cal hyperexcitability such as autism spectrum disorders (Ludlow, Taylor-
Whiffen, & Wilkins, 2012; Ludlow & Wilkins, 2016; Whitaker, Jones,
Wilkins, & Roberson, 2016), migraine headaches (Evans et al., 1999), photosen-
sitive epilepsy (Wilkins et al., 1999), and stroke (Beasley & Davies, 2013).
Alternatively, the ToSI theory concerns the relationship between the sus-
tained visual system (SVS) and the transient visual system (TVS), two parallel
spatiotemporal divisions of the neuro-visual network that simultaneously pro-
cess visual information transmitted via the parvocellular and magnocellular
retino-geniculo-cortical pathways, respectively (Pammer & Wheatley, 2001;
Stein & Walsh, 1997). The SVS primarily responds to low temporal and high
spatial frequencies (important for color and fine spatial details), while the TVS is
sensitive to high temporal and low spatial frequencies, and its high-velocity
conduction of neural signals is believed to be crucial for inhibiting (masking)
prior SVS-transmitted images formed from visual data received in immediately
preceding saccades (hence the term ToSI). Accordingly, highly efficient magno-
cellular pathway processing is essential for optimal functioning of the TVS and
is also crucial in controlling saccades, fixations, binocular coordination, and
general ocular stability.
4Perceptual and Motor Skills 0(0)
To date, it appears that only two studies have analyzed spectral overlay
effects with an eye-tracking system. Solan, Ficarra, Brannan, and Rucker
(1998) investigated the effects of filters on ocular motor skills (using
Visagraph
TM
II equipment) among elementary school children with and without
reading disabilities. Despite using only three spectral filters (Lee Filters
TM
clear,
gray and blue), Solan et al. (1998) found that 75% of the reading-impaired
participants demonstrated an increased reading rate and a decreased number
of fixations and regressions when using the blue filter to the point that earlier
statistical differences between the reading-impaired and control groups on these
variables disappeared. More recently, Razuk et al. (2018) found that a group of
18 dyslexic children showed reduced eye-fixation durations when reading with a
“green” versus a “yellow” filter (p<.02) and versus no filter (p<.05). For the
age-matched control group without dyslexia, there were no differences in mean
fixation durations between any filter conditions.
Although these prior studies shed light on improved ocular motor skills from
the use of colored filters when reading, they did not use a wide variety of spectral
overlays (with broad-ranging transmission specificities) and may not have
obtained optimal or comprehensive results. Moreover, participants in both stud-
ies were children with reading disabilities who may or may not have had VS that
is presumed to be the basis for needing spectral filters. Thus, this study used
state-of-the-art eye-tracking technology (Visagraph
TM
III equipment) to
observe the effects of VS child and adolescent participants’ self-selected overlays
(from a set of 10 colors) on their reading-related ocular motor skills.
Method
Participants
We performed this study at the NeuroVision Department of the Hospital de Olhos
de Minas Gerais, which mainly attends to patients with vision-related learning
problems. We reviewed records of all patients (n¼883) assessed from June 2007
to April 2015 in relation to ophthalmic variables (including visual acuity [far and
near], high-order aberrations, phorias, stereopsis, color vision, contrast sensitivity,
and visual field). All of these patients underwent assessments for the presence of
VS symptoms (including patient responses to spectral overlays) and, for all
patients, eye-movement data were recorded while reading. From this large data
pool, we identified patients who met the following five criteria: (a) self-reported
“visual distortions while reading” and “reduced distortions when viewing text
through an overlay,” (b) clinical ophthalmologist affirmation of their VS symp-
tomatology, (c) good binocular visual acuity (better than 20/20 Snellen Chart)
and normal color vision (Pseudoisochromatic Ishihara 25 Plates Test and
Farnsworth D15 Dichotomous Test), (d) a score of at least 70% on a
Comprehension Test, and (e) no extreme anomalies in their eye-tracking
Guimar~
aes et al. 5
recordings (we applied the Outlier Labeling Rule [with a g-value of 2.2] and found
that eye-tracking data from 22 of the 883 patients were extreme). It was crucial to
apply these criteria in order to separate those patients who could be definitively
categorized as having VS morbidity from those who may have other disorders
that can affect reading ability, as a common flaw of many prior studies of overlay
effects has been the use of cohorts with general reading disabilities, creating a
participant sample bias, as spectral filters are presumed to mainly benefit people
with VS (Evans & Allen, 2016).
The final “VS Group” consisted of 323 VS-diagnosed patients who met all of
the above criteria. We then divided this sample into two age-related subgroups:
children (n¼184; age range ¼8–12; Mage ¼10.1, SD ¼1.3 years; 67% male)
and adolescents (n¼139; age range ¼13–17; M
age
¼14.6, SD ¼1.5 years; 63%
male), as age can affect the scale of any intervention-related changes in reading
skills. The expected grade norms calculated for participants (according to the
Visagraph III Test-Manual: Taylor Associates, 2006) indicated that mean group
values closely corresponded to the reading performances of 5th-grade children
and 10th-grade adolescents.
When first seen, all participants’ parents or legal guardians consented (and
participants assented) to participate in a future study. The study was conducted
in accordance with the Declaration of Helsinki (2008).
Instruments
We assessed VS symptom levels with the Irlen Reading Perceptual Scale (IRPS;
Irlen, 2003), a tool that challenges patients with various visually stressing images
and tasks (e.g., counting how many lines or symbols are in an image). The IRPS
is designed to increase visual discomfort in order to quickly identify VS symp-
toms. After assessing baseline visual discomfort levels with the IRPS, the
10 Irlen Overlays were individually presented to participants in the same
order (Gray, Blue-Gray, Turquoise, Aqua, Green, Peach, Rose, Goldenrod,
Yellow, and Purple) and were placed over a page of a text written in Dutch
(meaningless to the patient). Participants were then asked to assess whether each
overlay improved or worsened their visual comfort and the image quality, until
they eventually selected an overlay (or two-overlay combination) that they felt
gave the most reading comfort.
Participants were also given the option of choosing no overlay at all; however,
among the initial 883 patients, only 14 (2%) did so. This small group did not take
part in the comparisons of reading eye movements with and without an overlay
and were not included in the VS group. Following each participant’s selection of
their preferred overlay(s), we presented them with 11 images illustrating possible
visual distortions while reading in order to verify whether they felt such symptoms
were minimized when viewed through their selected overlays.
6Perceptual and Motor Skills 0(0)
As noted, participants’ ocular motor skills were measured using a Visagraph
III Eye-Movement Recording System (Taylor Associates, New York).
This system uses lens-free goggles with inbuilt infrared sensors to record eye
movements during reading. As these goggles are worn by the participant, the
goggles automatically compensate for any small movements of the head or
body. The following oculomotor and reading parameters were measured and
analyzed: (a) Fixations: number of eye pauses (stationary periods) in a reading
from left to right per 100 words, (b) Regressions: number of times eye move-
ments are directed from right to left per 100 words, (c) Span of Recognition:
number of words read divided by the number of fixations, (d) Reading Rate
(with comprehension): number of words read in 1 minute without rereading, (e)
Relative Efficiency: reading rate divided by fixations and regressions, and (f)
Comprehension: percentage of correct answers in a questionnaire concerning the
content of the text that was read (10 yes or no questions).
Procedure
We administered the Visagraph III eye-tracking examination after the partic-
ipants self-selected their most preferred overlay(s). We adjusted the eye-
movement recording system to each participant’s interpupillary distance,
taking into account any refractive corrections. All participants were provided
with a text appropriate for their reading level and cognitive capacity in order to
minimize abnormal reading eye movements and allow a continuous reading
performance to be recorded. Participants read the texts aloud, first without an
overlay (baseline) and then with their chosen overlay(s).
The order in which the two tests were given remained consistent for all
participants, as there is prior broad research agreement that marked deteriora-
tions in the reading skills of individuals with VS usually occur within a
few minutes and would be expected to occur during the second reading test.
Thus, a key premise underlying this aspect of the study design was that any
results inferring improvements in eye-movement reading efficiency while using
the overlays would (in theory) be manifested on the second, rather than the first,
of the two reading tests. All texts were read from a viewing distance of 40 to
45 cm, and under standard office lighting (two-tube cool-white fluorescent lamp
ceiling-fixtures; 20 W 60 cm-tubes; correlated color temperature: 5,000 K; 120 Hz
flicker cycle).
The reading material consisted of a single paragraph of black text, printed on
a white paper, in Times New Roman font size 18 (we used a larger font to
highlight any reading-fluency problems that might be attributable to an inade-
quate Span of Recognition). The paragraph was 11.5 cm wide and made up of
10 lines (approximately 7 words in each); however, data from the first and last
lines were excluded from the analysis. After each reading, participants answered
Guimar~
aes et al. 7
10 questions about the text, permitting us to evaluate whether reading compre-
hension was good.
Statistical analysis
We used IBM SPSS Statistics (version 21.0, Chicago, IL) for all data analyses.
As Pearson bivariate correlations were above 0.97, the average values of eye-
movement data for the right and left eyes were calculated in relation to
Fixations, Regressions, and Span of Recognition.
To check for gender and age differences in the effects of spectral overlays
interventions on the VS patients’ eye movements and reading performance, we
conducted a series of two-factor split-plot analyses of variance (ANOVAs), with
Fadjusted as per the Greenhouse–Geisser method. The between-group variable
was gender group (girls vs. boys) or age-group (children vs. adolescents), and
the within-group variable was the reading condition (without overlay vs.
with overlay).
To establish the clinical significance of any group differences, we calculated
Cohen’s dto determine the effect size and interpreted results using Cohen’s
(1988) criteria of 0.2 for a small effect, 0.5 for a medium effect, and 0.8 for a
large effect. Pearson bivariate correlations were used in all sample comparisons,
effectively merging the ocular motor skills parameters with the two conditions
(“with” and “without” spectral overlays). Accordingly, we considered a pvalue
of less than .05 to be statistically significant.
Results
In this study, participants’ preferred-overlay selections ranged across all 10 of
the overlays presented (including 35 combinations), with the most frequently
chosen colors being “Purple,” “Gray,” and “Turquoise.” The results for each
parameter measured by the Visagraph III (with and without spectral overlays)
are shown in Table 1, and split-plot ANOVA analyses (Group Condition) are
illustrated in Figure 1.
With respect to any changes in the reading efficiency parameters when mea-
sured during the intervention condition (spectral overlays), there were statisti-
cally significant improvements across all six measures, with small-to-moderate
effect sizes found in each of these analyses (Table 1). When using spectral over-
lays, the children’s number of Fixations immediately decreased by 21%
(p<.001, d¼0.50) and the adolescents’ Fixations decreased by 13% (p<.001,
d¼0 .27). Likewise, Regressions were reduced by 26% (p<.001, d¼0.45) and
19% (p<.001, d¼0.26), respectively. Reading with overlays was significantly
improved on the other parameters as well. Span of Recognition (the amount of
information captured in each eye fixation) improved by 24% (p<.001, d¼0.51)
and 18% (p<.001, d¼0.40) for the children and adolescents, respectively.
8Perceptual and Motor Skills 0(0)
Table 1. Ocular Motor Skills, Without and With Spectral Overlays (Means), Intervention Differences (D), and Interaction Statistics (Groups
or Conditions).
Parameters
Children (n¼184) Adolescents (n¼139)
Interaction statistics
(Group Condition)
Without overlay With overlay
D(%) Pd
Without overlay With overlay
D(%) pd
F(1,
321) pMean SD Mean SD Mean SD Mean SD
Fixations 163.6 75.3 129.6 61.1 –20.8 <.001 0.50 135.7 63.8 118.2 64.3 –12.9 <.001 0.27 11.4 .0008
Regressions 42.9 28.1 31.6 21.5 –26.3 <.001 0.45 31.5 22.2 25.6 22.6 –18.7 <.001 0.26 8.15 .0046
Span Recognition 0.75 0.33 0.93 0.38 24.0 <.001 0.51 0.89 0.36 1.05 0.43 18.0 <.001 0.40 0.46 .4975
Reading Rate 167.7 83.1 214.9 94.0 28.1 <.001 0.53 212.8 86.9 255.6 107.1 20.1 <.001 0.44 0.40 .5265
Relative Efficiency 1.21 1.26 1.93 1.57 59.5 <.001 0.51 1.81 1.39 2.67 2.01 47.5 <.001 0.50 1.18 .2777
Comprehension 87.2 10.8 92.3 8.7 5.8 <.001 0.52 85.8 10.5 90.7 9.7 5.7 <.001 0.48 .003 .9582
Note. SD ¼standard deviation; D¼difference between conditions (Without and With overlays); p¼statistical significance; d¼effect size.
9
Figure 1. Split-plot analysis of the interaction effects of spectral overlays on Visagraph III Eye-
Movement Recording System parameters. (a) Fixations, (b) Regressions, (c) Span of
Recognition, (d) Reading rate, (e) Relative Efficiency and (f) Comprehension. Legend: gray
line ¼children; black line ¼adolescents.
10 Perceptual and Motor Skills 0(0)
Reading Rate was 28% faster for the children (p<.001, d¼0.53) and 20%
faster for the adolescents (p<.001, d¼0.44), with the two groups able to read
43 and 47 additional words per minute. Relative Efficiency improved by 60%
among the children (p<.001, d¼0.51), and 48% among the adolescents
(p<.001, d¼0.50). In addition, Text Comprehension also significantly
improved when reading with spectral overlays in both age groups (p<.001,
d¼0.52 and p<.001, d¼0.48), with the sample as a whole scoring 92% on a
comprehension test following each participant’s reading of a text in the overlay
condition compared with 87% after reading an equivalent text without spectral
overlays.
Split-plot analyses (see Table 1) revealed a statistically significant interaction
between Age Groups and Conditions (without and with overlays) regarding
Fixations, F(1, 321) ¼11.4, p¼.0008, and Regressions, F(1, 321) ¼8.15,
p¼.0046. No significant interactions were observed in relation to the other
parameters (Table 1). Post hoc analyses of these interactions showed that the
reductions in the number of Fixations, and Regressions, were significantly more
pronounced among children compared with adolescents (Figure 1). In other
words, children’s ocular motor skills appear to show greater immediate
improvements using spectral overlays in comparison to adolescent readers.
We found significant gender-related eye-tracking differences (with post hoc
analyses favoring girls better reading-related eye movements), with small effect
sizes in relation to Fixations (p¼.013, d¼0.21), Span Recognition (p¼.0096,
d¼0.21), Reading Rate (p¼.0023, d¼0.25), and Relative Efficiency (p¼.012,
d¼0.21), but only a nonsignificant trend in Regressions (p¼.07, d¼.15) and no
significant Comprehension differences. The gender sample did not differ in rela-
tion to age, and split-plot analyses revealed no significant interaction between
gender and age.
As seen in Table 2, the number of Fixations were strongly positively corre-
lated with Regressions (r¼.90) and strongly negatively correlated with Span of
Recognition, Reading Rate, and Relative Efficiency (r¼–.88, –.80, and –.75,
respectively). Regressions were also negatively correlated with Span of
Recognition, Reading Rate, and Relative Efficiency (r¼–.77, –.66, and –.64,
Table 2. Pearson Correlations Between Eye-Movement Parameters.
Parameters 2 3 4 5
1. Fixations .90
**
–.88
**
–.80
**
–.75
**
2. Regressions –.77
**
–.66
**
–.64
**
3. Span of Recognition .92
**
.95
**
4. Reading Rate .95
**
5. Relative Efficiency 1.0
Note. **p<.0001.
Guimar~
aes et al. 11
respectively). It was also of note that increased Span of Recognition was very
strongly and positively correlated with increases in Reading Rate and Relative
Efficiency (r¼.92, .95).
Discussion
The eye-tracking data recorded in this study showed immediate and significant
improvements in six oculomotor and reading parameters when children and
adolescents with VS read using self-selected spectral overlays compared with
their baseline results. With overlays, there were statistically significant decreases
in the number of Fixations and Regressions, whereas there were significant
increases in Span of Recognition, Reading Rate, Relative Efficiency, and
Comprehension. All of these eye-movement changes represent improvements
for reading purposes. We observed more efficient eye movements from spectral
filters with regard to the number of Fixations (per 100 words), as these were
reduced by 21% for children and 13% for adolescents. Similarly, the use of
spectral overlays decreased the proportion of regressive saccades by 26%
among children and 19% among adolescents with VS in this study, reducing
time and effort in the reading process.
The Span of Recognition (breadth of text in words or letters perceived during
one fixation) averaged .75 of a word per fixation at baseline for the children, and
this value jumped by 24% to almost full word recognition (.93) per fixation
when children read using the spectral overlays intervention. A wider Span of
Recognition should also assist the short-term memory for processing and
manipulating larger amounts of information during each eye fixation.
We obtained similar improvements with adolescents who were able to visualize
in excess of one word (1.05) per fixation when using spectral overlays, an
increase of 18% from their baseline levels. This implies that the spectral inter-
vention increased both foveal and parafoveal visual information processing and
this, in turn, would likely assist in predirecting the ensuing saccade to the next
optimal fixation point and allow more fluent reading (Ashby, Yang, Evans, &
Rayner, 2012), as, in fact, evidenced by reductions in Fixations and Regressions
in both age groups.
With respect to Reading Rate, both children and adolescents read faster
during the intervention condition (averaging 28% and 20% more words per
minute, respectively). Such immediate and substantial improvements in reading
rates also suggest that spectral overlays can promote more fluent reading for
many young people with VS. The Relative Efficiency parameter provided a
means of further evaluating reading performance by using a single, reliable
value that integrates the three most important eye-movement variables:
Fixations, Regressions, and Reading Rate. Moderate gains in Relative
Efficiency (Cohen’s d¼0.51) for the children and (d¼0.50) for the adolescents
showed that both groups of patients with VS improved their reading
12 Perceptual and Motor Skills 0(0)
performances. Our results also showed that Comprehension was markedly
improved with the use of spectral overlays.
Comparatively, we found that the reductions in the number of Fixations and
Regressions with the use of overlays were significantly greater in children com-
pared with adolescents, although these differences might have been partly due to
younger children starting from a lower reading efficiency baseline. In addition,
our data seemed to confirm the higher incidence of reading disorders (and of
neurodevelopmental problems generally) that have been found for males versus
females (Quinn, 2018). Even with respect to reading-related eye movements, our
post hoc analyses revealed that girls significantly outperformed boys on most
measures that were responsive to the intervention (Fixations, Span Recognition,
Reading Rate, and Relative Efficiency).
The high number of eye-movement regressions observed in the VS group
(at baseline) may be indicative of a greater necessity in these individuals for
corrective eye movements to recheck words (or phonemes) that were not suffi-
ciently attended to initially (i.e., were “skipped over”). Alternatively, this eye-
movement characteristic may reflect a need to adjust vergence (simultaneous
pupil movements) to allow a clearer visualization or it may occur due to con-
fused interpretation of prior content that then requires rereading. In individuals
with VS, however, regressions usually trace to an inefficient tracking of the lines
of text (Loew & Watson, 2013; Loew et al., 2014). In a sample of 27 children
with reading difficulties, Solan et al. (1998) found that using spectral filters
reduced the regression rate for their total group by 34%, a value similar to
our finding of 26% reduction among child participants. Thus, our results, dem-
onstrating that colored filters can significantly improve left-to-right eye-move-
ment efficiency and enhance perceptual accuracy, concur with Solan et al.’s
(1998) findings and are also consistent with positive reports of spectral overlay
effects for readers with VS in studies using dependent measures other than
eye tracking (Evans & Joseph, 2002; Garcia et al., 2017; Kriss & Evans,
2005; Ludlow et al., 2006, 2008; Nichols et al., 2009; Singleton & Henderson,
2007; Wilkins, Jeanes, Pumfrey, & Laskier, 1996; Wilkins et al., 2001; Wright
et al., 2007).
Past research has shown that students with reading disorders demonstrate a
higher number of Fixations while reading compared with other students
(Okumura, Wakamiya, Suzuki, & Tamai, 2006; Solan et al., 1998), possibly
due, at least in some instances, to the presence of visual distortions that neces-
sitate increased comprehension effort. Neurobiologically, to generate clear and
acute text visualization, the TVS and SVS must be highly synchronized so that
the viewer can continually erase the image created from preceding eye fixations.
This visual inhibition process is also referred to as visual backward masking
(Solan et al., 1998; Williams, Breitmeyer, Lovegrove, & Gutierrez, 1991).
A slight delay in the TVS may lead to delayed masking (inhibition) of the pre-
vious image, allowing it to outlast the normal duration of stimuli received
Guimar~
aes et al. 13
from the SVS and creating an after-imaging effect (or “visual noise”) that may
then interfere with new detailed text perception. The superimposed older image
inputs might generate a smeared or over-lapping image, explaining many of the
visual distortions reported by patients with VS (e.g., “halos” surrounding
words).
As it is already known that proficient, versus less capable, readers require
fewer eye fixations (eye pauses) and regressions (backward eye movements) to
read an identical passage of text, and prior research has shown that spectral
filtering increases the efficiency of the magnocellular pathway (Ray, Fowler, &
Stein, 2005; Stromeyer, Chaparro, Tolias, & Kronauer, 1997) and TVS–SVS
synchronization (Croyle, 1998), eye-tracking technology for refined eye-
movement analysis is a very logical next step for acquiring highly objective
measures of reading efficiency within research to assess the reported benefits
of spectral filters for VS, especially as ocular motor skills are only weakly
influenced by voluntary control during reading (Chase, Ashourzadeh, Kelly,
Monfette, & Kinsey, 2003; Greatrex & Drasdo, 1995; Stein, 2019).
Among the limitations of this study (and others) is its failure to fully control
for placebo effects, as some participants might expect any overlays placed before
them to be helpful. In the future, researchers might provide one overlay at
random, in addition to a clear overlay, presented in counterbalanced order to
all participants. This would allow testing for differences between self-chosen and
randomly chosen overlays, as it would limit building expectations of benefits
(placebo effect). Our own research design would have been improved by com-
paring reading-related eye-movement differences among participants with both
self-chosen spectrally tinted overlay and a randomly assigned clear overlay.
In partial response to this limitation, our use of four (of six) parameters that
measured large involuntary micro eye movements meant that some of our
dependent measures were less vulnerable to a placebo effect than dependent
measures in other studies. Meanwhile, a number of separate studies, not using
eye-tracking systems, have shown that self-chosen overlays yield greater perfor-
mance gains in comparison to: (a) randomly selected color filters (Bouldoukian,
Wilkins, & Evans, 2002; Wilkins & Lewis, 1999), (b) complementary colors
(Jeanes et al., 1997), and (c) aesthetically preferred overlays (Ludlow et al.,
2008). However, future research in this area should include an experimental
condition involving reading with a clear spectral overlay. Our study had several
clear and significant strengths in that our participant sample was very large, we
excluded participants without professionally identified VS, and we required all
participants to have 70% comprehension and good visual acuity. Yet, general-
ization of these findings may be limited by the fact that there may be VS severity
differences between our VS participants, identified by ophthalmologists from
among eye hospital inpatients, and ophthalmologist-identified individuals with
VS from among an outpatient population. Further research might next replicate
this study with a broader outpatient sample of VS participants.
14 Perceptual and Motor Skills 0(0)
An important demonstration within this study was that eye-movement
recording systems are important tools in reading research. They provide objec-
tive data reflecting eye-movement reading activity that may either result from or
cause reading problems, perhaps depending on the nature of different reading
disorders. In what appears to be only the third eye-tracking study of the VS
disorder and related overlay intervention strategies, we demonstrated that spec-
tral filtering can be beneficial for some children and adolescents who are strug-
gling with unexplained reading difficulties. This study showed that using spectral
filters during reading significantly improved participants’ ocular motor skills
(e.g., fewer Fixations and Regressions) and reading rate, presumably alleviating
baseline levels of print and background distortions among a clinical sample of
participants with VS. We propose that such improvements may also free work-
ing memory to permit greater time and effort to be directed toward “the mean-
ing of what is being read.”
Acknowledgments
The authors wish to thank Nigel V. Marsh, PhD, Department of Psychology, James
Cook University, Singapore, for his valuable assistance and advice concerning statistical
analysis.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research,
authorship, and/or publication of this article.
Ethical Statement
The Research Ethics Committee of the Universidade Federal de Minas Gerais approved all
procedures in the study (approval no. 49765115.0.0000.5149), and the study was con-
ducted in full accordance with the Code of Ethics of the World Medical Association
(Declaration of Helsinki, 2008) for research involving human participants.
Funding
The author(s) disclosed receipt of the following financial support for the research, author-
ship, and/or publication of this article: This study was financed in part by the
Coordenac¸~
ao de Aperfeic¸oamento de Pessoal de N
ıvel Superior—Brasil (Capes)—
Finance Code 001.
ORCID iD
Douglas de Ara
ujo Vilhena https://orcid.org/0000-0003-2670-7963
Guimar~
aes et al. 15
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Author Biographies
Ma
´rcia Reis Guimar~
aes, MD, PhD, is an ophthalmologist and Eye Pathologyst,
head of the Neurovision Department at Minas Gerais Eye Hospital. She earned
a doctorate degree in Ophthalmology and Neurosciences at Universidade
Federal de Minas Gerais (UFMG), a Master’s Degree in Molecular Biology
at Universite
´Paris VI, and is Graduate in Medicine at UFMG. She has a
Fellowship in Eye Pathology at Hospices Civils de Strasbourg (France),
Moorfields Eye Hospital (England) and Armed Forces Institute of Pathology
(USA). Guimar~
aes’s key research interests focuses on visual neuroscience, func-
tional vision and visual-related reading disorders.
Douglas de Ara
ujo Vilhena, MSc, is a doctoral student in Neuropsychology in
the Department of Psychology at UFMG with part in the Faculty of Psychology
and Education Sciences at Universidade do Porto. He has a Master’s Degree in
Human Development at UFMG, and is a Graduate in Psychology at UFMG
with part at University of Leeds. Vilhena’s key research interests focuses on
reading difficulties and aims to develop psychometric tests to evaluate reading
ability. He was granted by the Coordenac¸ ~
ao de Aperfeic¸ oamento de Pessoal de
N
ıvel Superior.
Stephen J. Loew, PhD, is an associate researcher of reading difficulties in the
School of Psychology at the University of New England and a research partner
with the Laboratory of Applied Research in Neuroscience of Vision at the
Federal University of Minas Gerais. Loew’s key research interests include the
nature of Meares-Irlen/visual stress syndrome, the overlap of associated symp-
toms with ADHD and other learning disorders, and the effects of increasingly
brighter classroom lighting on present-day literacy rates and learning in general.
Ricardo Queiroz Guimar~
aes, MD, Ph.D., is an ophthalmologist and head of the
Minas Gerais Eye Hospital. He earned a doctorate degree in Ophthalmology
and medical degree at UFMG. He has a Fellowship in Hospices Civils
Strasbourg (France), Moorfields Eye Hospital (England), Hotel Dieu Paris
(France) and Georgetown University (USA). Guimar~
aes is an active lecture
and his key research interests focuses on visual neuroscience, functional vision
and visual-related reading disorders.
20 Perceptual and Motor Skills 0(0)