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Inter-individual Differences among Native Right-to-Left Readers and Native Left-to-
Right Readers during Free Viewing Task
Zaeinab Afsari1, Ashima Keshava1, José P. Ossandón1,2, and Peter König1,3
1 Institute of Cognitive Science, University Osnabrück Germany
2 Institute of Psychology, University of Hamburg, Germany
3 Institute of Neurophysiology & Pathophysiology, University Medical Centre Hamburg-
Institute für Kognitionswissenschaft
Wachsbleiche 27, D-49090 Osnabrück
Phone: +49 (541) 9693380
Zaeinab Afsari’s work was supported by grant ERC-2010-AdG#269616-MULTISENSE.
Peter König’s and Ashima Keshava’s work was supported by grant H2020-FETPROACT-
2014, SEP-210141273, ID: 641321 (socSMCs).
José Ossandón’s work was supported by grant SFB 936, project B1
Human visual exploration is not homogeneous but displays spatial biases. Specifically, early
after the onset of a visual stimulus, the majority of eye movements target the left visual space.
This horizontal asymmetry of image exploration is rather robust with respect to multiple
image manipulations, yet can be dynamically modulated by preceding text primes. This
characteristic points to an involvement of reading habits in the deployment of visual attention.
Here, we report data of native right-to-left (RTL) readers with a larger variation and stronger
modulation of horizontal spatial bias in comparison to native left-to-right (LTR) readers after
preceding text primes. To investigate the influences of biological and cultural factors, we
measure the correlation of the modulation of the horizontal spatial bias for native RTL readers
and native LTR readers with multiple factors: age, gender, second language proficiency, and
age at which the second language was acquired. The results demonstrate only weak or no
correlations between the magnitude of the horizontal bias and the previously mentioned
factors. We conclude that the spatial bias of viewing behaviour for native RTL readers is
more variable than for native LTR readers, and this variance could not be demonstrated to be
associated with interindividual differences. We speculate the role of strength of habit and/or
the interindividual differences in the structural and functional brain regions as a cause of the
RTL spatial bias among RTL native readers.
Eye movement and attention are jointly studied in research on overt attention.
Specifically, the decision to shift the eyes towards specific locations and not at other locations
is considered a complex cognitive process. This process is influenced by several factors:
stimulus-dependent tasks, task-related factors, and spatial properties (Kollmorgen, Nortmann,
Schröder, & König, 2010).
Even though these factors can be activated simultaneously, each one has its own
specific characteristics. Image features such as colours, intensity, orientation, shape, and
motion are considered stimuli attracting attention and processed by a bottom-up directed
pathway (Corbetta & Shulman, 2002; Itti & Koch, 2000, 2001; Ossandón et al., 2012). This
pathway consists of ventral and dorsal streams of the visual cerebral cortex (Kastner &
Ungerleider, 2000), as well as subcortical structures such as the superior colliculus
(Ignashchenkova, Dicke, Haarmeier, & Thier, 2004). At the same time, memories, goals, the
individual’s emotional state, and expectations can redirect and control the attention by a top-
down signalling pathway (DeAngelus & Pelz, 2009; Kaspar & König, 2011). Initiated by
internal goals, the executive frontal cortex sends signals to the visual motor areas to perform
appropriate eye movements (Buschman & Miller, 2007; Corbetta & Shulman, 2002; Itti &
Koch, 2001). Additionally, spatial properties influence the selection of fixation locations. One
aspect of these properties is the tendency to fixate more often toward the central parts of a
scene rather than its periphery (Tatler, 2007). This bias has been observed not only in
association with static images, but also when freely exploring dynamic scenes (Hart et al.,
2009; Tseng, Carmi, Cameron, Munoz, & Itti, 2009). Furthermore, several studies have
reported a left/right horizontal asymmetry (Ossandón, Onat, & König, 2014) and a statistical
dependence on saccadic angles (Dorris, Taylor, Klein, & Munoz, 1999; Wilming, Harst,
Schmidt, & König, 2013). Jointly, these aspects explain a sizable fraction of the selection of
The spatial preference for the left visual field has been observed in many
behavioural studies. For example, in the chimeric faces task, participants have to choose
which half of mixed (happy & neutral) human faces pictures are happier. In general, the left
side of the pictures is preferred based on subject’s reports as well as the starting location and
number of fixation points (Butler & Harvey, 2005; Phillips & David, 1997). Another example
is the cancellation task, in which subjects cancel out targets that are distributed between
distractors as quickly and as accurately as possible. Subjects tend to have directional bias
toward the left visual hemispace (Rinaldi, Di Luca, Henik, & Girelli, 2014). In the SNARC
effect, people usually associate small numbers with the left hemispace and large numbers with
the right hemispace, which is associated with the habit of finger counting (Fischer, 2008;
Shaki & Fischer, 2008). The line bisection task, in which participants have to draw a vertical
line through the middle of a horizontal line, usually demonstrates a slight bias toward the left
(Bradshaw, Nettleton, Nathan, & Wilson, 1985; Rinaldi et al., 2014). Moreover, in the free
viewing task, in which subjects explore images freely, the subjects demonstrate an initial bias
toward the left side of the screen (Ossandón et al., 2014). What is interesting is that these
behavioural studies not only show a preference for the left hemispace, but they can also be
modulated to the opposite direction (from right to left) or reduced toward the centre when
performed by participants who are native RTL readers (Afsari, Ossandón, & König, 2016;
Dehaene, Bossini, & Giraux, 1993; Eviatar, 1997; Göbel, Shaki, & Fischer, 2011; Rashidi-
Ranjbar, Goudarzvand, Jahangiri, Brugger, & Loetscher, 2014; Rinaldi, Di Luca, Henik, &
Recently, we conducted series of eye-tracking experiments, which showed that
horizontal spatial bias is modulated not by the reading itself but by a habitual scanning
process. While exploring images freely, LTR readers did not show a change in the leftward
spatial bias after reading non-habitual texts (mirrored LTR texts that resembled the RTL texts
in the reading direction), nor after tracking RTL moving dots. On the other hand, LTR/RTL
bilinguals showed flexibility in changing the direction of the spatial bias according to the type
of text (LTR or RTL) they read prior to image exploration. This has been explained by the
process of developing two scanning direction habits. When starting to learn reading, a habit of
moving the eye toward the direction of the first word of the sentence is developed.
Sequentially, this long-term habit development affects the laterality of the visual attention
system to a certain extent (Afsari et al., 2016).
The dynamic nature of the spatial bias opens the door to investigate other biological
and cultural factors that might have an impact on the left/right visual spatial bias. One of the
factors that may contribute to the horizontal spatial bias is age. Several behavioural studies
have shown that older adults pay less attention to the local features of the images (Açık,
Sarwary, Schultze-Kraft, Onat, & König, 2010) and perform slower in visuospatial tasks than
younger ones (Robinson & Kertzman, 1990). They also preferred to focus on smaller regions
of space, contrary to young adults (Kosslyn, Brown, & Dror, 1999). Furthermore, the
HAROLD (Hemispheric Asymmetry Reduction in Older Adults) model suggested that the
activity of the prefrontal cortical area during cognitive performances is less lateralized in
older adults (Cabeza, 2002). Hence, during aging, the cognitive skills decline but with cortical
compensations (Li, Lindenberger, & Sikström, 2001; Madden, 2007; Robinson & Kertzman,
1990; Verhaeghen & Cerella, 2002).
Another suggested factor that could contribute to the left/right spatial bias is gender.
Sex differences were reported in landmark learning for virtual navigation (Andersen,
Dahmani, Konishi, & Bohbot, 2012; Chamizo, Artigas, Sansa, & Banterla, 2011). In addition,
female performance in the spatial attention task was superior to that of the male participants
when performing trials with endogenous cueing (Bayliss, Pellegrino, & Tipper, 2005; Merritt
et al., 2007). Many authors have attempted to explain the difference in results based on
evolutionary reasoning and the role of estrogen hormonal levels (Ecuyer-Dab & Robert, 2004;
Frischen, Bayliss, & Tipper, 2007; Robinson & Kertzman, 1990). Hence, we speculate that
the gender of the participant could have an effect on the horizontal spatial bias.
Moreover, we are interested in examining the role of second language proficiency
and the age of second language acquisition in the left/right spatial bias. Early bilinguals have
been shown to have a bilateral hemispheric interference, while late bilinguals who are less
proficient have higher interference of left hemisphere when conducting a dichotic listening
test (Hull & Vaid, 2006, 2007). In a different study, late bilinguals were reported to be less
accurate in English sentence judgment than early bilinguals (Birdsong & Molis, 2001). In the
same sequence, Yang and Lust showed that becoming an early bilingual can improve multiple
cognitive skills (Yang et al., 2011). Sequentially, we will focus on finding a correlation
between these two factors and the horizontal spatial bias.
In this paper, the goal is to investigate the interindividual differences among
RTL/LTR bilinguals’ and native LTR participant’s horizontal spatial bias by considering
multiple biological and cultural factors that might have an impact on the spatial attention. We
examined the interindividual variations by looking at the relationships between age, gender,
second language proficiency, and the age at which the second language was acquired, and
their relationship with the magnitude of the horizontal spatial bias. To our knowledge, this
study is the first study to examine the interindividual differences for a horizontal asymmetry
Two groups of subjects participated in this study. The first RTL/LTR group consisted of 56
native RTL readers who learned a LTR language as a second language. The LTR/LTR group
consisted of 23 native LTR readers who learned a second LTR language. The LTR/LTR
group is also considered a control group. Part of the data was already used in Experiment 1(a)
and 2 in a previous study (Afsari, Ossandón, & König, 2016), which was extended by the
addition of 17 new subjects recruited specifically for this study. All participants performed the
experiment for 5-15 € or for student credit points. They filled out consent forms and
handedness tests (Edinbrugh Test; Oldfield, 1971) and performed a visual acuity test using
Sneller chart and dominant eye test (Miles Test; Miles, 1929). We verified that all of them
were right-handed and had normal or corrected-to-normal vision.
Visual stimuli in the form of texts and images were presented on a 21” CRT monitor
(Samsung SyncMaster 1100 DF, Samsung Electronics, Suwon, South Korea) at a refresh rate
of 85 Hz and a resolution of 960 x 1280 pixels. The texts served as primes for the images.
English or German texts were the LTR stimuli. The English texts were quoted from
Wikipedia and the British Broad Casting Corporation (BBC), while the German texts were
quoted from German newspapers. Arabic, Urdu or Persian texts were the RTL stimuli
obtained from Wikipedia. All the texts in the experiment were centred and designed to cover
the whole screen. The image stimuli were: 60 urban scenes, 60 natural scenes, and 60
artificial fractal images. The urban scenes were taken in Zürich (Onat, Açık, Schumann, &
König, 2014). The natural scenes were from a calibrated colour image database (Olmos &
Kingdom, 2004). The artificial fractals were self-similar computer-generated shapes from
different Web databases: Chaotic N-Space Network
(http://www.cnspace.net/html/fractals.html), Elena’s Fractal Gallery (http://www.elena-
fractals.it/, in http://web.archive.org), and Maria’s Fractal Explorer Gallery
(http://www.mariagrist.net/fegal). All the images were presented in either original condition
or mirrored condition in order to cancel the effect of the bias towards the image contents
(Ossandón et al., 2014).
Text stimuli appeared for 12 seconds followed by 9 test images, each shown for 6 seconds.
One text stimulus followed by 9 test images formed an experimental block. The whole
experiment consisted of a total of 20 blocks: 20 texts as primes and 180 images from the three
different categories. The experimental paradigm was sorted as the following: five blocks
contained texts from the first language, and five blocks contained texts from the second
language. After a 5-minute optional break, the experiment continued with five blocks of
second language texts followed by five blocks of first language texts (Figure 1). Prior to each
image or text presentation, a fixation point appeared in the middle of the grey background to
restore the participant’s gaze toward the center of the screen and to avoid the influence of the
spatial location of the written texts on the viewing behaviour. Calibration of the eye-tracker
took place prior to the very first trial and after the break. The images were presented to one
participant in the original condition and for the following participant in the mirrored condition
to balance the images’ content spatial biases.
(Insert Figure 1 about here)
Figure 1: The experimental paradigm: A) 20 blocks, where each block consists of a 1st
language or 2nd language text followed by 9 images, form the experimental paradigm. B)
Examples of RTL text (upper panel) and LTR text (lower panel) used as primes prior to image
The participants attended the eye-tracking lab in the Institute of Cognitive Science at the
University of Osnabrück. First, they signed an informed consent. Then, they filled out the
questionnaires and sat 80 cm away from the monitor. They had been instructed to read the
texts silently at their normal reading speed and to explore the images freely without moving
their head. A head-mounted video-based eye-tracker system of binocular pupil tracking at 500
Hz (Eyelink II, SR Research Ltd, Mississauga, Canada) was used to record the eye
movements. The Osnabrück University Internal Review Board approved the experiment.
Custom-made Matlab and Python scripts were used to analyse the data. We used
SPSS for statistical evaluation. For the purpose of this paper, we consider the subjects the unit
of observation. For each subject, we pooled the data across the images and calculated the
difference between left and right horizontal coordinates during the first second of trial
duration. First, we extracted the fixation points and their horizontal positions for each subject.
Second, we classified the fixation points into two categories: fixation points after reading
texts in native languages and fixation points after reading texts in second languages. Third, we
separated the fixation points for the images from the fixation points for reading text primes.
Fourth, to calculate the percentage of horizontal bias from the centre of the screen, the total
number of fixation points on the left side of the images was subtracted from the total amount
of fixation points on the right side of the images. Then, the result was divided over the
summation of the right and left fixation points. We multiplied the results by 100 to get the
fraction amount of the horizontal bias. We ended with two measurements for each individual:
the fraction of bias after reading native language primes (RTL spatial bias) and the fraction of
bias after reading second language primes (LTR spatial bias). Ultimately, the data in the
following sections represents the fraction of horizontal bias on the images during the first
second of trial duration after reading primes for each individual subject.
To assess the impact of RTL language primes on the leftward spatial bias, we
analysed the data of 56 native RTL/LTR readers and 23 native LTR/LTR readers after they
read texts in their native and second language, followed by a free-viewing task. Starting with
the RTL/LTR group, reading RTL texts as primes shifted the mean score of the horizontal
spatial bias to the right side of the screen (1.19 ± 24.42, mean ± standard deviation), while
reading LTR texts as primes shifted the mean score of the horizontal bias to the left side of the
screen (-10.63 ± 22.78). On the other hand, the LTR/LTR group demonstrated a strong
leftward shift for the horizontal spatial bias after reading native LTR and second LTR text
primes; (-34.09 ± 19.23) and (-35.81 ± 17.65) respectively. Additionally, a one sample t-test
was conducted to determine whether a statistically significant difference existed between each
group and the no bias state (zero score). RTL/LTR group showed no significant bias toward
the right side of the monitor after primed with texts from their native language compared to
the centre of the monitor (t(55)= 0.365, p = 0.717). However, the LTR/LTR group showed a
significant leftward bias after primed with texts from their native language compared to the
center of the monitor (t(22) = -8.51, p≤0.001). Furthermore, an independent t-test indicated
that the mean of the RTL/LTR group was significantly different than the mean of LTR/LTR
group after reading texts in their native language (t (77) = 5.781, p < 0.01). Figure 2 shows
the distribution of spatial bias for the two groups after being exposed to native language
primes. The distribution of the data for the spatial bias of the RTL/LTR group is broad and
shifted toward the center of the images, compared to the distribution of the data for LTR/LTR
group, which is narrower and shifted to the left side of the screen.
(Insert Figure 2 about here)
Figure 2: Distribution of horizontal spatial bias for the RTL/LTR group and LTR/LTR group
after reading texts in their native language. The positive values on the abscissa represent the
fraction of bias toward the right, and the negative values represent the fraction of bias toward
the left from the viewer’s perspective.
Because subjects originated from 14 different countries, their heterogeneous
multilingual and cultural backgrounds could influence the direction and the magnitude of the
horizontal spatial bias. Therefore, the next goal is to assess the effect of biological and
cultural factors on the individual bias scores for the two groups presented in Figure 2
Effect of age
To begin with, we studied the correlation between the age of the participants and the
horizontal bias after reading native language primes. For the RTL/LTR group, the age of the
participants ranged between 21 and 60 years. The data analysis showed no significant
correlation between RTL spatial bias and age (r (56) = 0.110, p = 0.418). As for the LTR/LTR
control group, the age of the participants ranged between 18 and 27 years. Again, no
significant correlation was detected between the age factor and the magnitude of bias after
reading texts in their native language (r (23) = 0.172, p = 0.432) (Figure 3). Therefore, given
our current sample size, we no indication that age did not contribute to the interindividual
difference in the RTL/LTR group.
(Insert Figure 3 about here)
Figure 3: The scatter plot represents the correlation between the magnitude of the horizontal
spatial bias after reading native language texts and the age of the participants.
Effect of gender
Likewise, we were interested in the relationship between the gender of the participants and the
interindividual differences in the horizontal spatial bias. For the RTL/LTR group, out of 56
participants who performed the task, 10 were female (Table 1). After testing the normality,
the mean score of the male group (2.41 ± 24.72) was not significantly different than the mean
of the female group (-4.40 ± 23.37) (t (54) = 0.796, p= 0.737). For the LTR/LTR control
group, 10 out of 23 participants were female, and the results showed no significant difference
in the mean score of the bias between males (-35.79 ± 20.79) and females (-31.87 ± 17.82)
after reading texts in their native language (t (21) = -0.48, p=0.639). Thus, given our current
sample size, we did not observe evidence of the effect of gender on the manipulation of the
horizontal spatial bias.
Effect of second language proficiency
The following step was to investigate if there is an influence of the proficiency of second
language on the horizontal spatial bias. In the questionnaire, subjects evaluated their second
language proficiency by choosing the best choice from four options: Excellent, Very Good,
Good, and Poor. One-way ANOVA showed that there were no statistically significant
differences between the means of different levels of second language proficiency (F (3, 52) =
0.263, p = 0.852). For the LTR/LTR group, all participants evaluated themselves as either
excellent or very good in their second language proficiency; hence, the mean score for the
horizontal spatial bias of the excellent group (-29.03 ± 16.71) was not significantly different
from the mean score of the very good group (-41.95 ± 21.17) (t(21) =1.631, p = 0.118).
For additional measurement of the second language proficiency, the median heights
of reading the second language text levels were calculated. We assume that the amount of
reading represents the level of proficiency. That means, the more proficient the reader is, the
more lines of the text are read, and the greater the value of the median height. For each
subject, the median score was calculated for the vertical fixation points extracted from the
second language text primes. Statistically, there was no correlation between the median height
for reading LTR texts and the RTL horizontal spatial bias (r (56) = -0.198, p = 0.143).
Consequently, for this particular sample, we do not have evidence that the large variance in
the horizontal spatial bias between RTL/LTR subjects was modulated by the second language
Effect of age of second language acquisition
We also evaluated the correlation between the age of the participants when they acquired their
second language and the magnitude of the horizontal spatial bias. For the RTL/LTR group,
out of 56 participants, 45 participants answered this question. There was no correlation
between the age at which the subjects learned to read/write their second language and the
RTL horizontal spatial bias (r (46) = 0.043, p = 0.774) (Figure 4). Hence, given the current
sample size, the age at which participants required their second language did not contribute to
the interindividual variations of the rightward spatial bias for the RTL/LTR group.
(Insert Figure 4 about here)
Figure 4: The scatter graph shows the correlation between the age at which native RTL
readers acquired a LTR language and the RTL horizontal spatial bias.
The calculated statistical power
The data presented earlier did not show to have a significant impact on the
horizontal spatial bias. A further step is taken in this research by measuring the effect size of
the sample above and then estimate the sample size required to reach a higher statistical
power and reduce type II error. For this purpose, we used G*power software with the results
that are obtained earlier to estimate the number of subjects necessary in order to detect a
For the correlative analysis as applied e.g. with the age at test or the age at second
language acquisition, the statistical power for a sample of 56 subjects to observe a significant
correlation of size 0.11 is 0.47. To achieve a statistical power of 0.80, 120 subjects are
For the binary divisions like the gender and second language proficiency factor, the
statistical power to observe a difference with an effect size of 0.28 is 0.20. To achieve a
statistical power of 0.80, an estimated sample size of 524 subjects are required.
In this work, we analysed eye-tracking data of 56 native RTL/LTR readers and 23
LTR/LTR readers who performed free image exploration after being primed with texts. The
LTR/LTR group showed a strong leftward bias in the first second of image exploration. The
result of the LTR/LTR group is consistent with a previous eye-tracking study that showed an
initial leftward bias in a free viewing task without reading primes (Ossandón, Onat, & König,
2014). Hence, we claim that when native LTR readers read LTR primes, it strengthens the
natural leftward bias reported above.
On the other hand, the RTL/LTR group showed not only a rightward shifted
horizontal spatial bias after reading RTL texts, but also larger variance in comparison to the
LTR/LTR group. This raises the question of whether it would be possible to identify a factor
within the RTL group explaining the wide dispersion of the data. With this goal in mind, we
studied the relationship between the RTL spatial bias after reading RTL texts for the
RTL/LTR group and several parameters reported by the participants: age, gender, second
language proficiency, and the age at which the second language was acquired. However, we
found no significant correlation between these parameters and the spatial bias. Thus, the
higher variability might be explained by the fact that native RTL readers have two reading
habits that are conflicting in terms of reading direction, whereas the control group does not
have such a conflict.
The first factor we investigated in this paper was the age. We noticed no influence
of the “young and middle age” spectrum on the RTL spatial bias. One point to mention is that
we were able to recruit only one participant older than 50 years because of the limited
geographical area where it is difficult to find native RTL readers in general. In the study by
Açik, children, young adults, and older adults were requested to view natural and complex
images freely then perform a patch recognition task. Older adults (> 72 years old) were less
dependent on the low features of the images compared to children and young adults, and
relied more on a top-down mechanism, which suggests different strategies in exploring the
scenes (Açık et al., 2010). Thus, for this specific sample of the RTL/LTR group, the age
factor did not influence the horizontal spatial bias.
Gender was the second factor we analysed. We found no correlation with the RTL
spatial bias. The data of 10 females was compared to the data of 46 males and no significant
difference was noticed indicating no influence of gender factor on the general RTL bias. This
is in line with our previous report of there being no difference in viewing biases between
genders (Ossandón, Onat, & König, 2014).
Second language proficiency and age of second language acquisition are usually
investigated together, and their effect on several cognitive skills has been reported (Birdsong
& Molis, 2001; Hull & Vaid, 2006; Yang et al., 2011). However, in among this sample size,
we did not find an effect of these two factors on the RTL horizontal spatial bias for native
RTL/LTR readers. This might be explained by the strength of habit of reading direction,
regardless of the linguistic component. In contrast, Birdsong and Molis studied the
relationship between judging English sentences produced by early Spanish bilinguals (≤ 16
years old) and late Spanish bilinguals (> 17 years old) and found a negative correlation
between the late bilingual group and accurate English sentence judgment (Birdsong & Molis,
2001). Similarly, Hull and Vaid (2006 and 2007) conducted meta-analysis studies to compare
monolinguals with bilinguals and early bilinguals with later bilinguals in different
hemispheric laterality tasks and concluded that early bilinguals (< 6 years old) have bilateral
hemispheric interference. In addition, late bilinguals who are also less proficient have higher
interference of the left hemisphere when conducting a dichotic listening test (Hull & Vaid,
2006, 2007). In the same way, Yang and his team (2001) showed that becoming a bilingual
child at 4 years old can improve multiple cognitive skills (Yang et al., 2011). Although these
studies show an influence of the age of the participants and their second language proficiency
on some cognitive skills, these two factors did not demonstrate an impact on the horizontal
The post-hoc statistical power analysis for the four factors showed to have a low
statistical power, which indicates that there could be an undetected effect on the horizontal
spatial bias. In order to increase the statistical power, larger sample size is required (from 120
to 524 subjects, depending on the relevant effect size) which is much more that we could
recruit. In a country where RTL language is uncommon, we are not able get these numbers.
Therefore, we made our data open to the science platform by uploading the data that we
obtained to the Open Science Framework (OSF) to open the opportunity for scientific
collaboration and replication for the study to obtain low type II error for these factors; please
visit the link: (https://osf.io/tnxme/).
Because none of the factors evaluated explained the larger bias variance of the RTL
subject, we discuss next the role of other factors that have not yet been evaluated.
Habit strength factor
Habit is an automatic response that requires no involvement of consciousness (Lally,
van Jaarsveld, Potts, & Wardle, 2010). It is activated immediately at the moment the cue that
is linked to the specific habit is displayed. Counting fingers and the SNARC effect are two
behaviours that have been linked directly to habit formation. For instance in a cross-cultural
study for the finger counting test, while LTR readers preferred to start counting with the left
thumb, the majority of RTL readers started counting with the right little finger (Lindemann,
Alipour, & Fischer, 2011). In the counting coins test, four identical coins are arranged in a
linear array. The task is to count the coins loudly while pointing at them. The main influence
on the counting direction was the habitual reading direction. Interestingly, the illiterate group
and the mixed language group (where letters are written RTL but numbers are written LTR)
did not show a counting direction preference (Shaki, Fischer, & Göbel, 2012). Additionally,
finger counting habit is associated with the SNARC effect. When the subjects performed the
finger counting test and the SNARC test (parity judgment test), the SNARC effect was
stronger among left counters, and a reversed SNARC effect was reported among right
counters (Fischer, 2008). Thus, culture can reshape behaviours through learning and
The strength of a habit has a corresponding impact on the ability to change a
behaviour. For instance, when studying smokers with different levels of habit strength who
were trained to break their smoking habit, the effectiveness of minimizing the smoking habit
was dependent on the strength of the habit (Webb, Sheeran, & Luszczynska, 2009). Hence,
habit strength affects the process of changing the habit.
Thus, the reversed bias and larger variability of native RTL participants might be
explained by the result of averaging two strong habits with spatial biases effects that
antagonize each other. Assuming the existence of two habits in this task, LTR reading habit
and RTL reading habit, it could be that either these two habits are antagonizing each other,
ending with a net result of a certain percentage of RTL spatial bias, or it could be the strength
of RTL reading habit by itself that controls the RTL spatial bias. To further investigate this
point, a specific reading habit strength measurement would need to be developed to evaluate
the dependence between the magnitude of horizontal spatial bias with both RTL and LTR
This result supports the notion that learning to read at an early age (around 6 or 7
years) will form a habit that is difficult to deteriorate. Cunningham ran a 10-year follow-up
study for the 1st-grade students to measure their language skills and noticed that learning to
read quickly can affect the lifetime reading habit (Cunningham & Stanovich, 1997). Because
of this, we believe that another country’s cultural effect will not overcome the effect of the
native country’s influence.
Variability of brain structure and function among healthy individuals
The hypothesized effect of reading habit might be related to patterns of lateralization
and connectivity between left visual hemifields and the right hemisphere for attentional
mechanisms (Kastner & Ungerleider, 2000). A leftward bias induced by a LTR habit
coincides with and reinforces a leftward (in the visual field) attentional bias which is probably
secondary to the right lateralization of attentional networks. However, in RTL readers, these
two mechanisms have opposite consequences and therefore lead to a weaker and more
variable spatial bias. Thus, the low variability among LTR readers would be explained by the
congruence of lateralization of cortical regions and reading habits. The high variability of
spatial bias among RTL readers would be explained by the lack of congruence of the effect of
module lateralization on viewing bias and the effect of reading habits on attentional bias.
To summarize, our hypothesis suggests that the power of reading direction habit is
strong enough to manipulate horizontal spatial bias. We assume that developing a ”habit” to
scan a text with the eyes from one direction to the other, beginning in 1st grade, is an
important factor to implant a dynamic horizontal bias. Although this study is considered a
small multicultural experiment due to the diversity of the subjects’ cultural background, we
did not find any indication of the effect of the exogenous factors on the interindividual
variance on the rightward horizontal spatial bias such as age, gender, second language
proficiency, and the age at which the second language was acquired. As suggested by
previous works, we assume that the hemispheric lateralization of the spatial attention system
might be the leading role for the leftward preference of the naturally existing horizontal bias
(Afsari et al., 2016; Ossandón et al., 2014). In addition, we suggest the role of the scanning
habit on modulating the leftward preference of the horizontal bias. Lastly, we suggest two
other factors that may influence the wide variability of the RTL spatial bias: the strength of
the habit and interindividual differences at the cortical level for language/attention.
For future work, we suggest replicating similar studies by recruiting more subjects
who are RTL/LTR bilinguals. In addition, recruiting illiterates can add a lot to understand the
nature of the spatial bias without the effect of reading habit. Reporting the natural viewing
bias among illiterates will generalize the notion of the spatial attention with a minimal effect
of habitual scanning influence. RTL monolinguals could also contribute to this type of study
by revealing the effect of different scanning habits on the visual spatial bias without
conflicting with contrary scanning habit.
We thank Matti Krüger and Mattias Hampel Holzer for their technical assistance in the early
phase of the project.
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Second language proficiency
Table 1. The table represents the different sample sizes for the subgroups of RTL/LTR group and
LTR/LTR group tested for several parameters. (*) (The age when acquired the second language)
parameters was answered by 46 participants only.
5x 1st language
5x 1st langauge
5x 2nd language
5x 2nd language
5x 1st language
Block = 1x Text + 9x Images
Horizontal Spatial Bias (%)
-100 -80 -60 -40 -20 0 20 40 60 80
Age when acquired the second language
0 5 10 15 20 25 30
Horizontal Spatial Bias (%)
15 20 25 30 35 40 45 50 55 60 65
Horizontal Spatial Bias (%)