2011. Vol.2, No.2, 103-108
Copyright © 2011 SciRes. DOI:10.4236/psych.2011.22017
Influence of the Learnt Direction of Reading on
Temporal Order Judgments
Alejandro Pérez1,2, Lorna García1, Mitchell Valdés-Sosa3, Piotr Jaśkowski4
1Basque Center on Cognition Brain and Language, BCBL, Donostia-San Sebastian, Spain;
2Cognitive Neuroscience Laboratory, Faculty of Psychology, Universidad Diego Portales, Chile;
3Cognitive Neuroscience Department, Cuban Center for Neuroscience, Ciudad de La Habana, Cuba;
4Department of Cognitive Psychology, University of Finance and Management, Warszawa, Poland.
Received January 5th, 2011; revised February 18th, 2011; accepted February 22nd, 2011.
Our previous work has shown a leftward bias in the temporal order judgment task (Pérez, García, & Valdes-Sosa,
2008). This pseudoneglect was found in a sample of Spanish-speaking participants who read in a left-to-right
manner. The goal of the current study was to examine if the reading related scanning habits modulate the bias
observed in the TOJ task. To this aim, we replicated the study with Arabic participants who learned to read in a
right-to-left direction. Results showed no lateralization suggesting that reading habit is probably a factor affect-
ing the distribution of spatial attention. We suggested that our failure to obtain a reversed bias might be due to
the fact that they experienced both types of reading habits. We also presented a possible explanation of why the
finding of pseudoneglect in temporal order judgment tasks is rather unusual.
Keywords: TOJ, Pseudoneglect, Spatial, Bias, Attention
In the visual temporal order judgment task (TOJ) common
experimental setting, two targets are presented right and left of
a fixation point whilst the relative stimuli onset asynchrony
(SOA) of the two events is manipulated, and participants are
asked to report which of the targets appeared first (Shore,
Spence, & Klein, 2001). In line with the law of prior entry that
postulates: “the object of attention comes to consciousness more
quickly than the objects we are not attending to” (Titchener,
1908), this task allows to make inferences about the distribution
of visuospatial attention. Thus, TOJ had been commonly used,
among other things, to study visuospatial attentional asymmtries
(Sekuler, Tynan, & Levinson, 1973).
In TOJ, when the stimuli are presented simultaneously or
with a very short SOA, the order is judged at chance (50%) and
accuracy progressively rises by increasing the SOA (Bachmann,
Poder, & Luiga, 2004; Jaśkowski & Verleger, 2000; Sternberg
& Knoll, 1973). Two summary statistics can be extracted from
the TOJ data: the ‘point of subjective simultaneity’ (PSS) indi-
cating the SOA at which observers report maximal uncertainty,
and the ‘just noticeable difference’ (JND), a measure of how far
apart in time the stimuli must be presented for the subject to
reliably order them in time in 75% of the cases (Shore &
Spence, 2005). Theoretically, the maximal uncertainty of tem-
poral order should occur when stimuli are presented simulta-
neously (i.e., with SOA = 0). Therefore subject’s perceptual
bias to one side manifests as a deviation of PSS from zero
(Shore et al., 2001).
In patients with extinction and neglect syndromes consequent
to brain damage who show strong attentional bias, favoring
usually the right side (Halligan, Fink, Marshall, & Vallar, 2003),
the TOJ task is characterized by a strong tendency to perceive
the right stimulus as appearing first, even when it is presented
hundreds of millisecond after the left stimulus (Robertson,
Mattingley, Rorden, & Driver, 1998; Rorden, Mattingley, Kar-
nath, & Driver, 1997). In patients with developmental dyslexia,
a learning disorder with no apparent brain damage, researchers
also detected small disadvantages for one-hemifield in the TOJ
task (Hari, Renvall, & Tanskanen, 2001; Pérez, García, Lage,
Leh, & Valdes-Sosa, 2008). Specifically, the work by Hari et al.
(2001) showed that adult dyslexics processed stimuli in the left
visual hemifield significantly more slowly than normal readers.
They suggest that this abnormality could reflect right parietal
lobe hypofunction, a consequence of a general magnocellular
deficit. As the control of automatic attention is attributed com-
monly to the posterior right parietal lobe, the primary cause of
left hemifield disadvantage rather could be sluggish attention
shifting (Hari, Renvall, & Tanskanen, 2001). The TOJ task had
been also used to study attention-deficit/hyperactivity disorder
(ADHD), a child-onset disorder with negative adult outcomes
(Bellgrove et al., 2006). Results in the study of Bellgrove et al.
(2006), showed that the ADHD participants have an attentional
bias toward the left hemifield that enhances the rate of percep-
tual processing for stimuli on that side. Subjects with ADHD
could be impaired on those tasks requiring temporal attention
due to ADHD has been associated with the A2 allele of a Taq I
polymorphism of the Dopamine beta hydroxylase (DBH) gene,
which catalyzes the conversion of dopamine to noradrenaline,
and since catecholamines regulate visual attention, this could be
the link. However, the explanation to the presence of an atten-
tional asymmetry, remains unclear and may reflect the opera-
tion of a number of factors, including task demands (Bellgrove
et al., 2006). In the case of normal observers, the TOJ is more
commonly symmetrical (Hikosaka, Miyauchi, & Shimojo, 1993;
Rorden et al., 1997; Shore et al., 2001). Only if attention is
A. PÉREZ ET AL.
drawn to one side of the visual field by an exogenous cue (or in
less extent, by an endogenous cue), the TOJs are biased towards
the cued side as compared to a baseline in which attention is
equally distributed (e.g. Schneider & Bavelier, 2003; Shore et
al., 2001). This manipulation emphasizes the sensitivity of the
TOJ to attentional factors (Shore et al., 2001). However, in a
recent study using the TOJ task, a leftward bias was obtained
(Pérez et al., 2008). This phenomenon is consistent with the so
called pseudoneglect, a small but systematic leftward bias
found in healthy subjects (Bowers & Heilman, 1980) with nu-
merous spatial tasks (Luh, Rueckert, & Levy, 1991; Milner,
Brechmann, & Pagliarini, 1992; Nicholls, Mattingley, & Brad-
shaw, 2005; Orr & Nicholls, 2005). The aforementioned study
from Pérez et al. (2008), originally aimed at investigating the
influence of an endogenous process on TOJ, via an attentional
blink (AB) paradigm. To accomplish that, a first visual stimulus
(S1) was displayed at the fixation point for 30 ms, followed
(after either 250 or 1000 ms) by a pair of laterally located visual
stimuli (S2) whose order had to be judged (the TOJ task). Sub-
jects had to provide the TOJ responses in a forced choice man-
ner. As in an AB paradigm, delay between S1 and S2 is ma-
nipulated to reduce the attentional resources. Also, a control
block in which participants are asked to ignore S1 stimulus (i.e.
no dual-task) is introduced, to discard purely sensory effects
due to T1 such as visual masking deficits (this block resembles
a classical TOJ task). Study shows that for the dual task and
with the 280 delay between T1 and T2, accuracy in the TOJ
deteriorated evincing an AB and supporting the conclusion that
the perception of temporal order is also affected when available
attentional resources are reduced. The study also expected that a
rightward bias emerged during the AB (Manly, Dobler, Dodds,
& George, 2005; Bellgrove, Dockree, Aimola, & Robertson,
2004). Interestingly; this rightward bias under AB conditions
consisted in a significant bias away from the left favoring
asymmetry in normal attention conditions. In other words, dur-
ing normal attention condition (i.e. normal TOJ task, without
AB effects), accuracy for the left-leading conditions was higher
than for the right-leading conditions (87% versus 79%). These
results, in addition to a positive PSS mean value being signifi-
cantly different from zero, indicating that the right stimulus had
to precede the left one to be judged as simultaneous, indicated a
leftward spatial bias in the TOJ task used as control (for more
details see Pérez et al., 2008).
To our knowledge, only Sekuler et al. (1973) reported a left-
ward advantage in a visual TOJ task similar to the one obtained
serendipitously in the described experiment of Pérez et al.
(2008). Sekuler et al. (1973) suggested that their TOJ-pseu-
doneglect effect was due to an internal mechanism that scans
visual inputs in a left-to-right order, probably due to reading
scanning habits (Heron, 1957). It had been suggested that
pseudoneglect is related to reading scanning habits (Chokron &
Imbert, 1993; Chokron & De Agostini, 1995; Chokron, Bernard,
& Imbert, 1997), but results are not conclusive (Nicholls &
Roberts, 2002). Therefore, we decided to test readers who learn
to read in a right-to-left direction (right-to-left readers, RtLR)
using the same TOJ task as in our previous study and to com-
pare their results to those obtained with the exclusive left-to-right
readers (LtRR) (Pérez et al., 2008). Here we examined the pos-
sible influence of the direction of reading on TOJ. If we find a
TOJ pattern different to pseudoneglect in RtLR, this would
suggest that the reading habits could affect the distribution of
Twelve subjects (1 female and 11 males) between 23 and 43
years of age volunteered to participate in the study. They gave
informed consent in line with the Declaration of Helsinki. The
inclusion/exclusion criteria were the same as in our previous
study (Pérez et al., 2008): 1) they were in good health, had no
past history of psychiatric or neurological illness, and had nor-
mal visual acuity, 2) had right handed-ness as assessed by the
Edinburgh Handedness Inventory (Oldfield, 1971) with all
scores above 85 points and 3) had a high educational degree
(university students or graduated).
All subjects were bilingual (Arabian and Spanish idioms)
with the Arab as the primary language (RtLR). None of them
used Spanish or any other language different from Arab before
they were 17 years old, and all acquired writing and reading
skills before they were nine years old, reading and writing fluid
in their native language. Table 1 shows a description of the
RtLR’s participants. As the results of these subjects were com-
pared to the LtRR subjects from our previous study, description
of the latter was also given in Table 1.
Stimuli were presented on a 15” sVGA computer display
with 800 × 600 pixels resolution and a refresh rate of 85Hz,
controlled by a 933 MHz Intel Pentium III Copermine com-
puter driven by a custom written software. All stimuli were
displayed as white figures on a black background. The fixation
square of 0.8˚ of visual angle was present all the time. It con-
tained a small diamond shape. Disappearance of one of the
corners of this inner diamond was achieved by turning off 16
pixels. Horizontal bars of 1.4˚ in width and 0.1˚ high appeared
at symmetrical locations in the left and right visual fields, at the
same height as the central square. The outer edges of the bars
were subtending 4.2˚ from the fixation point warranting proc-
essing by the foveal area of the retina.
The procedures in this and the previous study were identical,
Description of the RtLR group studied here and the LtRR group from
the previous experiment.
Variables RtLR group LtRR group
Number of subjects 12 14
Sex distribution 1 female/11 male 3 female/11 male
Age range (years) 22-45 (mean 27) 23-43 (mean 32)
Handedness Right (> 85) Right (> 85)
Educational degree University University
Language Arab and Spanish Spanish
A. PÉREZ ET AL. 105
the same equipment was used, conducted by the same experi-
menter, using the same program and close in time to previous
study. All instructions were given in Spanish. In order to keep
the same experimental design of the previous study, partici-
pants also performed a ‘divided-attention block’ (see Pérez et
al., 2008 for more details), but data is not presented here.
Blocks order was counterbalanced.
The experiment was conducted in a quiet room with natural
illumination. Participants were seated in a chair at a distance of
50 cm from the screen. They were instructed to maintain fixa-
tion throughout the experiment on a diamond shape presented
in the middle of the screen and to remain still.
For each trial, a series of displays were presented as shown in
Figure 1. The sequence was triggered by pressing a key. After a
delay of 300 ms, the upper corner of the central diamond dis-
appeared (S1) for 30 ms (see inset in Figure 1). 250 or 1000 ms
(ISI) after the missing corner was restored, the stimuli for the
TOJ task were displayed. Note that the participants in this block
had to ignore S1. But to keep the tasks as similar as possible,
they also performed a ‘divided-attention block’ (not shown) in
which one of the corners of the central diamond could disap-
pear and they had to report it, dividing attention between S1
and the TOJ. TOJ stimuli consisted of two bars, one on each
side of the fixation point. The stimulus onset asynchrony (SOA)
of the two bars was varied from trial to trial. They were from
–120, –90, –60 or –30 ms (the minus sign indicates that the left
bar was presented before the right bar), 0 ms (both were dis-
played simultaneously), or 30, 60, 90 or 120 ms (positive num-
bers indicates that the right bar was presented before the left
After the two bars had been presented, the display was left on
until the trial complete of 1550 ms. After the sequence of stim-
uli, the subjects were prompted to respond. First, they pressed
the up-arrow key in the computer keyboard (while keeping the
tasks as similar as in the other block), and finally, they indicate
with the right or left arrow if the right or the left bar had ap-
peared first (forced-choice). All responses were given with the
The experiment was preceded by a short training period of
ten trials to ensure that the participant had fully understood the
instructions. A total of 360 trials were presented, uniformly
distributed over the eighteen conditions (2 ISIs × 9 SOAs). The
order of presentation of different trial types was pseudo-random
(trials from a similar condition should not be presented more
than seven consecutive times). The percent of responses in
which the subject indicated that the right bar was presented first
(% right-first responses) was calculated for each condition in all
Four-way ANOVAs with three within-subjects factors, ISI
(250 ms vs. 1000 ms), Side (‘right–first’ vs. ‘left–first’) and
SOA (excluding SOA = 0 ms or simultaneity for this analysis,
because neither ‘right–first’ nor ‘left–first’ answer is a correct
answer), and Group (RtLR group and LtRR group) as a be-
tween-subjects factor, were performed. A Greenhouse-Geisser
correction of the degrees of freedom was ap-plied when appro-
As expected the number of correct responses increased with
Experimental design. Sequence of events during each trial and time the
stimuli were shown on the screen. ΔT represents the 30, 60, 90 or 120
ms necessary for SOAs (also represents de 0 ms of simultaneity).
SOA, F(3,72) = 148.2, MS = 1.4, p < .001. Of some interest is
that the performance depended on ISI being better at an ISI =
1000 (83%) than an at ISI = 250 ms (78%), F(1,24) = 13.5, MS =
0.2, p < .01. This reduction in performance for the short ISI
could be explained by an attentional blink like effect. We will
return to this suggestion in the Discussion. The main effect of
Group was insignificant; however, the Group x Side, F(1,24) =
8, MS = 0.88, p < .01, and Group x SOA x Side, F(3,72) = 3.79,
MS = 0.04, p < .05, interactions reached sig-nificance, thus
indicating that the shape of psychometric functions depended
on Side and Group. To explain these interactions, planned
comparisons were performed for each Side showing that dif-
ferences between groups are significant for left-first, F(1,24) =
6.12, MSE = 1.06, p < .05, with lower accuracy for the RtLR
Group in the left-leading conditions (73% in the RtLR Group
vs. 87% in LtRR Group) and vanished for the right-leading
conditions (83% vs. 79%). In fact, the pattern showing a left-
ward bias in the LtRR Group (87% of accuracy for left-leading
conditions vs. 79% for the right-leading conditions) is actually
reversed in the RtLR Group (73% vs. 83%, respectively). This
confirms that the pseudoneglect phenomenon was not present in
RtLR Group. Planned comparisons were also performed for
Side in each group, showing differences between right-leading
and left-leading conditions only in the RtRR Group (F(1,24) =
4.59, MSE = 0.05, p < .01), indicating more accuracy in the
right-leading conditions compared with the left-leading condi-
tions in this group, an opposite pattern to the one shown by the
LtRR Group. Finally, being more detailed, planned comparisons
were performed for each SOA in each Side. For left-first condi-
tion, differences between groups, due to a larger accuracy for
the LtRR Group in all SOA values, are significant in all of it
(all p < .05) except for the 30 ms SOA in which it is marginally
significant (p = .057). On other hand, for the right-leading con-
dition the accuracy percentage is similar for both groups in the
larger SOAs and only differ in the 30 ms SOA (F(1,24) = 9.04,
MSE = 0.33, p < .01), being more accurate the RtLR Group
(72% vs. 56%).
In addition, we performed probit analysis to estimate the ba-
sic parameters of psychometric functions (Finney, 1964). To
this aim the proportion of ‘right-first’ responses was converted
A. PÉREZ ET AL.
to its equivalent Z-score using a probit regression, assuming a
cumulative normal distribution of the data. Transformed
Z-scores are obtained by applying the inverse of the standard
normal distribution function to the raw proportion scores (Sin-
nett, Juncadella, Rafal, Azanon, & Soto-Faraco, 2007). This
transformation allows us to perform a linear regression with the
transformed data and the nine SOAs. From the slope and inter-
cept of the fitted line, we derive the PSS (corresponding to the
intercept of the function) and the JND (corresponding to 0.675
point of the function). These two performance measures were
calculated separately for each participant.
One participant of the LtRR group was excluded from the
analysis because the estimated PSS value was greater than 120
ms, which was beyond the SOA range tested (see Spence et al.
2001, for similar criteria of exclusion). As no significant dif-
ference between ISIs emerged, we collapsed the data, consid-
ering both ISIs as independent observations; consequently
number of observations doubled. Figure 2 shows the collapsed
data of the responses obtained here (RtLR participants) jointed
with LtRR participant’s data from the previous experiment.
Table 2 show the summary statistics from the PSS and JND in
the two ISIs conditions.
In the LtRR group the PSS values were statistically different
from 0 ms (mean = 17.0 ms, conf. limits –95% = 9.5 and +
95% = 24.5, t(27) = 4.7, p < .001), indicating that the bar on the
right must be presented before the bar on the left for both
events to be perceived as simultaneous. This indicates a left-
ward advantage consistent with the pseudoneglect phenomenon.
In the RtLR group a trend to the left side was observed (PSS
mean = –14.4 ms), but it couldn’t be statistically validate. How-
ever, further between-group comparison revealed a difference
between the PSS parameters (t(48) = –3.5, p < .01). Moving on
to the JND measure, a mean SOA of 46.5 ms between the two
stimuli was required for a correct discrimination order in the
RtLR group which was not statistically different from the 36.0
ms required for the LtRR group, according to a t-test for inde-
pendent groups. Even when RtLR group is not as accurate as
the LtRR group, this result indicated equivalent precision in the
performance of the task.
In our previous TOJ experiment with LtRR it was obtained a
leftward bias consistent with pseudoneglect, which is in line
with Sekuler et al.’s (1973) finding. Here, we showed that with
RtLR readers this effect disappeared. Differences could not be
attributed to differences in sex or age and although participants’
IQ was not tested, the participants in both groups had a compa-
rable educational level.
An interesting finding is the reduction in performance when
the intervals between the warning signal and the TOJ were
short. We argue that this phenomenon could be an attentional
blink (AB) like effect. In the AB paradigm two sequentially
presented target stimuli (t1 and t2) have to be identified
(dual-task). Recognition of the second target (t2) is impaired,
the ‘attentional blink’, when it is presented within a few hun-
dred milliseconds of t1, but only when the latter must be ac-
tively recognized (Duncan, Ward, & Shapiro, 1994; Raymond,
Shapiro, & Arnell, 1992). Even when our paradigm is not a
dual-task because the first stimulus has not to be attended,
Mean probability of right-first responses as a function of SOA and
group in the TOJ task (data from different ISIs were collapsed). Nega-
tive SOAs indicate that the left bar was presented first and positive ones
that the right bar was presented first; zero SOA corresponds to simul-
taneous onset. Larger probabilities of ‘right-first’ responses were ob-
tained in the group of RtLR compared to the LtRR when the left stimu-
lus preceded the right.
Summary statistics from the PSS and JND of each participant from the
TOJ task in ISI 250 ms and ISI 1000 ms conditions. Mean, confidence
intervals and standard deviation a re showed.
RtLR Gr oup LtRR Gr oup
ISI 250 msISI 1000 ms ISI 250 ms ISI 1000 ms
PSSJNDPSSJND PSS JND PSSJND
Mean –14.251.9–14.540.9 16.3 36.6 17.7 35.3
Std.Dev. 48.625.138.516. 22.3 21.7 16.625.7
–95% –46.835.1–40.429.9 3.5 24.1 8.1 20.5
+95% 18.4 68.8 11.4 52.0 29.2 49.1 27.3 50.1
subjects performed an extra block (Divided-Attention block,
data not shown) and in this block a first stimulus do had to be
attended and responded, therefore a kind of task interference
could be expected when we ask to press automatically a key
before the response, something with a “meaning” in the other
block. Maybe these factors resulted in an “overinvestment” of
attentional allocation over S1 stimulus, provoking S1 to be a
spuriously active distractor which effect is likely to be highest
when it is closer to the stimuli which order was to be judged
(Olivers & Nieuwenhuis, 2006). This could be possible if we
consider that a ‘meta-contrast’ masking (which involves closely
adjacent but non-overlapping contours) is present. Then, an
integration mask (i.e. target and mask are perceived as part of
the same pattern) could happen for the shorter ISI as a conse-
A. PÉREZ ET AL. 107
quence of imprecise temporal resolution by the visual system
(Enns & Di Lollo, 2000). Sekuler et al. (1973) suggested that a
leftward bias in the TOJ task was due to reading scanning hab-
its, related to the idea that attention is preferentially allocated to
the side where the reading starts, affecting distribution of atten-
tion (Eviatar, 1997). In line with this hypothesis, the effect of
reading direction on performing of some spatial tasks was
found: on the ability to ignore irrelevant stimuli (Eviatar, 1995),
the direction of stroke movement in free-hand figure drawing
(Vaid, Singh, Sakhuja, & Gupta, 2002), the aesthetic preference
in a mirror-image (Chokron & De Agostini, 2000) and the
left-to-right bias in inhibition of return (Spalek & Hammad,
However, the leftward bias of the LtRR group was not re-
versed in the RtLR group. One may further argue that failure to
find the rightward bias in RtLRs was due to the fact that the
participants experienced both types of reading scanning habits.
Although their native language requires right-to-left reading,
they read from left-to-right from the moment they started their
Spanish education. So, they didn’t represent a pure sample of
right-to-left readers. It is, therefore, plausible that their potential
rightward bias was diminished due to the new reading condi-
tions. In fact for the RtLR group we find a different TOJ pattern,
a trend to a rightward bias. In addition, the power of the present
experiment might be too low to detect a small or medium right-
ward bias. We plan to increase the sample of the RtLR-Group in
a future study. However, the TOJ pattern is different to the
pseudoneglect found in the LtRR-Group, suggesting an interac-
tion between reading habits and distribution of spatial attention.
We think that even when the results suggest that reading hab-
its affected TOJ, there are further important reasons to argue for
an alternative explanation of a pre-existing leftward bias pre-
venting the bias revert to right. As we have mentioned, some
times a leftward bias has been reported irrespective of reading
habits (Nicholls et al., 2002) and has been proved to exist in a
wide range of perception aspects like: length, size, brightness
and quantity (Orr et al., 2005). In addition, there is evidence for
pseudoneglect in non-human species (Diekamp, Regolin, Gun-
turkun, & Vallortigara, 2005; Vallortigara, Rogers, Bisazza,
Lippolis, & Robins, 1998) suggesting some evolutionary role
for this bias. Other evidence suggesting a leftward bias, is the
revealed superior activation of a visuospatial attention-related
network for the left hemifield (Siman-Tov et al., 2007), giving
a neural substrate to the pseudoneglect phenomenon.
It remains to explain why our results are at odds with the re-
sults of some previous studies where TOJs were found to be
symmetrically distributed (Jaskowski & Rusiak, 2008; Shore et
al., 2001). One reason for this could be the first stimulus changes
that occurred in our experiment (i.e. S1). The spatial nature of
this change, even when we asked to ignore it, could evoke a
carry-over effect. The bias produced by the spatial nature of S1
could affect symmetry of TOJ. Indeed, it has been suggested that
the act of performing a spatial task is enough to shift attention
leftwards (McCourt, Freeman, Tahmahkera-Stevens, & Chaussee,
2001) because spatial tasks can preactivate the right hemisphere
due to its supposed dominance for spatial events (Weintraub &
These ideas are based in Kinsbourne’s functional distance
model which postulates that two cerebral hemispheres interac-
tively compete, in such a way that relative increases in activation
in one hemisphere will tend to bias attention towards the con-
tralateral hemi-space (Kinsbourne, 1970). In line with this rea-
soning, pseudoneglect commonly appears in visuospatial tasks.
For example, the advantage of the left over right hemifield was
found in the line bisection task (to bisect a line at its centre)
(Milner et al., 1992), the Grey-scales task (forced-choice lumi-
nance discriminations between two mirror-reversed luminance
gradients) (Nicholls et al., 2005; Orr et al., 2005) and the
free-vision chimeric tasks (judging in an image composed by
two different halves, for example, conjoined smiling and neu-
tral half-faces) (Luh et al., 1991), all with a strong spatial com-
In case of the TOJ task, it has been widely used to study vis-
ual field asymmetries, because of the fact that one stimulus is
presented in the opposite hemi field than the other, therefore
assuming a spatial component. However, the principal compo-
nent by definition is the temporal lag of stimulus onset, hence a
temporal component, not a spatial one is the principal. Some
research support a left hemisphere advantage for temporal
resolution (Nicholls, 1996). In TOJ, such a temporal rightward
bias could cancel the natural spatial leftward bias. This could be
a reason for the TOJ task to be often reported as symmetric
rather than asymmetric with a leftward bias.
Summarizing, reading habit is probably one of many factors
affecting the attentional distribution. It implies that we have to
be cautious in any study about visual lateralization taking into
account a wide range of factors that should be controlled. A
modulating effect of reading direction on spatial processing
would have a number of important implications for deciphering
the mechanisms for attention lateralization and may lead to
improved diagnosis and treatment of attention deficits in disor-
ders as neglect and developmental dyslexia.
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