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Into the Looking Glass: Literacy Acquisition and Mirror
Invariance inPreschool and First-Grade Children
Tania FernandesUniversidade de Lisboa
Isabel LeiteUniversidade de Evora
Regine KolinskyUniversite Libre de Bruxelles and Fonds de la
Recherche Scientifique-FNRS
At what point in reading development does literacy impact object
recognition and orientation processing? Is itspecific to mirror
images? To answer these questions, forty-six 5- to 7-year-old
preschoolers and first gradersperformed two samedifferent tasks
differing in the matching criterion-orientation-based versus
shape-based(orientation independent)-on geometric shapes and
letters. On orientation-based judgments, first graders
out-performed preschoolers who had the strongest difficulty with
mirrored pairs. On shape-based judgments, firstgraders were slower
for mirrored than identical pairs, and even slower than
preschoolers. This mirror costemerged with letter knowledge. Only
first graders presented worse shape-based judgments for mirrored
androtated pairs of reversible (e.g., b-d; b-q) than nonreversible
(e.g., e-) letters, indicating readers difficulty inignoring
orientation contrasts relevant to letters.
Learning to read is a gateway to culture and educa-tion, and
most impressively, it profoundly changesthe brain and mind.
Literacy acquisition leads tothe emergence of a neural network in
the ventraloccipitotemporal cortex tuned to the processingof
written strings, reproducible across literate peo-ple,
independently of script (e.g., in Japanese andFrench readers;
Dehaene, Nakamura, et al., 2010;e.g., for kana and kanji in
Japanese readers; Naka-mura, Dehaene, Jobert, Le Bihan, &
Kouider, 2005)and age of acquisition (i.e., in childhood for early
lit-erate adults or in adulthood for late literate adults;Dehaene,
Pegado, et al., 2010). Notably, learning toread also impacts on
evolutionarily older systems,including visual object recognition
(e.g., Dehaene,Nakamura, et al., 2010; Dehaene, Pegado, et al.,
2010; Pegado, Nakamura, Cohen, & Dehaene, 2011;Pegado,
Nakamura, et al., 2014). This agrees withthe neuronal recycling
hypothesis (Dehaene, 2009),which holds that the ventral
occipitotemporalregions, originally devoted to object
recognition,were partially recycled to accommodate literacy,with
spillover effects on the older function.
In fact, probably as a consequence of the inten-sive perceptual
training that it requires, literacyacquisition alters early visual
responses in theoccipital cortex, including in areas involved in
veryearly processing (i.e., primary visual cortex, V1;e.g.,
Dehaene, Pegado, et al., 2010; Pegado, Comer-lato, et al., 2014).
The impact of literacy can thus befound on several visual tasks
outside the writtendomain. For instance, visual integration is
enhancedin readers, as shown by early and late literateadults
superior capacity (compared to illiterates) inconnecting local
elements into an overall shape(Szwed, Ventura, Querido, Cohen,
& Dehaene,2012). The visual properties of the script itself
havealso a moderator role. For example, Chineseand Korean children
learning to read visuallycomplex and demanding scripts outperform
Israeliand Spanish children on visuospatial skills
Tania Fernandes and the work presented in this article
aresupported by the IF 2013 Program of FCT, Portugal (ref
IF/00886/2013/CP1194/CT0002) and by the Research Center
forPsychological Science (CICPSI). Regine Kolinsky is
ResearchDirector of the Fonds de la Recherche Scientifique-FNRS,
Bel-gium, and her work is supported by the Fonds de la
RechercheScientifique-FNRS under Grant FRFC 2.4515.12 and by
anInteruniversity Attraction Poles Grant IAP 7/33, Belspo. Wethank
Vanessa Neves for the assistance in experimental testing.We are
also very grateful to Ana Raposo, one anonymousreviewer, and Jon A.
Du~nabeitia for their comments on prior ver-sions of this
manuscript.
Correspondence concerning this article should be addressed
toTania Fernandes, Faculdade de Psicologia, Universidade de
Lis-boa, Alameda da Universidade, 1649-013 Lisboa, Portugal.
Elec-tronic mail may be sent to [email protected].
2016 The AuthorsChild Development 2016 Society for Research in
Child Development, Inc.All rights reserved.
0009-3920/2016/8706-0026DOI: 10.1111/cdev.12550
Child Development, November/December 2016, Volume 87, Number 6,
Pages 20082025
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(McBride-Chang et al., 2011, Experiment 1), and theimportance of
reading to spatial skills is strongerthan that of spatial skills to
reading, as shown bymultiple regression analyses run at two
testingmoments in a 1-year longitudinal study with Chi-nese
children (McBride-Chang et al., 2011, Experi-ment 2).
Learning to read in scripts such as the Latinalphabet also
requires quite specific adaptations,especially when considering
original properties ofthe visual system that may oppose to literacy
acqui-sition. One such property is mirror-image general-ization or
mirror invariance: Lateral mirror images(180 flip outside the image
plane, e.g., and ) areprocessed as equivalent percepts by humans
andother animals (e.g., Dehaene, Nakamura, et al.,2010; Logothetis,
Pauls, & Poggio, 1995; Pegadoet al., 2011; Tarr & Pinker,
1989). Yet, to learn ascript with mirrored symbols, one must
discrimi-nate mirror images, which collides with
mirrorinvariance.
Besides the Latin alphabet (which is used inmore than 400
languages; e.g., b and d), otherscripts such as the Japanese
hiragana (e.g., and) and the Cyrillic alphabet (e.g., e and )
alsoinclude mirrored or quasi-mirrored symbols. In anyof these
scripts, mirrored symbols are just a smallproportion, but this is
sufficient to trigger the abil-ity to discriminate them, which
transfers to nonlin-guistic categories (e.g., Dehaene, Nakamura, et
al.,2010; Kolinsky et al., 2011; Pegado et al., 2011),either novel
(i.e., blob-like and geometric shapes) orfamiliar (e.g., pictures
of tools or cloths). Indeed, incontrast to readers of the Latin
alphabet, illiterateadults present poor mirror discrimination
(Fernan-des & Kolinsky, 2013; Kolinsky et al., 2011),
andreaders of Tamil, a script with no mirrored sym-bols, have the
same difficulties as illiterates (Danzi-ger & Pederson, 1998;
Pederson, 2003). Therefore, itis not learning to read in general
that causes peopleto become able to discriminate mirror images.
Thetrigger is learning a script with mirrored symbols.
Importantly, Pegado, Nakamura, et al. (2014; seealso Kolinsky
& Fernandes, 2014) recently showedthat mirror discrimination
also extends to situationswhere orientation processing is
irrelevant and evenharmful to the task at hand. In a
samedifferent,identity-based, and orientation-independent
task,requiring a same response to both exact matches(henceforth,
identical pairs) and mirrored pairs ofthe same object, only
illiterate adults had as goodperformance for mirrored as for
identical pairs. Incontrast, adult readers of the Latin alphabet
showeda mirror cost, that is, worse performance for
mirrored than identical pairs of linguistic (i.e., pseu-dowords)
and nonlinguistic materials (i.e., false-fontstrings, composed of
letter-like characters; picturesof objects and faces). Thus, with
literacy acquisition,mirror discrimination seems to become part of
visualobject recognition, as readers of the Latin alphabetare
unable to ignore mirror-image differences evenwhen this hinders
performance. This specific impactof literacy could also explain the
weaker primingeffect found for targets preceded by mirrored
ratherthan by identical primes in short-term priming stud-ies with
adult readers (e.g., Dehaene, Nakamura,et al., 2010; Pegado et al.,
2011).
Although these studies have shown that learninga script with
mirrored symbols enhances sensitivityto mirror images, to the best
of our knowledge nostudy has hitherto examined when, during
literacyacquisition, mirror discrimination becomes part ofvisual
object recognition. Examining this questionin children differing on
reading skills (preschoolerswith no reading skills vs. beginning
readers at theend of the first grade) was the main aim of the
pre-sent study. Single letters and geometric shapes wereused to
investigate the effects of literacy acquisitionon linguistic and
nonlinguistic material.
Mirror discrimination probably develops earlierfor letters and
for nonlinguistic stimuli visually sim-ilar to letters, such as
geometric shapes, than forother nonlinguistic categories. Indeed,
even beforechildren are able to read, their letter knowledgealready
predicts attention to text (as measuredthrough eye movements;
Evans, Saint-Aubin, &Landry, 2009) and stronger responsiveness
of theleft occipitotemporal region to letters than to othervisual
categories (Cantlon, Pinel, Dehaene, & Pel-phrey, 2011).
Consistently, illiterate adults who areunable to decode but have
high letter knowledgeprocess letters differently than nonletters
(Fernan-des, Vale, Martins, Morais, & Kolinsky, 2014).Regarding
mirror-image processing, Kolinsky andFernandes (2014) recently
showed that, whereas forpictures of familiar objects illiterate
adults did notpresent any mirror cost on identity-based judg-ments
(as in Pegado, Nakamura, et al., 2014), forgeometric shapes they
did present a mirror cost.This sensitivity to mirror-image
differences in geo-metric shapes by illiterate adults is consistent
withthe hypothesis that the highly reproducible locationof the
brain regions devoted to letter and visualword recognition is due
(at least partially) to thefact that these neurons are specifically
tuned toshape features similar to those of letters (Hannagan,Amedi,
Cohen, Dehaene-Lambertz, & Dehaene,2015). Under this view, the
closer the features of
Literacy Acquisition and Mirror Invariance 2009
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nonlinguistic stimuli to those of letters, the earlierthe
consequences of literacy on visual (nonlinguis-tic) processing.
Notably, rudimentary reading seemsenough, as late literate adults
present the same mir-ror costs as early literates on both
linguistic andnonlinguistic materials (Kolinsky &
Fernandes,2014; Pegado, Nakamura, et al., 2014).
However, late literate adults are not comparableto young
children. Note that even explicit mirrordiscrimination, that is,
when orientation is criticalto the task, seems to develop slowly in
childhood.Children often present mirror errors in reading
andwriting during the first 2 years of literacy instruc-tion
(Cornell, 1985). Compared with fluent adultreaders, first-grade
children fixate more and forlonger time on distractors differing
from the target-word on two mirrored letters (e.g., meter,
lettersunderlined were mirrored in the distractor) than oncontrol
distractors (e.g., matar; Du~nabeitia, Dim-itropoulou, Estevez,
& Carreiras, 2013). For nonlin-guistic material, in contrast to
literate adults, 7- to8-year-old children present similar
short-term prim-ing effects when pictures of familiar objects
(e.g.,animals) are preceded by mirrored and by identicalprimes
(Wakui et al., 2013).
We thus decided to investigate the impact oflearning to read on
mirror-image processing of let-ters and geometric shapes in two
tasks where orien-tation was either critical or irrelevant for
successfulperformance using a within-participants
design.Furthermore, it is still unclear whether the impact
ofliteracy on orientation processing is restricted to oris at least
stronger for mirror images than for otherorientation contrasts.
Thus, we contrasted the pro-cessing of mirror images with the
processing ofrotations in the image plane (henceforth, plane
rota-tions; e.g., 180 clockwise rotation: and ). Indeed,as
highlighted by Gibson, Pick, Osser, and Gibson(1962), both mirror
images and plane rotations dis-tinguish letters of the Latin
alphabet, for example,d-b and d-p, respectively. Given that letters
are acategory of expertise for readers (McCandliss,Cohen, &
Dehaene, 2003), dimensions that maxi-mally distinguish letters,
like orientation, wouldbecome enhanced through perceptual learning
(e.g.,Folstein, Palmeri, & Gauthier, 2013). Literacy shouldthus
impact both mirror-image and plane-rotationprocessing. Yet, the
neuronal recycling hypothesispredicts that this impact should be
stronger for theformer contrast (Dehaene, 2009) because the
visualsystem is originally sensitive to plane rotations butnot to
mirror images (e.g., Logothetis et al., 1995).Consistently, both 4-
to 6-year-old children and illit-erate adults find it harder to
explicitly discriminate
mirror images than plane rotations of nonlinguisticobjects
(Fernandes & Kolinsky, 2013; Gregory, Lan-dau, & McCloskey,
2011). Whether a similar patternwould be found when orientation is
irrelevant tothe task is not clear. In Pegado, Nakamura, et
al.(2014), mirror images were the only orientation con-trast
examined. In Kolinsky and Fernandes (2014),although for
identity-based judgments of familiarobjects illiterate adults
presented no orientationcosts, for geometric shapes both illiterate
and liter-ate adults presented stronger interference forrotated
than mirrored pairs.
Therefore, to examine orientation processingwhen critical versus
irrelevant to the task, childrenperformed two samedifferent tasks,
on which theydecided in each trial whether the second stimulus(S2)
was the same or not as the first one (S1). Asillustrated in Figure
1, the two tasks were per-formed separately on geometric shapes and
singleletters, and had the same four trial types: fullydifferent
trials (on which S2 differed from S1 onshape and on orientation;
e.g., b-u), identical trials(S2 had the same shape and same
orientation as S1;e.g., b-b), mirrored trials (S2 was a mirror
image ofS1; e.g., b-d), and rotated trials (S2 was a planerotation
of S1; e.g., b-q). The mirror-image andplane-rotation contrasts
differed from the standardstimulus (S1) by the same 180 difference
and pre-served all object-based properties (global shape,parts, and
relation between parts). Thus, any differ-ence in performance
between mirrored and rotatedtrials would not be due to low-level
factors.
Both tasks examined mirror-image and plane-rotation processing,
and differed only on the match-ing criterion: Orientation was
either irrelevant orcritical for successful performance. In the
shape-basedtask, children were asked to classify a stimulus pairas
same if S2 had the same shape as S1; orientationwas thus irrelevant
to the task, and hence not onlyidentical but also mirrored and
rotated pairs shouldbe classified as same. In this task,
orientation pro-cessing would hinder performance, leading to
anorientation cost on mirrored or rotated trials com-pared to
identical trials, which were used as base-line. In contrast, in the
orientation-based task,orientation was the critical dimension:
Childrenwere asked to classify a stimulus pair as same onlyif S2
was identical to S1same shape and same ori-entationand to classify
as different both the fullydifferent pairs and the mirrored and
rotated pairs.Orientation processing was assessed by examiningthe
performance drop on trials on which only orienta-tion varied
(mirrored and rotated trials) relative tofully different
trials.
2010 Fernandes, Leite, and Kolinsky
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Given the original property of mirror invarianceof the ventral
visual system (Dehaene, 2009; Logo-thetis et al., 1995; Tarr &
Pinker, 1989), we expectedpreschoolers to be better able to
tolerate, that is, toclassify as same, the mirrored pairs in the
shape-based task than to discriminate them in the
orienta-tion-based task, whereas they would be as able totolerate
as to discriminate plane rotations. Indeed,in the shape-based task,
preschoolers would exhibitno mirror cost at all. Conversely, in the
orientation-based task, they would present the worst perfor-mance
for mirrored pairs, even when comparedwith rotated pairs. This
pattern of results wasexpected for both materials. If mirror
discriminationtransferred to nonlinguistic categories early on
inreading acquisition, first graders would presentgood mirror
discrimination of both letters and geo-metric shapes in the
orientation-based task. If itbecame part of visual object
recognition, theywould also present a mirror cost for both
materialsin shape-based judgments. Given the importance
ofplane-rotation contrasts in letter discrimination, weexpected
first graders to be less able to tolerateplane rotations in the
shape-based task than to dis-criminate them in the
orientation-based task. There-fore, the strongest difference
between preschoolersand first graders was expected for the
mirroredpairs. Note that by using the two normalizedindices (i.e.,
the orientation cost and the perfor-mance drop), we ensured that
any difficulty to be
found on explicit mirror discrimination bypreschoolers could not
be due to overall differencesbetween groups.
We also examined the mirror cost for reversibleletters (i.e.,
differing only by orientation; e.g., u-n)and nonreversible letters,
for which orientation con-trasts do not map onto different
representations(e.g., e-). As mirror discrimination is most
rele-vant to reversible letters (Perea, Moret-Tatay, &Panadero,
2011), the orientation cost on shape-based judgments of first
graders should be stron-ger for these letters, but no difference
wasexpected for preschoolers due to their limited
letterknowledge.
Finally, to assess whether literacy-related skills(i.e., letter
knowledge in preschoolers, and readingskills and phonological
awareness in first graders)were associated with mirror
discrimination or ori-entation processing in general, we conducted
corre-lation analyses in each group for each material.
Method
Participants
Twenty-eight preliterate preschoolers (17 males;Mage = 65.9
months, SD = 3.2) and 24 first graders(7 males; Mage = 82.7 months,
SD = 3.6), all Por-tuguese native speakers, from schools in
Lisbonand Evora, Portugal, with no known history of
Figure 1. Experimental material. (A) Sequence of events in each
experimental trial and illustration of the four trial types. The
presenta-tion of the first stimulus (S1) and the second stimulus
(S2) was separated by a mask to ensure no involvement of iconic
memory in per-formance. S2 was presented until response or for the
maximum of 2.5 s if no response was given, after which another
trial began. Thetwo geometric shapes presented as S2 in the fully
different and identical trials are the new figures used in this
study (see text). (B) Thetwo letter types (reversible and
nonreversible) organized by the four trial types.
Literacy Acquisition and Mirror Invariance 2011
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developmental and/or neurological disorders, par-ticipated
voluntarily (the study followed the ethicalguidelines of the
Declaration of Helsinki). Datawere collected between March and June
2011, andMarch and June 2013. Due to the end of the schoolyear, six
preschoolers did not perform the orienta-tion-based task for
geometric shapes and three didnot perform it for letters. These
children wereexcluded, as well as those who performed at thechance
level on the fully different and identical tri-als, which led to
same responses in the two tasks(for geometric shapes: two
preschoolers and onefirst grader; for letters: two other
preschoolers andthe same first grader). The final sample
thusincluded 20 preschoolers for geometric shapes and23 for
letters, plus 23 first graders for both materi-als.
Table 1 presents childrens results in fivedomains: nonverbal IQ
(Colored Progressive Matri-ces of Raven, Portuguese Version;
Sim~oes, 2000),visuospatial working memory (Corsi block
test,Wechsler Memory Scale, 3rd ed.; Wechsler, 1997),phonological
awareness (i.e., samedifferent task onthe target unitthe phoneme,
the rhyme, or thesyllableof two words; 6 practice trials plus 16
tri-als per unit), letter knowledge (naming and recog-nition of
lower- and upper-case letters of thePortuguese alphabet), and
reading skills for firstgraders only, that is, reading fluency of
isolateditems (3DM Battery, Portuguese Version; Reis,Faisca,
Castro, & Petersson, 2013) and reading com-prehension (Lobrot
L3 test, Portuguese adaptation;Sucena & Castro, 2008).
The phonological awareness task was examinedusing signal
detection theory (SDT) d scores(Macmillan & Creelman, 2005).
The reading indexwas the summed result across the 3DM subtestsand
the Lobrot L3 test, given their high correla-tions, r(21)s >
.85, ps < .001.
In the Portuguese educational system, literacyinstruction starts
only at Grade 1. There are no offi-cial directives concerning
literacy-related activitiesin preschool years, and hence, usually
no (or onlylimited) instruction on letter knowledge is
given,explaining the low letter knowledge of thesepreschoolers (see
Table 1), and the independencebetween their letter knowledge and
phonologicalawareness, r(18) = .26, p = .13. In contrast, for
firstgraders, phonological awareness was significantlyassociated
with reading skills, r(21) = .59, p < .005.In both groups,
visual working memory was signif-icantly associated with nonverbal
IQ (visuospatialabilities): preschoolers, r(18) = .46, and first
graders,r(21) = .40, both ps .03.
Material
Two types of asymmetrical black-line materialwere used: nine
geometric shapes and eight letters(see Figure 1). The geometric
shapes were thoseused by Fernandes and Kolinsky (2013), except
fortwo stimuli that were replaced by those presentedin Figure 1A.
As shown in Figure 1B, half of theletters were nonreversible and
the others werereversible (for b and p both orientation
contrastscorresponded to real letters, but not for m and u).
For each material, three versions were createdwith irfanview
(www.irfanview.com): the standard,its mirror image (180 lateral
reflection), and itsplane rotation (180 clockwise rotation). For
eachstandard stimulus, four pairs were prepared to cre-ate the four
trial types (S1 was the standard):
Table 1Age and Average Performance in the Ancillary Tests
Preschoolers(n = 23)
First graders(n = 23)
Age (in months) 66.04 (3.34)[64.60, 67.49]
82.65 (3.64)[81.08, 84.22]
Nonverbal IQ:Raven testa
17.70 (2.99)[16.40, 18.99]
26.74 (5.37)[24.41, 29.06]
Visuospatial workingmemory: Corsi blocksb
6.61 (2.71)[5.44, 7.78]
13.17 (2.39)[12.14, 14.20]
Phonologicalawareness: d score
1.51 (1.40)[0.91, 2.12]
5.19 (0.92)[4.79, 5.58]
Letter knowledgec 24.65 (13.67)[18.74, 30.56]
65.26 (7.45)[62.04, 68.48]
Reading performance3DMdhigh-frequencywords
17.13 (11.22)[12.28, 21.98]
3DMlow-frequencywords
10.87 (7.40)[7.67, 14.07]
3DMpseudowords 11.52 (6.29)[8.80, 14.24]
Lobrot L3e 9.39 (6.45)[6.60, 12.18]
Reading index(summed score)
48.91 (29.85)[36.00, 61.82]
Note. SD in parentheses; 95% CI in brackets. aTotal of
correctresponses out of 36 in the Colored Progressive Matrices
ofRaven. bNumber of trials correctly performed in forward and
inbackward sequences. cTotal number of correct responses out of68
items, that is, 2 (naming and recognition tasks) 9 22 upper-case
letters of the Portuguese alphabet (excluding letters H, K,W, Y),
plus 2 (naming and recognition tasks) 9 12 lower-case let-ters
(i.e., b, d, p, q, f, g, r, s, i, o, m, x). dNumber of items
readcorrectly per list in 30 s. eSilent reading test with 5-min
timelimit, on which participants select the word that correctly
com-pletes each sentence (out of five possible words).
Performancecomputed as number of items correctly completed (total
of 36sentences).
2012 Fernandes, Leite, and Kolinsky
http://www.irfanview.com
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identical trials (S2 was the same as S1), mirroredtrials (S2 was
the mirror image of S1), rotated trials(S2 was the plane rotation
of S1), and fully differenttrials (S2 was a different standard
stimulus).
Procedure
Children were tested in a quiet room of theirschool. They
performed the two samedifferenttasks for the two materials in four
sessions. Theshape-based task was performed first to ensure thatany
orientation cost to be found would not be dueto prior performance
of the orientation-based task.Sequence of events in experimental
trials was thesame for each task and material (see Figure 1A),and
was controlled by E-Prime 2.0 (www.pstnet.-com/eprime). Children
sat at a distance of ~70 cmof the computer screen (resolution: 640
9 480 pix-els; refresh rate: 60 Hz) and were asked to performa
samedifferent judgment on S2 in each trial (ineach task, half of
the trials were expected to lead toa same response). Instructions
were given orallywith six demo trials using animals as stimuli.
Next,to ensure that children understood the task, theyperformed 12
practice trials (six with animals, sixwith the experimental
material; half of the trialsleading to a same response), with
feedback onresponse accuracy.
In the shape-based task, on each trial childrenwere asked to
decide as accurately and quickly aspossible whether S2 had the same
shape as S1,independently of orientation, by pressing one of thetwo
keys of the response box (same response givenwith the right index
finger). It was emphasized thatstimulis name was irrelevant to the
task; S2 shouldbe classified based on shape and not on name.
Notethat at least for letters, especially for reversibleones, an
identity-based criterion (same identity,same name) would induce an
incorrect response(e.g., d and b are different letters, with
differentnames, but have the same shape). In the orienta-tion-based
task, children were asked to decidewhether S2 was an exact match of
S1. They shouldrespond different (using the left key, left index
fin-ger) if S2 had a different orientation than S1 even ifthey had
the same shape. Accuracy and reactiontimes (RTs; measured from S2
onset to responseonset) were collected in each trial.
Children performed 108 trials for geometricshapes in each task
(i.e., shape-based task: 54 fullydifferent, 18 identical, 18
mirrored, and 18 rotatedtrials; orientation-based task: 54
identical, 18 fullydifferent, 18 mirrored, and 18 rotated trials).
For let-ters, they performed 96 trials per task (for each
letter type: in the shape-based task, 24 fully differ-ent, 8
identical, 8 mirrored, and 8 rotated trials; inthe
orientation-based task, 24 identical, 8 fully dif-ferent, 8
mirrored, and 8 rotated trials).
Results
The mean accuracy and correct RTs (after the trim-ming of
outliers 2.5 SD above or below the grandmean RT for each
participant by material and task;< 3% data excluded) were
examined separately foreach material, with group (preschoolers,
first gra-ders; between-participants), task (shape- vs.
orienta-tion-based), and trial type (fully different,
identical,mirrored, rotated) as factors, plus letter type
(re-versible vs. nonreversible) for the analyses run onletters. We
also checked that a similar pattern ofstatistical significance was
found when analyseswere run on SDT d scores adapted for
samediffer-ent designs (i.e., hits correspond to proportion
ofcorrect responses on different-response trials, andfalse alarms
correspond to the proportion of incor-rect responses on
same-response trials; cf. Macmil-lan & Creelman, 2005), with
group, task, andcondition (fully different; mirrored; rotated) as
fac-tors, plus the letter-type factor in the analyses runon
letters.
Geometric Shapes
The three-way interaction between all factors attest was
significant on both accuracy, F(3, 123) = 3.72,p = .013, g2p :08 (d
scores, F(2, 82) = 3.97, p = .022, g2p :09) and RTs, F(3, 123) =
2.94, p = .036,g2p :07. Consistent with our predictions, as shownin
Figure 2 (see also Table 2), whereas preschoolerswere immune to
mirror-image differences, first gra-ders were sensitive to them
even if harmful for per-formance. Specifically, preschoolers were
perfectlyable to tolerate (i.e., responding same to) the
mirroredpairs in the shape-based task (Figure 2A) and had
thestrongest difficulty in discriminating them in the
ori-entation-based task (Figure 2B), whereas first graderspresented
a mirror cost on shape-based judgmentsand were quite able to
explicitly discriminate the mir-rored pairs.
Shape-Based Task
In the shape-based, orientation-independent task(Figure 2A),
preschoolers had a similar overall per-formance level as first
graders on both accuracy,F(1, 41) = 2.02, p = .16 (d scores, F <
1), and RTs,
Literacy Acquisition and Mirror Invariance 2013
http://www.pstnet.com/eprimehttp://www.pstnet.com/eprime
-
F = 1; we thus directly compared their perfor-mance. Notably, it
was only for mirrored trials thatfirst graders were significantly
slower thanpreschoolers by 118 ms on average, t(41) = 1.65,p = .05
(accuracy: t(41) = 1.40, p = .10; d scores,t < 1) other ts <
1. Furthermore, although firstgraders showed a significant mirror
cost, withslower performance on mirrored than on identicaltrials,
F(1, 22) = 10.05, p = .004 (accuracy, F < 1),preschoolers did
not show any mirror cost (accu-racy and RTs: Fs < 1). For plane
rotations, no
difference was found between groups, ts < 1, asboth presented
a rotation cost, with worse andslower performance on rotated than
on identical tri-als: preschoolers, F(1, 19) = 10.85 and 39.36,
respec-tively, both ps < .005; first graders, F(1, 22) = 9.34and
19.84, respectively, both ps < .010. On d scores,whereas
preschoolers were not affected by orienta-tion, with similar d
scores for mirrored, rotated,and fully different conditions, Fs 1,
first graderswere affected by orientation, F(2, 44) = 6.20,p =
.004, with higher d scores in the fully different
Figure 2. Mean performanceaccuracy on the top, reaction times on
the bottomof preschoolers and first graders for geometricshapes.
(A) Performance in the shape-based task. (B) Performance in the
orientation-based task. Error bars represent the SEM -
standarderror of the mean in each condition.
2014 Fernandes, Leite, and Kolinsky
-
(which did not differ from the mirrored condition,F < 1),
than in the rotated condition, F(1, 22) = 9.09,p = .006 (see Table
2).
Orientation-Based Task
As illustrated in Figure 2B, preschoolers had aspecific
difficulty in discriminating mirrored pairs,presenting the worst
and slowest performance forthese trials compared with either fully
different tri-als, F(1, 19) = 23.15 (d scores, F(1, 19) = 14.47)
andF(1, 19) = 16.93, respectively, ps .001, or rotatedtrials, F(1,
19) = 4.73 (d scores, F(1, 19) = 16.11) andF(1, 19) = 4.55,
respectively, ps < .05. Preschoolerswere also less accurate and
slower on rotated thanon fully different trials, F(1, 19) = 16.91
(d scores,F(1, 19) = 4.40) and F(1, 19) = 7.05, respectively,ps
.05. Furthermore, on mirrored trials, preschool-ers were also worse
than first graders, t(41) = 5.97(d scores), t(41) = 10.44, ps <
.001, but not slower,t = 1.20, p > .10.
Although first graders were still less accurateand slower in
discriminating mirror images thanplane rotations, F(1, 22) = 14.18
(d scores, F(1,22) = 19.65) and 4.97, respectively, ps < .05,
theywere quite able to discriminate any orientation con-trast, with
average accuracy above 80% (see Fig-ure 2B). Additionally, they
were as accurate onrotated as on fully different pairs, F < 1 (d
scores,F(1, 22) = 2.42, p = .13; see Table 2), albeit slowerfor the
former pairs, F(1, 22) = 17.84, p < .001.
In contrast to what happened in the shape-basedtask, in the
orientation-based task first graders wereoverall more accurate than
preschoolers, F(1,41) = 37.84 (d scores, F(1, 41) = 122.11), ps
< .001,but not faster, F < 1. As shown in Figure 2B,
firstgraders were especially better than preschoolers formirror
images (Group 9 Trial Type: accuracy, F(3,123) = 7.94, p < .001;
RTs, F < 1; d scores, F(2,82) = 3.00, p = .05).
To ensure that this result was not merely due tothe overall
difference between groups, we next used
a normalized index to compare preschoolers withfirst graders on
their performance drop for mir-rored and rotated trials relative to
fully different tri-als: [(x y)/(x + y)] 9 100, where x is
theproportion of correct responses on fully differenttrials, and y
is the proportion of correct responseson either mirrored or rotated
trials (cf. Fernandes &Kolinsky, 2013). The higher the
performance drop,the stronger the relative difficulty to
discriminatethe pair on the basis of only orientation (on mir-rored
or rotated trials) rather than on the basis ofboth shape and
orientation (on fully different trials).For mirror images, the
performance drop was sig-nificantly stronger in preschoolers than
in first gra-ders (M = 11.89%, [SEM] = 4.19 vs. M = 6.06%,SEM =
2.19, respectively), F(1, 41) = 6.74, p = .013;for plane rotations,
the difference between groupsdid not reach the conventional level
of significance,but preschoolers tended to present a larger
perfor-mance drop (M = 4.31%, SEM = 2.76 vs.M = 1.37%, SEM = 1.46,
respectively), F(1,41) = 3.57, p = .07.
Comparison Between the Two Tasks and the TwoGroups
The comparison between tasks revealed thatpreschoolers found it
harder to explicitly discrimi-nate (in the orientation-based task)
than to tolerate(in the shape-based task) the mirrored pairs:
accu-racy, d scores, and RTs, F(1, 19) = 14.90, 14.11, and20.78,
respectively, all ps .001. For the other trialtypes (including the
rotated trials), they were as fastand as accurate (with similar d
scores) on shape-based as on orientation-based judgments, all Fs
< 1(see Figure 2). Yet, the association between perfor-mance in
the two tasks was not significant, for mir-rored trials (accuracy:
r(18) = .22, p = .18; RTs:r(18) = .35, p = .12), for rotated trials
(accuracy andRTs: r(18) = .05 and .13, ps > .25), or across
trials(accuracy: r(18) = .26, p = .13; RTs: r(18) = .30,p = .10;
one-tailed t tests).
Table 2Mean d Scores of Preschoolers and First Graders for
Geometric Shapes in the Three Conditions at Test (Mirrored,
Rotated, and Fully Different) inthe Shape-Based and
Orientation-Based Tasks
Preschoolers First graders
Mirrored Rotated Fully different Mirrored Rotated Fully
different
Shape-based task 2.96 (.23) 2.75 (.18) 2.81 (.19) 3.10 (.21)
2.69 (.17) 3.09 (.18)Orientation-based task 2.07 (.18) 2.68 (.19)
3.01 (.24) 4.61 (.17) 5.49 (.18) 5.13 (.22)
Note. Standard error of the mean (SEM) in parenthesis.
Literacy Acquisition and Mirror Invariance 2015
-
The pattern of results of first graders differedfrom that of
preschoolers in three ways. First gra-ders were as accurate and
fast in discriminating asin tolerating the mirrored pairs, both Fs
< 1.25, yet,the association between the two tasks for these
tri-als did not reach statistical significance: accuracy, r(21) =
.13, p = .28; RTs, r(21) = .32, p = .07. More-over, on d scores,
they were even better on orienta-tion-based than on shape-based
judgments in themirrored condition, F(1, 22) = 36.57, p < .001.
Sec-ond, a similar advantage for the orientation-basedover the
shape-based task was observed for theother trial types, especially
for rotated pairs. Onaverage, first graders were 24% more accurate
indiscriminating than in tolerating these pairs, F(1,22) = 44.13, p
< .001, and their average d score forthese pairs in the
orientation-based task was almostthe double of that in the
shape-based task, F(1,22) = 153.78, p < .001 (see Table 2).
Finally, theassociation between the two tasks was significantfor
rotated trials, on RTs, r(21) = .50, p = .008 (not
on accuracy, r = .09), and across trials, accuracyand RTs,
rs(21) > .50.
Letters
In the analyses of variance run on accuracy andRTs, the Group 9
Trial Type 9 Letter Type interac-tion was significant, F(3, 132) =
4.79, p = .003,g2p :10, and F(3, 132) = 2.63, p = .050, g2p
:056(see Figure 3). Similarly, on d scores, theGroup 9 Condition 9
Letter Type interaction wassignificant, F(2, 88) = 5.72, p = .02,
g2p :115.Indeed, preschoolers were not affected by lettertype at
all (neither the main effect of letter type norany interaction with
other variables was significanton accuracy, d scores, and RTs, all
Fs < 1.62,ps > .21). In contrast, in first graders, letter
typeinteracted with trial type (accuracy: F(3, 66) = 13.81,p <
.001, g2p :39, and RTs: F(3, 66) = 5.33,p = .002, g2p :19; and on d
scores, with condition,F(2, 44) = 3.08, p = .05, g2p :122) and with
task
Figure 3. Mean performanceaccuracy on the top, reaction times on
the bottomfor reversible letters (in black) and nonreversible
let-ters (in gray) by preschoolers and first graders in the
experimental tasks. (A) Performance in the shape-based task. (B)
Performance inthe orientation-based task. Error bars represent the
standard error of the mean in each condition.
2016 Fernandes, Leite, and Kolinsky
-
accuracy: F(1, 22) = 47.03, p < .001, g2p :68; dscores: F(1,
22) = 6.70, p = .017, g2p :233; and RTs:F(1, 22) = 5.20, p = .032,
g2p :19. Actually, theimpact of letter type on first-graders
accuracy wasquite specific: It was modulated by task and trialtype,
F(3, 66) = 9.53, p < .001, g2p :30; LetterType 9 Task 9 Trial
Type was not significant foreither d scores, F = 1.38, or RTs, F
< 1. As afore-mentioned, for preschoolers, performance was
notaffected by letter type, but it was modulated bytask and trial
type, on accuracy, F(3, 66) = 5.61,p = .002, g2p :20, and RTs, F(3,
66) = 3.89, p = .01,g2p :15, similarly, on d scores, the Task 9
Condi-tion interaction was significant, F(2, 44) = 9.89,p <
.001, g2p :31; see Table 3. Therefore, we fur-ther examined the
preschoolers results in each taskacross letter type, whereas for
first graders theimpact of letter type was also considered.
Shape-Based Task
In contrast to what happened for geometricshapes, for letters
first graders presented an overalladvantage over preschoolers in
the shape-basedtask (see Figure 3A), on accuracy, F(1, 44) = 9.63,p
= .003 (d scores, F(1, 44) = 19.80, p < .001) butnot on RTs, F =
1.25 (the only significant effecton RTs was the main effect of
trial type,F(3, 132) = 11.32, p < .001). This advantage
wasmodulated by letter and trial type, F(3, 132) = 9.16,p < .001
(d scores: Letter 9 Condition, F(2,88) = 2.44, p = .09).
Nevertheless, both groups exhibited the samequalitative impact
of trial type on their perfor-mance. As shown in Figure 3A,
preschoolers pre-sented a rotation cost on shape-based judgmentsof
letters: worse and slower performance on rotatedtrials (M = 59.5%,
SEM = 3.8; M = 1,125 ms,
SEM = 62) than on identical trials (M = 71.5%,SEM = 3.4; M =
1,003 ms, SEM = 49), F(1,22) = 6.85 and 11.96, respectively, ps
.016. Simi-larly, they had lower d scores on the rotated thanon the
fully different condition (see Table 3), F(1,22) = 4.91, p =
.03.
Contrary to what happened for geometricshapes, preschoolers also
presented a mirror costfor letters, with worse performance on
mirrored tri-als (M = 62.4%, SEM = 2.5; M = 1,082 ms,SEM = 61) than
on identical trials: accuracy, F(1,22) = 6.10, p = .022; RTs, F(1,
22) = 3.39, p = .079,an effect that was also found on d scores,
F(1,22) = 4.91, p = .03.
Similarly, first graders presented rotation andmirror costs on
shape-based judgments of letters:For reversible letters, a rotation
cost, accuracy, F(1,22) = 50.63, RTs, F(1, 22) = 9.71, both ps
.005, anda mirror cost, accuracy, F(1, 22) = 31.79, p <
.001,RTs, F = 1.14 (also found on d scores, with lowerperformance
on the mirrored and rotated trials thanon the fully different ones,
F(1, 22) = 10.82 and16.92, respectively, both ps < .005); for
nonre-versible letters, the rotation and mirror costs
weresignificant on RTs, F(1, 22) = 16.16 and 11.99,respectively,
both ps < .001, but not on accuracy ord scores, Fs < 1 (see
Table 3).
More important, first-graders shape-based judg-ments were
modulated by letter and trial type onaccuracy, F(3, 66) = 17.38, p
< .001 (RTs: F(3,66) = 1.55, p = .207; Letter 9 Condition, on
dscores, F(2, 44) = 5.07, p = .01), because their orien-tation
costs were stronger for reversible than fornonreversible letters.
They were less accurate onshape-based judgments of reversible than
nonre-versible letters for mirrored pairs, F(1, 22) = 13.53,p =
.001 (d scores: F(1, 22) = 5.96, p = .023), androtated pairs, F(1,
22) = 62.86 (d scores: F(1,
Table 3Mean d Scores of Preschoolers and First Graders for the
Two Letter Types and Across Letter Type in the Three Conditions at
Test in theExperimental Tasks
Reversible letters Nonreversible letters Across letter type
Mirrored RotatedFully
different Mirrored Rotated Fully different Mirrored
RotatedFully
different
PreschoolersShape-based task 2.58 (.20) 2.57 (.16) 3.03 (.28)
2.57 (.23) 2.40 (.24) 2.77 (.23) 2.57 (.17) 2.48 (.17) 2.90
(.25)Orientation-based task 1.77 (.26) 2.59 (.19) 3.40 (.27) 1.77
(.29) 2.77 (.31) 3.12 (.28) 1.77 (.24) 2.68 (.21) 3.26 (.23)
First gradersShape-based task 3.36 (.29) 3.02 (.25) 4.16 (.29)
4.27 (.30) 4.39 (.33) 4.30 (.30) 3.81 (.23) 3.70 (.25) 4.23
(.25)Orientation-based task 3.65 (.26) 4.46 (.33) 4.86 (.28) 4.63
(.28) 3.52 (.24) 4.56 (.32) 3.58 (.18) 4.51 (.28) 4.75 (.25)
Note. Standard error of the mean in parenthesis.
Literacy Acquisition and Mirror Invariance 2017
-
22) = 18.63), ps < .001, but not for identical or
fullydifferent pairs, Fs < 1. Thus, first graders found itharder
to classify as same the pairs that map ontodifferent letter
representations, either mirrored orrotated (e.g., d-b, or d-p) than
those that do not(e.g., e-).
In order to directly compare the orientation costof the two
groups in the shape-based task, weadopted the orientation cost
index used by Pegado,Nakamura, et al. (2014) and Kolinsky &
Fernandes(2014), that is, [(x z)/(x + z)] 9 100, where x isthe
proportion of correct responses on fully differ-ent trials and z is
the accuracy on identical trials:The higher the orientation cost,
the stronger theinterference due to an orientation transformation
onshape-based judgments. This orientation cost wassignificantly
modulated by group, letter type, andorientation contrast, F(1, 44)
= 5.92, p = .019,g2p :12. For nonreversible letters, the
orientationcost of first graders was similar to that ofpreschoolers
(M = 1.34%, SEM = 3.24 vs. 8.72%,SEM = 4.35, respectively), F(1,
44) = 2.60, p = .12,and was not modulated by the orientation
contrast,F(1, 44) = 2.34, p = .132. In contrast, for
reversibleletters, first graders presented stronger
orientationcosts than preschoolers for both mirror images(M =
19.46%, SEM = 3.56 vs. M = 5.72%,SEM = 2.26, respectively), F(1,
44) = 5.40, p = .025,and plane rotations (M = 42.77%, SEM = 6.92
vs.M = 10.79%, SEM = 5.83, respectively), F(1,44) = 12.48, p <
.001.
Orientation-Based Task
Although preschoolers were somewhat sensitiveto mirror-image
differences in the shape-based task,they still presented a specific
difficulty in discrimi-nating mirrored letters. Their
orientation-basedjudgments were the worst for the mirrored pairs(M
= 50.2%, SEM = 4.1; M = 1,147 ms, SEM = 59;for d scores, see Table
3) relative to fully differentpairs (M = 78.2%, SEM = 2.8; M =
1,022 ms,SEM = 37), accuracy, d scores, and RTs, F(1,22) = 30.79,
25.72, and 8.87, respectively, allps < .01, and to rotated pairs
(M = 68.7%,SEM = 3.3; M = 1,175 ms, SEM = 42), accuracy andd
scores, F(1, 22) = 19.23 and 16.59, respectively,ps < .001 (on
RTs, F < 1), which also differed fromeach other on accuracy,
F(1, 22) = 5.95, p = .02 (dscores = 6.88, p = .016), and RTs, F(1,
22) = 23.78,p < .001 (see Figure 3B).
Contrary to what happened for shape-basedjudgments,
first-graders orientation-based judg-ments were not affected by
letter type, all Fs < 1.25
(either on accuracy, on d scores, or RTs). Althoughthey had an
overall advantage over preschoolers inthe orientation-based task,
on accuracy and dscores, F(1, 44) = 58.90 and 39.49, respectively,
bothps < .001 (RTs: F < 1), discrimination of mirroredpairs
was still harder than discrimination of rotatedpairs, for both
reversible letters, on accuracy and dscores, F(1, 22) = 4.34 and
4.60, respectively, bothps < .05 (RTs, F < 1), and
nonreversible letters, onaccuracy, d scores, and RTs, F(1, 22) =
9.65, 13.25,and 14.45, respectively, all ps .005 (see Figure 3Band
Table 3).
To directly compare the two groups, we nextexamined the
performance drop index previouslyconsidered for geometric shapes,
and a similar pat-tern of results was found. The performance drop
onmirrored trials was stronger for preschoolers thanfor first
graders (M = 23.85%, SEM = 3.54 vs.M = 8.20%, SEM = 2.10,
respectively), F(1,44) = 9.68, p = .003, whereas on rotated trials
thetwo groups presented similar performance drops(M = 7.48%, SEM =
2.70, SEM = 2.70 vs. M = 2.06%,SEM = 1.98, respectively), F(1, 44)
= 1.92, p = .17.
Comparison Between the Two Tasks and the TwoGroups
As already reported for geometric shapes,preschoolers had more
difficulty in discriminating(in the orientation-based task; Figure
3B) than intolerating (in the shape-based task; Figure 3A)
mir-rored letters, on accuracy, F(1, 22) = 5.81, p = .025,and on d
scores, F(1, 22) = 7.87, p = .01; RTs, F < 1.Note, however, that
for the other trial types (includ-ing rotated trials), preschoolers
were as able to per-form orientation-based as shape-based
judgments,on accuracy: Fs(1, 22) 2.94, on d scores: Fs(1,22) <
1.07, ps > .30, and on RTs: Fs 2.63, allps .10. Yet, no
association was found (on accuracyor RTs) between tasks, for
mirrored or rotatedpairs, or across trials, all rs(21) < .25, ps
> .25.
For first graders, discrimination of mirror imagescontinued to
be harder than discrimination of planerotations for both reversible
letters, accuracy, F(1,22) = 4.34, p = .049 (d scores = 4.70, p =
.041), RTs,F < 1, and nonreversible letters, accuracy, d
scores,and RTs, F(1, 22) = 9.65, = 13.25 and 14.45, respec-tively,
ps .005. Indeed, for nonreversible letters,first graders were still
slower in discriminating thanin tolerating mirror images, F(1, 22)
= 7.46,p = .012, on accuracy, F < 1; d scores, F(1,22) = 4.27, p
= .051; this was not the case for planerotations, all Fs 1. In
contrast, for reversibleletters, they were actually more accurate
in
2018 Fernandes, Leite, and Kolinsky
-
discriminating than in tolerating both the mirroredand rotated
pairs, F(1, 22) = 9.76 and 62.94, respec-tively, ps .005, d scores,
F = 1, and F(1,22) = 13.06, p = .001, respectively; RTs, bothFs
< 1.5. Moreover, the association between taskswas significant
for mirrored and rotated trials, onRTs, both rs(21) > .64, ps
< .001 (accuracy, rs < .01),and across trials, accuracy and
RTs, r(21) = .59 and.85, both ps .001.
As for geometric shapes, for letters the perfor-mance drop was
stronger for preschoolers than forfirst graders on mirrored trials
(M = 23.85%,SEM = 3.54 vs. M = 8.20%, SEM = 2.10, respec-tively),
F(1, 44) = 9.68, p = .003, but not on rotatedtrials (M = 7.48%, SEM
= 2.70, SEM = 2.70 vs.M = 2.06%, SEM = 1.98, respectively), F =
1.92,p = .17.
Correlation Analyses
We next examined at the individual levelwhether orientation
processing was associated withliteracy-related skills (i.e.,
preschoolers letterknowledge and first graders reading skills, as
wellas phonological awareness) rather than with visu-ospatial
abilities, by considering the correlationcoefficients between these
cognitive domains andthe orientation cost (in the shape-based task)
andperformance drop (in the orientation-based task) formirror and
rotation contrasts, separately for eachmaterial. The correlation
coefficients presented in
Table 4 refer to accuracy, which was a more reliablemeasure of
preschoolers orientation-based perfor-mance than RTs (but these
correlation coefficientswere also checked; see Table 4, p values
reportedcorrespond to one-tailed t tests; RTs indexes
weremultiplied by 1 so that the correlation pattern forRTs and
accuracy would be in the same direction).
Geometric Shapes
In preschoolers, sensitivity to mirror images wassignificantly
associated with letter knowledge: Thebetter their letter knowledge,
the stronger the mir-ror cost in shape-based judgments and the
smallerthe performance drop in orientation-based judg-ments of
mirrored pairs (which was also associatedwith phonological
awareness; see Table 4). No asso-ciation was found between
sensitivity to plane-rota-tion contrasts and any cognitive ability
examined.
For first graders, mirror discrimination was asso-ciated with
reading skills and phonological aware-ness (which were associated
with each other, seeMethod): The better their literacy-related
skills, thesmaller the performance drop (on both accuracyand RTs)
for mirrored pairs in the orientation-basedtask. In contrast to
what was found for preschool-ers, the performance drop for rotated
pairs was alsoassociated with literacy-related skills (but onlywhen
computed on RTs) and with nonverbal IQ.For the shape-based task,
only one correlation wassignificant: The better the first-graders
phonological
Table 4Correlation Matrix (Correlation Coefficients) Between the
Ancillary Cognitive Abilities and the Orientation Cost and
Performance Drop
Cognitive abilities
Geometric shapes Letters
Orientation cost(shape-based
task)
Performance drop(orientation-based
task)Orientation cost
(shape-based task)
Performance drop(orientation-based
task)
Mirror Rotation Mirror Rotation Mirror Rotation Mirror
Rotation
PreschoolersNonverbal IQ (Raven) .150 .268 .016 .161 .095 .360*
.149 .045aVisuospatial working memory (Corsi blocks) .068 .270 .291
.209 .015 .372* .047 .078aPhonological awareness .111 .177 .522**
.153 .438* .378* .267 .104Letter knowledge .481* .128 .349 .140
.474**,a .451** .332*,a .397*
First gradersNonverbal IQ (Raven) .262 .261 .088 .325 .341*
.476** .216a .308,aVisuospatial working memory (Corsi blocks) .008
.137 .053 .151 .103 .100 .065a .103aPhonological awareness .025
.339 .355*,a .241a .038a .177 .163 .170Reading index (3DM and
Lobrot L3) .178 .272 .402*,a .127a .280a .043 .338,a .178
Note. Significant results (p < .05, one-tailed) are in bold,
marginal results are underlined. aSignificant association (at
least, |r| > .29,p < .05) for the indexes computed on
reaction times.p < .10. *p < .05. **p .01.
Literacy Acquisition and Mirror Invariance 2019
-
awareness, the stronger the rotation cost. Althoughin the same
direction, the association betweenphonological awareness and the
mirror cost (onRTs) was unreliable, r(21) = .27, p = .10.
Letters
Preschoolers sensitivity to mirror images wassignificantly
associated with letter knowledge: Thebetter their letter knowledge,
the stronger the mir-ror cost in shape-based judgments and the
smallerthe performance drop for mirrored pairs in
orienta-tion-based judgments (see Table 4). Letter knowl-edge was
also correlated with sensitivity to planerotations (but only for
the indexes computed onaccuracy).
Unexpectedly, preschoolers phonological aware-ness was
negatively correlated with the orientationcosts. This might be
related to their adoption ofphonological labels to identify each
letter shape inan orientation-invariant manner due to their
limitedletter knowledge.
For first graders, mirror discrimination wasspecifically
associated with reading skills: The bet-ter their reading skills,
the stronger the mirror cost(on RTs) on shape-based judgments, and
the lowertheir performance drop (on both accuracy and RTs)on
orientation-based judgments of mirrored letters.
For both groups, the better their visuospatialabilities (i.e.,
nonverbal IQ and visuospatial work-ing memory), the smaller their
performance drop inthe orientation-based task and the smaller their
ori-entation cost in the shape-based task. This associa-tion was
specific to plane rotations for preschoolersbut for first graders
it was reliable for both orienta-tion contrasts.
Discussion
Learning to read leads to deep neurocognitivechanges outside the
written domain, including onvisual object processing (e.g.,
Dehaene, Pegado,et al., 2010; Fernandes & Kolinsky, 2013;
Kolinskyet al., 2011; McBride-Chang et al., 2011; Pegado,Comerlato,
et al., 2014; Pegado, Nakamura, et al.,2014; Szwed et al., 2012).
In this context, the pre-sent study targeted two open issues on the
earlyinfluences of learning a script with mirrored sym-bols.
First, it was hitherto unknown when, duringreading development,
the spillover effect of literacyon object recognition and
orientation processingwould emerge. More specifically, we
examined
when, in the course of literacy acquisition,
mirrordiscrimination (a consequence of learning a scriptwith
mirrored symbols) would become part ofvisual object recognition. To
investigate this ques-tion, two groups of 5- to 7-year-old
children, differ-ing on reading skillspreliterate preschoolers
andfirst gradersperformed two samedifferent match-ing tasks on
which orientation was either critical orirrelevant for successful
performance, that is, orien-tation-based versus shape-based
(orientation-inde-pendent) tasks, respectively. To our knowledge,
thisis the first study to adopt a within-participantsdesign to
examine in a fine-grained mannerwhether the impact of literacy
would be similarwhen orientation processing was critical
versusirrelevant to the task. Each task was performed ontwo
categories matched in visual complexity: singleletters and
geometric shapes. The latter was thenonlinguistic category used
given the proximity ofits features to those of letters (cf.
Hannagan et al.,2015). We thus expected that if (even
incipient)changes in visual processing started to emerge earlyon,
then by using this material we would be able tograsp them. We also
conducted correlation analysesfor each group on each material to
examine at theindividual level whether orientation processing
wasassociated with literacy-related skills.
Second, it was still unclear whether the impactof learning a
script with mirrored symbols wasspecific to mirror image processing
or whether itwould generalize to other orientation contrasts
thatare relevant for letters, like plane rotations (e.g.,d-p;
Gibson et al., 1962). To study this point, thesame four trial types
were used in both tasks: fullydifferent (with different shape and
different orienta-tion), identical, mirrored, and rotated pairs.
Wethus directly examined mirror-image versus plane-rotation
processing in two tasks where orientationprocessing was critical
versus irrelevant for success-ful performance.
This study represents one of the first demonstra-tions of early
changes in the mirror-generalizationsystem due to literacy
acquisition and providedfour original contributions on the impact
that learn-ing a script with mirrored symbols has outside
thewritten domain.
First, we presented the first evidence of an abso-lute and
specific mirror cost on visual nonlinguisticobject recognition. For
geometric shapes, a nonlin-guistic material novel for both
preschoolers andfirst graders, the two groups were overall
equallyable to perform shape-based judgments. Most inter-estingly,
the groups differed only on mirrored pairs:Although preschoolers
were immune to irrelevant
2020 Fernandes, Leite, and Kolinsky
-
mirror-image differences, first graders exhibitedsuch strong
mirror cost that they were even slowerthan preschoolers. We thus
found an absolute mir-ror cost on shape-based judgments of
nonlinguisticobjects, a consequence of literacy acquisition
pre-dicted by the neuronal recycling hypothesis(Dehaene, 2009). In
the first study to show a mirrorcost in literate adults, no other
orientation contrastwas examined and the mirror cost was only
rela-tive, as illiterate adults were overall slower andmore
error-prone than the literate groups (Pegado,Nakamura, et al.,
2014). In Kolinsky and Fernandes(2014), only literate adults (and
not illiterates) wereaffected by mirror and rotation contrasts of
familiarobjects, and for geometric shapes, all
participants,whatever their literacy level, were sensitive to
theirrelevant orientation contrasts, at least on responselatencies
and mostly for plane rotations. Yet againilliterate adults were
overall slower and more errorprone.
Second, by examining orientation processingwhen it was critical
versus irrelevant for successfulperformance in a
within-participants design, thepresent study is the first to
conclusively show thatpreliterates specific difficulty with mirror
discrimi-nation cannot be attributed to a general difficultywith
orientation processing or because orientationis a dimension less
salient than shape. On the onehand, if preschoolers had a general
difficulty withorientation, then plane-rotation
discriminationshould have been as hard as mirror discrimination.On
the contrary, they were quite capable ofdiscriminating rotated
pairs, and when comparedto first graders using the normalized
index, the twogroups presented a similar performance drop
forrotated pairs. On the other hand, if orientation wasa dimension
less salient than shape, preschoolersshould have been worse on
orientation-based thanon shape-based judgments of rotated pairs.
Quitethe opposite, they presented similar rotation costsas first
graders on shape-based judgments of geo-metric shapes, in line with
the plane-rotation sensi-tivity of the ventral visual system
(Logothetis et al.,1995; Tarr & Pinker, 1989), and more
important,they were as able to explicitly discriminate
plane-rotation contrasts as to tolerate them. They pre-sented the
same level of interference from the irrele-vant dimension of
rotated pairs in both tasks (i.e.,orientation in the shape-based
task and shape inthe orientation-based task). To put it
differently,preschoolers were equally sensitive to the
twoincongruent dimensionsorientation and shapeasthey were as able
to attend to shape as to orienta-tion of rotated pairs.
Consequently, their difficulty
with mirror discrimination cannot be due to lowsensitivity to
orientation in general; it seems rathergrounded on the original
mirror invariance prop-erty of the ventral visual system (Dehaene,
2009;Logothetis et al., 1995). This difficulty with
mirrordiscrimination is consistent with the absence of amirror cost
on their shape-based judgments, denot-ing mirror invariance, and
agrees with prior find-ings on illiterate adults and preliterate
children(e.g., Casey, 1984; Danziger & Pederson, 1998;
Fer-nandes & Kolinsky, 2013; Gibson et al., 1962; Kolin-sky et
al., 2011; Nelson & Peoples, 1975; Pederson,2003), which argues
for the robustness of this effect.
Third, the adoption of a within-participantsdesign also allowed
us to demonstrate that theexpression of the visual consequences of
literacydepends on the type of processing at stake.Whereas this
impact was mirror specific when thetask did not required
orientation processing andvisual object recognition was involved,
it wasinstead general when explicit orientation processingwas
required. The overall advantage of first gradersover preschoolers
on orientation-based judgmentsdoes not seem to be due to a generic
age effect, asno overall difference between groups was found
onshape-based judgments of geometric shapes.Instead, it seems to be
due to perceptual expertisewith the written code: Learning to read
enhancesthe relevance of orientation, which then becomes acritical
dimension of visual objects. In fact, the ori-entation-based task
used here required both shapeand orientation processing (only exact
matches hadto be considered as same), and the conjunction ofshape
and orientation is essential in letter andvisual word recognition,
and hence, the advantageof first graders is not surprising.
Perceptual exper-tise with a visual category leads to enhancement
ofthe relevant dimensions (e.g., Dehaene, Pegado,et al., 2010;
Folstein et al., 2013; McCandliss et al.,2003). Thus, when learning
to read, children learnto attend to critical reading-related cues,
such asorientation, which were not relevant to perceptualexperience
before this cultural activity took place(e.g., Casey, 1986; Gibson
et al., 1962; Kolinskyet al., 2011; Nelson & Peoples, 1975).
Moreover,during literacy acquisition, beginning readersbecome as
able to attend to orientation as to theshape of mirrored pairs of
nonlinguistic objects, asshown by their similar performance in the
twoexperimental tasks for these pairs. The differentialimpact of
literacy found in the shape-based versusorientation-based tasks
also agrees with prior stud-ies showing that, even when the same
material andprocedure is adopted, different tasks tap into
Literacy Acquisition and Mirror Invariance 2021
-
different processes underpinned by different neuralsubstrates.
Although parietal regions, part of thedorsal stream, are important
for explicit orientationprocessing, regions of the ventral visual
stream aremainly important for processing objects shape andidentity
(e.g., Gauthier et al., 2002; Harris, Benito,Ruzzoli, &
Miniussi, 2008). This distinction couldalso explain why no
significant association wasfound between performance in the two
experimen-tal tasks for preschoolers on either geometric shapesor
letters, whereas for first graders the associationwas reliable.
Additionally, it was only for first gra-ders that performance in
the two experimental taskswas associated with visuospatial
abilities known tobe related with dorsal stream functioning (e.g.,
Chi-nello, Cattani, Bonfiglioli, Dehaene, & Piazza, 2013).It
thus seems that literacy acquisition enhances thecross-talk between
the two visual streams. In thisvein, Chinello et al. (2013)
recently examined thebehavioral performance of kindergarteners
(from 3to 6 years old) and adults in an extensive set offunctions
related to the dorsal versus ventralstreams (e.g., visuospatial
memory and grip aper-ture during grasping versus face and object
recogni-tion) and found that it was only for adults, not
forchildren, that visuospatial memory (assessed withthe Corsi
blocks test) was associated with objectrecognition.
Fourth, the present study shows that the mirror-specific impact
of literacy on visual (nonlinguistic)object recognition begins to
emerge, though cru-dely, before literacy instruction, allied with
letterknowledge. Although as a group preschoolers didnot present a
mirror cost on their shape-based judg-ments of geometric shapes,
the correlation analysesrevealed that letter knowledge was
specificallyassociated with sensitivity to mirror-image
differ-ences (and not to plane-rotation differences): Thehigher
preschoolers letter knowledge, the strongerthe mirror cost on
shape-based judgments and thesmaller the performance drop on
orientation-basedjudgments of mirrored geometric shapes.
This association between letter knowledge andthe mirror cost on
shape-based judgments ofpreschoolers is probably related to the
nonlinguisticmaterial used here. Indeed, the degree of similarityto
letters should influence the magnitude of thespillover effect of
literacy on visual recognition ofother categories (Hannagan et al.,
2015). This is alsoconsistent with the observation of orientation
costsin identity-based judgments of illiterate adults forgeometric
shapes but not for pictures of familiarobjects (Kolinsky &
Fernandes, 2014). In fact, famil-iarity with letters can explain
the discrepancy
between the present results (i.e., the absence of amirror cost
on shape-based judgments of geometricshapes by the preschool group)
and those of Kolin-sky and Fernandes (2014) with illiterate
adults,given that the latter group has a long life experi-ence in a
literate world (Fernandes et al., 2014).
Nevertheless, the fact that preliterate childrenalready present
some sensitivity to mirror imagesagrees with prior findings
suggesting an earlyimpact of the visual properties of the script to
belearned on nonlinguistic visual processing(McBride-Chang et al.,
2011). The present pattern ofresults adds to this evidence by
showing that suchspecific impact of literacy as the one on
mirror-image processing starts to emerge with letterknowledge
before children are able to decode. Italso explains why the
preschoolers examined herealready present a mirror cost in
shape-based judg-ments of letters, which was also associated
withtheir letter knowledge. This latter result is consis-tent with
former observations that preschoolerswho are able to correctly
write their names withoutmirrored errors are also able to
discriminate mir-rored pairs of geometric shapes (Casey,
1984;Casey, 1986). It might seem at odds with the origi-nal mirror
invariance of the ventral visual system(e.g., Dehaene, 2009;
Logothetis et al., 1995), butprior studies have shown that the
emergence of let-ter-specialized processing begins before formal
liter-acy instruction in both preliterate children andilliterate
adults (e.g., Cantlon et al., 2011; Fernandeset al., 2014).
Perceptual expertise with letters can explain theremarkable
advantage of first graders on bothshape- and orientation-based
judgments of lettersafter only ~8 months of reading instruction. On
thedownside, it also explains first graders worse per-formance on
shape-based judgments of mirroredand rotated pairs of reversible
compared to nonre-versible letters. Experts usually show less
flexibilityin selectively ignoring the dimensions relevant totheir
category of expertise (e.g., Folstein et al.,2013), which explains
orientation interference onletter recognition by adult readers
(e.g., Corballis &Nagourney, 1978; Jolicoeur & Landau,
1984; Pegadoet al., 2011; Pegado, Nakamura, et al., 2014) andthe
orientation costs found here on letters shape-based judgments by
first graders. In fact, their ori-entation cost for reversible
letters was so strongthat it canceled out any advantage over
preschool-ers.
This pattern of results seems to agree with theresults found by
Perea et al. (2011) in literateadults, using the masked priming
paradigm:
2022 Fernandes, Leite, and Kolinsky
-
Mirrored versions of reversible letters (e.g., ibea,mirrored
letter underlined) significantly inhibitedthe recognition of target
words (i.e., IDEA). Giventhe present observation of both mirror and
rotationcosts in first-graders shape-based judgments ofreversible
letters, it remains to be confirmedwhether the mirror interference
reported by Pereaet al. is exclusive for mirror images. It could
ratherbe due to activation of an existing letter representa-tion
that is incompatible with the target word.Thus, the same
interference would be expected forrotated versions of reversible
letters (e.g., if ipeapreceded the target IDEA). Future research
shouldexamine this prediction.
The association between explicit orientation pro-cessing of both
linguistic and nonlinguistic materialand first-graders reading
skills suggests that forthese beginning readers mirror
discrimination is notyet fully accomplished and might continue
todevelop after first grade (Cornell, 1985). For thesechildren,
mirror discrimination continued to beharder than plane-rotation
discrimination for bothgeometric shapes (i.e., average accuracy of
80.0%for mirrored pairs vs. 91.0% for rotated pairs, seeFigure 2)
and letters (with slower performance onmirrored than rotated
pairs); and this continues tobe the case in adults, even after
years of readingpractice (Fernandes & Kolinsky, 2013; Gregoryet
al., 2011; Kolinsky et al., 2011). Thus, mirror dis-crimination is
triggered by learning a script withmirrored symbols, but it is not
a dichotomous phe-nomenon fully determined by literacy. The
originalmirror invariance of the visual recognition systemis not
fully erased (Dehaene, 2009) and couldinstead be inhibited during
recognition of visualobjects, including letters (e.g., Du~nabeitia,
Molinaro,& Carreiras, 2011; Perea et al., 2011).
Neuropsychological, functional magnetic reso-nance imaging,
(fMRI), and transcranial magneticstimulation studies have shown
that mirror discrim-ination of linguistic and nonlinguistic objects
hasdifferent neurocognitive loci. For linguistic material,mirror
discrimination is underpinned by ventraloccipitotemporal regions,
which are mirror invari-ant for pictures of familiar objects (e.g.,
Dehaene,Nakamura, et al., 2010; Nakamura, Makuuchi, &Nakajima,
2014; Pegado et al., 2011; Vinckier et al.,2006). What is, however,
unclear is the temporallocus and the cognitive mechanism
responsible formirror discrimination. Although beyond the scopeof
the present work, this is still hotly debated, andtwo accounts have
been proposed. According toone account, mirror discrimination
occurs due toinhibition of mirror invariance at a late,
possibly
attention-dependent, stage of visual processing(Du~nabeitia et
al., 2011; Du~nabeitia et al., 2013;Perea et al., 2011). The other
account proposes thatmirror discrimination becomes part of visual
pro-cessing from an early time window (i.e., 100148 ms after
stimulus onset; Pegado, Comerlato,et al., 2014), and evidence in
favor of both has beenon the table.
These mixed results could be due to the adoptionof different
paradigms, tasks, and materials, becausedifferent experimental
conditions tap into differentphases of visual processing. In fact,
this could alsobe the reason for the discrepancy between the
mirrorcost that we found for shape-based judgments ofgeometric
shapes by first graders and the mirrorinvariance found by Wakui et
al. (2013) for short-term priming of familiar objects by children.
Besideslow-level differences between the materials used, thelatter
paradigm may tap into an earlier processingstage than the
samedifferent task used in the pre-sent study (for discussions, see
Kolinsky et al., 2011;Nakamura et al., 2005).
In addition to the aforementioned theoreticalimplications, the
present study can also contributeto the growing interest from
multiple developmen-tal perspectives on childrens print awareness
andon its unique contribution to reading acquisition.Indeed, in
parentchild conversations, more visualattributes are used to
describe letters than pictures,and not only parents but also
children emphasizeletters visual properties (Robins, Treiman,
Rosales,& Otake, 2012), as if (at least implicitly) they
recog-nize the importance of visual features on letterlearning and
subsequent reading development. Theengagement in these
conversations, especially aboutthe childs initial, was associated
with better read-ing outcomes even after other factors, such
asvocabulary, were controlled for (Treiman et al.,2015). More
important, even before children knowwhat letters represent (i.e.,
the letter-sound corre-spondence), they are already sensitive to
lettersvisual statistical patterns (Pollo, Kessler, &
Treiman,2009; Treiman, Cohen, Mulqueeny, Kessler, &Schechtman,
2007; Treiman & Kessler, 2011).Preschoolers are better at
copying and writing let-ters with the most frequent arrangement of
visualfeatures in the Latin alphabet, that is, letters with ahasta
on the left and a coda on the right (e.g., band F) than letters
with the opposite arrangement(Pollo et al., 2009) and, hence, make
more mirrorederrors on letters of the latter type (e.g., writing
binstead of d; Treiman & Kessler, 2011). The presentstudy adds
to this literature, showing that mirrordiscrimination, which is a
necessary condition for
Literacy Acquisition and Mirror Invariance 2023
-
mastering the Latin alphabet, can be promoted byliteracy-related
activities about letter forms, and thiscould happen at home during
parentchildren inter-actions or at the kindergarten. Additionally,
ourresults show that training orientation discriminationin general
is not the best practice; preschoolers donot have difficulties with
discrimination of planerotations, and this ability is not related
to mirrordiscrimination. It is letter knowledge and familiaritywith
letter forms that are the key. Thus, our workis part of an emergent
line of research showing thatliteracy has a visual facet, crucial
for learning toread, to which letter knowledge strongly
con-tributes.
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