International Journal of Psychophysiology 49 (2003) 187–199
Are poor readers semantically challenged? An event-related brain
potential assessment
a
c
´ Fernandez
´
´
Juan Silva-Pereyraa,b, *, Maritza Rivera-Gaxiolab, Thalıa
, Lourdes Dıaz-Comas
,
a
a,d
d
d
´ Harmony , Antonio Fernandez-Bouzas
´
´
Thalıa
, Mario Rodrıguez
, Jorge Bernal ,
Erszebet Marosid
b
a
´ Universidad Nacional Autonoma
´
´
Instituto de Neurobiologıa,
de Mexico,
UNAM-UAQ, Queretaro, Mexico
Center for Mind, Brain and Learning, University of Washington, 358 Fisheries Center Box 357988, Seattle, WA 98195, USA
c
Centro de Neurociencias, La Habana, Cuba
d
´
´
Neurociencias ENEP Iztacala, Universidad Nacional Autonoma
de Mexico,
Mexico City, Mexico
Received 8 October 2002; received in revised form 6 May 2003; accepted 13 May 2003
Abstract
This study explores visual event-related potentials components in a group of poor readers (PRs) and control
children who carried out figure and word categorization tasks. In both tasks, every child had to categorize between
animal and non-animal stimuli in an odd-ball GO–GO paradigm. During the word categorization task, PRs presented
longer reaction times, a poorer performance, longer and larger P2 amplitudes, and smaller amplitudes and longer
P300 latencies than controls. There were no differences in the N400 component between groups. These results suggest
that semantic processing underachievement in PRs may not be a semantic deficit per se, but the late reflection of an
early word codification problem, deficient use of attentional resources and lack of target identification during reading.
䊚 2003 Elsevier Science B.V. All rights reserved.
Keywords: Poor readers, semantic processing, N400, P300, P2; Categorization tasks; Event-related potentials, reading disabled
children
1. Introduction
Children who score between 1 and 2 years
below their expected reading level have been
considered to be poor readers (PRs) (Rayner and
Pollatsek, 1989). Children scoring 2 or more years
below their expected reading level are referred to
as dyslexics. In both cases, children have IQ scores
*Corresponding author. Tel.: q1-206-2216471; fax: q1206-2216472.
E-mail address: jfsp@u.washington.edu (J. Silva-Pereyra).
that fall within the normal range. One of the main
factors involved in the development of reading
skills is to create a transparent interface between
orthographic input and phonological structure.
Phonological skills that are required to segment
words into their constituent phonemes not developing normally, very likely give rise to poor
reading. However, it is unlikely that all reading
problems are solely due to this factor. Among the
prime candidates that have also been proposed are
deficits in syntactic processing (Byrne, 1981),
0167-8760/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0167-8760(03)00116-8
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J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
limitations in working memory capacity (Swanson,
1992; Swanson and Sachse, 2001) and impairments in the time course of the processing of the
rapid, transient characteristics of auditory and visual input (Tallal et al., 1993).
Our approach to the present study was to obtain
behavioral data while simultaneously recording
event-related potentials (ERPs) from electrodes
placed over different regions of the scalp. ERPs
reflect the stimulus-locked cognitive information
processing activities in terms of distributed assemblies of neurons firing synchronized across time.
Thus, different patterns of brain electrical activity
recorded during a task may reflect different cognitive processes and the differences in amplitude
and latency of the ERP components across different populations may represent cognitive abilities
andyor disabilities.
One ERP component that has traditionally been
studied in PRs is the so-called P300 component.
The P300 wave is an endogenous positive deflection with an average peak latency at 300 ms or
more after stimulus onset and is typically elicited
by a rarely and randomly presented target stimulus
in a detection task. One prominent interpretation
of the P300 is that it represents stimulus evaluation
and memory updating (Donchin and Coles, 1988;
Polich and Kok, 1995). ERP studies have shown
smaller amplitudes and longer latencies of the
P300 component in PRs (Diniz et al., 1997;
Holcomb et al., 1985; Silva-Pereyra et al., 2001)
and dyslexics (Taylor and Keenan, 1990). Some
other studies have found that PRs have lower
scores than controls during working memory tasks
(De Jong, 1998; Isaki and Plante, 1997). Holcomb
et al. (1985) found that reading disabled and
control subjects could be better differentiated from
one another by the amplitude of the P300 when
non-target word stimuli were contrasted with nonlinguistic symbols: symbols elicited larger P300
than words in reading disabled children, while the
two kinds of stimuli elicited equivalent amplitudes
in controls. There is also evidence that PRs have
longer P300 latencies during a color discrimination
task (Silva-Pereyra et al., 2001). Some authors
have suggested that the long P300 latency of
dyslexic and reading disabled children is due to
the fact, that in these children, stimulus evaluation
and memory updating processes take more time
(Holcomb et al., 1985). Early auditory and visual
sensory processing deficits also seem to be an
important feature in the profile of reading disabled
children. Such deficits apparently lead to compensatory increases in the effort required to integrate
words into a context and to a greater reliance on
context for word recognition than control subjects
(Neville et al., 1993). Several studies have found
larger P2 amplitudes to a surprising sound in
reading disabled children (Bernal et al., 2000;
Iragui et al., 1993). Holcomb et al. (1986) also
found larger P2 amplitudes to unexpected stimuli
in reading disabled and in children suffering attentional deficit with hyperactivity when compared to
controls. The P2 is a component that has been
associated with reallocation of attentional
resources during task performance (Luck and Hillyard, 1994).
The design used in the present experiment
implies that subjects make semantic category decisions with different probabilities of stimulus in a
word (or figure)-list presentation. The decision
process could produce a large P3 in addition to a
previous N400 (Halgren, 1990; Hill et al., 2002;
Nielsen-Bohlman and Knight, 1994; Polich, 1985;
Stelmack et al., 1988). The P3 usually overlaps
the N400, and is also sensitive to priming, and
manipulations of expectancy (Deacon et al., 2000).
However, some studies have shown that this overlapping is only partial (Chwilla et al., 1995; Kutas
and van Petten, 1994) or not at all affected by the
P3 component (Nobre and McCarthy, 1994). The
N400 has been associated with semantic processing and it is a negative-going wave between 300
and 600 ms, peaking approximately at 400 ms
after stimulus onset, with a posterior, slightly right
amplitude predominant asymmetry (Kutas and
Hillyard, 1980). The N400 effect has been
observed in sentence (Kutas and Hillyard, 1980)
and priming paradigms (Bentin et al., 1985).
Sentence processing developmental studies (Holcomb et al., 1992; Juottonen et al., 1996) have
shown that with age, the N400 effect decreases in
amplitude and increases in latency. These results
suggest that as children acquire better language
skills, they rely less on semantic context for
language comprehension.
J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
In contrast to the previous, the N400 elicited
during word-list tasks without priming has a more
anterior distribution and is the largest at central
and frontal locations (especially the midline)
(Nobre and McCarthy, 1994). Despite the distributional difference, the anterior N400 is thought
to be closely related to the classic N400 and
probably reflects similar cognitive processes. In
the present study, during word categorization task,
a similar anterior N400 is anticipated.
On the other hand, picture-processing paradigms
also show an N400 effect that may mirror the
pattern found in word-prime studies (Barret and
Rugg, 1990; Holcomb and McPherson, 1994). The
N400-like effect elicited by pictures is the result
of both a frontally distributed N300 and a more
widely distributed N450 (Barret and Rugg, 1990).
There is no evidence of amplitude change with
age on picture processing development, although
latency decreases with increasing age (Friedman
et al., 1990). Although it has been suggested that
the N450 could be related with the processing of
semantic relationships between non-verbal stimuli,
other studies comparing picture with word semantic processing using ERPs have suggested that the
semantic analysis of words and pictures may
involve different, at least partially non-overlapping, neural systems (Holcomb and McPherson,
1994).
While there is abundant and convergent evidence showing that PRs tend to be deficient in
phonologically based skills (Beitchman and
Young, 1997) or working memory capacity (Swanson, 1992; Swanson and Sachse, 2001), there is
also evidence of a deficiency in semantically based
skills (Champion, 1997; Ben-Dror et al., 1995;
Gillon and Dodd, 1994; Stelmack et al., 1988;
Vellutino et al., 1988). Some studies have reported
differences favoring normal readers in semantic
memory as well as semantic learning tasks using
visual symbols and paired associates (Vellutino
and Scanlon, 1985; Vellutino et al., 1995; Waterman and Lewandowski, 1993). Stelmack et al.
(1988) found larger frontal N400 amplitudes for
normal readers with respect to reading disabled
children during word recognition. They believe
that this effect is consistent with a more extensive
189
semantic evaluation or memory search attributed
to that component.
In summary, deficiencies in semantic tasks in
PRs may be produced by a less effective processing of stimuli, taking more time for their evaluation, which may be reflected by a smaller and later
P300. Although reading disabled children have
difficulties with the translation of visual information into a speech code, they also appear to have
deficits in the classification and memory processing of the non-verbal visual stimuli (Silva-Pereyra
et al., 2001). This deficiency in early processing
may also affect semantic processing in PRs (Stelmack et al., 1988). In an attempt to evaluate the
access to semantic information independently of
stimulus kind, in the present study, categorization
tasks of animalynon-animal presented as figures
and words were used.
2. Materials and methods
2.1. Subjects
Thirty-four children participated in this study.
They were selected from a group of third and
fourth grade volunteers from two elementary
schools.
Children were divided into two groups according
to an evaluation carried out by three of the authors,
based on interviews with parents and child, the
teacher’s opinion and academic achievement (18
controls and 16 PRs). In order to evaluate subject
allocation into each group, a battery for the computerized analysis of reading in Spanish was
´ para los
applied to each child. This is the ‘Baterıa
Trastornos de la Lectura’ (BTL, Reading Disabilities Battery, Reigosa et al., 1994).
The mean age for the control group was 10.1
years (1.6 S.D.) and 10.2 years (1.9 S.D.) for
PRs. The male:female ratio was 1:1 for normal
readers and 2.5:1 for PRs. None of the children
had a history of school problems or a neurological
disorder. They were all right-handed and had a
normal neurological examination, as well as normal IQ scores (WISC-R in Spanish; mean IQEs
106.33 S.D.s14.68, mean IQVs105.11 S.D.s
8.81 for controls; mean IQEs100.81 S.D.s12.36,
mean IQVs98.81 S.D.s14 for PRs). Comparison
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between groups using the IQ scores showed no
significant differences.
Each figure was presented for 2000 ms and the
interval (ISI) between figures was 3000 ms.
2.2. Stimuli
2.3.2. W task
This task was analogous to the F task in requirements, except that full words instead of figures
were displayed. Correct and incorrect responses
were automatically marked in the electroencephalogram (EEG) recording.
The 260 figures presented were obtained from
Snodgrass and Vanderwart’s study (1980) and
were digitized and displayed on the center of a
computer video. The figures were white line drawings on a black background, with a 3.12=3.12
degrees visual angle. In order to obtain the list of
words corresponding to the figures, a pilot study
was carried out with another sample of 15 children.
After presenting the figures, each child had to say
the first word that came to mind. All words
produced by each of the 15 children were stored
and analyzed for frequency of occurrence and the
corresponding percentage. The highest frequency
word for each figure was selected. In this way, a
list of 201 words produced by figure nomination
and the corresponding figures was created.
Two categorization tasks were designed: a figure
categorization (F task) and a word categorization
task (W task). In the W task, the words employed
were obtained from the nomination of the 201
figures to be used in the F task. The words of this
list were displayed in 1-cm uppercase letters in the
center of a 14-inch computer monitor (white letters
on a black screen). At the viewing distance
employed, each letter subtended a visual angle of
approximately 0.573=0.573 degrees.
2.3. Procedure
2.3.1. F task
All 201 figure trials were randomly presented:
44 figures were animals and 157 were non-animals
(household items, utensils, tools, personal objects,
fruits and vegetables and vehicles). Participants
were instructed to respond by pressing one button
of the computer keyboard (letter B) with their
index finger if the stimulus presented was an
animal and a different button (letter M) with the
middle finger if it was not; in a GO–GO task. The
use of buttons was counterbalanced across subjects. Children were instructed to respond as rapidly and accurately as possible to each stimulus.
2.3.3. EEG recording
The EEG was recorded with AgyAgCl electrodes referenced to linked earlobes from Fp1,
Fp2, F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T3,
T4, T5, T6, Fz, Cz, Pz and Oz of the 10y20
international system. The amplifier bandwidth was
set between 0.05 and 30 Hz. All electrode impedances were at or below 5 kV and amplified with
a gain of 20 000. EEG was sampled every 5 ms
and stored on a hard disk for further analysis. EEG
segments of 1280 ms with a pre-stimulus time of
100 ms were selected and averaged off-line to
obtain the ERPs. The electro-oculogram (EOG)
was recorded from a supra-orbital electrode and
from an electrode placed at the external canthus
of the right eye. Special care was taken to reject
segments with eye movements or other artifacts.
In addition, trials on which EEG or EOG activity
exceeded "75 mV were rejected. Baseline correction was performed in relation to a pre-stimulus
time of 100 ms.
2.4. Data analysis
2.4.1. Behavioral data
The median of reaction times (RTs) for correct
responses from each subject was calculated and
the data used to perform a three-way ANOVA.
The variables included were: group (PRs and
controls), task (F and W) and category (animal
and non-animal). A second three-way ANOVA
was performed using percentage of error. Tukey
honest significant difference post hoc tests were
done.
2.4.2. ERP data
ERPs from correct responses by task (F, W) and
by category (animal, non-animal) were obtained.
J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
191
Fig. 1. The top figure shows RT mean values from the group=task and group=category interactions. PRs showed longer RT during
the W task, even this difference was larger to non-animals category. The bottom figure shows proportion of error interaction effect
(task=category=group). Differences were observed between PRs and controls on the animal category in the word categorization
task. Significant differences are marked with an asterisk (P-0.05).
Approximately an equal number of EEG segments
(f25 segments) were taken to average by experimental condition across subjects.
According to their appearance in the grand
average waveforms, the P2 peak was defined as
the most positive voltage within the interval of
200–300 ms, the N400 peak was defined as the
most negative voltage within the interval of 400–
600 ms and the P300 as the most positive value
within the interval of 600–900 ms.
2.4.3. Amplitude
Separate five-way ANOVAs were carried out
for each component using the following variables:
group=task=category=hemisphere (left and
right)=anterior–posterior (Frontal F3–F4, frontotemporal F7–F8, Central C3–C4, Parietal P3–P4,
anterior temporal T3–T4, posterior temporal T5–
T6 and Occipital O1–O2). The Huynh–Feldt epsilon was applied to the degrees of freedom of those
analyses with more than one degree of freedom in
the numerator. Tukey honest significant difference
post hoc tests were done. Because the latency of
the P2 varies across the head, the data were
analyzed using ten electrode positions (Fp1–Fp2,
F3–F4, C3–C4, T3–T4 and F7–F8).
2.4.4. Latency
Separate three-way ANOVAs for each component were done using latency measurements at Cz.
The variables were group (PRs and controls)=task
(figures and words)=category (animals vs. nonanimals). Tukey honest significant difference post
hoc tests were done.
3. Results
3.1. Behavioral results
3.1.1. Reaction times
There were significant group=task (F(1, 32)s
8.3 Ps0.007) and group=category (F(1, 32)s
10.05 Ps0.003) interactions. The first interaction
revealed significantly longer RTs for PRs in the
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J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
W task (Ps0.0003) (see left-top of Fig. 1). The
second one shows longer RTs for PRs than controls
to animals (Ps0.001) and to non-animals (Ps
0.0002) (right-top of Fig. 1).
3.1.2. Percentage of error
Regarding percentage of errors, there was a
significant group=task interaction (F(1, 32)s
8.94 Ps0.005), indicating a higher percentage of
error in PRs during the W task (Ps0.0003). There
was also a significant group=task=category interaction (F(1, 32)s7.35 Ps0.001). PRs may have
therefore been less efficient than controls in categorizing when the stimulus was an animal during
the W task (Ps0.0002) (Fig. 1).
3.1.3. ERP results
For both groups and tasks, three components
were visible. The first major positive peak, most
pronounced over anterior sites, began approximately at 175 ms during post-stimulus onset and
reached its maximum amplitude at 240 ms. The
next component was a negative wave of approximately 400 ms. This negativity was larger to the
non-animal than to the animal category. This negativity was more visible in the F task over anterior
sites, and in both groups; during the W task, it
showed two peaks with 100 ms of difference (Fig.
2). The third major component was a positive
waveform which was more prominent at posterior
regions of approximately 600 and 90 ms. This
peak was larger to infrequent stimuli (animal) than
to frequent stimuli (non-animals).
3.2. P2
3.2.1. Amplitude
The P2 was distributed over the scalp with a
most pronounced amplitude over frontal areas
(main effect of electrode site F(2.6, 82.4)s47.7
P-0.0001), and the left hemisphere (hemisphere
main effect (1, 32)s10.7 Ps0.003). It was larger
in amplitude for the W than for the F task (main
effect of task (F(1, 32)s80.18 P-0.00001). The
distribution of the P2 during the F with respect to
the W task was different (task=electrode site
interaction F(2.7, 85.73)s8.53 P-0.0001). During the F task, the P2 could be seen on fronto-
polar (Fp1–Fp2), frontal (F3, F4, F7, F8) and
central (C3, C4, T3, T4) sites. On the other hand,
during the W task, the distribution was frontal
(Fp1, Fp2, F3, F4), central (C3, C4, F7, F8) and
temporal (T3, T4).
There was a significant group=task interaction
(F(1, 32)s8.22 Ps0.007), that is, PRs showed
larger P2 than controls during the W task (Ps
0.03). PRs also showed larger P2 amplitudes than
controls (Ps0.003) on the left hemisphere for
animals (group=category=hemisphere interaction
F(1, 32)s5.7 Ps0.023).
Finally, there was a significant group=hemisphere=electrode site interaction (F(2.7, 86.3)s
2.86 Ps0.047; Fig. 3), indicating that PRs had
larger P2 amplitudes on Fp1 (P-0.0001), F3 (Ps
0.0002) and F7 (P-0.0001), whilst the control
group showed larger amplitudes than PRs on T4
(Ps0.02).
3.2.2. Latency
Significantly longer P2 latencies during the W
than during the F task (main effect of task F(1,
32)s5.62 Ps0.024) and for animals than nonanimal (main effect of category F(1, 32)s11.96
Ps0.0016) were observed in both groups.
PRs showed longer P2 latencies than Controls
(Ps0.0013) during the W task (group=task interaction F(1, 32)s15.1 Ps0.0005; Fig. 3). PRs
also showed longer latencies than controls (Ps
0.0007) for the non-animal category (group=category interaction F(1, 32)s6.9 Ps0.01). Finally,
there was a significant group=task=category
interaction (F(1, 32)s11.6 Ps0.002): Controls
had longer latencies than PRs (Ps0.001) for
animals during the F task. On the other hand, PRs
showed longer P240 latencies than controls for
animals (Ps0.0002) and non-animals (Ps
0.0009) during the W task.
3.3. N400
3.3.1. Amplitude
There were no significant main effects of group
or interactions by group. However, there was a
significant main effect of task (F(1, 32)s20.8
P-0.001) which means larger N400 amplitudes
for the F than the W task. This difference was
J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
193
Fig. 2. This figure shows: (a) grand average ERPs to figures (animal and non-animal) for PRs and controls; (b) ERPs to words
(animal and non-animal) for both groups. Larger P2 amplitudes and smaller P300 amplitude for PRs during the word categorization
task were observed. Two cursors on both N400 peaks are shown at Cz from 350 to 560 ms
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J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
Fig. 3. This figure shows: (a) group=category=hemisphere
interaction for the P2 amplitudes. The PRs shows larger P2 for
the left hemisphere but for the animal category there were significant differences; (b) group=task=category interaction for
the P2 latency measurements. PRs display longer P2 latencies
during W task. Significant differences are marked with an
asterisk (P-0.05).
seen over frontal (F3–F4 P-0.0001), frontotemporal (F7–F8 Ps0.003) and parietal (P3–P4
P-0.0001) regions (task=electrode site interaction F(2.8, 90.3)s21.33 P-0.001).
There was a significant task=category=
electrode site interaction (F(2.13, 68.25)s5.66
Ps0.005), which means that there was an N400
effect in both groups, but only during the F task
on posterior temporal (T5–T6, Ps0.0009) and
occipital regions (O1–O2, Ps0.00002).
3.3.2. Latency
There were no significant effects.
3.4. P300
3.4.1. Amplitude
There was a significant group=task=category
=hemisphere interaction (F(1, 32)s5.99 Ps
0.02). The P300 effect (larger amplitudes for
animals than non-animals) was observed for controls on the left hemisphere during the F (Ps
0.002) and the W tasks (Ps0.0006). Controls also
showed this P300 effect on the right hemisphere
during both tasks (F, Ps0.04 and W, Ps0.02). In
contrast, PRs showed a P300 effect on the left
hemisphere only during the F task (Ps0.0002;
Fig. 4). The topographical distribution of this
effect was different regarding task and group
(group=task=category=electrode site F(2.26,
72.45)s2.98 Ps0.05). In the control group, the
P300 effect was significant on parietal (P0.0001), posterior temporal (Ps0.0001) and
occipital (P-0.0001) areas during the F task.
Controls also showed a significant P300 effect on
central electrodes (Ps0.0005), parietal (P0.0001), posterior temporal (Ps0.0001) and
occipital (P-0.0001) during the W task. In contrast, PRs showed a significant P300 effect during
F task on central (Ps0.014), parietal (P0.0001), posterior temporal (P-0.0001) and
occipital (P-0.0001), but there was P300 effect
during W task.
3.4.2. Latency
Latency differences between animals and nonanimals were bigger in both groups only during
the F (task=category F(1, 32)s7.26 Ps0.01).
PRs showed significantly longer P300 latencies
(Ps0.03) during the W task (group=task interaction F(1, 32)s4.83 Ps0.035; Fig. 4).
4. Discussion
In the present study, animalynon-animal figures’
and words’ categorization tasks elicited three ERP
components in PRs and control subjects: P2, N400
and P300. An anterior P2 was seen on fronto-polar
and frontal leads and more pronounced over the
left hemisphere mainly during the W task. Following the P2 component, a frontally negative waveform of approximately 445 ms and a posterior
negativity of approximately 520 ms were clear
during the F task. A dual-negative-going, anteriorly maximal, but widely distributed negative peak
between 350 and 560 ms in the W task was
evident. At posterior sites a positive-going com-
J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
195
Fig. 4. This figure shows: (a) group=task=category=hemisphere interaction for the P300 amplitudes; (b) group=task interaction
for the P300 latency measurements. PRs display longer P300 latencies and smaller amplitudes during W task. Significant differences
are marked with an asterisk (P-0.05).
ponent peaking approximately at 750 ms (P300)
was present and largest for the animal condition
which has the lowest presentation probability. This
peak was practically absent in PRs during the word
categorization task.
In order to compare both groups exclusively at
the semantic level, it is of great importance to
assume that the tasks are equivalent in cognitive
terms. It could be argued, for example, that in
order to categorize figures, subjects rely on shape
similarity and other physical attributes, which
could facilitate a successful performance (Snodgrass and McCullough, 1986). In such a case, one
should obtain shorter RTs andyor earlier latencies
of semantic related late ERP components during
the F task in both groups. If anything, the results
of the present study showed only earlier P2 latencies in the F task than in the W task in both
groups. We argue that this difference could reflect
a lower complexity in stimulus’ evaluation (Taylor
and Khan, 2000) to access the semantic system,
but not semantic differences per se. In this way,
we believe the comparison between tasks is valid.
PRs presented longer RTs and a higher percentage of errors with respect to the control group
during the word categorization task. Phonological
processes such as accessing a word by first decoding the written symbols into sound representations
and phonological coding to maintain information
in working memory have been implicated in reading failure (Beitchman and Young, 1997; Wagner
and Torgesen, 1987). Deficiencies at the phonological level interfere at least with the activation of
word meaning or slow down the semantic information access (Zecker and Zinner, 1987). It has
also been suggested that PRs could primarily
activate the meanings of words using the phonological route, which could make the whole process
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even slower. Good readers, on the other hand,
primarily activate the meanings of words using the
direct route (i.e. without the translation processing
from grapheme to phoneme) (Jared et al., 1999).
This evidence could therefore explain the lower
performance of our PRs group during the W task.
Our results showed that PRs have a larger and
longer anterior P2 than controls during the word
categorization task. This effect was also seen more
pronounced over the left hemisphere and on frontopolar and frontal leads. The anterior P2 peak has
been associated with attentional demands (Johnson, 1989) and stimulus evaluation (Luck and
Hillyard, 1994). Its amplitude decreases with age
(Taylor and Khan, 2000) but increases with the
difficulty level of the task (Stelmack et al., 1988;
Taylor and Khan, 2000). Right)Left posterior P2
hemisphere asymmetries have been related to better reading skills (Segalowitz et al., 1992) and
L)R anterior P2 asymmetries have been found in
children at risk for reading difficulties (Khan et
al., 1999). Although there is a controversy about
distributional ERP component differences between
poor and normal readers, the lateralization of
semantic processing with increased age has also
been previously reported (Holcomb et al., 1992).
Our results clearly showed L)R P2 asymmetries
in the PRs group and, in agreement with Khan et
al. (1999) we claim that this group employs less
mature strategies in the word processing; even the
allocation of more attentional resources could be
the expression of an inappropriate strategy.
The maturation of the prefrontal cortex is
extremely important during cognitive development
(Stauder et al., 1993) and therefore, reading. Segalowitz et al. (1992) argue that PRs may have
difficulty with attentional requirements for visual
processing and metacognitive strategies associated
with reading, which place a demand on the frontal
system. According to Taylor and Smith (1995),
the latency of the P2 component decreases with
age. This developmental trend could mean that
children become faster or that they have more
efficient strategies to evaluate stimuli with increasing age. Khan et al. (1999) observed longer
anterior P2 latencies on a group of children at risk
for reading difficulties. Our PRs also showed
longer P2 latencies which may mirror the use of
an immature stimulus evaluation strategy and a
deficit to reallocate attentional resources.
In contrast to the previous ERP component
results, there were no clear significant differences
between groups regarding the N400 component.
Both groups showed an anterior negativity of
approximately 445 ms and a posterior negativity
of approximately 520 ms during the figure categorization task. These two negativities were previously reported during picture priming (Barret
and Rugg, 1990) and picture list studies (Coch et
al., 2002). Both groups also showed a more pronounced anterior N400 during figure categorizations than word categorizations. These amplitude
topographical distribution differences could show
that different cognitive components may be
involved in the figure and word semantic processing (Holcomb and McPherson, 1994). The point
we wish to emphasize here is that PRs showed no
differences in their performance and N400 component with respect to the controls during the
figure categorization task where they can easily
access the semantic information provided by these
stimuli.
Both groups showed a negative dual-peak during
the word categorization task. Prior studies have
shown that stimuli presented in list form tend to
elicit such anteriorly distributed negativities
(Nobre and McCarthy, 1994). Approximately, the
first peak was observed at 350 ms and the second
at 560 ms, they were mainly distributed on C3,
Cz and C4. This finding has also been previously
reported by other groups (Coch et al., 2002;
Dykman et al., 2000). Dykman et al. (2000)
compared the performance of a failure to thrive
group (FTT)1 with controls during a lexical decision task. Dykman et al. (2000) as well as Coch
et al. (2002) observed the dual-peak negative
waveform. According to their explanation, the later
peak may mirror a postlexical confidence. The two
peaks of the N400 in both groups may have shown
the postlexical revision necessary to match or
mismatch the target.
1
FTT was a group of children with abnormally low weight
for age and gender and some studies have shown that the FTT
have poorer language development and less developed reading
skills.
J. Silva-Pereyra et al. / International Journal of Psychophysiology 49 (2003) 187–199
A P300 amplitude effect was expected during
both F and W tasks given the different presentation
probabilities of animals and non-animals. PRs
displayed larger P300 amplitudes for animals compared to non-animals during the F task, as expected, but not during the W task. The non-significant
P300 effect during the W task in PRs can be
interpreted as a less efficient categorization processing of two types of stimuli. Previous studies on
dyslexic, reading disabled andyor subjects with
attention deficit disorders have also reported an
attenuation of the P300 effect (Diniz et al., 1997)
and attributed it to less efficient processing systems. A prolonged P300 peak latency in the W
task was also found in PRs as previous studies
have shown (Silva-Pereyra et al., 2001). Latency
of the P300 seems to reflect stimulus classification
speed (Magliero et al., 1984) and it has also been
commonly interpreted as reflecting the time needed
for stimulus evaluation and memory updating (Polich and Kok, 1995). According to the so-called
‘memory updating model’ (Donchin and Coles,
1988), infrequent events elicit large P300 because
the immediate memory for the preceding target
stimulus has decayed and is refurbished by the
neural events which occur upon the presentation
of a new target stimulus. In contrast, frequent
stimulus events, maintaining stronger representations, do not require as much updating and therefore yield smaller P300 waves. Our results support
the notion that PRs take more time than controls
to update their context model during the W task,
because their processing system is not fast enough
to read the odd trial and accommodate the new
information in the previous memory model. The
word categorization task we used needs both word
recognition and semantic processes to allow a
decision on whether an item belongs to one or
other semantic category. The developing ability to
read quickly, accurately and effortlessly is critical
to skillful reading comprehension (Adams, 1990),
because it frees cognitive resources to allow for
the integration of a word and their context, which
leads to understanding the meaning of a text
(Stanovich, 1980).
Taking together our behavioral and ERP results,
PRs may appear as underachievers in semantic
tasks but not because of a semantic processing
197
deficit itself (Waterman and Lewandowski, 1994).
Our study suggests that PRs have deficiencies very
early in the processing of words. Every word
presented is a problem for these children because
it takes much time and effort to be read, although
when finally read, they can decide the semantic
category to which the word belongs. PRs may use
a less efficient and demanding strategy to process
words. This strategy consumes extra attentional
resources and seems to be slow, with the subject
storing and accommodating new difficult information into a memory model before the next trial
arrives. We suggest that the most invasive deficit
that PRs face when reading takes place very early,
probably at the first encounter with the processing
of graphemes. In this way a chain reaction of
general slowness is triggered. Thus, previous
behavioral studies may have mistakenly concluded
that the deficit is at semantic level. Our results
challenge this interpretation.
Acknowledgments
This project was partially supported by Grant
IN209998 from DGAPA and J30964-H from
CONACyT. The authors acknowledge Miguel
´
Rodrıguez
Espinosa for technical support.
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