Impulsivity and semantic/emotional processing: An examination
of the N400 wave
Vilfredo De Pascalis*, Brian Arwari, Laura D’Antuono, Immacolata Cacace
Department of Psychology, University of Rome “La Sapienza”, Italy
*Corresponding author.
Address: University of Rome “La Sapienza”
Department of Psychology,
Via dei Marsi 78,
00185 Roma, Italy
Tel: +39 06 76907199
Fax: +30 0649917711
e-mail address: v.depascalis@caspur.it
Keywords: Impulsivity; Language; Event-related potentials, N400 wave; Semantic processes;
Affective processes
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Abstract
Objective: The study investigated (a) to what extent semantic/emotional processing modulates the
N400 wave of the event-related potentials (ERPs) during reading, (b) the influence of Impulsivity
trait on neurocognitive systems underlying semantic/emotional processing related to the generation
of the N400 wave.
Methods: A canonical semantic sentence processing paradigm, known to selectively elicit the N400
wave was used. The ERPs were elicited to emotionally valenced (neutral, positive, and negative)
sentence final words that were either semantically congruent or semantically incongruent with the
previous sentence context.
Results: Congruent negatively valenced words produced longer reaction times (RTs) than congruent
positive and neutral words. Incongruent words elicited more pronounced N400 peak amplitudes
than congruent ones, while, for the congruent trials, the N400 amplitude was greater for negative
words as compared to positive and neutral words. High impulsive participants, compared to lowimpulsive ones, (a) made more errors and longer reaction times in identifying incongruent words,
(b) displayed more pronounced N400 peak amplitudes over frontocentral midline scalp sites.
Conclusions: This pattern of results indicated that the activity of frontocentral system may account
for individual differences of impulsivity with high impulsive individuals showing more difficulty in
integrating incongruent final words into a sentence context.
Significance: Results open up new perspectives for future investigations on language disorders
characterized by substantial impulsivity.
1. Introduction
Impulsivity has been defined as acting on the impetus of the moment without being aware of
the potential risks involved (Eysenck et al., 1985; Patton et al., 1995), the tendency to act without
much deliberation, which often results in fast and error-prone responding (Dickman, 1990; Daruna
and Barnes, 1993), the tendency to act for immediate gratification, risky activities, novel sensations
and easier routes of self-gratification (Mitchell, 1999). There are important individual differences in
impulsivity (Depue and Collins, 1999; Gray and McNaughton, 2000; Revelle, 1997) and these are
closely related to other personality constructs, such as extraversion, sensation seeking and
psychopathy (Depue and Collins, 1999; Pickering and Gray, 2001; Revelle, 1997; Zuckerman and
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Kuhlman, 2000). Most findings suggest that impulsivity is multifactorial, although there is little
agreement as to what these factors are (Evenden, 1999). Among others, it includes cognitive
dimensions, such as decision time, response inhibition, timing, behavioral switching, motor
impulsivity, premature responding and lack of persistence (Buss and Plomin, 1975; Evenden, 1999).
Highly impulsive individuals consistently score low in vocabulary, reading comprehension,
receptive and expressive language, sentence repetition and completion, and verbal intelligence and
memory (Harmon-Jones et al., 1997; Lewis et al., 1980; Richman and Lindgren, 1981; Spellacy,
1977; Stanford et al., 1996). Impulsivity coupled with deficits in verbal ability has been related to
delinquent activities, poor school performance, and increased behavior problems (Maughan et al.,
1996; Miller, 1988; Silva et al., 1987). Impulsivity, as well as incidence of physical and verbal
aggression, is inversely correlated with reading accuracy, reading comprehension, and verbal skills
(Barratt et al., 1997; Harmon-Jones et al., 1997; Stanford et al., 1996).
Personality traits like Impulsivity or Extraversion have been found associated with P300
wave of the ERP (see e.g., Daruna et al., 1985; De Pascalis, 2004; De Pascalis et al., 2004; De
Pascalis and Speranza, 2000; Ortiz and Maojo, 1993; Russo et al., 2008; Polich and Martin, 1992;
Pritchard, 1989, Stelmack et al., 1993), suggesting a reduced P300 amplitude in impulsive (and
extraverted) subjects. A negative relationship between Impulsivity, reading levels and the amplitude
of the P300 ERP component was also reported (e.g., Barratt et al., 1997). However, no enough
attention have been devoted in the literature in evaluating the influence of individual differences in
Impulsivity on ERP components during language processing. Among late ERP waves, the N400
have been suggested to reflect semantic processing. The N400 is a broad negative ERP wave that
peaks around 400 ms after a semantically incongruous word in a meaningful sentence, such as “The
man liked his coffee with dog” (Kutas and Federmeier, 2000). It does not occur after syntactic
incongruities or physical deviations such as changes in typescript (Kutas and Hillyard, 1980a,b).
The amplitude of the N400 is, in fact, an inverse function of the semantic congruence between the
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target word and the priming effect afforded by its prior context (Kutas and Hillyard, 1984), whether
that context is a single word, sentence or discourse (van Berkum et al., 1999; Kutas, 1993; St.
George et al., 1997).
It is known that emotionally unpleasant and pleasant stimuli spontaneously arouse and
capture the viewer’s attention and are processed in a facilitated manner. This stimulus driven
reorientation of attention helps to increase the chance with which potentially threatening or
rewarding information can be perceived and evaluated (Lang et al., 1997; Bradley and Lang, 2000).
A great amount of evidence in support of this thesis comes from ERP studies investigating temporal
evolution of emotional picture processing. However, there is experimental evidence that verbal
emotional material, due to its abstract description of emotional contents, is less perceptually
engaging than other types of visual affective items such as facial expressions or emotional pictures
(Keil, 2006; Kissler et al., 2006; Mogg and Bradley, 1998; Vanderploeg et al., 1987; Codispoti et
al., 2007). Consequently, emotional pictorial material would be more capable of disrupting an
ongoing cognitive task due to attentional capture than verbal emotional stimuli. However,
experimental evidence to support this is really sparse and recent studies on cognitive interference by
emotional words suggest that effects for processing of emotional words are qualitatively similar as
effects found in pictures (or face) studies ( see e.g., Keil, 2006; Ortigue et al., 2004; Karrétié et al.,
2008; Kissler et al., 2007; Herbert et al., 2008).
Among ERP studies investigating emotional word processing, the modulation of the N400 by
emotional word content has hardly been investigated, although some studies have found amplitude
variations of N400 or N400-like waves to emotional words in normal controls and in psychopaths
(Kiehl et al., 1999; Williamson et al., 1991). Usually, larger N400 amplitudes reflect a violation of
semantic expectations and difficulties with context integration. However, Federmeier et al. (2001)
provided experimental evidence that mood can modulate N400 amplitude in sentence processing, as
unexpected and distantly related spoken words elicit smaller N400 amplitudes in mildly positive
mood, indicating facilitated semantic integration in positive mood. In a later study, Kiefer and
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colleagues (Kiefer et al., 2007), investigating the effect of mood on cortical processing of pleasant
and unpleasant adjectives, found that pleasant adjectives, in contrast to unpleasant adjectives,
facilitated semantic integration when subjects were in a positive mood as indexed by reduced N400
amplitudes. Very recently, Herbert and collaborators (Herbert et al., 2008) reported a facilitation
processing selectively for pleasant adjectives that were associated with a reduced N400 and were
also better remembered in an incidental memory test. Thus, there is experimental evidence
suggesting that both a word’s emotional content and the participants’ emotional state may affect the
N400 ERP response.
On these bases, the purpose of the present study for the N400 component was exploratory,
because, as yet, very few experimental studies have investigated the impact of emotional content on
this ERP wave. In particular, the present study attempted to examine the simultaneous impact of
word incongruency and emotional content of a sentence final word on N400 amplitude and to
determine whether: (a) semantically incongruent words elicited a more pronounced N400 wave as
compared to congruent words; (b) positively valenced words, in contrast to negative words,
facilitated semantic integration as indexed by reduced N400 amplitudes.
Personality dimensional models have always emphasized relationships between normal
traits and personality disorders (see e.g., the five-factor model, Costa and Widiger, 2002). Within
this tradition, the relationship with the Zuckerman–Kuhlman Personality Questionnaire (ZKPQ;
Zuckerman, Kuhlman, Joireman, Teta, & Kraft, 1993) is of particular interest because this provides
an alternative five-factor structure that includes five basic personality dimensions: Impulsiveunsocialized Sensation Seeking (ImpSS), Neuroticism–Anxiety (N-Anx), Aggressivity–Hostility
(Agg-Host), Activity (Act) and Sociability (Sy). In general, the relationships between Zuckerman’s
model and personality disorders are still largely unknown. This personality model is of particular
interest, however, providing as it does an alternative five-factor structure that includes, among
others, a dimension of Impulsive sensation seeking that is of particular clinical significance.
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Impulsive Sensation Seeking is the most studied normal trait in relation to personality disorders. For
instance, Ball, Carroll, and Rounsaville (1994) found that sensation seeking correlated with
antisocial personality and life-time drug abuse and Thornquist and Zuckerman (1995) reported
significant correlations between ImpSS and Agg-Host with the Total score of the Psychopathy
Check List (Hare, 1991).
A number of ERP/language studies have been carried out for the psychopathy, a germane
personality dimension of impulsivity. Some studies found language abnormalities in psychopaths
engaged in tasks requiring semantic processing (Hare, 1979; Hare and Forth, 1985; Hare and
McPherson, 1984). In particular, Kiehl and colleagues (1999) found that psychopathy is associated
with language abnormalities during semantic processing of abstract word stimuli. These authors, for
non-psychopathic individuals, reported that concrete words elicited a greater negativity of the eventrelated potential (ERP) in the 300–500 ms (i.e., N400) window than did abstract words (Kiehl et al.,
1999; Kounios and Holcomb, 1994; Paller et al., 1987). Psychopaths made more errors than did
non-psychopaths when having to classify word stimuli as abstract during a concrete/abstract
discrimination task and, in these individuals, the normal electrocortical differentiation between
concrete and abstract words was lacking. These authors argued that psychopaths may differ from
others in the process responsible for the generation of the N400 wave, i.e., to the process of
integration of a word into ongoing cognitive context (Holcomb, 1993; Kutas and Hillyard, 1980c,
1983, 1984). More recent findings failed to support this hypothesis (Kiehl et al., 2006b). However,
in a further study, Kiehl and collaborators (Kiehl et al., 2006a) found that processing of oddball
targets elicited larger frontocentral negativities (N550), enlarged N2 and reduced P3 components in
psychopaths than in non-psychopaths. These findings were interpreted as supporting the hypothesis
that psychopathy may be related to dysfunction of the paralimbic system—a system that includes
parts of the temporal and frontal lobes.
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Given the known link between psychopathy and impulsivity, and the known difficulty for
impulsive individuals in reading and verbal processes (see e.g., Barratt et al., 1997; Harmon-Jones
et al., 1997; Stanford et al., 1996), it is surprising that no attention has been devoted to examine how
individual differences in Impulsivity may be reflected on N400 component of the ERPs during
semantic/affective processing.
In line with previous findings, the aim of the present study was to test the hypothesis that
high impulsive subjects, rated within a normal range of impulsivity trait, should evidence more
difficulty in the processing of semantic and affective verbal information. The use of sentences
ending with a semantically congruent or semantically incongruent neutral, negative and positive
valenced word, in our experiment, permitted to evaluate whether previous N400 findings observed
for psychopaths could also be observed with emotional stimuli in normal individuals differing in
impulsivity levels. Moreover, considering the link between impulsivity and sensation seeking (SS,
Zuckerman, 1993, 2005), impulsivity-related differences in N400 amplitude will be investigated by
controlling for individual differences in sensation seeking in order to highlight the pattern of
covariation among these variables. Accordingly with the past literature, we expected that high
impulsive individuals would show poorer behavioral performance and enhanced N400 waves for
incongruent terminal words than would the low impulsive ones with little or no differentiation
between positive and negative emotional words.
2. Materials and Method
2.1 Participants
Participants were 56 right-handed women between the ages of 19 and 36 years (M=24.5,
SD=3.2). Hand preference was assessed with the Italian version of the Edinburgh Handedness
Inventory (Salmaso and Longoni, 1985).
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Subjects were admitted to participate in the experiment only if they reported absence of drug abuse,
use of medication (e.g., psychoactive drugs, antihistamines) or medical conditions that might
interfere with vigilance and task performance (e.g., high blood pressure, diabetes mellitus, heart
diseases, asthma, neurological or psychiatric disorders) and had 10/10 or corrected to 10/10 vision
with no history of neurological problems. In addition, participants who were on their menstrual
cycle or who had taken medication that might cause drowsiness or otherwise interfere with EEG
recordings, were rescheduled. In accordance with the ethical norms of the Italian Association of
Psychology (AIP), all participants gave informed consent prior to their inclusion in the study.
Subjects performed their tasks during two sessions scheduled about two weeks apart. During the
first session all participants were administered the Italian adaptation of the Zuckerman Kuhlman
Personality Questionnaire (ZKPQ; Zuckerman et al., 1993; De Pascalis and Russo, 2003). Seven
subjects had gross EEG artifacts, one disattended the experimental session, thus 48 woman
volunteers were used for data analysis.
From the available qualified pool (N=48 Ss), two extreme-groups were selected on the basis of
Impulsivity subscale of the ZKPQ. Those persons whose Impulsivity score was respectively above
the median (Md= 3.0) were defined as High Impulsive subjects (Hi-Imp, n=23, M=5.3, SD=1.3),
while those persons whose impulsivity score was below the median were defined as Low Impulsive
subjects (Lo-Imp, n= 21; M=0.9, SD=0.9). It may be useful to emphasize that, at least as far as we
can tell, high- and low-impulsive subjects were psychiatrically normal since impulsivity scores
reported by the participants were still within a normal range of impulsivity. The same can be said
for sensation seeking scores (for normative scores see Zuckerman et al., 1993, De Pascalis and
Russo, 2003).
In order to control the influence of gender factor on personality measures, only women were
invited to participate in the experiment. Gender differences in ratings of impulsivity have been well
documented in personality research, showing increased impulsivity scores in men (Miller, 1991;
Nagoshi et al., 1991). Similarly, men significantly outscored females on sensation seeking and
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impulsive sensation seeking scores (Zuckerman et al., 1991; Zuckerman et al., 1993; Aluja et al.,
2003).
2.2. Stimuli
Two-hundred and seventy sentences (four to seven words in length) were presented one word at
a time on a computer monitor. The number of syllables of sentence final words ranged from one to
four. Sentences ended with a word that was either semantically congruent (50% of trials) or
semantically incongruent (50% of trials) with the previous sentence context. The order of sentence
presentation was pseudo random. All words were presented in green letters (Arial font, 68 point) on
a black background centered on a 15-in. computer monitor positioned about 100 cm from the
participant’s eyes. Word duration was of 350 ms. The second to last word was underlined to serve
as a warning for the incoming last word (target). Inter-stimulus interval (ISI) between words was of
1000 ms. The inter-trial interval (ITI) between two sentences was of 2500 ms.
Sentences were grouped on the basis of emotional valence (positive, negative, neutral) and
congruence/incongruence into six groups, each formed of 45 sentences (positive/congruent,
positive/incongruent, negative/congruent, negative/incongruent, neutral/congruent,
neutral/incongruent). Sentences were selected from a sample of 600 rated by a group of 30 students
on a 7-point pleasant/unpleasant rating scale. Sentence final words rated as more than 1.5 SDs
above or below the mean pleasantness ratings were defined as positive (e.g. ‘caress’) or negative
(e.g., ‘dead’), respectively; neutral words (e.g., ‘bridge’) were those that fell less than .5 SDs from
the mean. A subgroup of 50 subjects was required also to rate the congruency/incongruency level on
a 7-point likert scale. Words rated as more than 1.5 SDs above or below the mean congruency
ratings were defined as ‘congruent’ or ‘incongruent’, respectively. The list of positive, negative, and
neutral sentence final words was defined in such a way that they were balanced for frequency of use
in Italian (De Mauro et al., 1993) [Frequency of use (per 490,000 words): M= 21.40, SD=23.59,
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M=19.22, SD=38.72, and M=31.67, SD=41.77, respectively for positive, negative and neutral
words; all comparisons were not significant, all ts<1]. Types of words were also balanced in number
of syllables, i.e., there were no significant differences on the number of syllables between emotional
words [Number of syllables: M=2.55, SD=.78, M=2.50, SD=.73, and M=2.47, SD=.57,
respectively for positive, negative and neutral words; all comparisons were not significant, all
ts<1].
2.3. Procedure
The subjects were seated in a comfortable reclining armchair, placed in a dimly lit, sound
damped, and electrically shielded booth. Sentences were presented to the participants by using a
one-by-one word reading paradigm. Subjects were invited to silently read each word and to press a
right-handed button whenever a sentence final word was congruent with the sentence context, and a
left-handed button if the final word was incongruent with sentence context. The hand used to make
the response was counterbalanced across participants. The experiment was divided into three 90
phrase blocks, each lasting about 10 minutes. After each block, subjects were allowed to rest for a
few minutes. At the end of the EEG recordings, subject’s mood was measured using the Positive
and Negative Affective Schedule (PANAS; Watson, Clark and Tellegen, 1988). The PANAS, used
widely in mood research, provides scores for two orthogonally related dimensions of mood states:
positive and negative. There are 10 adjectives covering positive affect (PANAS-PA), and 10
adjectives covering negative affect (PANAS-NA), and each affect is rated from 1 (‘’very slightly or
not at all’’) to 5 (‘’extremely’’).
2.4. EEG recording and ERP measures
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EEG and electro-ocular (EOG) were acquired continuously and simultaneously with the
performance measures by using a 40-channel NuAmps DC amplifier system (Neuroscan Inc.), set at
a gain of 200, sampling rate of 500 Hz, and with signals band-limited to 100 Hz. In addition, a 50
Hz notch filter was applied. The signals were amplified by NuAmp DC amplifiers (Neuroscan Inc.).
Data were recorded and stored on a computer running Neuroscan Acquire 4.2 software. Electrode
impedance was lower than 3 k. The horizontal EOG was monitored via a pair of tin electrodes
placed 1 cm lateral to the outer canthus of each eye and the vertical EOG was monitored via a
separate bipolar montage placed above and below the centre of the left eye. EEG data were recorded
from 30 scalp sites (Fp1, Fp2, F7, F8, F3, F4, FT7, FT8, T3, T4, FC3, FC4, C3, C4, CP3, CP4, TP7,
TP8, T5, T6, P3, P4, O1, O2, Fz, FCz, Cz, CPz, Pz, Oz) referenced to linked-ear electrodes by using
an electrocap (Blom and Anneveldt, 1982) with pure tin electrodes. The ground electrode was
located 10 mm anterior to Fz.
The EEG was later reconstructed into discrete, single-trial epochs. For each sentence, an
EEG epoch length of 1050-ms was used with a 150-ms pre-stimulus baseline and a 900-ms period
following the onset of the sentence final word. Epochs were rejected from averaging if amplitude
exceeded +75 V, and eye blinks were corrected for statistically in accordance with Gratton’s et
al.’s procedure (Gratton et al., 1983). When the recording was split in two equal parts, the mean
percentages of rejected trials were ranging from .05 to 0.08. No participants had less than 35
accepted trials in any condition. There were no significant differences between groups in the
number of trials averaged in any condition. All data average files were digitally filtered (15 Hz low
pass), and baseline corrected. An ERP response was obtained for each of the six experimental
conditions.
2.5. Performance, ERP measures, and data analyses
The following performance measures were calculated: (1) False Alarm/Hit ratio (i.e., the
ratio between the number of errors and the number of correct target detections), (2) RT or the
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latency of correct detections (i.e., the interval between the onset of the target stimulus and the
depressing of the response button), (3) Coefficient of Variation (CV) of the RT scores. These
measures were submitted to a split-plot analysis of covariance (ANCOVA; SAS-8.02, glm
procedure) by considering Impulsivity as the between groups factor and Sensation Seeking as the
covariate. The experimental design was the following: 2 Personality level (High, Low) x 3
Emotional valence (Positive, Negative, Neutral) x 2 Word congruency (Congruent, Incongruent).
Sentence final word stimuli elicited a centroparietal ERP negativity with an approximate
peak latency of 390+ 18.0 ms. We termed this negative waveform as N400 wave since had similar
shape to the known N400 wave typically observed in semantic word and sentence processing tasks
(Kutas and Hillyard, 1980c, 1983, 1984). For this ERP wave a mean amplitude measure within a
300 to 420-ms time window from sentence final word onset was provided. This time window was
derived from the grand average waveform by centering on the peak of this component. For N400
amplitude scores, two separate ANCOVAs were performed. One ANCOVA was performed on
midline electrodes location (Fz, FCz, Cz, CPz, Pz). A second ANCOVA was focused on scalp
quadrants (i.e., left-frontal: Fp1, F3, F7, FC3, FT7; right-frontal: Fp2, F4, F8, FC4, FT8; leftcentral: C3, T3, CP3; right-central: C4, T4, CP4; left-posterior: T5, TP7, P3, O1; right-posterior: T6,
TP8, P4, O2). As for behavioral measures, both analyses had Impulsivity as between factor and
Sensation Seeking as covariate. The ANCOVA performed on the quadrant scores included
Personality level (High vs. Low) as between-subjects factors and Hemisphere (Left vs. Right), Site
(Frontal, Central, Posterior), Word congruency (Congruous, Incongruous) and Emotional Valence
(Positive, Negative, Neutral) as within-subjects factors. To prevent the risk of falsely significant
results, as may happen using repeated measures analysis if the sphericity assumption has been
violated (Vasey and Thayer, 1987), the Huynh–Feldt epsilon correction of significance levels was
applied when necessary. Post hoc comparisons of the means were performed by using a t-test
procedure with alpha=0.05 (Kirk, 1968, pp. 90–93).
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The Pearson r coefficient and partial r of impulsivity and sensation seeking measures with
N400 amplitude were computed. In addition, N400 amplitude scalp measures were used as
predictors in separate stepwise regression analyses in order to assess their predictive power for
impulsivity.
3. Results
3.1. Impulsivity, behavioral and self-reported data
High and low impulsive subjects did not differ in the false alarm/hit ratio [F(1,41)=1.69,
p=0.21; low impulsives, M=0.21, SD=0.15; high impulsives, M=0.20, SD=0.18]. Moreover, for
congruent words, low impulsives had higher ratios than high impulsives (M=0.30, SD=.24, and
M=0.14, SD=0.12, respectively), while an opposite trend was found for incongruent words between
low and high impulsivity groups (M=0.15, SD=.17, and M=0.21, SD=0.28, respectively)
[Impulsivity x Word congruency interaction, F(1,41)=6.08, p=0.018].
Across all participants, negative valenced words had longer RT than positive and neutral
words [main effect of Emotional Valence, F(2, 82) = 4.59, p=0.0129; M=1027.9 ms, SD=128.0 vs.
M=965.9 ms, SD=120.2, t=5.93, p<.0001, and vs. M=962.6 ms, SD=107.8, t=6.49, p<.0001; for
negative vs. positive, and vs. neutral words, respectively]. Furthermore, congruent sentence negative
final words produced a longer RT as compared to congruent positive and neutral words (M=1071.1
ms, SD=113.3 vs. M=939.0 ms, SD=95.3, t=8.40, p<.0001 and vs. M=909.9 ms, SD=107.9; t=9.54,
p<.0001), while there were no significant differences among incongruent negative, positive, and
neutral words (M=992.3 ms, SD=137.9 vs. M=1015.7 ms, SD=115.8 t=-1.34, p>.05, and vs.
M=1015.3 ms, SD=118.7; t=-1.66, p>.05) [Emotional Valence x Word congruency interaction, F(2,
82)=7.49, p=0.002]. There were no significant differences on RT scores between Impulsivity groups
[low Impulsives, M=971.8 ms, SD=129.0; high Impulsives, M=986.8 ms, SD=103.4; F(1,41)=0.89,
p=.352]. Nevertheless, low impulsives, for incongruent words, had shorter RTs than high impulsives
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(M=966.5 ms, SD=83.4, and M=1029.4 ms, SD=149.9), while there were no RT differences beween
low and high impulsivity groups for congruent words (M=961.2 ms, SD=97.4, and M=964.1 ms,
SD=113.7) [Impulsivity x Word congruency interaction, F(1,41)=4.47, p=0.041)].
The CV of the RT scores did not yield any significant effect involving Impulsivity,
Emotional Valence or Word congruency.
High impulsives had higher PANAS-PA scores than low impulsives (M=2.9, SD=.6 vs.
M=2.4, SD=.6; t=2.22, p=.032), while high and low impulsivity groups had the same PANAS-NA
score (M=1.3, SD=.38 vs. M=1.3, SD=.39; t<<1).
3.2. Relationship between Impulsivity, Sensation Seeking, and positive and negative affect measures
The ZKPQ measures of Impulsivity and Sensation Seeking were slightly, but significantly
correlated (r=.316, p<.05). The positive affect, as measured with PANAS, was slightly correlated
with Sensation Seeking (r=.295, p<.05), while the correlation between PANAS scores of negative
did not reach the significance level (r=.12, p>.05).
There were no significant correlations between performance measures, i.e., False Alarm/Hit
ratio, RT, and CV of the RT scores and Impulsivity, with the exception of False Alarm/Hit ratio of
positive congruent words that was significantly correlated with Impulsivity (r=-0.389, p<0.006).
3.3. Impulsivity, N400 amplitude, and semantic/emotional processing
There was a smaller overall N400 amplitude in low impulsives as compared to high
impulsives [main effect of Impulsivity, midline, F(1, 41)=4.62, p=0.037], although this difference
was more pronounced over fronto-central and central sites [Impulsivity x Site interaction, midline,
F(2, 82) =4.90, p=0.026; quadrants, F(2, 82)=5.62, p=0.016] (see Figure 1).
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Across all participants, N400 was larger for incongruent than for congruent sentence endings
[main effect of Word congruency, midline, F(1, 41)=57.2, p<0.0001; M=-3.0, SD=0.3 vs 0.03 V,
SD=0.4; quadrants, F(1, 41)=49.07, p<0.0001; M=-2.0, SE=0.2 vs 0.2V, SD=0.2]. This effect was
largest at central, centro-parietal and parietal midline sites [Word congruency x Site interaction,
midline, F(4, 164) =3.72, p=0.023; quadrants, F(2, 82)=3.73, p=0.047]. The N400 for incongruent
words was slightly larger over left hemisphere posterior sites and over the right hemisphere frontal
and central sites than the analogous right and left hemisphere sites [Word congruency x Hemisphere
x Site, quadrants, F(2, 82)=6.35, p=0.0042]. This effect is displayed in Figure 2.
Negative emotional words, as compared to positive and neutral words, elicited a larger N400
wave over central and posterior sites [Emotional Valence x Site, quadrants, F(4, 164)=4.61,
p=0.006]. Moreover, positive words elicited larger N400 waves in the right as compared to the left
hemisphere, while there were no hemispheric asymmetries for negative and neutral terminal words
[Hemisphere x Emotional Valence, quadrants, F(2, 82)=4.75, p=0.012]. This effect is shown in
Figure 3.
____________________________________
Insert Figures 1, 2, and 3 about here
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Considering that high impulsives scored significantly higher on PANAS-PA than low
impulsives, two separate ANCOVAs were performed, respectively for midline and quadrant N400
amplitude measures, by using median split PANAS-PA score as the between groups factors and
Sensation Seeking as the covariate. No main or interaction effects involving PANAS-PA were
found to be significant [PANAS-PA, midline, F(1, 42) =0.38, p=0.538; quadrants, F(2, 82)=0.70,
p=0.408; 0.4<F<2 for all interactions involving PANAS-PA factor]. These lacking differences
indicated that differential N400 results found between impulsivity groups were not due to
differences in positive affect.
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3.4. Predictors of Impulsivity
Correlation coefficients were calculated between midline N400 amplitude measures and the
Impulsivity scores. There were significant negative correlations between Impulsivity and N400
amplitude elicited by neutral, positive, and negative words over midline frontal and fronto-central
sites. However, the highest correlation was found for neutral incongruent words at fronto-central
site. These correlations are reported in Table 1. As it can be clearly seen in Table 1, the relationship
between Impulsivity and N400 amplitude was not affected after controlling for Sensation Seeking
(compare the first and second column in Table 1).
In order to highlight which of the significantly correlated behavioral and N400 amplitude
measures was the best predictor of Impulsivity, a stepwise regression analysis was conducted using
False Alarm/Hit ratio, and N400 amplitude over Fz, and FCz sites for neutral, positive, and negative
words as predictors. This procedure retained the N400 amplitude at FCz scalp site and False
Alarm/Hit ratio for Neutral incongruent words as the best predictors of Impulsivity scores (beta=0.31, F=12.62, p=0.0009; beta=-2.60, F=4.61, p=0.037, respectively for N400 amplitude at FCz and
False Alarm/Hit ratio). The regression model was statistically significant [F(2,47)=11,46; p<0.0001]
with N400 measure accounting for the 27.0% of the total variance [F=16.99, p=0.0002] and False
Alarm/Hit ratio accounting for the 6.8% of the total variance, with no other variables entering in the
equation. The adjusted R-square for the total equation was of 0.31. The scatterplot for the most
significant correlation between Impulsivity and N400 measure is reported in Figure 4.
_______________________________
Insert Table 1 and Figure 4 about here
_______________________________
4. Conclusion
16
The present study was designed to examine (a) the simultaneous impact of word
incongruency and emotional content on behavioral performance and N400 wave of the ERPs as
elicited by a sentence final word, and (b) the relationship between impulsivity and N400 amplitude
during emotional word processing.
In terms of semantic processing, as expected, it was found that semantically sentence
incongruent final words elicited a more pronounced N400 wave as compared to congruent ones.
This finding is in line with the classic evidence that N400 amplitude is, in fact, an inverse function
of the semantic congruence between the target word and the priming effect afforded by its prior
context (Kutas and Hillyard, 1984; van Berkum et al., 1999; Kutas, 1993; St. George et al., 1997).
In terms of emotional word processing, for positive valenced words compared to negative words,
shorter RTs and smaller N400 amplitudes were evidenced. This finding was seen as indicating
facilitated semantic integration for positive valenced words, a finding that is in line with previous
reports by Federmeier et al. (2001), wherein spoken words elicited smaller N400 amplitudes in
mildly positive mood, and by Kiefer et al. (2007) and Herbert et al. (2008) reporting facilitated
semantic integration, i.e., reduced N400 amplitudes to pleasant adjectives reading compared to
unpleasant adjectives reading. Furthermore, in terms of behavioral performance, this study has
provided experimental evidence that congruency interacted with emotional valence of sentence final
word given that congruent positive words had shorter RTs than congruent negative words, while
there were no significant differences for incongruent words.
High impulsive subjects, compared to low impulsive ones, made longer RTs and more errors
when categorizing incongruent words, while there were no RT differences between impulsivity
groups for congruent words. This finding is in line with previous reports suggesting that impulsives
have more difficulty in processing complex information (Harmon-Jones et al., 1997; Schweizer,
2002).
17
In terms of N400 amplitude, high impulsive participants, as compared to low impulsive
ones, had more pronounced peaks of this ERP component over fronto-central scalp regions for
either congruent or incongruent sentence final words. This finding generally supported the
prediction that normal impulsive individuals would not show significant ERP differentiation
between congruent and incongruent words and between positive and negative words. These
observations resembled those previously reported between inmate psychopaths and nonpsychopaths for oddball target detection (Kiehl et al., 2006a), emotional polarity discrimination
(Khiel et al., 1999), and emotional lexical decision task (Williamson et al., 1991) wherein ERPs of
psychopaths did not differentiate word type and were found associated with aberrant larger
negativities in the 300-600 ms time window. There are at least two possible interpretations of the
lack of significant ERP word type effects for the impulsive participants. First, it may be that
impulsives simply do not differentiate word stimuli in a matter similar to that found with nonimpulsives. Second, impulsives may differ from others in the time course and degree of activation
necessary to differentiate between word stimuli. This latter interpretation is strengthened by the
presence of behavioral differences for incongruent words between impulsivity groups. It may also
be the case that impulsives were using an alternative strategy to perform the tasks, although the
exact nature of this strategy is not known.
Interestingly, stepwise correlational analyses indicated that fronto-central N400 amplitude
and false alarm/hit ratio for neutral incongruent words, were the best predictors of Impulsivity by
respectively accounting for 27% and 6.8% of the total variance. This finding also parallels the
significant correlation between psychopaty and N400 amplitude reported by Kiehl et al. (1999).
However, to the best of our knowledge no study analyzed the N400/Impulsivity relationship
controlling for individual differences in sensation seeking. On this issue, a relevant result of the
present study is that N400/Impulsivity relationship is not affected when controlling for sensation
seeking, the latter being positively correlated with Impulsivity.
18
It is important to note that there are some limitations to this study that should be addressed in
future research. First, our findings are restricted to a sample of only women and cannot be extended
to the general population, especially because there is experimental evidence for increased
impulsivity in men (Miller, 1991; Nagoshi et al., 1991). This procedure if on the one hand has
produced more homogeneous behavioral and N400 data scores with a relatively small sample size,
from the other hand has leaved out possible main or interactionl effects of gender with impulsivity
factor. Second, direct measures of language fluency and reading ability were not assessed in the
present study. Thus, we cannot totally exclude that these factors may have influenced the observed
differences between impulsivity groups even if all the participants were undergraduate psychology
students.
In summary, although impulsivity is thought to play a crucial role in emotional processes
(Gray and McNaughton, 2000), the present findings have evidenced that this personality trait is also
associated with differences in semantic aspects of language processing.
In this respect, this research suggests that impulsive individuals are associated with increased
difficulty in the processing of language. This may place impulsives at a clear disadvantage in
teaching programs and may indicate that these individuals need of alternative forms of teaching.
In conclusion, our behavioral and N400 findings suggest that impulsivity is associated with
abnormalities in the scalp-recorded potentials associated with the integration process of information
conveyed by a final word into a sentence context and that these abnormalities appear to be localized
to the fronto-central cortical region and surrounding cortex. However, it should be outlined that
this interpretation is speculative and further studies using a greater number of participants including
gender factor are needed before any robust conclusions can be carried out.
Acknowledgements: We wish to thank Mr. Sante Moretti, and Mr. Pietro Fermani (Department of
Psychology University of Rome “La Sapienza”), for technical support.
This study was supported by a biennal grant from the Faculty of Psychology-1, and AST, University
of Rome “La Sapienza” to A.A. (Years: 2006-07 to A.A. prots. C26F06MW7H and C26F07472B).
19
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FIGURE CAPTIONS
Fig. 1. Grand-average event-related potentials (ERPs) for high impulsives (black) and low
Impulsives (gray).
Fig. 2. Grand-average event-related potentials (ERPs) at frontal, central and parietal scalp quadrants
for congruent (solid) and incongruent terminal words (dashed) of sentences.
Fig. 3. Grand-average event-related potentials (ERPs) at frontal, central and parietal scalp quadrants
for negative (dashed), neutral (gray) and positive (solid) emotional terminal words of sentences.
Fig. 4 Scatterplot illustrating the relationship between Impulsivity and N400 amplitude at
frontocentral (FCz) scalp site for emotionally neutral incongruent terminal words of sentences.
26
Table 1.
Correlation between N400 amplitude at midline and Impulsivity
(Imp) and partial r after controlling for Sensation Seeking (SS).
Imp Controlling for SS
Congruent Words
Fz-Neu
FCz-Neu
Cz-Neu
CPz-Neu
Pz-Neu
Fz-Pos
FCz-Pos
Cz-Pos
CPz-Pos
Pz-Pos
Fz-Neg
FCz-Neg
Cz-Neg
CPz-Neg
Pz-Neg
-0.417
-0.370
-0.248
-0.229
-0.181
-0.284
-0.304
-0.192
-0.219
-0.180
-0.268
-0.300
-0.201
-0.135
-0.082
-0.401
-0.360
-0.244
-0.215
-0.165
-0.264
-0.283
-0.169
-0.198
-0.161
-0.222
-0.241
-0.131
-0.067
-0.011
Incongruent Words
Fz-Neu
FCz-Neu
Cz-Neu
CPz-Neu
Pz-Neu
Fz-Pos
FCz-Pos
Cz-Pos
CPz-Pos
Pz-Pos
Fz-Neg
FCz-Neg
Cz-Neg
CPz-Neg
Pz-Neg
-0.317
-0.519
-0.275
-0.269
-0.190
-0.287
-0.310
-0.211
-0.213
-0.121
-0.290
-0.253
-0.076
-0.044
-0.012
-0.351
-0.544
-0.295
-0.281
-0.200
-0.292
-0.309
-0.226
-0.229
-0.139
-0.274
-0.254
-0.096
-0.061
-0.037
.
Note: Bold, p<.01; Italic, p<.05
27
Fig. 1
28
Fig. 2
29
Fig. 3
30
Fig. 4
31