Running head: INDIVIDUAL DIFFERENCES AND EVENT RELATED
POTENTIALS
Individual Differences and Event Related Potentials
Kristyn Kelsey
Dr. Michael Houlihan
St. Thomas University
Authors Note
Kristyn E. Kelsey, Student Department of Psychology, St. Thomas University.
Special thanks to Dr. Michael Houlihan, Department of Psychology, St. Thomas University.
Correspondence concerning this article should be addressed to Dr. Michael Houlihan,
Department of Psychology, St. Thomas University, 51 Dineen Dr, Fredericton, N.B., Canada,
E3B 5G3. Email: mhoulihan@stu.ca
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INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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Abstract
Individual differences and their neural correlates have long been an interest of psychology.
Using EEG technology to determine how event-related potentials relate to personality types is a
useful tool in the discovery of these neural correlates. Multiple theories indicate that individuals
who score high on extraversion (E) tend to be less aroused than introverted individuals. These
low levels of arousal have been implicated in low amplitudes of specific event related potentials.
Using tonal stimuli, the amplitudes of the event-related potential N1 were measured and the
hypothesis was confirmed. Individuals who scored high in E displayed lower amplitude N1
responses to the tonal stimuli. This supports the multiple studies that hypothesis that extraverted
individuals are characterized by low levels of arousal.
Keywords: N1, Event-Related Potentials, Individual Differences
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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Extraversion and Event Related Potentials
Individual differences in behavior and physiology have long been examined in the field
of psychology. Extraversion is a well-studied dimension of personality and is included in any
widely accepted formulation of trait models. Eysenck described extraversion (E) as “sensation
seeking, dominant, and venturesome” with similar theoretical attributes as that of Jung (Eysenck,
1973; Eysenck & Eysenck, 1985; Jung, 1921). The multiple dimensions of personality have
been observed as early as the ancient Greek study of the humors (Eysenck, 1973). Personality is
an area of research interest often because of its influence on quality of life (Costa & Mcrae,
1980). Personality is considered to be the unchanging characteristics of an individual that result
in their perception and reaction to their environment (Eysenck, 1973). Individuals who are
characterized by higher levels of E often reflect a desire to be involved in activities that allow for
great stimulation, such as parties and physically demanding activities (Eysenck & Eysenck,
1985). Individuals who did not have such high levels of E are more likely to seek solitary
activities often these activities involved low levels of stimulation (Eysenck & Eysenck, 1985).
Theories of the biological bases of personality provide insight into many aspects of
individuals’ daily lives. Eysenck (1973) attributes underlying deficits in cortical arousal to
account for extravert’s need for constant stimulation. Naturally low levels of cortical arousal in
extraverts also relate to easily lost attention, as well as physical reactions to varying modalities
and intensities of stimuli (Eysenck & Eysenck, 1985). This low level of arousal often causes
extraverts to respond to unexpected stimuli with lower levels of brain activity than introverts
(Eysenck & Eysenck, 1985). Eysenck (1973) explained the differing levels of arousal between
extraverts and introverts as a function of the existing levels of arousal in the cortex combined
with the level of incoming stimulation. These differing levels of arousal correspond to
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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differences in behavior as well. Introvert’s lower threshold for arousal in the reticular activating
system is related to both learning and attention (Stelmack, 1990). Extravert’s low levels of
arousal are also a reasonable explanation for the two defining traits of extraversion. Specifically,
impulsivity as a function of E may cause increased levels of cortical arousal, therefore bringing
extraverts to an optimum arousal level. Sociability can be seen as another attempt to stimulate
an extravert by being in the presence of others. This explanation accounts for the differing
reactions of extraverts and introverts when exposed to identical levels of stimulation.
Eysenck and Gray approached personality using a ‘top-down’ procedure to first describe
then explain the biological basis of specific traits. To discover the underlying systems involved
in behavioral aspects of personality Gray examined how both animals and humans respond to
differing sets of stimuli by studying the effects of certain drugs on behavioral paradigms (Corr
& Matthews, 2009). The results of Gray’s work led to reinforcement sensitivity theory. This
theory consists of three underlying categories of neural processes responsible for outward traits.
Firstly, the behavioral inhibition system (BIS) is related to conditioned negative stimuli (Corr &
Matthews, 2009). The BIS is considered to be related the personality trait anxiety. The second
system, “fight, flight, or freeze”, is a response to unconditioned negative stimuli and is associated
with Eysenck’s trait of psychoticism (P). Finally, the behavioral approach system (BAS) is a
conditioned response to positive stimuli and is related to impulsivity (Corr & Matthews, 2009).
This contradicts the aspects of Eysenck’s theory that indicates extravert’s need for stronger
stimulation. Gray (Corr, 2008) explained that sensitivity to stimuli is dependent on the stimuli’s
relation to punishment or reward. Eysenck (1973) argued that reinforcement effects are not
direct indicators of personality traits, but are a consequence of arousal levels and therefore may
be mediated by differing arousal levels related to personality traits.
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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Another biological theory regarding the bases of E comes from Brebner (1983). This
particular model of E cited the differences between extraverted and introverted individuals as
displayed through preferred ways of processing sensory information. Extraverted individuals
tend to respond quickly to presented stimuli, gaining excitation from the organization of
incoming stimuli as well as the response. Introverted individuals tend to be slower to respond, as
they derive excitation from the analysis of incoming stimuli (Brebner 1983).
Geen (1984) observed the behavior of extraverted and introverted individuals during
stimulation levels that were chosen by the individual. As would be expected, extraverted
individuals chose high levels of intensity for the noise levels they were exposed to while
introverts preferred lower levels of intensity (Geen, 1984). Responses of individuals to their
chosen level of intensity were similar, with no differences in the pulse rate between extraverts
and introverts. When the intensity was not chosen, extraverts responded with lower arousal than
introverts. However, during higher levels of stimulation that was not chosen, both groups
showed no difference in pulse rate (Geen, 1984). This phenomenon can likely be explained
through trans-marginal inhibition. Gray (1967, as cited by Eysenck & Eysenck, 1985) described
trans-marginal inhibition as a decrease in response when individuals are exposed to very high
intensities of stimulation. According to Geen’s (1984) research, extraverts are less sensitive to
trans-marginal inhibition and, therefore, will respond with similar reactionary levels of arousal to
very high levels of stimulus intensity.
Preferences towards levels of stimulation also effect performance on a variety of tasks.
Performance evaluation of extraverted and introverted individuals that were exposed to either
high arousal or low arousal music genres supports Eysenck’s (1973) arousal theory. Overall, on
a number of tasks introverts performed better in the absence of distracting stimuli. However,
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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when both groups were exposed to high arousal music genres, extravert’s scores were generally
unaffected. Introverts scores decreased significantly during the presence of high arousal music
(Cassidy & MacDonald, 2007). While in some cases it appears that extraverted individuals hold
the ability to handle higher levels of stimulation, this possible benefit may affect their ability to
distinguish between differences in stimuli. Studies have shown (Stelmack & Campbell, 1974;
Stelmack et al., 1977) that extraverts have higher threshold levels involved in the detection of
differences in tonal stimuli.
Another aspect of the biological bases of E is attentional abilities and individual
differences. The attentional abilities of extraverts may be related to a susceptibility to
habituation (Eysenck & Eysenck, 1985). Habituation occurs when an individual has been
exposed to a sequence of repeating stimuli. The individual develops a neuronal model of the
sequence and the subsequent stimuli are to be expected (Eysenck & Eysenck, 1985). As a result,
levels of response to stimuli that match the sequence decrease and eventually ceases (Sadler,
Mefferd, & Houck, 1971). The subsequent lack of response to the repeating stimuli is
habituation. Extraverts tend to display minimal reactions to novel stimuli because of their
susceptibility to habituation. This finding has been examined in many studies. Cooper and
Brebner (1987) found that, during a task with low response demands, introverts remained alert
while extraverts quickly reported feeling bored by the task. The excitation-inhibition theory
states that analysis of stimuli and response organization can occur in either excitatory or
inhibitory state, and that these differ between introverts and extraverts (Brebner, 1983).
Introverts will tend to elicit a greater response to the analysis of stimuli but experience inhibition
upon the organization of response. For extraverts, this process is reversed (Cooper & Brebner,
1987).
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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Even-Related Potentials and the N1
Event-Related Potentials (ERPs) are a valuable tool for discovering brain activities that
are related to processing sensory information as well as other higher ordering functions (Duncan
et al., 2009). Using electrodes connected to amplifiers researchers are able to view voltage
variations that occur over time (Coles & Rugg, 1995). For extra-cranial measurement the
electrodes are placed on a cap that correspond to various areas within the brain (Coles & Rugg,
1995). These variations are called the electroencephalogram (EEG) and allow for inferences to
be made regarding physiological and psychological activity in the brain. By presenting stimulus
to an individual while recording their EEG, the voltage changes that occur in response to the
stimulus represent an event-related potential. ERPs are time-locked events, meaning that they
occur in response to a physical or mental event. In order to separate the ERP that has occurred in
relation to an event it is important to extract this signal from the background EEG (Coles &
Rugg, 1995). Once this signal has been extracted it is possible to examine the components of an
ERP. A component of an ERP is a specific characteristic within the waveform that is of interest
to the researcher. Measuring the characteristic, or component, of interest involves finding its
specific amplitude and latency (Coles & Rugg, 1995). Components are often defined in terms of
either their source within the brain or the cognitive function that is occurring to elicit the
specified component (Coles & Rugg, 1995). This function can be determined by the
manipulation of experimental variables and the observation of the manipulation’s effects on the
component. ERPs are labeled for their positively or negatively directed waves caused by voltage
differences in the recording and reference electrodes (Duncan et al., 2009). They are also labeled
for their latency, which is the time it takes for the presentation of stimuli to generate a response
in the brain.
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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A particular component that is often elicited through auditory stimuli presentation is the
N1. The N1 is a large, negative going potential that has its peak latency 100 ms after a stimuli is
presented. This wave is biphasic meaning it has both a negative and positive wave (N1-P2)
(Wang, Mourax, Liang, & Ianetti, 2008). During presentation of an auditory stimulus, the N1
occurs following an unpredicted stimulus in the absence of any task demands (Nataanen &
Picton, 1987). In an extensive review of the components underlying N1 generation, Naatanen
and Picton (1987) outlined three central components that contributed to N1 generation. The first
component is generated in the supratemporal plane of the auditory cortex. The second
component is likely generated on the superior temporal gyrus, having its maximal amplitude
recorded at the midtemporal lobes. The final component is ambiguous in its location of
generation but the authors suggest its generation may come from the frontal motor and premotor
cortex under the influence of the reticular formation and the ventralateral nucleus of the
hypothalamus. This component is likely related to the initial response to novel stimuli (Alcaini,
Giard, Thevenet, & Pernier, 1994; Naatanen & Picton, 1987). These processes indicate the
dichotic nature of the N1 as being both exogenous and endogenous as a component. The
processes outlined by Naatanen and Picton (1987) point to both manipulation of the stimulus as
well as the state of the individual exposed to the stimulus.
The N1 component is shown to contain both stimulus specific as well as stimulus nonspecific components (Naatanen & Picton, 1987). These stimulus specific components can be
directly affected by the alteration of presented stimulus, through change in tonal frequency of a
continuous auditory stimulus as well as by change in stimulus intensity. The N1’s elicitation is
often dependent upon the lack of expectation towards the stimulus. Stimuli that are presented
having a slow onset do not elicit the N1 response (Naatanen & Picton, 1987). A sudden onset of
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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the stimulus will produce a pronounced N1 as well as the sudden offset of stimulus (Naatanen &
Picton, 1987).
Changes known to affect the N1 often do so in terms of latency and amplitude. However,
these changes can also refer to the elicitation of the N1. There are two types of specific changes
that can occur to elicit an N1 response. Naatanen and Picton (1987) label these changes as
change-1, which reflects a change from a preceding level of stability to one of instability. This
can be exemplified through the change from silence to sound when using auditory stimulus. The
second change (change-2) is a change that occurs within the stimulus, such as a particular change
in tone or frequency. Both of these changes require a neuronal trace that involves the memory of
preceding stimulus or non-stimulus levels (Naatanen & Picton, 1987). This memory of the
preceding levels, whether they are a stimulus or silence, is necessary as the N1 is generated by
change in the physical characteristics from the preceding to the current level (Naatanen & Picton,
1987). The presentation of an unrecognized tone (often termed the ‘deviant’ tone) reactivates the
N1 after the individual has developed a neuronal trace of the current stimulus (Naatanen &
Picton, 1987). The amplitude of the N1 can be affected by intensity of the deviant stimulus
(Naatanen & Picton, 1987). Butler (1968) found that the greater the difference between the
deviant and standard stimuli, the greater the amplitude of the N1. Also, slight differences in
between standard and deviant stimuli produced an N1 response, the closer the levels of intensity
between the stimuli came, the smaller the amplitude of the N1. The intensity of the stimuli
presented can also affect the latency of the N1. Miller, Ulrich, and Rinkenauer (1999) found that
louder tones produced shorter latencies in the N1. Conversely, softer tones produce shorter
latencies. The changes produced by stimulus intensity tend to have a greater effect on amplitude
than latency. In certain individuals, the N1 amplitude at levels of very high intensity may
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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saturate and therefore level off or even reduce (Naatanen & Picton, 1987). Other individuals
respond to very intense stimuli by continuous increases in amplitude. This phenomenon has
been related to the differences of individuals who ‘augment’ and ‘reduce’ (Naatanen & Picton,
1987). Augmenters are individuals who attempt to increase incoming stimuli while reducers
attempt to reduce the incoming stimuli (Herzog & Weintraub, 1982). The amplitude and latency
are also affected by the inter-stimulus intervals (ISI) during the presentation of auditory stimuli.
The ISI refers to the length of time from the offset of one stimulus to the onset of the next
(Teder, Alho, Reinikainen, & Naatanen, 1993). Upon the decrease of ISI for auditory stimuli,
the amplitude of the N1 response decreases as well (Teder et al., 1993). The first discovery of
the effects of ISI are attributed to Vaughan, Costa, and Ritter (1968). Vaughan et al. (1968)
found that upon a presentation of a block of stimuli, the shorter the ISI became there was a
subsequent decrease in the amplitude of the N1. However, this decrease in amplitude was not
attributed to habituation and was rather seen as indication of a ‘refractory’ period in the auditory
system (Naatanen & Picton, 1987; Vaughan et al., 1968). The presence of refractoriness in the
auditory system indicates that a large amplitude N1 cannot occur within the short time between
stimuli, specifically given a short ISI.
N1 and Extraversion
Heightened levels of sensory sensitivity in introverts have been observed in numerous
studies (Gale, Coles, & Blaydon, 1969; Stelmack, Achorn, & Michaud, 1977; Geen, 1984).
Stelmack, Achorn, and Michaud (1977) found that in a low frequency auditory stimulus
condition, extraverts had smaller N1 amplitudes than introverted individuals. A significant
difference between extraversion and frequency was also observed. At lower frequencies the
amplitude of the N1 tended to be smaller in comparison to the amplitude of N1s evoked by
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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higher frequencies. However, extravert’s N1 amplitudes were still significantly smaller in most
frequency and intensity condition than introverts (Stelmack, Achorn, & Michard, 1977). This
indicates that extraverted individuals are not as sensitive to low frequency and low intensity
auditory stimuli. The latencies of the N1 were also affected. Extraverted individuals displayed
longer latencies than that of introverts that was also affected by level of stimulation and
frequency. It is important to note that the differences between extraverts and introverts were not
significant at higher frequencies and higher intensities. Therefore, the notable difference in
extravert’s response to low intensity and low frequency stimuli may depend upon their high
levels of auditory threshold. When exposed to low frequency tones extraverts were recorded as
having lower N1-P2 amplitude than introverts (Stelmack, Achorn, & Michaud, 1977). This
would indicate that extraverts have higher thresholds for the frequency of tones, and therefore
require higher frequency levels to detect the tones. This is indicated by the amplitude of the N1
component of an event related potential, which occurs upon detection of stimulus. These
findings provide support for the theory that extraverted individuals maintain lower levels of
cortical arousal, and therefore require stimuli of greater intensity to elicit detection (Stelmack,
Achorn, & Michaud, 1977).
The current study hypothesizes that individuals who maintain high levels of E will have
lower amplitude N1’s. This is hypothesized to be the result of low levels of natural stimulation
that in turn, lead to low abilities of recognition of new stimuli. This could also be a result of the
higher auditory thresholds held by individuals high in E. It is unlikely that individuals with high
auditory thresholds register changes in auditory stimuli.
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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Method
Participants. Participants were female undergraduate students between the ages of 18 and 24 (n
= 58, m = 18.6, sd = 1.04). Individuals completed a health questionnaire intended to screen out
individuals with issues that could confound our results. This included any hearing disabilities, as
well as participants were currently taking any centrally acting medications. These students were
completing the experiment for credit for introductory psychology courses and were also given a
monetary compensation if maximum accreditation for courses had been previously obtained.
Participants were asked to abstain from alcohol 24 hours before their participation in the EEG as
well as abstinence from nicotine and caffeine one hour prior. Ethics approval was received from
the St. Thomas Research Ethics Board.
Materials
Personality Measures. Participants were required to complete the Eysenck Personality
Questionnaire-Revised (Eysenck, Eysenck, & Barrett, 1985; Eysenck & Eysenck, 1985) online
before subsequent participation in the EEG segment of the study. This EPQ-R measure of
personality has shown a reliability of 0.76 for females (Eysenck, Eysenck, & Barrett, 1985).
Individuals are scored based on their answers to 100 questions meant to measure their levels of
E, psychoticism, and neuroticism. Questions on the EPQ-R evaluated individuals on qualities
such as sociability and risk taking.
Equipment. EEGs were recorded from the EasyCap electrode cap with 32 Ag AgCl
sites. An electrode was placed on the nose as a reference while another was placed under the eye
to factor out the artifact of blinking. Filter setting were applied through Neuroscan NuAmp 0.5
to 100 Hz settings, with a sampling rate of 500 Hz. Offline analysis used electrodes placed
below the right eye, as well as FP2, to measure vertical EOG. Electrode sites F7 and F8
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
13
measured horizontal EOG. Epoch ERP averages were computed separately for the three
conditions, with averages for the standard and deviant tones separated as well. N1 latency was
observed as falling between 80ms and 140ms from the stimulus onset.
Auditory Stimulus. Participants were exposed to the auditory stimulus binaurally using
foam ear tips. Six auditory oddball sequences with varying standard and deviant tones were
presented to the participants while viewing the aforementioned film. The sequences consisted of
680 standard tones and 120 deviant tones, which varied in intensity. The standard tones,
presented in a white noise format, were at threshold level, twice threshold level, thrice threshold
level. Each stimulus presentation was 200ms in duration. The auditory threshold for the
standard tone was determined in pilot study, resulting in a standard tone of 75db. The
differences in tone necessary to elicit a response were shown to be minimal. The ISI was set at
600ms between the presentation of one stimulus to the presentation of the next. Rise time and
fall tie were at 10ms. This was the length of time required to reach full amplitude and allow for
listener processing of the stimulus.
Procedures. Participants were shown into a room where the cap was placed on their scalp. The
cap was then connected to the amplifier and finally to the computer where the NeuroScan
program was used to record the EEG’s. Participants were shown to a separate room where they
were placed in front of a television screen. They were then given choice of animated films to
view while receiving exposure to the stimuli. Once the stimulus sets had been presented, the
individuals performed a discrimination task using the same auditory stimuli as the previous sets.
The participants were then shown to the other room where the cap was removed.
Results
The relationship between N1 amplitudes and E was calculated using Pearson’s product-
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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moment correlation coefficient. Correlations of the N1 amplitudes and E revealed there was a
significant, positive relationship between high scores of E and the amplitude of the N1.
Localization of correlations showed a significant, positive relationship at FC1 Rare, r(37) = .346,
p < .05. This was the only significant relationship between E scores and N1 amplitudes for the
rare tones. Significant, positive relationships between standard tones and E scores were found
for FC1[ r(33) = .321, p < .0], FC2 [r(32) = .287, p < .05], and CZ [ r(35) = .278, p < .05].
Table 1
Correlations between Extraversion and N1 Amplitudes
Extraversion
N
FZ Rare
.238
35
FC1 Rare
.346*
39
FC2 Rare
.163
41
CZ Rare
.197
43
FZ Standard
.269
32
FC1 Standard
.321*
35
FC2 Standard
.287*
34
CZ Standard
.278*
37
P< .05*
Discussion
The results of the current study indicate that individuals who scored high in E had
significantly lower amplitudes of N1’s. These findings support Eysenck’s cortical arousal
theory, indicating low levels of arousal in individuals high in E (Eysenck & Eysenck, 1985).
These low levels of arousal are relative to low amplitude N1 responses based on concurrent
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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findings that indicate high arousal as being related to high amplitude N1’s (Naatanen & Picton,
1987). The standard tones presented were positively correlated with N1 amplitudes at all four
electrode sites, while the rare tones were correlated only with FC1. The low amplitudes observed
at all four electrode sites for the standard tones may be related to extravert’s high auditory
thresholds. As Smith (1968) indicates, individuals high in E have significantly higher auditory
thresholds than that of introverted individuals. Smith (1968) relates this to Eysenck’s theory of
cortical arousal. The results of Smith’s (1968) work indicate the physiological differences
between extraverts and introvert as the source of these differing auditory thresholds. The
standard tones presented may not produce the same effect for individuals high in E due to these
high auditory thresholds. Similarly, the deviant tones may not be as readily recognized by these
individuals, as the change in stimuli may not be significant to this high threshold.
Another factor that could be responsible for the decreased amplitude of N1’s in the
standard tone series is habituation. Sadler, Mefferd, and Houck (1971) provide confirmation of
extravert’s susceptibility to habituation. During a series of repeating auditory stimuli,
individuals scoring high in E indicated increasing boredom as the series progressed. This
boredom was marked by a decrease in the magnitude of galvanic skin responses, therefore
indicating further evidence of physiological differences between those high in E and introverts
(Sadler et al., 1971). This is relative to the N1 response, as habituation to an auditory stimulus
results in a decrease of N1 amplitude (Megela & Teyler, 1979; Naatanen & Picton, 1987). The
potential of habituation is dependent on a repetition of stimuli and habituation often ceases when
a novel stimulus is introduced (Naatanen & Picton, 1987). The ceasing of habituation may be
indicated by a lack of correlation in many of the deviant tones. This lack of correlation for three
of the four electrode sites indicates larger amplitude N1 responses when participants were
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
16
exposed to the deviant tones. Therefore, if habituation had occurred during the presentation of
the standard stimulus, the presentation of the deviant stimulus would interrupt the habituation
and cause a larger N1 amplitude.
The limitations in this study included the selection of only female participants. This is
due to the inherent difference in EEG’s that occur males comparatively with females. Females
tend to display naturally larger amplitudes than males (Ikezawa et al., 2008), allowing for easier
readings of the amplitude of the N1 response. The study was also limited to participants in a first
year psychology course, as to ensure their participation based on specific course requirements.
Finally, the study required participants to attempt to ignore incoming auditory stimuli. However,
when individuals are paying attention to the stimuli and making attempts to predict the oncoming
deviant tones, studies indicate larger N1 amplitudes given the selective attention to incoming
stimuli (Naatanen & Picton, 1987).
Perhaps, in future studies, measures can be taken to include both male and female
participants with efforts made to equalize amplitudinal readings for evaluation of N1 amplitudes.
This would allow for further examination of extraverted individuals and allow for a larger
generalization. Secondly, allowing a larger population of students to participate in the study
would result in a lager sample size regardless of attrition. Finally, separate conditions of
attentional demands. Giving the participants conditions of both discrimination of stimuli and
ignorance of stimuli could allow for speculation regarding the amplitudes of the N1 response in
regards to attention.
The current study has confirmed the hypothesis that individuals who are high in E
tend to display lower amplitude N1 responses to auditory stimuli. These amplitudes are affected
by the deviance of the tones presented. Tones that are recognized to be different from the
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
17
previously established sequence, whether consciously or otherwise, have larger amplitude N1
responses than standard tones from the previous sequence. There are many potential causes for
this change in amplitude that have been thoroughly reviewed. This indicates that biological
differences may mediate differences in personality as well as differences in response to
stimulation.
INDIVIDUAL DIFFERENCES AND EVENT RELATED POTENTIALS
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